Engine not reaching operating temperature

[Matahoe]

Ugh. Today was a real challenge for my Tahoe it seems. It was 32 F this morning and the coolant never reached half way on the gauge (about 175 F according to my scan tool). I drove about 3 miles, let it idle for about 15 min and it still didn't reach operating temperature. I even revd up the engine to 2000 rpm for a few minutes and it still didn't budge. I actually saw temps drop a bit. So I decided to see if there was anyway to check the cooling system per the repair manual. Maybe there is something in there with troubleshooting steps or perhaps a time vs temperature plot? Maybe there is something that tells you if it is taking too long to warm up? Well I looked and depressingly found only basic information. The only thing I found was this brief troubleshooting guide. Needless to say there needs to be a better way to check a cooling system other than making the technician take out the thermostat and check it in a pot of hot coolant. Have things improved any with more late model vehicles?

 

[SnowDrifter]

Honestly I'm not even sure it's worth pulling the tstat to test it

That's pretty well indicative of a bad thermostat. There's literally nothing else that would cause it unless you're some absurd -60 degree weather or something where just the air passing over the engine bay would cool it

 

[swathdiver]

Test and or replace your thermostat. If still won't heat up, cover the grill up like the big rigs do. The K2s have shutters too I think, some of them anyway. I know a guy on another forum who has covered up a large portion of his grill already.

 

[Matahoe]

Test and or replace your thermostat. If still won't heat up, cover the grill up like the big rigs do. The K2s have shutters too I think, some of them anyway. I know a guy on another forum who has covered up a large portion of his grill already.

Thats not a bad idea for an engine with a belt driven fan...but I have an electrical fan. It doesn't run until coolant gets to 225 F. So airflow cooling down the radiator isn't the problem. It seems more likely that cold coolant in the radiator is flowing into the engine via a bad / stuck open tstat.

 

[swathdiver]

Thats not a bad idea for an engine with a belt driven fan...but I have an electrical fan. It doesn't run until coolant gets to 225 F. So airflow cooling down the radiator isn't the problem. It seems more likely that cold coolant in the radiator is flowing into the engine via a bad / stuck open tstat.

My comment was mean as an If/Then statement. It's very likely a thermostat problem. Always better when they stick open than close like the old days!

 

[Big Mama]

A thermostat stuck open is almost like not having one. It can foul plugs and run rich for what they cost and little time to install

 

[Matahoe]

Ok. Looked at the temps again this morning. This time i turned off the front and rear heater fans and it warmed up within 15 minutes at idle. So now there seems to be no problem

 

[Big Mama]

Great just keep an eye on your coolant level and if the temp drops when you turn the heat on. Heater cores leak where you can’t see them. Just helped a guy where the hose going into the core was warm but the one going out was cool. Heater core was clogged. Good luck

 

[Doubeleive]

eh, I would say it is more likely the thermostat was not stuck this time, I would go ahead and replace the thermostat anyway. running or not running your heater fans will not make any difference if your vehicle gets up to normal operating temperature or not

 

[Fless]

Ok. Looked at the temps again this morning. This time i turned off the front and rear heater fans and it warmed up within 15 minutes at idle. So now there seems to be no problem

The heater cores are like mini radiators and will cool down the engine if the blower fans are running. But your engine should be warming up enough even with the fans on if the thermostat is the right temp and working properly (unless like @SnowDrifter said you have crazy cold ambient temps).

 

[SnowDrifter]

Damn that's wild. Can't say I've ever seen the heater out pace the engines ability to produce heat

Glad it's sorted

 

[Matahoe]

engine should be warming up enough even with the fans on if the thermostat is the right temp and working properly

Ok, let's just say for the moment that you are right...and I still have a stuck open thermostat. Turning off the heater fans makes the coolant warm up quicker. So what is left to test? The coolant in the radiator? If it is still stuck open then I should be able to use a handheld laser thermometer and see if the radiator or hose is gradually getting warmer when the thermostat should be closed? That seems like a valid test.

 

[Matahoe]

Damn that's wild. Can't say I've ever seen the heater out pace the engines ability to produce heat

Glad it's sorted

With the heater fans blowing at high speed and the engine at idle I would not doubt it. Especially if you have good coolant flow (to and from) the heater cores.


Again, this is why I am flabbergasted at the lack of a better service manual procedure. Everything (other than removing and testing the thermostat) is left to speculation it seems. In other words...they don't give you any explanation as to what the proper operating characteristics are. For example: how should the engine coolant temperature look when given a certain outside temperature? How about coolant temperature vs rpm/ engine load or different driving scenarios?

 

[Doubeleive]

life experience of myself and probably several others tells me that the thermostat is the primary suspect, provided that you have not done any work to the cooling system previous to this occurring and it happened totally random. Its just not normal and given the thermostat is a mechanical hot/cold spring activated device that I have seen get jammed open, sometimes jammed open and stuck closed that would be the first thing to tackle there cheap and easy on these trucks.

 

[rjr]

I find that between 4-cylinder mode and an aluminum block, engine takes a long time to warm up. Some engines can lose so much heat through the block that engine can't warm up. Two examples were my 1950 Studebaker Commander 245ci 6, and I under stand the old Chrysler slant 6.
To test a thermostat without taking anything apart, let engine run until gauge stops rising. Touch radiator hose above thermostat. If it's cold, thermostat is good. If warm but temp is below where it should be, thermostat is not good.

 

[Matahoe]

The thermostat was replaced 2 years ago with ACDelco 15-11057 . This morning it only took 3 miles at 45mph to heat up with heater fans on.

 

[Doubeleive]

The thermostat was replaced 2 years ago with ACDelco 15-11057 . This morning it only took 3 miles at 45mph to heat up with heater fans on.

That would confirm that it is a sometimes sticky thermostat then.

 

[Matahoe]

That would confirm that it is a sometimes sticky thermostat then.

The only time it over-cools is when the vehicle is at idle and the heater fans are on.

 

[Doubeleive]

The only time it over-cools is when the vehicle is at idle and the heater fans are on.

Then it's stuck open a little, your temp should stay very solid, the only time it may fluctuate is if you were towing up a hill or driving at high altitude and pushing it hard. Some people may disagree but I've never seen a healthy cooling system budge from where it normally sits, maybe a hair or two if it was really really hot out

 

[Matahoe]

I am going to take some temp measurement at the hoses and see if the coolant is heating up in the radiator. Guess it won't hurt replacing the thermostat again. I just hate having to drain the coolant as there is no drain plug.