4.2 keeps losing oil pressure

[chuey_316]

Hey everyone. I'm working on my girlfriend's 05 Envoy with the 4.2 and could use some help.

The issue started with the pressure gauge dropping to 0 while driving. Would jump back up and then down again. I know the gauge is fake, so I figured just a bad switch.

I replaced the switch, and did an oil change, but the problem persists.

When the truck is first started, everything is fine, but after driving for about 10 minutes the gauge drops to 0 and stays there.

It's definitely a pressure issue, because the lifters will start to sing if the truck isn't shut off when this happens.

I've ran a quart of flush through the engine, followed by draining the oil, and filling the pan with a gallon of diesel through the dipstick tube, and letting it soak for a few days, hoping that maybe the pickup screen was getting clogged.

Today I drained the diesel, filled with new oil, ran the engine for about 5 minutes, drained again, followed by new oil, 5 more minutes running, then drained again and added 7 qts of new oil, and a new filter.

Took the truck for a drive and the problem is still there. Not sure what to do from this point. I thought about changing the pump, but it's a 4wd, and I'm told that it's about a 4 day job.

I plan on hooking up a manual gauge to it today to see what the real pressure is.

Only other problem with the truck that I'm aware of is that it needs a new thermostat. The one in it now won't allow the engine to get over about 135-140f while driving, and about 150f at idle, which is causing condensation buildup.

 

[chuey_316]

I'm debating on cutting an access hole in the pan under the pickup so I can get to it without having to disassemble half the truck to drop the pan, but I'm concerned that I may not be able to get it to seal afterward. I know plenty of people have drilled and tapped new plugs in their pans, but it still worries me.

 

[Mooseman]

Sounds like the pickup seal may be leaking. When the oil is cold and thick, it can overcome the leak and create enough pressure but as the oil thins, it can't keep up. A failed bypass would still create some pressure.

A hole in the pan won't help you as you need to be able to also access the front where the pickup tube connects to the oil pump, which is integral with the timing cover. You can't even cheat like you can with LS engines.

 

[chuey_316]

I thought about that, and hoping that's not the case, but you're probably right. I've seen from a few people with these engines that have this issue, where soaking the pickup cured the problem, but just as many people or more where it didn't, and a tear down was necessary.

I'm going to have a look at the pickup with an inspection camera, and if it looks bad then I'll have one more go of soaking it, since I have a new gallon of Chem Dip on hand. If the screen looks fine, then the truck will have to go. Hate to get rid of it, but I no longer have a garage to work in, and I can't leave the girlfriend without a vehicle til spring.

 

[Reprise]

OP - you did such a great job with diagnosing this issue. And then a really terrible thought process about potentially cutting an access hole in the bottom of the pan. Don't do that! A bung for a pressure gauge or oil return is fine - on the side of the pan. 'Nuff said

One thing I haven't seen in this thread... how many miles are on this engine? A lot?
If 'yes' (like over 250K ?) - might be actual wear (but the gauge wouldn't drop to '0').

More likely, it's a blockage - either in the pickup tube, or (if your truck has it) the screen between the oil pressure sensor and the oil galley that supplies it. I know later-year LS motors (especially those with DOD / AFM) have this screen... not sure if the 4.2L does as well.) I'd definitely check this screen first, if you have it, as it's LOTS less work.

And, yes -- the pickup tube is fastened at both ends, so your 'access hole' wouldn't work, like Moose said. When I took the oil pan off my Sierra a few months ago, I couldn't believe what was in the bottom (no pressure issues; just freshening things up during a cam / head swap). You can see pics of it in my build thread, here

 

[chuey_316]

Engine has just over 200k. Definitely don't want to cut into the pan, but I have seen others do it to get to the pickup screen with success. I was just thinking of ways to clean it since I don't have anywhere that I can work on the truck to drop the pan.

I haven't had a chance to connect a manual gauge to it yet, but hope to be able to get to it tomorrow so I can see what the real pressure is from startup to when the gauge drops out.

Really hoping the pickup screen is plugged, and not the tube. The screen I'm sure can be cleaned with a Chem Dip soak, but I don't know of any way to clean out the tube without dropping the pan. I mean, I could possibly run some Seafoam with the oil and start it each day for a bit, but I'm sure it would take forever to clear any blockage if it could even clear it at all.

