Why won't my truck get hot?

[divorced]

.



1996 K1500 Suburban with a 5.7 Vortec.

From a cold start start, the temp gauge will rise to just above the 210* mark, then fall to about 150* to 160* and stay at 160* until I get into town, then it drops to about 150*. The heater doesn't get very warm because of this. I've replaced the t-stat and it operates just as it did with the old t-stat.

Where should I start?

 

[goldwing2000]

Did you clean off the intake manifold where the t-stat sits? I've seen people replace them but the mounting surfacr is so gunked up with corrosion that it doesn't seat right and the coolant just flows on by.

Do you have an electric fan? It might be staying on.

Do you have a clutch fan? The clutch might be seized up and causing the fan to spin full-on all the time.

 

[1979jimmy350]

maby you have a clogged heater core or lines, it is pretty common on the early truck that came with dexicool from the factory, Gm had a problem with leaks on the assembly line so they put stop leak in new truck in the mid 90's, over time this can cause clogs in the system, I worked on a s-10 that the heater core was so clogged that a full pressure hose would barley trickle out of the other end

 

[MTChevy]

you gotta sex the truck up... oh wait this is the garage... I'm gonna say its a t-stat issue still just because it will heat up and then drop down and stay there. what t-stat is reccommended?

 

[divorced]

Did you clean off the intake manifold where the t-stat sits? I've seen people replace them but the mounting surfacr is so gunked up with corrosion that it doesn't seat right and the coolant just flows on by.



Do you have a clutch fan? The clutch might be seized up and causing the fan to spin full-on all the time.

Both surfaces were clean when I took the neck off, there was no corrosion. I wiped them with some paint thinner to be sure they were clean.

How can I check the fan? It has a fan clutch, not electric fans.

maby you have a clogged heater core or lines, it is pretty common on the early truck that came with dexicool from the factory, Gm had a problem with leaks on the assembly line so they put stop leak in new truck in the mid 90's, over time this can cause clogs in the system, I worked on a s-10 that the heater core was so clogged that a full pressure hose would barley trickle out of the other end

I hope you're wrong... I really don't want to mess with a heater core! It does seem to blow hot air when the temp gauge rises high. I'll check the flow if the fan idea doesn't work.

 

[1979jimmy350]

I hope you're wrong... I really don't want to mess with a heater core! It does seem to blow hot air when the temp gauge rises high. I'll check the flow if the fan idea doesn't work.

if it is try and flush it before you go to the extream of replacing it, the reason i replaced the one i was working on is the guy i was doing the work for said just to put a new one in, and it only took me 3 hours for a 8 hour job

 

[bigbluesuburban]

Get some radiator flush and follow the directions exactly. I have used the stuff on several occasions and been horified at what was in a cooling system. Especially on a vehicle that I just purchased.

If your cluth fan is seized up... If you try to turn the fan when the engine is cold and NOT RUNNING then the clutch if FROZE UP. It should spin very freely when the engine and the air is COLD. But as the engine bay heats up the clutch engages and the fan starts to turn.

 

[buffblazer]

i agree with the t-stat idea i put one im my 86 k-5 and it did not fix a thing, i went 6 months before i forgot that i replaced it and found out that the one i put in was in three pieces. so you might have been stuck with a defaulty t-stat

 

[dyeager535]

t-stat controls engine temp, not the fan. If the t-stat is working, the engine can't run too cool. (well, I'm sure there are instances, but not without extreme extenuating circumstances)

New t-stat doesn't=good t-stat, parts store cheapies have a pretty high out of the box failure rate.

 

[3 on the tree]

Are both heater hoses getting hot? If one is a bunch hotter than the other, I would suspect a clogged core. Does yours have a valve that controls water flow thru the core. That would be another suspect. If you can get to the control valve, just replace it with a plastic barb fitting and try running with that, to see if heater temp improves.
I just replace the core on my 70. Low heat and not much air flow. Turns out my ductwork was full of mice nest, and you could not even see thru the heater core fins.

 

[Chaddy]

.



1996 K1500 Suburban with a 5.7 Vortec.

From a cold start start, the temp gauge will rise to just above the 210* mark, then fall to about 150* to 160* and stay at 160* until I get into town, then it drops to about 150*. The heater doesn't get very warm because of this. I've replaced the t-stat and it operates just as it did with the old t-stat.

Where should I start?

I had this happen when I had a -fail safe- thermostat, They stay open all the time and dont work so well for heaters in the winter.

 

[6.2Blazer]

I still think the obvious problem is the lack of total engine heat. If the engine is only getting around 150-160 F then the heater just will not feel that warm when it's cold outside. I know at least two guys who felt the need to put 160 t-stats (despite the trucks being FI and really needing a higher temp t-stat) in their vehicle during the summer and both complained about a lack of heat when it got cold outside. Replacing the t-stat with the correct temp range fixed the problem.

Based on your description I would guess the t-stat is bad as there really should not be that big of a temperature jump between it opening and the operating temperature. Also make sure you have the right temp. range t-stat (I usually recommend the factory version, which in your case is probably a 195 degree.

 

[divorced]

I had this happen when I had a -fail safe- thermostat, They stay open all the time and dont work so well for heaters in the winter.

I'm not sure if mine is a fail safe or not. It did have a small pin off to the side if I remember correctly, but I'm not sure if that's a fail safe or not. I can't remember if I bought my new t-stat at Napa or Advance Auto Parts.

Where should I buy another new one from? The dealer?

 

[divorced]

Are both heater hoses getting hot? If one is a bunch hotter than the other, I would suspect a clogged core. Does yours have a valve that controls water flow thru the core. That would be another suspect. If you can get to the control valve, just replace it with a plastic barb fitting and try running with that, to see if heater temp improves.

