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Thermostat??

2K views 16 replies 10 participants last post by  King Pin 
#1 ·
Ok here goes!
Last week I started my truck to let it warm up a bit before I left my jobsite. After 10 minutes I jump in to go and my temp gauge is almost redlining and the heater blowing cold air. So I kept a very close eye on the gauge while I drove away slowly. Once I got going the temp started to drop back to normal and heater is now blowing nice warm air. So I'm thinking , thermostat is sticking.

I got a new thermostat, put it in and the same problem is happening. It's only doing this when it's cold. Once the I start to drive and the truck is warm it's fine, temp stays normal, heater blows warm. My "low coolant light" is on when the truck is at normal temps, but when it's starts to overheat the light goes out. This makes me think the truck is air locked.
Does this sound right? If it is air locked what is the best way to cure it?
 
#2 ·
Bleeder Screw...

My '98 has a bleeder screw in the thermostat housing. Not sure if yours does or not. If not, I would idle it with the pressure cap off and see if it "burps" the air out. That's the way I used to do it on gassers.
 
#3 ·
Sounds like a weak water pump to me. My dad had a van that would do the same thing.
 
#4 ·
g. vaughn;1321718; said:
Sounds like a weak water pump to me. My dad had a van that would do the same thing.
i second that
 
#6 ·
I also thought about the water pump. The pump thats on my truck is only a couple months old, if even that old. I don't want to change it again unless I'm certain I need another one.

I have been thinking I need head gaskets for quite some time. It's always low on coolant w/o signs of leakage anywhere. No residue on the filler cap and no smoke. But the coolant had boiled over twice on me, so thats why I think I need head gaskets.

But even if I do need head gaskets, why would my heater blow cold? To me if my gaskets were gone (or going) it wouldn't affect my heater? Air locked or weak water pump make sense to me.
Suggestions????
 
#8 ·
An easy way to check for a bad head gasket is to squeeze the top radiator hose before the thermostat opens. It should be soft, if it's hard than you have exhaust gases in the coolant and this is real bad.
 
#9 ·
How long should it take for the upper rad hose to get hard? Mine gets hard but not right away, seems normal to me.

I noticed today, and this is when the temp is normal and everything seems fine. At idle the furnace blows luke warm. If I increase rpms slightly, it blows nice and hot. Is this normal? I've been playing with this thing so much lately that I can't remember what is normal and what is not!

I also filled the expansion tank back to level with coolant and then let it idle. After it was fully warmed up, it blew a gallon or so of coolant back out. It has done this before, but it's been awhile.

Oh yeah I also replaced the rad cap somewhere throughout this process too. Didn't make any difference. Thought I'd try it since its cheap:)

Man this is really starting to sound more and more like gasket, head or block problems isn't it?
 
#10 ·
"How long should it take for the upper rad hose to get hard?"

Depends on the looks of the driver ):h Sorry man, could'nt help it.:lol:
 
#11 ·
Hey Viking, I just read my last post again and started laughing my *** off!! I didn't realize how it looked until I read it again.):h
 
#12 ·
If coolant level is low, the heater will sometimes blow cold air, but if you are loosing coolant without traces of a leak on the outside, you definitely have a more serious issue. Usually these types of coolant leaks will progressively get worse.

You can borrow radiator pressure testers from Autozone, this can really help to diagnose coolant loss.
 
#13 ·
We have a pressure tester at work. I tried it and had no significant loss over the coarse of 10 minutes or so. I took the cap off, put the tester on and started the truck to see how quickly it built pressure and it built pretty fast. This pretty much tells me its at least a head gasket gone!

I need my truck every day until work starts to die down and that doesn't happen until about January. So I will baby it until I can get time to tear it down. When I do tear it down I will get the heads checked and go from there!

Thanx for everyones input, even you "viking" ,:lol:
 
#14 ·
teroma25;1327537; said:
Thanx for everyones input, even you "viking" ,:lol:

NP bud :rolleyes: , hope she holds out for ya.
 
#15 ·
teroma25;1327537; said:
I need my truck every day until work starts to die down and that doesn't happen until about January. So I will baby it until I can get time to tear it down. When I do tear it down I will get the heads checked and go from there!

Thanx for everyones input, even you "viking" ,:lol:
Try the "thermogasket" ? ?? fix by Instarx iirc. Do a search and see because I think if you just don't do anything, it will be blown motor time soon.
 
#16 ·
Yeah I've been following his posts about thermogasket. I am considering it. Today I picked up a package of those AC Delco seal pucks and threw them in. I've been out driving all day and it seems to be holding a good temp and not boiling over. Of course that is only today, but we'll see!
 
#17 ·
head gaskets?

Remove the belt & remove the stat housing. Fill cooling system to full at T-Stat housing. Start engine & see if it bubbles.
 
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