Cool Off Period After Driving

Joined
Oct 3, 2008
Messages
4,644
Location
Kuwait
It's gotten pretty hot again here recently; 100°F at 06:00 hrs, and usually in the 118°F-125°F range by the time I get off work around 16:30 hrs.

The 4.2L L6 in the Envoy has a 195°F thermostat, which is alright during the cooler months of the year, but does make for some cringe worthy moments in the summer as my eyes are glued to my ScanGuage-II. A reading of 216°F at a constant 62 MPH, and anywhere between 218°F-224°F waiting at the lights is common, sometimes hitting the 228°F-234°F mark in heavy traffic. If I turn the air conditioning off, coolant temperatures will slowly drop, but the truck also becomes a moving oven, so it can be a bit of a delicate balance. The 50 MPH mark seems to be this vehicle's sweet spot with the AC running, where coolant temperatures will be in the 200°F-206°F range when cruise control is engaged. But that's not exactly a safe speed to be driving at on any highway here either.

If memory serves me right, a 50/50 mixture of Dex-Cool and distilled water has a boiling point of 265°F, which is exactly what I have in there. The electro-viscous fan on this application has been tested and functions as intended; attached are the factory stock settings for those interested, when the electro-viscous fan will fully engage.

While a tune to lower temperatures and pressure points in the stock settings is a possibility, along with changing the coolant concentration to something like 70/30, and perhaps a higher pressure radiator cap along with a lower temperature thermostat, I'm more interested in the long term affects of these coolant temperatures, such as the impact on the lifespan of gaskets, seals, etc.

With the exception of cooling system components - specifically radiator hoses, water pump, thermostat, radiator and radiator cap - all seals and gaskets are factory original and do not leak. The replacement cooling system parts are GM Original Equipment, not ACDelco Professional or Advantage, or aftermarket. The vehicle has accumulated approximately 146,000 miles over the years and has zero issues, and no oil consumption between intervals.

After driving in the summer, I will pop the hood and allow the engine to idle with the air conditioning off for at least 5-8 minutes, until coolant temperatures drop of a minimum of 198°F before shutting off the engine. While this is a "feel good" thing for me to do, how much of an overall impact does this really have?
 

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Joined
Jan 22, 2011
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Ohio
Unfortunately, going with a lower thermostat won't accomplish anything. There will only be a small delay and then you will get back up to those temperatures you have now.Stronger coolant mixes and pressure will not help with temperatures but will slightly raise the boiling point of your coolant. You are still a long way from that. Highway speeds you are doing fine. You could improve your city driving temps by increasing airflow. Fan and radiator upgrades would be worth investigating, otherwise there's not much else you can do with it.

Considering the blistering heat you are encountering in Kuwait, I think your engine is coping with it pretty good.
 
Joined
Nov 11, 2018
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Chicagoland
Honestly I wouldn’t worry about it. My Durango, albeit with a 203F thermostat, would do the same thing you’re describing, except at about 235F like when in traffic my electric fan sounded like it would ramp to 100% which would drop the coolant to about 195F, where it would wind down and repeat unless I was moving >20mph.
 
Joined
Nov 20, 2006
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26,858
Location
MA, Mittelfranken.de
Ab, the extremes you experience are very hard on gaskets and seals, that's why when you and I get into a project build for use there we use a lot of teflon and kalrez seals.
There are a few things you can do, as Lubener said increase the size of the heat sink which in this case is the radiator and increase the amount of air flowing over it.
Increasing the size by adding more rows is the easiest way although you may need to make some slight mounting modifications.
Adding a large electric fan is another possibility.

All that being said you may be dealing with another phenomenon that Land Rover did a lot of research into because their vehicles were often operated in extreme conditions called heat soaking. I have experienced this twice over the years in hot summer driving at Autobahn speeds for a long period, you turn the engine off and a hose or gasket blows, letting it idle for a few min is one of the tricks in preventing this.

I have also noticed the thermostat being lower rated than on the same car with the same engine sold in the USA. Combined with improved cooling it does help control heat soak. I will try to find the original paper from Land Rover and email it to you.
Today, some manufacturers are using an auxiliary electric water pump that kicks on after shut down. Lots and lots of papers about this, a very interesting topic indeed.






 
Joined
Dec 28, 2014
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1,520
I’m not sure if this would help, but I suppose you could reduce the amount of coolant in your mixture and go with more water...water absorbs the heat from the engine better than coolant, but then you’d have to worry about boil over (and then maybe add a higher pressure rated cap)? Couldn’t hurt I guess, then just make sure you adjust it for winter.

I’d go on the forums for vehicles in the Middle East and see if they have some tricks that are working efficiently without causing damage.

Honestly I don’t think you’re damaging much of anything anyway...lots of taxis in the Caribbean are running 12 hours a day in blistering heat with their air conditioning on...car loaded with people and luggage...driving like maniacs...stuck in traffic...sun heat and pavement just pounding on these high mileage vehicles. But then again, I shouldn’t say...not damaging much of anything...when I talk to these guys half of them tell me they just put their third engine into it...and I’m like, man, you have 300,000 miles on this thing, time for a new one. Lol.
 
