4.2 keeps losing oil pressure

[Mooseman]

I have to tell you upfront that we're not a bunch that favour these types of shortcuts for such critical parts.

I suppose it could be possible to drill a hole exactly where the pickup tube to pump bolt is located, but there won't be enough material to tap for a plug. It's thin cast aluminum. You'd be better off using a sheet of steel and JB Weld.

This will also not allow you to completely check the pickup tube. What if one of those seals from oil bottles fell in there and is stuck in the pickup? No amount of solvent will get rid of it. Or hard caked on sludge? The whole thing with Chem Dip is an untested idea by one of our members. What if it's cracked at the hanger weld? Who knows.

 

[chuey_316]

Fair enough. I thought the pan was a bit thicker. If it can't be tapped then it'll get removed if needed. The idea wasn't so much for the pickup tube or screen, but a way to lessen the workload to remove just the front cover to do timing work, or replace the oil pump. Although I suppose if it couldn't be tapped, a bung could be welded on. In all reality, this is something that GM should have done in the 1st place.

 

[chuey_316]

Is this the correct gasket for the pickup tube?

 

[Reprise]

I'm with Moose on this one. My worry would be the shavings from drilling the hole, since you wouldn't be removing the pan as a result. And since it (looks to me) like the oil filter is the *last* place in the oil delivery chain (so... pickup > pump > oil galleys > bearings, etc. > galley > oil filter) -- if even a couple of those shavings get through the screen... you've got a whole bunch of new problems.

Now, I looked for your gasket, since you put a pic of it in your last post. And I may have some bad news for you... I can't find a 'new' oil pump for your application, at least where I'd expect to find it. Nor can I find 'just the gasket'.

If it's like mine, you have the O-ring that joins the pickup tube to pump (and tightly), and then the gasket like you show, which is what goes between the outside of the pickup boss and the bottom of the pump inlet.

Went to Rock, and I see pickup tube, oil pump *rebuild* kit, etc. ... but no actual pump.

Went to Melling's site, b/c when it comes to oil pumps, I trust them for anything short of a race application. They also recommend replacing the pickup tube at the same time as a pump (and they discount the two as a set, vs. buying both separately.

Take a look at the screencap here... *no* oil pump!



They're listing a rebuild kit for the 4.2L, but no full / new pump that you could do a straight R&R with. Which is strange to me, given how many copies of this engine GM sold over the years. (there is a '2nd design' on the pump / pickup, apparently, btw.)

I'll see what I can find for you, especially if I can find the pump / pickup as a kit. That's how I replaced mine a few months back. But for now... it really worries me that a 'rebuild kit' might be all that's in the aftermarket channel.

 

[chuey_316]

I noticed the same thing. I can find the gasket, and the o-ring separate, as well as a couple different oil pumps, but only rebuild kits for Melling, which would also be the brand that I would want to run if I were going through the trouble of replacing it.

 

[Reprise]

I think I found out the 'why'... the oil pump is considered integral with the front cover (it forms part of the housing. Found a GM site that sells cover / pump & associated parts for $232 (plus shipping, etc.) GM # 12628565 . Pickup tube is 12589061 (2nd design).

Apparently, that front cover assy fits all Atlas-style inline engines -- 2.8, 2.9, 3.5, 3.7, 4.2

Went back to Rock, and looked under front cover... Dorman sells one for $115 and change, but they state that there's NO oil pump that comes with it.

That must be why a standalone pump is difficult to find.
I also note that the front cover, to be removed, also incorporates the water pump housing.
In short... I think you've got a PITA job staring you in the face, TBH.

On edit: I went back to Melling's site. They sell K322 as the kit for your application (and state that neither the pickup tube nor the front cover be reused). Pickup tube is 358S (2nd design part).
They don't sell a front cover replacement, and don't list a kit containing K322 and 358S together.
One more thing.... K322 looks more like a standalone pump, rather than something that integrates with the front cover.
Since I don't own a 4.2, I don't have the knowledge / experience that some others here have with that motor. Hopefully, some will chime in (I know Moose will, when he sees this post).

