Can I get more power from my 4.2?

JayArr

Active Member
I just took a cross country vacation with my 05 Envoy (4.2) and it was less than "worry free" I was pulling a 4800 pound travel trailer and within all the specs that GM laid out in the manual (GVWR, towing capacity etc)

The engine overheats going uphill in the mountains, to keep it from blowing the head gasket I would reduce speed but that meant that by the time I reached the summit I was often only going 10 miles per hour with my emergency flashers on.

Is that normal? Am I asking too much of the Envoy?

The trailer is a small 19 foot with dual axles and electric brakes and the guy I bought it from said he had no trouble in the mountains with his six cylinder Toyota Truck so I figured the Envoy would be OK.

Should I try a separate trans oil cooler? a bigger rad? flash the ECU?

Or is it time to move up to a vehicle with a V8.
 

gmcman

Guru
What gears do you have? Were you towing in 3rd? Could be many factors, 4800lbs is a decent load for sure. What did you have the Envoy loaded with not counting the trailer?

Your GCWR, depending on gearing, is likely somewhere between 10K and 11K, keep in mind a SWB Envoy with 4WD is right about 4700 lbs without driver.

What were the ambient temps?

A trans cooler would surely help a little.
 

Chemman

Registered Member
Besides what gmcman mentions, how is your fan clutch behaving? One would think if it were up to snuff, it would have engaged and pulled more air through the radiator for some extra cooling as the temperature increased.
 

JayArr

Active Member
Thread Starter
According to the RPO codes in the glove box I have 3.42 gears and a GVWR of 6400 pounds. Tow rating is 5800 lbs and GCWR is 11000 lbs.

I took it to the government scale on a Sunday night when no truckers were around and they let me take some weights.

Envoy XL with my wife and I and two dogs (no trailer) = 5934 lbs. > within spec
With trailer attached (adding 400 lbs of tongue weight) = 6329 lbs > within spec
Trailer weight = 4725 lbs > within spec
That makes my CGW 10659 lbs. > within spec

All within spec of what GM says I should be able to tow. I admit it is at the high limit but it is within limit.

Ambient temps were hot but not excessive, 80-90 degrees. I wasn't even running the AC for fear it would overheat faster.

The fan clutch is working, I tested it with my tech2.

I'll start looking for an external transmission fluid cooler. Is there an aftermarket radiator with more rows or better cooling for these?
 

Mooseman

Master Blaster
Moderator
I was looking for the SS aluminum rads when I saw this one:

Not much for details but seems beefier in the core. There are some for the SS but are VERY expensive.

I've got about the same setup as you. My trailer is 5200# and my 4.2 TB with the 3.42 gears struggled up grades and would just run up on 2nd gear. No heating issues though but I didn't have an OBD reader hooked up so don't know what temps I was running except for the cluster's gauge, which never went past its usual temp. Only towed it a couple of times with that truck when I switched to the Saab with its 5.3 V8 and 3.73. Even that truck would get warm (230f) on the highway flat at 60mph with A/C on and low 90's and it would then show one tick to the right on the gauge.

Towing with the V8 is much better since the torque makes a huge difference. I think at these weights, the 4.2 is not the best especially with the shitty 3.42. 4.10 would be the best I would think to increase what little torque these engines have.
 

JayArr

Active Member
Thread Starter
Thanks Mooseman.

I brought my Tech2 on the trip and boy was I glad I did! Using the long lead I could plug it in and route the cord over the dash then down to the passenger side where my co-pilot (wife) would read it. It sat on top of the eBrake for most of the trip. She got really good at clearing codes and reading live data but it wasn't her idea of a great holiday to be concerned about the car all the time.

When I say overheat I don't mean just a little or a "tick" over center. The vehicle ran anywhere from 240 - 265 (gauge between three quarters and full-right) When it reaches 250 the dash light comes on and chimes once to get you to look at your gauges. When it hits about 260 the chime is constant to warn you that you are too hot.

I don't mind slowing down on an uphill climb to a summit, it's the fear that I'm going to blow the head gasket before I reach the top that is disconcerting. On one summit we were at 260 degrees climbing at 10mph in first gear with a mile to go to the top and the "clench factor" was pretty intense.

Maybe I don't have a power issue, maybe I've got a cooling issue.
 

Mooseman

Master Blaster
Moderator
At those temps, the fan would have been commanded to 99%. You would have heard it for sure. If you didn't, the clutch is at fault. It would have been screaming.

BTW, you WERE overheating at those temps.

noname-jpg.56927
 

JayArr

Active Member
Thread Starter
Oh, it was screaming alright! I will also say that once the summit was reached the engine cooled right down within 5-10 miles. I have no doubt the clutch was working. I had double checked that the SS relay was working as well as the wiring from the fusebox to the clutch, it clicked when power was applied, the internal solenoid drew current when it was applied and if I pulled the relay and jumped the outputs it would lock on at 100% and scream really loud.