They both feel about the same. This thing has front and rear heat, so it has a rear heater core and a lot of hose running along the frame to get back there.

 

[mulletman671]

you might want to check out the radiator cap. if it gets to temp and then spews out, you're not gonna reach the temp that it would normally reach with a good, functional cap. i've heard many instances where the engine reaches temp, and there's no heat, 9 times outta 10 it's the cap. not only that, it's $4 of cheap insurance.

 

[dyeager535]

Where should I buy another new one from? The dealer?

I'd say Delco, I haven't heard of any bad out of the box. (although I'm sure it HAS happened)

 

[6.2Blazer]

you might want to check out the radiator cap. if it gets to temp and then spews out, you're not gonna reach the temp that it would normally reach with a good, functional cap. i've heard many instances where the engine reaches temp, and there's no heat, 9 times outta 10 it's the cap. not only that, it's $4 of cheap insurance.

I could be wrong, but I don't think this would cause the engine temp to lower.

 

[diesel4me]

a chilling tale..

My brother had a Citation come into the dealership he worked at not long after they were introduced...the owner complaind "I cant get any heat out of this thing!--cant defrost my windows,or keep warm!--It threw great heat when I first got the car,now it just blows cool air!"...

So he does all the usual tests and checks things like the thermostat,which was opening at 185 degrees,so he puts a new 195 degree one in,but little or no improvement..then checks to see if it had a hot water shut off valve in the heater hose blocking coolant flow--nope,none there!.. then he checked all the doors in the heater box,to be sure they were all in the "heat" position--yup,all were working correctly..both heater hoses felt warm,but not "hot"..--he was running out of things to blame!..

He asked the guy if he did anything out of the ordinary to the car,as far as maintenence..he said no,but I did try putting cardboard between the radiator and grille to see if that would help--it did a bit,but I shouldn't have to do that on a brand new car,right??..Other than that,all I did was change the oil--I used that new "Mobil 1 synthetic stuff--boy,its expensive!!--but I want this car to outlast me,so its worth it in my opinion"..

The car also had a leaking valve cover gasket,so he decided to have it fixed under warranty..my brother noticed after pulling the cover,the puddles of oil in the head were not even hot,and he'd had the motor running for at least a half hour before he removed the cover!--he'd usually get burned on most engines oil, after running that long!..he then wondered if the OIL could be making the motor run cool--so he asked the guy if he'd be willing to have him change the oil back to "regular" petroleum oil--the owner said ok,but hated to see 25 bucks worth of fresh synthetic wasted,so my brother drained it into a clean empty antifreeze jug,so the guy could put it back in,if the heat didn't improve..

After the car was all back together and fresh 10W-30 was installed,after running for 10 minutes the heater was blowing HOT!--almost couldn't keep your hand in front of it!..he never found out if the synthetic oil caused it or not,all he could figure was the oil reduced friction so good the motor never got hot,or maybe a air pocket in the heater was finally "bled" and restored the heat...but it is something to think about...

 

[Chaddy]

My brother had a Citation come into the dealership he worked at not long after they were introduced...the owner complaind "I cant get any heat out of this thing!--cant defrost my windows,or keep warm!--It threw great heat when I first got the car,now it just blows cool air!"...

So he does all the usual tests and checks things like the thermostat,which was opening at 185 degrees,so he puts a new 195 degree one in,but little or no improvement..then checks to see if it had a hot water shut off valve in the heater hose blocking coolant flow--nope,none there!.. then he checked all the doors in the heater box,to be sure they were all in the "heat" position--yup,all were working correctly..both heater hoses felt warm,but not "hot"..--he was running out of things to blame!..

He asked the guy if he did anything out of the ordinary to the car,as far as maintenence..he said no,but I did try putting cardboard between the radiator and grille to see if that would help--it did a bit,but I shouldn't have to do that on a brand new car,right??..Other than that,all I did was change the oil--I used that new "Mobil 1 synthetic stuff--boy,its expensive!!--but I want this car to outlast me,so its worth it in my opinion"..

The car also had a leaking valve cover gasket,so he decided to have it fixed under warranty..my brother noticed after pulling the cover,the puddles of oil in the head were not even hot,and he'd had the motor running for at least a half hour before he removed the cover!--he'd usually get burned on most engines oil, after running that long!..he then wondered if the OIL could be making the motor run cool--so he asked the guy if he'd be willing to have him change the oil back to "regular" petroleum oil--the owner said ok,but hated to see 25 bucks worth of fresh synthetic wasted,so my brother drained it into a clean empty antifreeze jug,so the guy could put it back in,if the heat didn't improve..

After the car was all back together and fresh 10W-30 was installed,after running for 10 minutes the heater was blowing HOT!--almost couldn't keep your hand in front of it!..he never found out if the synthetic oil caused it or not,all he could figure was the oil reduced friction so good the motor never got hot,or maybe a air pocket in the heater was finally "bled" and restored the heat...but it is something to think about...

Thats 1 of the craziest things Ive ever heard

 

[divorced]

Ok, today I bought an AC Delco t-stat from the Chevy dealer and installed it... but still no change. Then I tried the radiator cap... still no change. This thing will blow warm air, but it doesn't seem to get near as hot as it needs to, and the temp gauge doesn't run above 160 degrees.

I'm not saying it isn't the heater cores (front and rear), but it seems that I would need engine heat first.

Does the antifreeze/water mixture have anything to do with it? My mixture is probably real rich with antifreeze.

Someone told me today that they had the same problem in a '98 'Burb using the orange antifreeze. The shop changed it to green antifreeze and the problem went away. Any thoughts or opinions on this? I also have a '95 with a rich mixture of dex-cool that won't get to operating temps either, but being a regular cab the heater still works ok... just not great.