 

[chuey_316]

I could be wrong, but I believe they mean not to use the front cover or pickup tube from the 1st design with the newer style pump. I think the cover could be reused with that pump so long as it's the newer cover. Again, I may be wrong on that.

I don't think I really need a new pump right now, but if I end up being in there with it exposed anyway, it would probably be a good idea to change it anyhow with 215k miles on it.

 

[Mooseman]

You could just get the rebuild kit unless the interior of the pump or pressure regulator casing was damaged, which are part of the cover. Yours being an 05, it does have the 2nd design and uses that flat gasket.

If you are heading down that road, I would get the complete kit from GM instead of mix and match from Dorman and Melling. I'd also replace the pickup for good measure.

And since it (looks to me) like the oil filter is the *last* place in the oil delivery chain (so... pickup > pump > oil galleys > bearings, etc. > galley > oil filter) --

Um, no. All oil passes from the pump through the filter before heading to the bearings UNLESS the filter itself is plugged and in bypass.

 

[Reprise]

Um, no. All oil passes from the pump through the filter before heading to the bearings UNLESS the filter itself is plugged and in bypass.

Not that I have to say this, but... you're right. I stopped looking at the diagram, and looked up the text description. Found multiple places where it's exactly as you describe. Pickup > pump > filter > galleys > lower end / upper end. I wish the LS' stock oiling was similar.

Found a site that has some good info (IMO) on the 4200's oiling; the poster looks to be an engineer / rebuilder of some sort.

4200 oiling system - notes and mod's

The 4200 uses an oil pump in line with the crank driven directly from the front crank snout. The oil pump is contained in the front cover, the crank drive interface is part of the lower timing gear and "floats" on the crank snout. The lower timing gear is driven off the c...

www.inliners.org

 

[chuey_316]

Looks like I'll be tearing it down. Pressure was good at almost 90psi at startup, and was still good and around 12psi at idle when fully warmed up. Soon as I shut it off for a second, and restarted, the pressure dropped to 0psi and stayed there, and now the pressure is dropping to 0psi after warming up again.

I'll end up getting the rebuild kit for the pump, unless the case looks bad like you said Moose, and I'll replace the pickup and gasket while I'm in there as well. If I end up going through all that hassle and it still doesn't work, then as much as it pains me, the truck will be either sold for parts, or will head to the scrapyard.

In the meantime though, since I have to wait awhile before I can get it in the garage, I may try some 10w40 to see if it'll hold pressure enough to get through till I can get into it, but I doubt it'll make any real difference at this point. Maybe just take a bit longer before losing pressure.

It only gets driven within a mile or two radius of our house anyhow, with the exception of Sunday when she makes the 20 minute drive to her mothers, but we can figure out something else for Sunday's for now. I'd run 20w50 now that it's back in stock, but I worry about dry starts with it being 20f on avg right now where I'm at. Local store has some 5w50, but at $10 a quart, it's too much to spend on something that may make no difference.

 

[chuey_316]

I decided to do a little experiment. I let the truck cool down a bit, from 200f to about 130f, and started it. At this point it was still 0psi. I killed the engine and put a new filter on, and my pressure jumped back up to 20psi at idle, but eventually went back down to 0.

If the problem is indeed my pickup seal, or pump, why would just a filter change restore pressure, if even only for a few minutes?

Just seems odd that after a flush and drain or a soak of the pickup, the pressure is right where it should be, but after being shut off for a bit and restarted, the pressure is really low, and goes to 0, and won't pick back up unless flushed or soaked again, yet when I drain the pan it's clean other that a few small pieces of grit at the end.

I would think that if my seal were leaking, either the pressure would stay low at all times, or would at least pick back up on a cold start, then go low again when warm, and I would expect the pressure to rise with the rpm of the engine, and drop back down at idle. Once I shut it down and the pressure drops, even raising the rpm has no effect on the pressure.