Maybe I should wire some way to put the fan on at 100% at the beginning of the climb instead of waiting for the engine to heat up.
 

JayArr

Active Member
Thread Starter
I was looking at the rad posted the link but I'm afraid it's Chinese made and I've been burned before by a shiny car part on eBay so I also checked Rock Auto. They list a different rad for the V8 but it's the same dimensions.

Has anyone done a side by side comparison of the 5.3 rad (AC Delco 21506) and the 4.2 rad (AC Delco 21505)?

Maybe using the 5.3 rad would help.
 

Blckshdw

Likes lights and stuff
Moderator

JayArr

Active Member
Thread Starter
Thnaks for the heads up Blckshdw, I didn't notice that, since they are the same size I bet the core is the same as far as rows and capacity so this is no improvement.
 

Mooseman

Master Blaster
Moderator
I have both. They are basically the same except for the lower hose position. GM really cheaped out on these trucks for rads, which is why they were never equipped with electric fans.

There are aluminum TBSS radiators but very pricey (~$1000) on eBay. You might be able to fit one of those and make something up for the lower hose. The regular SS rad is the same as the other V8 trucks with the 5.3 so no gain there.

I dunno. I think you have something wrong in your cooling system. No matter how hard the engine was working., it shouldn't have gotten that hot. Putting in a switch to have the fan pull at 100% before hitting the grade might just buy you some time but it would still eventually overheat. How's everything in there? Age of parts? Maybe the thermostat bit the dust and not opening enough. Rad clogged? And the tranny throwing all that extra heat in there as well couldn't have helped.
 

JayArr

Active Member
Thread Starter
The water pump was replaced 18 months ago when I installed the engine, brand new GM water pump.

During the trip it developed a seal leak and was leaking a small amount of fluid so I changed it with a New Chinese unit from Napa (it was all they had) This stopped the leak but did not change the overheat problem.

It is the original rad, I didn't change it when I installed the new engine so it's possible the rad is partially blocked or plugged. If that's the case I would think the $200 one from Rock Auto would solve the problem just as well as the $1000 aluminum one. I don't really know how to test a rad to see if it's plugged.
 

gmcman

Guru
The fact you were reaching 260 deg, I would perform a leak-down test before you go throwing $$ at a radiator and fan.

There's a slight risk that you could have a failing head gasket, especially running those temps, also compromising the head in terms of a warp.

If the head gasket allows air bubbles into the water jackets that could cause overheating

Hopefully the head and gasket are in good shape, but a leak-down test or a radiator pressure test is in order for sure.

Also, have you tried replacing your thermostat and coolant temp sensor? Are they the original?
 
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Ilikemy3s

Active Member
I always thought the manual specs were for flat roads to slight inclines and not up steep mountains for extended lengths. I agree with everyone that you could have a blockage. If it where me and I had my temps that high for that long, I would replace the Transmission, transfere case fluids as well as an oil change to et fresh non burned fluid in. Just my thoughts on an ounce of prevention
 

Mooseman

Master Blaster
Moderator
Max towing specs put out by OEMs were optimistic at best at the time. This video explains and shows the testing that is now done under the SAE J2807 standard, which was implemented starting in 2013.


We all know that this platform would not pass this standard today for any of these tests except possibly for acceleration with a V8.
 
In addition, to the "weight specs", there are other considerations when towing. The "early specs" for alot of vehicles didn't not include spec like frontal area limits / adjustments. These have significant impact on limits especially when one is pushing the limits. I would suggest that you are likely about 10-15% over the "equivalent GVW" if you take those into account along with the terrain that was being encountered. You could have some "less than optimum" performing components (ie. rad, fan) but I wouldn't expect those to ultimately resolve the situation.
 

Mooseman

Master Blaster
Moderator
Also the brakes, at least on the 4.2 shorties, are marginal at best. Upgrading to the bigger V8 rotors and brackets will help some. SS rotors have more mass for better heat dissipation.

If you absolutely want to keep using this truck for towing, I think you'll need to do one or all of the following:
- bigger brakes
- 4.10 gears
- improved cooling (maybe some Water Wetter might help)
- aux tranny cooler (the bigger the better)

Another thing that could be contributing to overheating is a partially blocked cat. A backpressure test should confirm or dispel this.
 
According to the RPO codes in the glove box I have 3.42 gears and a GVWR of 6400 pounds. Tow rating is 5800 lbs and GCWR is 11000 lbs.

I took it to the government scale on a Sunday night when no truckers were around and they let me take some weights.