Just waiting on my inspection camera now before moving forward with the soak. Don't want to waste a $30 gallon if the screen isn't plugged up.

Would it be possible to attach a hose with a fitting to the oil filter location and blow back through to clear a blockage? Just brainstorming at this point, but if that may work, I could possibly clear the blockage, then with a few flushes, and some Seafoam or MMO with each oil change it should be able to dissolve a bit more with each run.

 

[Reprise]

If the 4.2L oiling system is like the LS, I think the oil filter boss is at the other end of the system from the pickup tube (e.g.; all the galleys are in between.) But if you had a decent enough air compressor, it could (?) work. I know you're outside, so that's likely not an option at all, even if you had one available.

I'll look up the oil flow diagram for the LS (I know I have it); maybe the 4.2L is somewhere online? Let's see what I can find out. Back in a bit.

(on edit: ) Well, that didn't take long... take a look at this thread. The diagram is in post #3.
In a way, I like it better than the LS' system, as it's pretty close to priority oiling (the crank bearings get oil before the top end does). Although I can't tell from this diagram at first look how the filter boss and the pickup fall in order to one another.

Here's a pic, if you don't want to look through the thread.

 

[Mooseman]

No such screen under the pressure switch. It is only on LS engines with DOD/AFM.

The oil filter is located right next to the pump.

If the Chem Dip doesn't help, then it's obviously not blockage at the piskup. Either the seal is broken or the bypass is stuck open (which is similar in design to the LS but built into the timing cover). An idea I just had, you could try some really thick oil and see if the pressure holds. If the bypass is stuck, maybe this extra pressure will push it off its stuck position. If you have a real pressure gauge hooked up, this could also give you some info. I'd consider this a hail Mary though.

 

[chuey_316]

Thanks, I appreciate it. I have a garage available to work in, and a large compressor, but not enough room to close the door, so any work I do can only be a 1 day job unfortunately.

I'm going to hook up a gauge tomorrow to get a baseline reading, then run some Berryman's B-12 in with the fresh oil that I just put in to try and dissolve what I can, and recheck the pressure afterward. Then when I drain the oil, I'll have a look at the screen and go from there on whether to do the Chem Dip soak, try to blow through the filter inlet, or both.

If that fails, I'll grab some 20w50 and give that a shot.

 

[chuey_316]

I may be able to get access to a garage to use that'll fit the truck. I've heard now that it's an 8hr job, a 3-4 day job, and a week long job. How long would you say on average it really takes to drop the pan on a 4wd, along with replacing the pump while in there?

I'm not a master mechanic by any means, but I generally do all my own work, including engine and transmission swaps. Biggest thing I've done on these trucks is a trans swap. I have access to air tools, and plenty of hand tools. Only thing I can think of that I'd need to grab is a slide hammer.

I know it'll be a bitch of a job, but if I can get this garage, I'm willing to do it rather than get rid of the truck, or have to pay a shop what I could buy another truck for to do it.

 

[Reprise]

Reading your experience level, and access to tools, I'd say you could do it yourself. But how fast can you work?

(tip: on the slide hammer, rent one from your local auto parts store beforehand, and have it stashed on the side, as a 'just in case'). You'll get the rental fee back when you return it, so it's a net 'free' rental. You probably know this, but I figured I'd mention it.

I know I couldn't do it in one day -- but I work very slowly / deliberately, compared to most people.

Someone with both experience with the 360s and not encountering any 'issues' along the way might do it in 8 shop hours. But that's a guess, on my part.

Let's see what some other people with the 4.2L think. I have the 5.3 in mine, so I'm not the best person to estimate for the inline six.

(on edit: since we both have the same suspension, after reviewing the OffroadTB.com link below, except for maybe some minor things like size of the outer tie rods, etc. -- I know it would probably take me an entire day to get to the pan. If I were lucky).

Since I've had my front suspension apart a couple of times, I might save some time, vs. the first time I did it. And I have more / better tools than I did a few years ago, too.