Hopefully I won't have to wait to long to get it in the garage. I'd really like to get it apart and be able to have a look at what's happening.

 

[TJBaker57]

I killed the engine and put a new filter on, and my pressure jumped back up to 20psi at idle, but eventually went back down to 0.

If the problem is indeed my pickup seal, or pump, why would just a filter change restore pressure, if even only for a few minutes?

Did you fill the new filter with oil before installing it? Even if you did, removing the old filter allowed oil to drain from the galleries somewhat, creating a void. At startup this air space could be compressed by the pumping action of the pump. This can make it easier for the pump to draw oil up through the pickup tube, even with the leak at the seal. Anyone who has experienced trying to prime a pool pump, oil burner pump, well pump or whatever may have learned it is far easier to get flow established by opening the discharge to allow some flow without backpressure.

That's my guess.

 

[chuey_316]

Did you fill the new filter with oil before installing it? Even if you did, removing the old filter allowed oil to drain from the galleries somewhat, creating a void. At startup this air space could be compressed by the pumping action of the pump. This can make it easier for the pump to draw oil up through the pickup tube, even with the leak at the seal. Anyone who has experienced trying to prime a pool pump, oil burner pump, well pump or whatever may have learned it is far easier to get flow established by opening the discharge to allow some flow without backpressure.

That's my guess.

Yes, I filled the filter. The pool analogy makes perfect sense.

 

[Mooseman]

I can't see how after replacing the oil pump, seal and pickup won't fix this. You are a brave man wanting to tackle this because I've been there, done that and got the scars, both mental and physical. I'd rather set it on fire than go through that again. Go through my threads I posted. Lots of info in there.

 

[chuey_316]

Yeah, I'm definitely not looking forward to this. I remember how much of a pita it was just to swap a trans in my 03 TB, and that was iirc, a 12hr job, and the "new" trans ended up not working. Although with that job, I was on a very tight deadline, which always makes things worse.

This time around I can take my time with it, as I'm down to 2 days a week on avg at work, which will take allot of pressure off to rush through. My motivation will be to keep telling myself that the alternative is to either spend thousands on another vehicle, or thousands for a shop to do the job.

I'm confident that between the info here, the threads you posted, and some YT vids, I can slowly and methodically get the job done, and hopefully live to tell the horror story to future generations. It's times like these that I really wish I had a lift though. Laying under a truck for days is no fun when you have back problems to begin with.

 

[Mooseman]

And you have someone here with the experience if you need counseling

 

[Reprise]

My motivation will be to keep telling myself that the alternative is to either spend thousands on another vehicle, or thousands for a shop to do the job.

I use this as motivation quite frequently. Amazing how effective it is.

It's times like these that I really wish I had a lift though.

Same. My real envy is workspaces with lots of floor area. Working in cramped quarters is not fun (and can be dangerous).

I'm sure you know the following, living in the salt belt, but I'll just jot it down...
Make sure to wear eye protection, as rust will come from places you never knew.

And you have someone here with the experience if you need counseling

Like, as in PTSD?

 

[TJBaker57]

This guy has several videos on youtube detailing his experiences with replacing the pickup tube, oil pump, etc. If nothing else you can get a feel for the job and troubles he ran into...

Given any consideration to swapping in a used engine? Maybe as a 'plan B'?

 

[Mooseman]

I've watched his video series on this and it's pretty good even though he cuts out some parts of the work. He also reused the pickup tube however it was very obvious his was badly clogged. You could save some cash by doing that, just be sure it's not cracked and leak free. I'd say block one end and fill it with solvent through the other end. He also doesn't mention the pump a whole lot except that he isn't touching it but he did as it looks like it's a new cover stripped of its oil pump parts or it was cleaned really well. I'd still rebuild the pump just in case. He also replaces the whole timing set. It might be worth it if it looks like the tensioner is completely out but I do recommend in any case to replace the tensioner and check the guides for wear.