Envoy XL with my wife and I and two dogs (no trailer) = 5934 lbs. > within spec
With trailer attached (adding 400 lbs of tongue weight) = 6329 lbs > within spec
Trailer weight = 4725 lbs > within spec
That makes my CGW 10659 lbs. > within spec

All within spec of what GM says I should be able to tow. I admit it is at the high limit but it is within limit.

Ambient temps were hot but not excessive, 80-90 degrees. I wasn't even running the AC for fear it would overheat faster.

The fan clutch is working, I tested it with my tech2.

I'll start looking for an external transmission fluid cooler. Is there an aftermarket radiator with more rows or better cooling for these?
wondering about your "calculations"... were these actually measured on a truck scale... In particular, how was the tongue weight measured (it seems light)....
According to the RPO codes in the glove box I have 3.42 gears and a GVWR of 6400 pounds. Tow rating is 5800 lbs and GCWR is 11000 lbs.

I took it to the government scale on a Sunday night when no truckers were around and they let me take some weights.

Envoy XL with my wife and I and two dogs (no trailer) = 5934 lbs. > within spec
With trailer attached (adding 400 lbs of tongue weight) = 6329 lbs > within spec
Trailer weight = 4725 lbs > within spec
That makes my CGW 10659 lbs. > within spec

All within spec of what GM says I should be able to tow. I admit it is at the high limit but it is within limit.

Ambient temps were hot but not excessive, 80-90 degrees. I wasn't even running the AC for fear it would overheat faster.

The fan clutch is working, I tested it with my tech2.

I'll start looking for an external transmission fluid cooler. Is there an aftermarket radiator with more rows or better cooling for these?
how did you weigh your tongue weight?
 

JayArr

Active Member
Thread Starter
Hi Budwich

Yes, the government truck scale on Hwy 7.

I pulled in and disconnected the trailer.

I weighed the vehicle by itself, without the trailer, but with my wife and I and two dogs. Basically what it would have in it for the trip. That weight was 5934 lbs. I thought that was a little high since I had seen curb weights in the 4200 lb range but I chalk that up to it being the XL, 4WD, with three rows of seats and 650 pounds of passengers (BIG dogs) and a full tank of gas.

I reconnected the trailer and drove onto the scale so the Envoy wheels were on and the trailers were not. The weight was 6329. Simple math says that the difference is the tongue weight right? 395 lbs.

I pulled forward so that the Envoy was off the scale but the tandem axels of the trailer were on. It reads 4329 lbs. I add the tongue weight of 395 lbs to this to get the total trailer weight of 4725 lbs.

Is my procedure or math wrong?
 

JayArr

Active Member
Thread Starter
Thanks all, good advice.

That video is eerily familiar, I basically performed that last test over and over the last two days of the trip.

Crowsnest Pass - elevation 1,358 m (4,455 ft)
Kooteney Pass - elevation 1,774 m (5,820 ft)
Bombi Pass - elevation 1215 meters (3986 ft)
Bonanza Summit - elevation 1535 m (5,036 ft)
Eholt Summit - elevation 1028 meters (3372 ft)
Anarchist Summit - elevation 1,491 metres (4,892 ft)
Richter Pass - elevation ~650 m (2,130 ft)
Sunday Summit - elevation of 1,284 m (4,213 ft)
Allison Pass - elevation of 1,342 m (4,403 ft)

The thermostat was new 18 months ago when I installed the engine but that doesn't really mean anything, I can remove it and take a test drive to see if that helps. I've got the Stant kit to pressure check radiators/cooling jackets, I can do that this weekend.

The cat is new, I put it on in July.

This is the XL so if my research on Rock Auto is correct it already has the big brakes.

I'll look for a separate transmission fluid cooler and 4.10 gears
 

gmcman

Guru
FWIW, I weighed my SWB Envoy, 4WD, 4.2L when it was new.

Just the vehicle, full tank of fuel, only cargo was the owners manual and the cargo net, as it was equipped when I took delivery.

On a certified scale, it was 4720 lbs, which is within + - 20 lbs.

The LWB models must be easily pushing 5000+ in 4WD trim when empty.
 

JayArr

Active Member
Thread Starter
I think you're right gmcman, 5934 minus 650 for passengers, 130 pounds of gas, my 50 pound bin of fluids/belts/parts would leave a dry weight of about 5100 pounds.
 

gmcman

Guru
I was looking for the SS aluminum rads when I saw this one:
Not much for details but seems beefier in the core. There are some for the SS but are VERY expensive.

Thanks for the link. As I stated in a different thread, when I had my radiator replaced due to someone taking the nose of my Envoy, I started seeing slightly higher than normal temps when driving in the city on hot days and when towing. I don't ever remember seeing the needle 2-3 ticks past 210.