Joined
Sep 10, 2005
Messages
5,005
Location
Massachusetts
Back in the day, Jeep Cherokee (the XJ's) guys would add louvers to their hood to lower the underhood temp and improve flow.
It seemed to work for a friends XJ who drove and wheeled his XJ in Moab.

BTW, after driving home from Boston, I'm the one who needs a cool off period. LOL
 
Joined
May 17, 2021
Messages
740
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open range
Easiest do deal with it: ignore and drive on. Second easiest: Change coolant concentration to 65 % distilled water and 35 % Dex-Cool. Don't overdo as you'd affect the coolant's anti-corrosion properties, however more frequent coolant changes would help to counteract any adverse effects. With 65/35 you're still safe I'd say.


There's a coolant section on this forum btw.:

 
Joined
Oct 9, 2004
Messages
11,394
Location
Cincinnati, OH, USA
I’m not sure if this would help, but I suppose you could reduce the amount of coolant in your mixture and go with more water...water absorbs the heat from the engine better than coolant, but then you’d have to worry about boil over (and then maybe add a higher pressure rated cap)? Couldn’t hurt I guess, then just make sure you adjust it for winter.

I’d go on the forums for vehicles in the Middle East and see if they have some tricks that are working efficiently without causing damage.

Honestly I don’t think you’re damaging much of anything anyway...lots of taxis in the Caribbean are running 12 hours a day in blistering heat with their air conditioning on...car loaded with people and luggage...driving like maniacs...stuck in traffic...sun heat and pavement just pounding on these high mileage vehicles. But then again, I shouldn’t say...not damaging much of anything...when I talk to these guys half of them tell me they just put their third engine into it...and I’m like, man, you have 300,000 miles on this thing, time for a new one. Lol.
You beat me to it-a lot of racers run a product called Water Wetter to prevent corrosion with NO coolant, the OP in Kuwait likely never sees subfreezing temperatures-even a reduced percentage of Dexcool in the coolant, say 30%, would increase heat transfer. That would be an easier experiment than a bigger radiator, a big electric fan, etc. The thermostat only really serves to keep UP the coolant temperature, at 250F both a 195F & 165F are both as open as they’re going to get.
 

JC1

Joined
Nov 29, 2008
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6,516
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Oshawa, Ontario Canada
Does the fan on the Envoy stay on when the engine is very hot after the key has been removed?

If it's a real concern, I would do as Trav recommended and upgrade the Rad and Fan components. What you are doing by letting it cool off is good preventative practices. Are those parts easy to get in Kuwait or do you need to order online and ship them to you?
 
Joined
Dec 11, 2011
Messages
199
Location
USA
I would think you are using synthetic oils for the transmission and engine to stand these higher temperatures, right?

Also, in my experience idling before shutdown is a great idea. Turbo cars do this to prevent coking on the bearings and while you have no turbo, it certainly seems like a good idea. We had to do this with our military vehicles - five minute "cool down" after reaching destination.
 
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Joined
Feb 25, 2019
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Cypress, Texas
I wouldn't worry about it as that's what the block can take and I don't believe GM used 195f thermostats. It's actually good to have a hotter block for efficiency until it gets too hot. Didn't that car have a 210f one from the factory? And If you try to go to a lower one which I don't know if they even exist it'll just delay the amount of time it'll take. I think the cooling system in my 05 Yukon is overbuilt because the temp never goes beyond 210f in city driving. Only went to 220 after over a half hour of idling in stalled traffic but went down quickly once I went going. To be honest I'd just put the scan tool down and perhaps use a bit more coolant like 60/40 and I think you'll be good.
 
Joined
Sep 14, 2015
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ne & sw
pop the hood release lever but leave hood latch still in place? yeah, kinda rednecky and i wouldn’t do it on highway but around town the half inch venting may offer some relief and still be safe.

i was in saudi arabia 1996-98 with a volvo 245. as i recall it preferred its cool northern european origins over the sandbox. i found a great pakistani indie mechanic, he swore by mobil1 and put me onto it. i wouldn’t run a thin oil there. pay special attention to tires, i saw some spectacular roadside wrecks due to blowouts. in those days the rwd chevy impala was the preferred ride.
 
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Joined
Apr 28, 2020
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353
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North Dakota
I've found the worst part of engine heat in high temps is what it does to my garage. It's been around 100 here the last 3 days for a high and pulling a car in at full temp as made it hard to keep the garage under 85. For the OP, as long as your cooing system is maintained well, which it sounds like it is, you'll be fine.
 
Joined
Aug 17, 2016
Messages
842
Location
Alberta
As Trav said, opening your hood after a drive to reduce heat soak is a good idea IMO. At the ambient temps you mentioned, reducing heat soak would help extend the life of all underwood components (including the battery).
For the climate your driving in, the higher operating temps you mentioned sound normal to me.
 
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