 

[Reprise]

I'm about 2/3 of the way through the series, and just got to the part where the oil pan is off and we get our first look at the pickup screen. Or, putting it another way... "trust me, there's a screen under there"


Was surprised to see it looked this bad -- you can tell he pretty much kept the oil changed, when he took this off at 265K (?) and he had the truck from new.
By comparison, my pickup tube on the 6.0L wasn't clogged at all - and it had a TON of sludge inside the pan (I bought it with ~ 230K on the clock). My build thread shows the pan in detail. The shape of the inlet is different between the 4.2L and mine - but the amount of surface area looks to be about the same.

So... things I've picked up from watching this series, so far...
- The video creator, and some people who entered comments... have stated that shutting down the engine for a few seconds, then restarting it, temporarily resolves the problem. If the OP has found the same... I'd definitely apply that process, and let this wait until temps get warmer, given the typical usage of the vehicle that he's described earlier.

- I'd do a semi-permanent install of a good oil pressure gauge, like he did in the series, and teach the GF to look at it. Maybe run it along the D/S fender / cowl, so she doesn't have to look across to see the tiny markings. Also teach her that that dash 'gage' (I hate to even use the term) is utter crap, and not to be trusted. It's basically an on/off switch.
I'd also install it in the same place he did - the galley plug, and *not* replace the pressure sending unit with it, as someone advised in the comments. While it may not be 'as' accurate as connecting it to the boss for the sending unit... if the pressure sensor is eliminated, the truck is going to show 'no oil pressure', because it won't be receiving a report from the sensor. Plus it will worry the GF.

- If the pickup winds up looking like the pic above, that has to be the issue. I'd look less toward the pump & rebuilding it -- but if you really have to take the front cover off to remove the front hold down bolt on the pickup tube... then I'd replace / rebuild the associated parts. I need to see a pic of how that front tube connects in from the underside -- it just might be possible to get a wrench in from underneath. And -- it may be possible to thread the bolt back in from the bottom end, vs. the top. But I have to look at that area before I can judge. You definitely want to replace the O-ring and gasket, and truth be told, I'd just replace the entire tube, unless you can snake a cam down the entire length and ensure there aren't areas in it that look like the inlet screen.

- It may be beneficial, while you have the colder winter temps, to change the oil viscosity -- not to a *thicker* rated, but to a *thinner* rated oil (I'm thinking 5w-20). My theory is that the viscosity of the 5w-30 thickens, and can't make it through the pickup screen, when it does (from all accounts -- both the OP, and YT --, this happens after about 20min of driving, about the time where you'd expect that oil to be at its 'hot' viscosity.
The beauty of this, is that you don't have to take a thing apart, to try it. It'll only cost what 7qts of what you can find 5w-20 for. I'd use a syn blend high-mileage (actually, I don't know if there's any 5w-20 that's not at least a synthetic blend, TBH.) That would get you through to the warmer temps, where this could be repaired correctly.

That would be my plan, in the short-term. YMMV.

Whenever you do go to do the repair, see if there's a 'HD' or revised pickup with more screen area. I'm just going by what I can see from the one pic, but I'd like to see more screen area (not a bigger diameter tube, as that will affect pressure & volume and probably put it outside the operating specs of the pump. But if I could find a pickup tube with more screen area, I'd look to make the spend for it.

I'll look for some pics of where the pickup tube front bolt connects to the pump, and jump back in once I can see what's going on in that area. Again, if the front cover *has* to come off... I'd rebuild the oil pump for sure (and put a new WP in, since that would have to be removed, as well). Of the two, the WP fails the most, by far. Not too often you hear of a crank-driven gerotor-style oil pump going bad (but it does / can happen.)

 

[chuey_316]

And you have someone here with the experience if you need counseling

Thanks, I'll probably be back with questions when the time comes I'm sure.