Maybe it was a cheap aftermarket radiator, fan, but I want to look into this and from what I understand the OE radiator is good and some aftermarket brands are better than most in regards to heat transfer.
 

Mooseman

Master Blaster
Moderator
Could very well be the radiator if it's not OEM or ACDelco, especially if there aren't as many passages or they're not as big. Who knows with these Chinese clones. I know the one I got from Prime Choice at the time for the EXT never had any cooling issues except when I was running efans. Never had an issue with the thermal fan and it was used a couple of times to tow a very heavy trailer with a medium sized tractor.

And of course, the ACDelco is the most expensive. At RA, it's $200CAD + shipping and taxes. Be sure to check the engine over to be sure it didn't suffer any damage.
 

TollKeeper

Gold Supporter
I guess the XUV (LWB) might be heavier. When I scaled it some years ago, just me, 3/4 tank of fuel, and nothing else except some papers in the glove box and center console. I was at 5980 lbs
 

gmcman

Guru
Something else that comes to mind is to confirm that the heater core is not restricted, and green coolant was never mixed with dexcool.
 

limequat

Hobbyist
Not really the same thing, but I just pulled a ~5000 lb with an explorer for 900 miles. Many miles through mountains. The Explorer is the twin turbo V6, so power wasn't my issue. Stopping was the issue.

Like OP, I was narrowly within specification. But tow ratings are largely marketing. In hindsight, if I was to do it again (especially with family aboard), I would have rented the largest/heaviest vehicle possible. I'm all about doing the most with the least, but 5k lbs is a lot, and they don't do crash tests with trailers attached.

IMHO, definitely move up to a different tow vehicle AND get the reflash :smile:
 
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JayArr

Active Member
Thread Starter
Hi Limequat

How will a reflash help me? can you do something specific that will help me tow?

I do have a spare ECM so if there is a way to make a special "Tow ECM" that I put on the car for vacations that would be a neat arrangement.

JayArr
 

Mooseman

Master Blaster
Moderator
It helps to put an @ in front of a user name, like this: @limequat
The user gets a notification that he's been mentioned in a post.
 

limequat

Hobbyist
Hi Limequat

How will a reflash help me? can you do something specific that will help me tow?

I do have a spare ECM so if there is a way to make a special "Tow ECM" that I put on the car for vacations that would be a neat arrangement.

JayArr

I was mostly joking because I'm obligated to recommend my own tune :smile:

The only difference I make for a tow tune is to delay the activation of powertrain enrichment mode. Otherwise your fuel economy could be even worse than normal when towing.

One of my old college profs made the statement that for every 1 HP put to the pavement, 1 HP is going out the tailpipe and another out the radiator.
While you definitely want more power, at this point it will only cause you to overheat faster.
 

JayArr

Active Member
Thread Starter
So, reading the old posts I get conflicting info, a few years back the Hayden fan clutches were the Go-To units but later posts say Hella - Behr.

Rock Auto doesn't sell the Hella-Behr but they have the Hayden for $130 less than the AC Delco.

If it was your car would you buy the Hayden or spring the extra cash for the AC Delco?
 

Mooseman

Master Blaster
Moderator
Hayden.
 

JayArr

Active Member
Thread Starter
Great!

OK, my cart has AC Delco radiator, hoses, water pump and a Hayden clutch.

Here's another left wing question: Would you replace the temperature sensor when replacing the rad/water pump/clutch if you had no reason to think it was bad?

Do these fail or go out of calibration regularly?
 

Mooseman

Master Blaster
Moderator
I would replace it for the only reason that it's right there just above the t-stat as a preventive and also eliminate that as a possible source of issues. Whenever it gets really hot like that, stuff tends to melt down. Cheap insurance.
 
I was mostly joking because I'm obligated to recommend my own tune :smile:

The only difference I make for a tow tune is to delay the activation of powertrain enrichment mode. Otherwise your fuel economy could be even worse than normal when towing.

One of my old college profs made the statement that for every 1 HP put to the pavement, 1 HP is going out the tailpipe and another out the radiator.
While you definitely want more power, at this point it will only cause you to overheat faster.
@limequat do u still do custom 4.2 tunes?
 

rchalmers3

Gold Supporter
Great!

OK, my cart has AC Delco radiator, hoses, water pump and a Hayden clutch.
@JayArr I'm late to the converstion, but I am curious to know if fitting that collection of cooling system pieces did anything to control the engine cooling issues you were experiencing. Prolly need hotter weather and another long summer trip, eh?

Another question: While making the hauls up the mountain passes, did your navigator and engineer happen to monitor the engine fuel trim, timing and knock suppression?

Those PIDS may give you further insight into being able to include or exclude mechanical issues, and hopefully put you on track for a remedy.
Rick
 

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