My heat fades, and winter is coming!

[dshannon]

1998 GMC Jimmy 4.3l, 4x4

The last few cold mornings, got in the truck, started it up, and drove away, got the engine warm, and turned the heat on. The heat gets pretty toasty warm on my toes:), but then fades to cold after about 5min.http://www.s10forum.com/forum/images/smilies/rant.gif :confused:Any clues what could be causing this? A/C and everything else works, including the blower and vent controls, just my heat fades after a few min with it on.

could this be my t-stat? ive noticed this past summer my truck gets pretty warm while sitting in traffic, or the fast food line for more than 5min, it gets up to the 3rd mark on the guage.:shake_125

Any thoughts? winter is coming way too soon........http://www.s10forum.com/forum/images/smilies/eek1.gif

thanks in advance for any input.

Dan

[87wildside]

First check you coolant level and condition. When was the last time you had a flush and fill? I would do a flush and fill plus the thermostat if you haven't had that done in the past year.

[Mikz86TA]

Welcome to The PLANET!! X2 on whart Eric said 4 starters

[T Man]

could be a solenoid problem in the heater ducting. Im not sure, but I believe they used vacuum solenoids in the trucks to the end, if the diaphragm on the heater door solenoid is bad it will activate the door, but bleed down eventually. If you turn the heat on, let it cool down, turn it off, then immediately turn it back on, what are the results?

[dshannon]

coolant level is fine. ive never flushed it though, maybe I'll do that next payday.

T man, After the heat fades out, which it goes from hot to cold in about 20seconds, Ive swithed it off, then back on again to no avail. Havent tried shutting the whole truck off though. Im hoping its just the heater core, and flushing with a garden hose will work.

just for reference, how much collant does it need to fill back up? I'm guessing 50/50 mix too

Thanks

dan

[C4Tom]

How about an upside down thermostat??? Flowing until it gets good and warm then closes... water cools down. Just a thought.

[dshannon]

How about an upside down thermostat??? Flowing until it gets good and warm then closes... water cools down. Just a thought.

I dont think thats it, I havent touched that, everything worked fine last winter.

[Blazer69]

i would still change the thermostat

[T Man]

How about an upside down thermostat??? Flowing until it gets good and warm then closes... water cools down. Just a thought.

Wouldnt work like that, it would still stay closed.

I still think it is somewhere in the ducting, and the doors. Do you have the automatic climate controls?

[dshannon]

T-man, I have manual controls

UPDATE:

ok, well, ive come to the conclusion that im 99.99% sure its the t-stat.

my temp fluctuated wildly from the 2nd mark to the 3rd on the guage. While going down the road at 50-70mph!! So I'll be changing that this weekend probly. Well see what happens.

[jswag5]

before u drain the fluid dump in some fluid flush, run the engine, then drain change thermostat, and refil

[C4Tom]

OKay okay you got me... trying to diagnose a problem at 2am... shame on me. :D LOL

[dshannon]

well, today for poops an giggles, and dad was off so i could use his truck too. I got a new thermostat, and flushed the rad and heater core. I also found the original problem. The petcock on the bottom of the radiator is leaking. the schmo who owned the truck before me broke it, causing a low fluid level. I had topped everything off a week or so ago, but i guess it went down enough to cause probs. I will be monitoring the level, and maybe replacing the petcock.

Thanks for all the replies, i appreciate it!

Dan