The 35mm nut for the front hub can be a b!tch to remove, but I got both of mine off with a 1/2" breaker, IIRC. Might've had a cheater pipe along with it - can't remember now. Torque on those for reinstall is about 160 ft/lb, IIRC (please verify; I'm reciting that from memory).

Also, another site that may have info is OffroadTB.com (some of our members started that site)
I have a page of theirs bookmarked, that goes into detail on how to rebuild the front disconnect (it'll be useful to show you what has to be removed to get the pan clear of all the 4WD stuff).
Note that the outer housing (#3 in the parts diagram) can be difficult to remove, and will likely break if you try and use a pry bar on it. I know there's at least one post on our site here that describes a good way to remove it without breakage.

Front Axle 4WD Disconnect Rebuild | offroadTB.com

offroadtb.com

 

[Sparky]

How long it takes to get apart will depend on how must corrosion there is, your tool set, and how much your truck hates you thay day. That's my experience, anyway - too many times something simple took forever and something else complicated was easy

 

[chuey_316]

Thanks Reprise, I'll check that site out, and I know what you mean Sparky. I've had easy 1/2 hour jobs turn into all day ordeals. I'll just count on it taking 5-6 days, and anything less than that will be a bonus.

 

[Mooseman]

Took me 3 months IIRC but that's including six stitches in my right hand (trip and fall while working on it) and working outside.
Remove the oil pan
How to replace I6 timing chain and tensioner

You won't need to do the timing chain part or valve cover however I would recommend replacing the chain tensioner while you're there and inspecting the chain guides, which was the reason for my getting in there.

 

[chuey_316]

Thanks. I'll have a look at those links. Didn't get a chance to hook up a gauge yet. I changed the thermostat earlier and had to get home. Wasn't as bad a job as I've been told. The worst part by far was the lower alternator bolt, but a 15mm open end wrench, and some inventive new curse words, and I had it buttoned up in about 45 minutes.

Now that the engine is able to get up to normal operating temps I'm running a can of Berryman B-12 in the crankcase right now. Been idling for about 30-40 minutes now, and no drop to 0 on the gauge yet. The lifters started to sing a bit at about the 20 minute mark, and I notice that a very slight amount of throttle (maybe 1000rpm) and they are quiet.

Going to let it cool down, and idle again for awhile, and keep repeating this over the weekend.

Edit: As I was finishing this post, the pressure finally dropped out on the dash gauge, but a bit of throttle, and it would come back up, whereas before no amount of throttle would bring it up from zero. Maybe a little progress? Won't really know anything till I can get a real gauge hooked up.

 

[chuey_316]

Well, it looks like I spoke to soon. Since the flush from my last post the pressure is dropping out much faster now, within a minute or two of starting it, meaning that I can't even let it run long enough to warm up. I'm really wondering now if the screen is in fact plugged, and the last flush loosened more grit and has blocked it more, or moved a blockage to a different spot.

The temps are pretty cold here right now, so I haven't been able to really do much with it for the time being, other than run it a minute or two here and there. It's supposed to warm up into the 20's in the next couple of days, so hopefully I can finally get my gauge hooked up, and drain the pan again to see what comes out.

 

[chuey_316]

Just got a chance to hook up a gauge. Granted, it's probably not the most accurate. It's one that I built from harbor freight parts, and it's only hand tight because I don't have all my tools right now, but I did not see any leaking during the test.

On a bone cold startup in 15F ambient temp, the gauge peaked right around 30psi, then I watched it slowly go down over the course of about 1 minute, till it hit 0psi. Numbers are approximate since it's a small 0-100psi pneumatic gauge and hard to get an exact reading. Something like a 0-60psi gauge would work allot better for measuring low pressure.

Tomorrow I plan to drain the oil that's been in there during this flush, and hope to see some kind of signs of cleaning. Then I'll put 3/4 gallon of Chem Dip in the pan, let it soak awhile, drain it all out, and put in fresh oil and a new filter, and cross my fingers.

Another thing too. I was talking to a mechanic friend, and he said that whenever they get a vehicle in that has signs of sludge, or a blocked screen, his boss makes them drain the oil, and refill with a gallon of LA Totally Awesome cleaner, and the rest with cheap oil, and let the engine run for a bit, and then drain, followed by doing it again if there's allot of chunks that come out. I thought this was completely crazy, since I'm pretty sure that the cleaner is water based, but he says it works really good. Seems pretty dangerous to me. What's everyone's thoughts on this?

