92GT5spd

Hey guys,
got a question for anyone who can help.
I have a '92 Gt 5.0,and when I use my heater,it works fine for about 3-5 minutes.But then it goes to blowing cold air.Also,I noticed when its about to start blowing cold air,my temperature gauge drops down as far as it will go.When the heat comes back on,the temp gaige shoots up to about 3/4 of the way.

Any suggestions?
I bet roundman has the answer to this one.
HELP!!!!!!!!!!!!!!!!!!!!!!!!!It's getting cold here.

Also,I changed the thermostat about a month ago.I think it was a 190.

92GT5spd

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nemethjames1

first thing i would guess is thermostat..... but since you replaced it.... not to sure... maybe your heater core is pluggin up

89stanglx

well if your not getting a stable engine temperature sounds like a cooling problem maybe your system is airlocked. flush everything with a garden hose. Remove the radiator cap and start the engine and keep that radiator full once the thermostat opens the water level will probably drop. I had a similiar problem my temperature guage was staying at or below 100f for the first 2 min then it shot up to 190 in like 6 sec.

nemethjames1

but he didnt mention an overheating problem.... thats why i diddnt think that would be it... but maybe?

86HOGT

You probably don't have enough coolant in the system, this is what happens. Check your coolant level. You probably let out some air after you did the thermostat and now since it's bled, the coolant level is low.

92GT5spd

Thanks for the tips guys,but the fluid level is perfect.
Also,to 89stanglx,I am able to get a stable temp,it's only when I run the heater that the gauge fluxuates.

I found a black box located beneath the air filter box.
This box has 2 vacuum lines going to it,and 2 rubber caps on top of it.The rubber caps cover some holes leading into this mysterious box.I know that vacuum lines play a big role in cars woth ECM's.So I plugged the hole using teflon tape,and some 140mph tape.Using ether I checked to make sure the hole wasn't still leaking.This seemed to help a great deal.Now when I run the heat it stays hot for about 10 minutes compared to 3 minutes before.And now when the heat goes out,it's only for about 30 sec.,whereas before it would take like 3 minutes to get hot again.It's gotta be a vacuum related problem I think.My father-in-law suggested spraying ether on all of my vacuum lines to check for leaks,as it would rev the engine,if it were to pull the ether in.

Anyone know what the black box is for?
Any ideas/suggestions?

nemethjames1

maybe you got some leaks behind your control panel? im not sure what box your talking about? maybe the purge canister setup?

ballzoutstang875.0

thats wierd!!!!!!! it should be the other way around, when u turn heat on, temp should drop!!! although, you dont have overheating problem. sounds to me like your heater cores leakin/clogged but hasnt given out yet. id say replace it! IF YOU DARE hahaha that box you found sounds ALOT like heater core box but maybe im wrong??? is it under dash almost halfway in the middle but more towards passenger side??? are u trying to find heater core box?? if so, let me know!

92GT5spd

Actually it was the vapor canister I was calling the black box.
I put a new cap on there,topped off the coolant checked the cables on the control panel,flushed the heater core,and pulled some hair out of my head.

It works perfect now!Thanks for the tips.
I have no idea which remedy worked since I tryed them all.LOL!
But thx for everything guys.