Overcooling issue

[Daggar]

I am noticing now that with the colder weather hitting my Burb is having trouble staying warm. I figured bad t-stat and upgraded it to the 209 Degree F because I have the rear heater as well. I think when I replaced the rad in the summer after I sliced open the old one changing the fan clutch that either I got the wrong rad sold to me (4 core?) or I have another issue alll together. Anyone have any insight into this issue? The next staep is putting on a winter front.

[tobiahr]

do you have a water temperature guage? i would be interested in the water temp in the radiator or block. i would check the temp there before changing the thermostat or blocking the radiator. the only time i've seen something like this it turned out to be blockage in the heater core. then again we don't get below freezing for much more than 10 days per year here.

[Daggar]

My gauge shows near 150F. Oh and I just replaced the heater core. I cut off the rear heater maunall and the temp gauge creeped up maybe 10 degrees. I am so baffled on this problem

[68Timber]

How cold is it outside when the truck won't heat up? Did the truck heat up properly last winter?

[cableguy0]

with a heavy duty cooling system fresh parts and a 4 core radiator. its very possible if the temp is low enough outside it could be over cooling. cover 1/2 the radiator with cardboard and see what happens. i had the same issue here in maryland after changing to a 4 core rad and having fresh cooling system parts. it was hard to get heat. i usually just blocked 1/2 the radiator with cardboard and problem was solved.

[HarrisonTX]

I agree with cable guy, simply blocking flow through the rad. would help.
2 other options is a bigger pulley to slow the water pump, which wouldnt effect that much....

What about a restrictor plate? Reduce the flow of water? I think that is a common deal, but im from texas, and have the opposite problem

[HarrisonTX]

Here ya go.
I knew i had heard of them.
You said you changed the thermostat yourself, so you can handle this

http://www.summitracing.com/search/?...strictor&dds=1

[Daggar]

Installed the winter front today and isolated the front heater core from the back. I probably got it to put out 70f heat from the vent. I am going to suspect another faulty thermostat. I am having bad luck with this motorad brand crap. I think I am going to go to the dealer and get a GM orginal and see what that does.

[Daggar]

Ok I am begining to get mad now. I went and got a AC/Delco thermostat and I still can't get any decent heat in my truck. The last thing I can think is the rad cap I replaced is faulty and the pressure is leaking out the overflow can. I suppose I should just cave in and take it to a rad shop and see what they say.

[tobiahr]

Just my 2 cents but i don't think it is the radiator but the coolant flow. You state the engine only gets up to about 150 degrees farenheit when running. first what is the outside temp when this is happening? The fact that you are running a higer temp thermostat should keep coolant from circulating through the radiator until it gets up to the thermostats rated temp. if you open the cap on the radiator when the engine is cold you should not see flow. second are you running the heater with the recirc air or fresh? running it with fresh air basically turns the heater core into a extra radiator further cooling the engine as well as bringing cooler air into the vehicle. third, is the heater core feeding off of the water pump or thermostat housing or another point on the engine? its possible that you are bypassing the engine and or thermostat housing by having it feed off of the water pump and return to the radiator there by never realling circulating through the engine enough to heat.

again just my 2 cents but i hope it helps

[motornut]

i removed my rear from both the 87 and 85 and found better heat but during the winter i cover the front ,found better heat covered and front only,then including rear,after replacing core because of low heat,note: if you overheat you can remove the cover quicker than re n re the stat.BTW put the settings on ac max in heat will fog windows but heats truck up quicker,then switch to defrost to clear

[HarrisonTX]

Jesus, all that work, and nothing?
Why not try a restrictor plate like i suggested. Its about a $2 part.
And youve already done the work it takes to do it, twice, as well as replacing a most likely good thermostat..... twice
Or, you could spend money on labor at a radiator shop...
or you could spend the $2.00

[Daggar]

Forgot to mention the restrictor plate I installed also. Gave a bit more improvement but now it's hitting -40 and gawd I am so cold. Hey is my fand supposed to blow outward or suck inward. Mine sucks air in and I always thought it was supposed to blow outward

[HarrisonTX]

Originally Posted by Daggar

Forgot to mention the restrictor plate I installed also. Gave a bit more improvement but now it's hitting -40 and gawd I am so cold. Hey is my fand supposed to blow outward or suck inward. Mine sucks air in and I always thought it was supposed to blow outward

Its supposed to draw air through the radiator. i guess it would be pulling from the radiator.