This guy has several videos on youtube detailing his experiences with replacing the pickup tube, oil pump, etc. If nothing else you can get a feel for the job and troubles he ran into...

Given any consideration to swapping in a used engine? Maybe as a 'plan B'?

Yeah, I've watched all of em, some more than once. Good info there. I thought about a swap. If I had my new garage built to store the one that's in it I would, and fix this one as a back up.

So... things I've picked up from watching this series, so far...
- The video creator, and some people who entered comments... have stated that shutting down the engine for a few seconds, then restarting it, temporarily resolves the problem. If the OP has found the same... I'd definitely apply that process, and let this wait until temps get warmer, given the typical usage of the vehicle that he's described earlier.

- I'd do a semi-permanent install of a good oil pressure gauge, like he did in the series, and teach the GF to look at it.

I'll definitely be installing a permanent gauge in both her truck, and my TB as well. Turning the engine off doesn't help. It pretty much has to cool down before there's any pressure. Sometimes once cool, the startup pressure will be goo at 75-85psi, sometimes it will only be about 30psi. and won't raise without another flush or soak.

I need to see a pic of how that front tube connects in from the underside -- it just might be possible to get a wrench in from underneath. And -- it may be possible to thread the bolt back in from the bottom end, vs. the top. But I have to look at that area before I can judge. You definitely want to replace the O-ring and gasket, and truth be told, I'd just replace the entire tube, unless you can snake a cam down the entire length and ensure there aren't areas in it that look like the inlet screen.

I saw a vid on YT where a guy took the bolt out without dropping the pan by using a wrench to loosen the bolt, and then used a big magnet attached to a push rod to keep the bolt from falling, but it didn't show how he got it back in. Would probably be a major pita the thread it in without dropping it, and having the remove the pan to get it out anyhow. I may try it just to see if I can get it.

- It may be beneficial, while you have the colder winter temps, to change the oil viscosity -- not to a *thicker* rated, but to a *thinner* rated oil (I'm thinking 5w-20). My theory is that the viscosity of the 5w-30 thickens, and can't make it through the pickup screen, when it does (from all accounts -- both the OP, and YT --, this happens after about 20min of driving, about the time where you'd expect that oil to be at its 'hot' viscosity.

I didn't even think the fact that oil actually thickens as it gains heat. That's a good idea. I'll give it a shot on Tuesday when I have a day off. Could also run a quart of MMO. I believe it drops the hot viscosity by 4w iirc. That would make it approx 5w16. Don't know if that thin when hot would cause any issues though.

 

[Mooseman]

I saw a vid on YT where a guy took the bolt out without dropping the pan by using a wrench to loosen the bolt, and then used a big magnet attached to a push rod to keep the bolt from falling, but it didn't show how he got it back in.

That would be D-ray on an LS engine. It can be done on that engine but impossible on the 4.2.

And the magnet version due to the welded on tab:

I had used this method on the Saab twice. I used washers with that second bolt hole however there is a brace that can be used instead.

Improved Racing Products EGM-500 Improved Racing Pickup Tube Braces | Summit Racing

Free Shipping - Improved Racing Pickup Tube Braces with qualifying orders of $109. Shop Oil Pump Pickup Tube Retainers at Summit Racing.

www.summitracing.com

Of course all this does not apply to the 4.2.

 

[chuey_316]

This is the one I seen.

 

[chuey_316]

Nvm. I see now that it's not an Atlas

 

[Reprise]

Back as promised, after watching the next couple of videos and looking at a couple of pics of the area... here's the best one I could find (which is on this site, btw)



- Given that the front retaining bolt is fastened from underneath, I would say that the pickup tube can be treated as a 'standalone', vs. replacing tube > oil pump > front cover (and WP). On the LS, the bolt is on top, so I thought this one would be, too. Some good news (about time, eh?) I also noted the video creator reinstalled the pickup tube *after* the front cover was reinstalled, and didn't seem to encounter issues doing things that way. (not that he's an expert mechanic, in terms of analysis, but he did try to do decent work on the repair, IMO).

