SOLVED! Cooling system test results.

JayArr

Original poster
Member
Sep 24, 2018
504
Mission BC Canada
Hi All

In the fall after returning from a cross country trip I had to repair/replace a lot of cooling components. There are threads around with the results of my comparison of Behr and Hayden fan clutches as well as the installation of the PCM transmission fluid cooler.

Replaced: Radiator, water pump, fan clutch, rad hoses and a full flush and fill on the block.
Installed: PCM tranny fluid aux cooler kit.

Unfortunately I re-used an older thermostat. In my defense I did check it in a bowl of boiling water to see if it opened and it did, What I didn't check was if it closed after and it doesn't. :Banghead:

The result is that the cooling system hasn't gone above about 160 all winter. I was going to fix it, I've had the part on my bench for months but then we planned a mini vacation with the trailer and I thought this would be a good experiment. With the thermostat stuck open I wanted to see how hot the coolant would get pulling a fully loaded trailer. I wondered if it would get above the 192 that the thermostat was supposed to regulate at.

The result was that, with new cooling components, the engine can pull the 5000lb trailer without overheating the coolant. I went up some major grades in second gear at 25MPH and the engine never got above about 175-180. I don't mind being slow, I just light a cigar and enjoy the drive!

This is good news, it means that when I install the new thermostat it will raise the operating temp to the desired 192 and towing the trailer won't cause it to go any higher.

I never really thought of the thermostat as a device that raises the operating temperature of the cooling system, I realized it was closed at startup and helped the engine warm up but I never realized it kept the temp up even after the engine was warmed up. I guess I just thought that once the engine warmed up the thermostat would stay open to keep the engine cool, this is not the reality.

I just thought I'd share this as a benchmark for anyone wanting to know how hot the engine should be under full load. If the cooling components are good then it should not rise above the thermostat temp.

JayArr
 

JayArr

Original poster
Member
Sep 24, 2018
504
Mission BC Canada
Installed a new thermostat on the weekend and am now running at 94C (200F). The engine now goes to closed loop, I didn't realize but I've been driving all winter in open loop mode because the coolant never reached operating temps.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,045
Brighton, CO
Now you just need to hope that you didnt clog your cat..
 

rchalmers3

Member
Jul 11, 2020
207
Irmo, SC
Thanks for the update and for restoring our understanding of the importance of the thermostat in engine cooling operations.

What I'm left with after reading your threads about your efforts to make the GMT360 a tow vehicle is that the vehicle is not going to ever be a competent tow platform. Would you now agree with my opinion?

As an aside, but related, I have a 2005 GMC 1500 Sierra 2wd standard Cab as my daily driver. I find it to be barely sufficient when I go out and fetch broken down Trailblazers and tow them home using the heavily built U-Haul rental car hauler. My half ton truck needs a stronger transmission, transmission cooler and improved engine cooling to be a reliable tow rig. While I will continue to use the old truck, I must keep it slow and easy, albeit without lighting any cigars!

Cheers,
Rick
 

JayArr

Original poster
Member
Sep 24, 2018
504
Mission BC Canada
I guess competent is a relative word.

If I was towing for a living or towing every weekend or such I'm sure my opinion would be different. I tow a half dozen weekends in the summer and one long two-three week trip each August.

I do now have a transmission cooler and as long as the Envoy will tow that trailer around the mountains and make it to the campsite without overheating, failing or breaking down then I'm fine and would define that as competent. When I'm on vacation I really couldn't give a rats ass how slow I go up a hill, it isn't a consideration or a factor at all.

One factor is that I don't want to have to buy a V8 vehicle just to have enough power to tow my trailer up a hill and stay at the speed limit. I already have one 05 Envoy, two 83 Cadillac Eldorados and a 90 Nissan 240SX in the driveway. I need another vehicle like a hole in the head. I also don't want to get rid of the Envoy to get a V8 because the Envoy gets better mileage and suits our lifestyle 90% of the time, it's just a little slow the 10% of the time it's hauling the trailer.

Now that the cooling system is all fixed I'm a Happy Camper!
 

JayArr

Original poster
Member
Sep 24, 2018
504
Mission BC Canada
I have 4WD and I haven't been able to find a full set at a reasonable price. Sometimes I see rear sets at a reasonable price but without the front set there is no point in buying it.

Good idea though, I haven't looked in months, I need to remember to keep searching.
 
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