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Engine not reaching operating temp

Slade001

Slade001

1/2 ton status
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New York but NOT NYC
I have tried everything that I can think of. I've changed the thermostat 3 times, 195º thermostat (2 AC Delco's and currently a Mr. Gastket High performance), new gasket, new radiator, new hoses, flushed radiator, flushed heater core, drained and refilled radiator, changed coolant temp sensor and blocked off most of the radiator with cardboard. The temp gauge won't go much above 170º. Keep getting SES code 15. What am I missing? What can I try next? With the temps being in the negatives here for most of the winter it hasn't made for a very comfortable ride. I'm at a loss on this one, any help would be appreciated.

Thanks
 
What are you running for coolant?

More antifreeze than water will release heat more slowly, where more water will be faster to release heat. Also, isn't the Mr. Gasket t'stat a "high flow" unit? That won't help keep temps down; I used a Robertshaw unit for a while but it was over-cooling, even though it was a 195 degree unit.

Otherwise I think you've got all the right ideas...

Clay
 
Prestone 50/50. I believe its the stock fan. I haven't changed it. I HAVE noticed that fan seems to be surging ie. running before the engine is at temp. Possibly the clutch?
 
Possibly the fan pulling too much air all the time.

Back when mine was still running, I had it set up for heavy duty cooling to deal with Phoenix,Arizona summer heat. 4 row radiator and a heavy duty fan clutch, it would always run at t-stat pretty much no matter what I did to it.

Then I moved to NE Indiana, yeah single digit and below zero temps didn't do any good. I couldn't get it to maintain or even reach t-stat temp although I had some ok heat, it wasn't the best.

I tried the cardboard thing, I even blocked off the whole front of the grille with some black vinyl, made it look like a winter cover. Still couldn't do it.

I believe the fan clutch is now too tight and pulling too much air through the radiator constantly even though it really shouldn't matter with the t-stat. I dunno either really.

Another option I was going to try and never did was that I saw Napa had a high temp t-stat available rated at 205*.
 
Your SES plus gauge reading leads me to believe your problem is mechanical, not electrical. If there are bleed holes in the new thermostat, that's not going to help.

I don't live in an extreme climate, but I've never had an issue with overcooling. Realistically the thermostat sets the minimum temp of the motor. The only way the motor can overcool is if fluid is getting through the motor.

At some temperature point, cooling by conduction (ice cold radiator fluid absorbing heat through the lower radiator hose) might be an issue, but I can't see conduction like that ever being enough to keep a 350 under load below rated temp. Your cardboard test IMO confirms that the problem is not conduction.

Pretty tough to test how well a thermostat is closing unfortunately. The heater core is the only "cooling" that should be done with the thermostat closed, as it's the only bypass to the thermostat...coolant comes out of the block under pressure, and dumps back into the radiator (or water pump depending on setup).

Did the problem just start, or has it occurred as long as you've owned the truck?
 
Are there 2 temp senders (gauge vs TBI)?
 
Yes, one for the computer to read, the other is for the gauge. Gauge is the side of the head, computer is up on top.
 
If this is for the OP's problem, technically no. For most, yes. :)

Sending unit is for the gauge, and the coolant temp sensor is for the ECM. Reason it matters as far as I am concerned, is that when people ask for replacement parts, calling a sender a sensor or the opposite, can result in getting the wrong part.

But yes, there are two, so both the ECM and his gauge are reflecting that the engine is running cold.

Edit: D'oh, one minute late!
 
The heater core is the only "cooling" that should be done with the thermostat closed, as it's the only bypass to the thermostat...coolant comes out of the block under pressure, and dumps back into the radiator (or water pump depending on setup).
Click to expand...
This may be it? If that hose is going into radiator from heater it may never warm up?
 
eagle mark said:
This may be it? If that hose is going into radiator from heater it may never warm up?
Click to expand...

Almost all the trucks were already plumbed this way. I don't see any way the heater going full blast would be enough to keep a 350 under 195*, if that was the only way the engine was cooling with a properly closed thermostat.

I suppose if you plumbed the intake hose directly to the radiator you might have problems in really cold weather, but I expect the OP might notice that in heater temps pretty quickly. :)

Dumping the heater core into the water pump would tend to keep the engine a bit warmer, but I think that would be grasping at straws, since GM figured the intake/radiator setup for heater coolant was ok for US sales.
 
No, the heater core isn't going to cool the engine so much it won't warm up.

As I stated before, i believe the thermostat is upside down. If so the water pressure can force it open. Make sure the spring is down (engine side).

If you want to test it you can put in a pan of water with a food thermometer and see when it pops open.
 
AR_K5 said:
No, the heater core isn't going to cool the engine so much it won't warm up.

As I stated before, i believe the thermostat is upside down. If so the water pressure can force it open. Make sure the spring is down (engine side).
Click to expand...

3 times??
 
You can put 12 of them in upside down and get the same result every time if you don't put it in right it won't work right. I've opened them up and found them upside down, had I not known and simply replaced it the same way I found it I would have had problems.
 
Its also worth noting that on a system with lower pump pressure the opposite could occur. The problem then would be the warm water not reaching the thermostat side because the water can't force the thermostat open because the spring is too stiff. That would cause overheating.
 
I work 3rd shift so I'm just getting to read all of you replies now. Sorry for the delay.

Let's run down the list.
1. I know the thermostat isn't upside down. I've done that before, never again.
2. The heater core return is going into the water pump not the radiator. I changed that last month hoping to get more heat.
3. This is an on going problem. I posted before about my CTS maybe being bad and I thought that I had fixed the problem. It's only more noticable now with the extremely cold temperatures here this winter.

This is the thermostat that I'm currently running.

thermostat.jpg
 
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We have several trucks that just don't get warm in this weather. The truck I lease (2013 Pete 320) runs at 180 F even in -15 F weather with no cardboard or winter front. Runs about 190 in the summer, only hear the clutch fan kick in once in a blue moon. Gotta be real hot and humid.

Driving the sister truck to it right now, full cardboard across the rad and -10 F and the highest temp I saw all day was 115 F.

Seems more of our trucks "overcool" in the winter than run normal. Not much help here...but I am following in case there is a clear fix I might pass along.
 
Probably end up being a pointless question, but is your upper hose under pressure once the vehicle starts? Does it stay pressurized (within reason) once you turn the truck off?
 
tRustyK5 said:
We have several trucks that just don't get warm in this weather. The truck I lease (2013 Pete 320) runs at 180 F even in -15 F weather with no cardboard or winter front. Runs about 190 in the summer, only hear the clutch fan kick in once in a blue moon. Gotta be real hot and humid.

Driving the sister truck to it right now, full cardboard across the rad and -10 F and the highest temp I saw all day was 115 F.

Seems more of our trucks "overcool" in the winter than run normal. Not much help here...but I am following in case there is a clear fix I might pass along.
Click to expand...

Thanks. Any help I can get. It's a little chilly here, especially at 0600 when I get off work. Typically its been in the single digits here with windchills below zero. Fortunately I only have a 3 mile drive to work so I can usually suck it up, but for those times that I take the Blazer out for a "long" drive, I would LOVE to:
1. have HEAT!!!
and 2. not get an SES light.
 
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