 

[Reprise]

I think I'd stay away, myself, unless I was just prepping a vehicle to flip. But you're trying to hang on to this one.

I looked up what's in that cleaner. If you're interested, the MSDS is here

It is mostly water... but here's another one of the ingredients in it...

Sodium Metasilicate

Now, as soon as I saw 'silicate', my spidey sense started a 'tinglin...
Wikipedia says it's water soluble, becoming alkaline in solution... but it also has another use, specifically for automobiles

• Automotive applications - decommissioning of old engines (CARS program), cooling system sealant, exhaust repair

Another name for that 'CARS program' was... Cash for Clunkers. Turns out, this was the stuff the dealerships had to use, after they took a 'clunker' in on trade, to utterly immobilize and lock up the engine, so it could no longer be used / repaired / put back in service. And talking to a salesperson I know fairly well, it was a sight to behold, when this was put into an engine (I know I'd have cried tears, personally)

Now, do I think this chemical (in a 1.5% concentration, and in liquid form) will do what it did in the 'clunkers' program? No -- or your mechanic friend wouldn't have recommended it.
However, I get pretty averse, personally, to putting something in the crankcase that I *know* can be harmful. For someone like me, I'd have anxiety for the rest of my life over it, thinking that 'tomorrow' was the day that the engine was going to seize. But that's me.

I know people have used kerosene, diesel, etc. as crankcase solvents, successfully. I'd have no problem with those (or even something like the non-flammable version of CRC Brakleen, if you were to run the engine with it). But that's as far as I'd go, personally. Hell, I might even put D-Limonene in it (which is the active ingredient in all of those 'citrus' cleaners that seem to work a treat). But not anything with 'silicate' in the name.


I'm going to take this slightly in another direction -- how's oil control / usage on this motor? Do you find yourself adding a lot between oil changes? (I know it's your GF's DD, but I'm guessing you get to maintain it for her). You probably already know why I'm asking, too.

 

[chuey_316]

Oil usage has been decent for the few years that we've owned it. It uses very little oil between changes. I'd say maybe 1/2 a qt for 5000 miles if that, maybe less. Never any smoke, or burnt oil smell, and no signs of oil in the coolant.

 

[Reprise]

Ok. That's actually pretty good. One of our members has a .sig that indicates he adds 2qts between changes. GM's 'acceptable' usage is 1qt / 1000mi. (which when you think of it, might negate the need to ever do an oil change, if it used that much... Just keep topping off.)

I was thinking rings / blow-by, and if it was using a lot of oil, maybe it'd be better to just retire the motor.

As you were, soldier! 🪖 Carry on!

 

[Mooseman]

By 05, it should have the new non o-ring type 2nd design pickup seal. Should be less prone to leaking but to me, that's what it sounds like. As the oil gets warm, it gets thinner and can't overcome the air getting sucked in at the leak, like the LS engines that suffered with a broken o-ring type pickup seal.

At startup, some have reported near 100 psi on this engine with some miles on it. At 30, I say it's sucking in air and like I mentioned, drops until it can't suck oil anymore. Even with a partial pickup blockage, you would still get some pressure.

And don't sweat your test oil pressure gauge setup. I have the same thing I've been using since the early 80's.

 

[chuey_316]

Drained to oil that had the Berryman B-12 in it, and I will be using this stuff at every oil change from now on. When I drained both the oil with the Motor Medic flush, and the diesel soak, I got nothing but just slightly dirty fluid. With the B-12 I actually saw grit and a couple small chunks come out.

Just put the Chem Dip in, and will let it soak awhile before draining, then since I'll be draining the oil I put in next to flush the Chem Dip out, I may even run another bottle of the B-12 through it.

How long should the Chem Dip stay in to soak for? I've seen people say everything from over night, a couple days, and to get it out within hours.

 

[Mooseman]

Since it's soaking only metal parts, I'd leave it in for as many days as possible. After that, I would just run a cheap mineral 20w50 since it will be contaminated with the Chem Dip and whatever it picked up in the oil pan. Be sure to watch your oil pressure to see what happens.