-40 degrees? Holy hell.
I would completely block off the entire front of the radiator, with a huge piece of cardboard.

Also, if it gets too crazy, summit racing sells a heater called the "mojave" a couple people in the northern states i know, says it will heat the car up in 3-4 minutes. would require a couple heater hoses ran into the cab, but supposedely they work great.

Is there by chance a valve somewhere in one of your 2 heater hoses? If so, it should be a very obvious handle, and that could be stopping water flowing to your heater core.

[Daggar]

Its supposed to draw air through the radiator. i guess it would be pulling from the radiator.

(I am thinking it's the fan clutch now. It locked on full cooling today 2 times. I think I got a defective one. Maybe it's time to consider electric cooling fans...

-40 degrees? Holy hell.
I would completely block off the entire front of the radiator, with a huge piece of cardboard.

(Tried 1/2 coverage today I finally got some heat inside)


Is there by chance a valve somewhere in one of your 2 heater hoses? If so, it should be a very obvious handle, and that could be stopping water flowing to your heater core.

(The previous owner removed the control valve that kills the water flow to the rear heater when the a/c is on. He installed a 4 valve setup and they all look new and work fine. I can section off the rear heater manually and when I do I get a few more degrees in the cab.)

[wildwilly4x4]

Sounds to me like you got a cheap fan clutch. Spend the bones and get an American made replacement. I had this same trouble on my truck using a Vato Zone fan clutch.

[motornut]

in the winter i have totally covered my rad to get heat (cover has real small openings for air like 6x4 on either side .and a few years ago when doing the core i found a broken controller see pic but this was to on/off ac vents........but there is also an ajustment inside on the left of this(air box)for amount of air flow from def/to floor some trucks come set for a little air flow up all the time (pin and clip inside behind area by air hose to diaphram).oh and for fan clutch yes stiff is not good,worse is when the (1978)4 blade stocker fan, blows off one blade BANG,(engine vibrates crazy) out of 360 degres of course it takes out brand new brake lines front and back.0 brakes rolled to a stop safely........heard there was a recall on the 4 bladers long ago?? all better now

[Daggar]

Originally Posted by wildwilly4x4

Sounds to me like you got a cheap fan clutch. Spend the bones and get an American made replacement. I had this same trouble on my truck using a Vato Zone fan clutch.

The sad thing is I paid 80.00 for the darn thing

Originally Posted by motornut

in the winter i have totally covered my rad to get heat (cover has real small openings for air like 6x4 on either side .and a few years ago when doing the core i found a broken controller see pic but this was to on/off ac vents........but there is also an ajustment inside on the left of this(air box)for amount of air flow from def/to floor some trucks come set for a little air flow up all the time (pin and clip inside behind area by air hose to diaphram).oh and for fan clutch yes stiff is not good,worse is when the (1978)4 blade stocker fan, blows off one blade BANG,(engine vibrates crazy) out of 360 degres of course it takes out brand new brake lines front and back.0 brakes rolled to a stop safely........heard there was a recall on the 4 bladers long ago?? all better now

Yeah when I took apart the heater box to replace the core. I found the previous owner had replaced the POS plastic part that snaps with a steel one he must have made and welded on.


Anyway tomorrow I buy a new fan clutch from a diffrent parts store and we shall see what happens.

[tvblazer78]

Originally Posted by HarrisonTX

Its supposed to draw air through the radiator. i guess it would be pulling from the radiator.

-40 degrees? Holy hell.
I would completely block off the entire front of the radiator, with a huge piece of cardboard.

Ya what he said... -40 is just about to cold to drive anything in..