BUT...

- The mounting surface on the front cover (for the pickup tube) will dictate...
Being that you have an '05, you likely have '2nd design' parts, meaning:

Flush mounting surface on the front cover (no inside beveling for an O-ring)​

No inner O-ring (2nd design dispensed with this)​

Only a flush gasket separating front cover mount <> pickup tube​

If that's what you've observed when removing the pickup tube, *and* you can validate the entire inside of the pickup tube is clean (solvent should work a treat... some acetone soaking in my oil pan had it down to bare metal in five minutes)... *and* you can see that the portion of the pump that you can see looks to be clean, itself...
Then I think you could reinstall the tube after cleaning.
If you have '1st design' parts, then I'd definitely reinstall, if you don't want to rip off the front cover. I doubt you'll find (new) replacement 1st design parts any longer in the retail channels.


Note that I *would* replace the water pump, in any event -- it's a known failure part, and you're 'there'. Plus it doesn't require the front cover be removed. And now, the existing one has been disturbed, as well. I think most people here prefer the ACDelco. I'd probably go for that one; it's not a job you want to do twice.

Again... this would be my plan; take it for what you will, as I don't own a 4.2L of my own

 

[chuey_316]

Thanks Reprise. I appreciate the info. I've only done one water pump on these motors. Only took me about 25min including finding tools, and putting tools away. I was able to undo the fan from the pump, and leave both the fan and the shroud in the truck. I could've done it a bit quicker, but I didn't use air tools like the guy in the video, and I took a bolt too far out on the clutch, and it fell in the shroud, so I had to play with it to get it bolted back up. Now that I've done it, I think I could get it down to 15 minutes like the video. Here's the video I referenced when I replaced the water pump on my niece's envoy.

 

[chuey_316]

We've had some pretty nasty cold weather here lately so I haven't been able to do much. Should be warming back up in a day or two, and I plan to try some thinner oil like Reprise suggested. Hopefully it'll help enough to be able to use the truck locally until the weather gets nicer.

I can get 5w20, and I'd like to run a quart of MMO as well, but don't want to end up going too thin. With a quart of MMO, the oil would end up somewhere in the area of 5w16.

Would it be a bad idea to go that thin with the 4.2? Temps here range from 0-30f this time of year, with a few sub-zero days mixed in.

 

[Redbeard]

You won't have any problems running with "thinner" oil. If you would like to learn a bunch about oil go the the web site "bob is the oil guy" https://bobistheoilguy.com/. He gets very in depth about oils, but for the gist of it problems with lubrication come from oils being to thick especially at starting before oil has begun circulating. Many of the newer vehicles (and two of mine) run 0-20w without any problems (and are recommended weight by the manufacturers). This makes sense since today's engines are much tighter clearances than when I was growing up (read '60's & '70's model american cars and liked running 20w-50 oils). It's been a year now since I let my trailblazer with the 4.2 go and it wasn't uncommon for it to have 0 weight oil in it without problems and the engine ran strong with nearly 200k miles on it. And many of the oil changes the oil was sent off to Blackstone for analyzing and ALL came back good. Until last month all these vehicles were in the warm climate of florida were lubrication usually flowed well all year around so this would be more important living in the cooler parts of the world.

 

[Mooseman]

If you're not going to stress the engine or drive it, it should be fine. As usual, keep an eye on your pressure.

 

[chuey_316]

It'll only be driven in town from time to time, and only if the pressure holds up with the thinner oil. Nothing more than a few blocks, and occasionally a mile or so, from 25-40mph. Nothing out of town until I can fix it properly.

I just need to make sure she has a way to get to the grocery store or whatnot while I'm at work. I'll be keeping the mechanical gauge installed as well, and will show her what to look for.