 

[chuey_316]

By 05, it should have the new non o-ring type 2nd design pickup seal. Should be less prone to leaking but to me, that's what it sounds like. As the oil gets warm, it gets thinner and can't overcome the air getting sucked in at the leak, like the LS engines that suffered with a broken o-ring type pickup seal.

At startup, some have reported near 100 psi on this engine with some miles on it. At 30, I say it's sucking in air and like I mentioned, drops until it can't suck oil anymore. Even with a partial pickup blockage, you would still get some pressure.

And don't sweat your test oil pressure gauge setup. I have the same thing I've been using since the early 80's.

Definitely not ruling it out, but want to exhaust every option before tearing it down. only thing is though, my pressure drops well before the oil has any chance to begin to warm up.

At first the truck would get up to operating temp before losing pressure, but now that I've ran the B-12 through it, it loses all pressure within 30 seconds to a minute at most of running, so the oil hasn't had any chance to thin out yet.

Also wouldn't a leaking pickup mainly cause a loss of pressure at idle, but pick up under acceleration? Giving it any throttle when the pressure drops doesn't make a change on the dash, nor on the manual gauge. It did at 1st while running the B-12 through, but not before or after using it.

I'll update with the pressure readings after the Chem Dip has sat for awhile, and I get new oil in there. If there's no change in the pressure after the soak, and possibly one more run of the B-12, then I'll be waiting until I can get access to the garage to strip it down, and replace the pickup, and probably the oil pump as well while I'm in there.

 

[chuey_316]

Since it's soaking only metal parts, I'd leave it in for as many days as possible. After that, I would just run a cheap mineral 20w50 since it will be contaminated with the Chem Dip and whatever it picked up in the oil pan. Be sure to watch your oil pressure to see what happens.

Thanks. I'll run and grab some 20w50 since all I have on hand is 5w30

 

[chuey_316]

Another name for that 'CARS program' was... Cash for Clunkers. Turns out, this was the stuff the dealerships had to use, after they took a 'clunker' in on trade, to utterly immobilize and lock up the engine, so it could no longer be used / repaired / put back in service. And talking to a salesperson I know fairly well, it was a sight to behold, when this was put into an engine (I know I'd have cried tears, personally)

Yeah, I remember watching video's of them killing those engines, including a complete Iroc in good condition, and it really upset me. Too many members of a "throw away" generation these days. People that think when something either gets old, or needs a repair, that it's time to throw it away, and go buy another.

Even My GF wanted me to scrap her Envoy, and go spend thousands on a new car. Told her if she wanted a new car, to go get a job and buy one. We fix things around these parts. Now granted, if I had a $200-300 pos vehicle that needed a couple thousand to get back on the road, that'd be different, but otherwise a little cash and wrench time is well worth it to me to keep an otherwise good vehicle out of the scrapyard.

 

[Mooseman]

Told her if she wanted a new car, to go get a job and buy one.

And you're still alive? You must have some brass balls!

But in all fairness, there is a time when to call it quits. Did that with my 02 TB when the tranny blew because the body was just not worth saving. Same with the Saab when I blew the engine. If the body and everything else is still in relatively good condition, sure, but you have to be objective.

 

[chuey_316]

Still alive, but my head still hurts

I agree, not everything is worth fixing, but this particular truck is in great shape, and the only thing I've ever had to replace has been 2 front hubs, ball joints, tie rods, and a lower control arm mount. It's ran great, and the trans still shifts like butter. If it were rusted out, or a money pit, then I'd throw in the towel.

 

[chuey_316]

Well, I got antsy and drained it out. Everyone says it's reusable, so I drained right back into the pail. Definitely did some cleaning.

I tried having a look inside with my boroscope. There was some build up, but it didn't look horrible. Couldn't get a look at the screen because I kept getting little pieces of sludge on the lens.

Question now is do I pour the cleaner back in to sit longer, or should I put some oil in and a new filter to catch some of the gunk, then re-soak?

 

[chuey_316]

I ended up putting oil and a filter in. The auto store was out of 20w50, so I used the 5w30 that I had on hand.

Oil pressure on startup was between 75-80psi. It held steady around 70 for a minute or two, and was at 30psi at idle after almost 10 minutes as the engine was warming up.