[Daggar]

Another thing. I replaced the fan clutch during the summer because when I bought the Burb it was stuck in full engaged. The new one always seemed tight but it never roared like the old one did at over 2500 rpm. Think they installed a bad one or the wrong one? It says in the manual there is supposed to be a little spin to it but mine always seems tight even after warmup

[Daggar]

And so we buy a new fan clutch and the result... 2 degrees more.. wow

I am guessing now that the rad is too big or maybe the fact it's mostly aluminium. Well I am gonna try covering the whole rad face with cardboard and see what happens now. Oh and I am gonna get the part number for the rad and see what the heck application the darn thing is for. I am guessing a 454 or something

[motornut]

just reading weather temps up here, how cold is it outside there.......i see -29 give or take a day or two.......you won't get much heat out of that cold.....your truck is dealing with wind chill.....so not only the ambiant -29 but then consider how cold the air is as it passes threw the fins will make the truck loose more heat.(like us humans)you only need a small opening.....try it all covered at -29C...... watch carefully and remove if gets too warm.....doin the math thats like -34F lol try to find that in texas.BTW cardboard will soften and may clog up the rad......lol hmmmm may get heat.

[tobiahr]

ok either something is wrong and the coolant is flowing the wrong direction or bypassing the thermostat somehow. the radiator can only cool what is passing through it and if the engine temperature is only getting to 150 the thermostat shouldn't be opening therefore the coolant isn't flowing and the radiator isn't cooling anything. the easiest way to tell if the flow is correct is to open the radiator cap and start the engine while it is cool. if you see any flow at all then it is bypassing the thermostat and that is the problem. the only other thing i can think of is insuring that you aren't running fresh air through the heater coils. they can only exchange so much heat and may not be efficent enough to heat -30 degree air to a comfortable temperature and would also keep the engine temperature down.
not saying covering the radiator won't help but i think there is a underlying issue.

[BLE 'BURBAN]

By chance have you "burped" the cooling system? If you've got an air bubble in the system somewheres, when the cooling/heating system gets warm and builds heat/pressure, an air bubble in the lines would actually slow down or even stop coolant flow through the heater lines/cores.
To burp your cooling system, remove your rad cap and start the engine.
let the engine come up to normal operating temp and let it run there at high idle for about 10-15 minutes WITH THE CAP OFF. Keep an eye on the coolant level in the radiator and top it off as needed to keep it full. If you can see more than 3 tubes down it's too low keep'er filled. put on a NEW NON VENTED rad cap and top off your over flow tank.
If you're still not getting enough heat, go ahead and block off the radiator by 1/2 to 3/4 of the way.

There is a way you can check your thermostat as well. You will need the following thing to do this;
1. An old sauce pan that won't be used for cooking again...EVER!
2. Fishing line.
3. Wooden spoon with handle long enough to span the top of the pan.
4. submersible cooking thermometer that'll read up to 300 degree's.


1. Fill pan with water and put it on the stove.
2. Tie thermostat to wooden spoon with fishing line so that the 'stat is suspended in the water WITHOUT TOUCHING the pan while the spoon is laying across the top of the pan.
3. Turn on burner on stove making sure it's the one you've got your pan on.
4. With cooking thermometer, monitor water temp while watching the t-stat.
NOTE: a 195* automotive t-stat is designed to START OPENING @ 195* but won't be fully opened until the temp is almost 10* above that. Or water ever temp your t-stat is (i.e. 165* = 175* fully open, 209*=219* fully open)
If your t-stat isn't opening up at it's prescribed temp, replace it with one that does.
If it does, install it and remember to "BURP" the cooling system.
Good luck, Have Fun & stay warm!!!
Dave

[Daggar]

Well problem solved. On Saturday the 6 month old rad blew. On closer inspection it was revealed that the rad must have had a small hole or improperly done solder joint which coolent kept coming out of unnoticed and it finally wore a big enough hole in the rad to finally notice. After installing the new rad (Same model and part) the gage returned to the proper operating temp and I had proper heat to run my rear heater. So I suspect I had a pressure leak all along.