Hopefully some 5w20 and a quart of MMO will do the trick short term until I can tackle the job in a couple of months.

 

[Reprise]

He gets very in depth

Just as an FYI... 'Bob' passed away several years back. "Mrs. Bob" actually maintains the site (not even sure she's still with us any longer, TBH. I don't visit the site as much as I used to.)
On edit... I thought I remembered that Shell / SOPUS purchased the site, actually (no, I'm not kidding).



And to answer the OP's question about thinning out 5W-20 to a -16 and running it... this is the time when you're safest to do so (while it's really cold).
Once temps get above 40-50F, I'd make sure it got drained out and replaced with the regular 5W-30, just to be safe. But you'll probably not leave this oil in that long, anyway.

We're not going to see 40F for another week here in N. IL, and prolly longer than that, in MI.

Hope it works to keep pressure up. Keep us posted (I know I'm curious, at least.)

 

[chuey_316]

Thanks. I'll pick up either some 0w20, or 5w20 synthetic tomorrow after work. Probably go with the 5w20 since I think our coldest temps are behind us for the most part. The rest of this month is supposed to range from 20's to upper 30's. I'll update on how it goes.

 

[chuey_316]

Bought 6 quarts of 5w20 synthetic and quart of MMO today. Tried warming the engine 1st before draining, but the startup pressure was only about 15psi, and dropped to 0 within the 1st minute of running.

One thing I noticed when I started draining the oil though, is that there was much more chunks of grit draining out than any of the previous drains, including the drains after flushing and soaking the pan.

The thinner oil helped out slightly, but still not good enough to be driven. Only real change is that when the pressure drops to 0, I can turn the truck off and restart with just enough pressure to trigger the dash gauge, and keep the lifters quite, but it doesn't last more than a minute or so before having to do it again.

It's looking like the truck will have to sit until nicer weather, when I can dive into the tedious task of tearing it down, and cursing GM engineers for designing these things in such a way as to try and deter people from repairing them themselves, and paying exorbitant amounts of cash to stealerships to do the work for them.

That said, I will continue to buy GM. I think I need mental help.lol

 

[Mektek]

My hot idle is at around 10 psi. I think I'll try draining the oil, and soaking with chem dip (filled through the dipstick tube). Then I'll drain that and pour a gallon of gasoline to rinse out the chem dip. The gas can be recycled in the lawnmower. After seeing the photo of the sludged up pickup screen I am suspecting I may have a similar issue in my high mileage engine.

 

[gmcman]

@Mektek My hot idle on 5W-30 when the oil temp is around 200 deg is about 11 PSI, that's with over 300K miles, but at 1200 RPM it's about 25 PSI. I don't have any issues.

These oil pumps flow a great deal of oil but at a low pressure. That's not saying you may have an issue, but what's your oil pressure at 800-1000 RPM or 1200 RPM?

 

[chuey_316]

10psi at hot idle isn't too bad. I think 10-12psi is normal iirc. I'd have to go back and look to be sure.

I'd be cautious using that fuel in the mower. Allot of mowers these days use nylon parts in the carbs, and the residual chem dip could possibly harm them, not to mention any rubber seals or o-rings in there.

 

[gmcman]

Something comes to mind, there's a mechanical bypass valve inside the oil filter housing. I wonder if the OP's conditions would be met if the valve was stuck open?

Pic of valve.

 

[chuey_316]

Worth a shot to check it before diving in. Should be easy enough to test, but may be a bit of a pain to remove. I believe they're pressed in.

 

[Mektek]

My hot idle on 5W-30 when the oil temp is around 200 deg is about 11 PSI, that's with over 300K miles, but at 1200 RPM it's about 25 PSI. I don't have any issues.

Same here. Sometimes I notice a faint knock, but it goes away when the engine warms up.
What readings would a new 4.2 have?

 

[NJTB]

If it's done it forever, it's probably piston slap. Synthetic oil will most likely lessen the noise.