Gave it a bit of throttle and the pressure did not raise any, and ended up dropping to 15psi at idle with the engine about half way warmed up, then slowly went to 0psi again a few minutes later.

Wondering if the Chem Dip cleared the screen enough to give me better pressure, but then as it ran, the loosened up gunk that didn't get liquefied by the shorter soak ended up getting sucked up and re-clogging the screen and/or filter, stopping flow.

I ended up pouring another can of B-12 in there and will run it for a few minutes after the engine cools down completely, then drain, and re-soak in Chem Dip for a day.

Still not ruling out a tear down, but after seeing the pressure raise that dramatically after a short soak definitely gives me hope that a few more flushes and/or soaks may just fix the issue.

 

[chuey_316]

Ok, sorry for all the updates, but it helps me to chronicle what I've done so far since I have bad short term memory, plus I figure it may possibly help the next poor soul who stumbles upon this thread searching for an answer to the same problem.

I just ran the truck at idle until fully warmed up, and then some.

The pressure at startup only went to 30psi again, same as before the 1st Chem Dip soak, but the engine maintained normal pressure throughout the rest of the test, which lasted at least 25 minutes. Pressure held out around 30psi while warming up, and slowly dropped until fully warmed up, and was at 15psi.

I let it idle another 15 minutes or so after that point, and the pressure was right around 10psi for the last 10 minutes, and was no longer dropping. I gave it a couple very light revs to observe the pressure, and it did rise and fall with the rpms.

Once it cools down, I'll idle it again before I go to bed tonight to continue the cleaning, and will still soak the pickup screen for a full day followed by an oil change, idling it till warmed up, then another oil change, and hopefully at that point this saga will be concluded.

If this does the trick, I'll be running a qt of MMO with each change, and run a can of the B-12 immediately before each change to keep everything nice and clean.

 

[Reprise]

But in all fairness, there is a time when to call it quits. Did that with my 02 TB when the tranny blew because the body was just not worth saving. Same with the Saab when I blew the engine. If the body and everything else is still in relatively good condition, sure, but you have to be objective.

This is what I was getting at, but forgot to say overtly. "How's the rest of it?"

Ok, sorry for all the updates, but it helps me to chronicle what I've done so far since I have bad short term memory, plus I figure it may possibly help the next poor soul who stumbles upon this thread searching for an answer to the same problem.

No problem from my end. I do the same thing, sometimes (and sometimes I'll jot notes down in Notepad++ or something similar). And at least two of us are still replying / commenting. We're rootin' for ya! LOL

and hopefully at that point this saga will be concluded.

I apologize for not displaying sunny optimism. But I think you're going to wind up doing the teardown, at some point. Keeping my fingers crossed that you're out of the woods.

 

[chuey_316]

I apologize for not displaying sunny optimism. But I think you're going to wind up doing the teardown, at some point. Keeping my fingers crossed that you're out of the woods.

Oh I'm sure a tear down is inevitably coming eventually, but if I can get it to sunny warm weather 1st, I'll be a happy camper.

I really think that the cause was the bad thermostat that I didn't know about until I drove it and seen the gauge fluctuating, and the GF told me that "it's been like that for awhile now". I think it caused enough condensation build up to start producing bits of sludge. Surprised that it didn't destroy any bearings, although I'm sure it produced some wear.

 

[Reprise]

Yep -- I'd have the same plan (although I don't have to worry about a SO driving anything I have to fix -- I can just park one vehicle till spring & drive another).

If you get the chime when oil pressure drops off, have the GF listening for it. If not, she'll have to watch it pretty carefully, and be ready to pull over / shut it down / call you / wait a few minutes for anything sticking to the screen, etc., to dislodge.

Keep in mind that what I'm about to quote is for the LS specifically, but probably applies to your engine, too...

- As little as 4psi is enough to float the crank on the bearings (startup / idling)
- GMs spec for 'adequate' oil pressure is 10psi / 1000rpm.

If you can get that out of it, I'll bet the engine makes it to spring.
Have the GF keep the speed down / off the interstate, if possible.

 

[chuey_316]

Good thing is she has anxiety, so she won't drive on the interstate.

I just went out to idle it for a bit before draining the oil, and noticed a small puddle under the truck. It would seem that I forgot that the fittings for my gauge were only hand tight, and began to leak. I wonder if it was sucking air through the threads, throwing off my readings, and lowering the pressure. Would make sense, as the last test held good pressure for 25 minutes or more, and this time the pressure dropped within a few minutes, and then I see the puddle.

I'll have to set a reminder on my phone to grab some of my tools tomorrow and tighten the fittings before I do any more testing.

 

[Reprise]

I don't think that lack of tightness would greatly affect the pressure, tbh, from what you're describing.

When you think about it, there's a ton of vehicles that have oil leaks (the slow drip / ooze type, like from valve covers, etc.), but people who have oil pressure gauges on their dash (real ones) never see the needle move. Same thing if they're a whole quart or two low.

I have some direct experience with this, but for now, you'll have to trust me (it's not 'you'; I'm being selfish. Apologies.)

 

[Mike534x]

@Reprise Is correct, my Envoy has a rear main seal leak and still holds great pressure. It sucks having to clean the spot in the garage/driveway but I get a free undercoating out of it. My needle stays at 40 PSI (V8), and doesn't move an inch but my cluster isn't entirely accurate so my readings are off by 1-3 notches on every needle. My truck is also an oil burner too, depending on my driving I go through 1 QT every 500-1000 miles. Though my problem is carbon build up, and possibly the piston rings being bad/heavily gummed up but won't know until I clean out the valves and intake with AC Delco Engine Cleaner.


My very first Envoy (02 4.2 w/134k) had a very similar to what you're experiencing. It would drive and run perfectly, and then after a bit of driving/coming to a stop the oil gauge would just drop and the chime would give me the "check gauges, stop engine" message in the DIC. This was usually after it was warmed up, and driven for a bit. I believe it suffered from the pick up tube o-ring failure, but it never made any abnormal engine noise. Changed out the oil sensor, which didn't fix it either. Unfortunately, I never got a chance to diagnose what the actual cause was. I ended up getting rid of it just as I found this site, but with how common the issues were with the earlier run models I'm almost positive that was it.

 

[Mooseman]

I would also suggest to install a real oil pressure gauge, mechanical or electric, to more easily keep an eye on it. I know the GF won't know squat what to do with it but can tell her to warn you if it drops below a certain point if she happens to glance at it. You can also check it once in a while yourself.

 

[TJBaker57]

I have a 2002 with similar oil pressure issues, though I believe my pickup tube leak is small while your appears greater. I installed an aftermarket mechanical gauge for peace of mind right up where it can be seen without taking your eyes off the road. Mine has been this way for several years and about 10000 miles. It's not a daily driver so I can afford to be less concerned even though I wish to keep it for a good long time to come. At any rate, the gauge also gives me the ability to observe the pressure at various operational states. Mine also starts with normal pressures when first started cold and drops as it warms but I do not drop below say 10 psi. Only when HOT like after a minimum 30 mile drive at highway speeds with warm ambient temps do I see pressure low enough to trigger the factory warning.

 

[chuey_316]

Jumping back in the thread a little, if drilling a smaller hole in the pan would be acceptable for a pressure gauge, or return line, how about drilling, and tapping a 3/4" hole directly under the the pickup tube to oil pump bolt?

This seems like it would allow direct access to the bolt, and enable one to remove the front cover to perform work on the timing chain, the oil pump, and to replace the pickup tube o-ring without having to spend days dissembling, and reassembling everything. Still would be some work involved, but not nearly as much.

I would think that a hole that size, would seal up fine with a 3/4" NPT threaded plug, and even some gasket maker for added peace of mind, or possibly a freeze plug, although I'd personally feel more secure with a threaded plug myself. It's not really on the bottom, or the side, but higher up on the front of the pan.

Obviously, a main concern would be metal shavings in the pan from drilling the hole, but that should be taken care of for the most part by drilling very slowly towards the end, while using a shop vac when drilling, then running some diesel or kerosene through the new hole and flushing any debris that may have made it inside the pan out the drain hole.

I may be way of base here, but it seems like it would work fine, and save people allot of work and time removing a whole bunch of parts in order to get to one hidden bolt.