Faulty thermostat, or something else?

[Electric Frost]

Lately, the red car has been having the following symptom: The temperature goes towards the upper part of the normal range following a cold start and then all of a falls to normal-cool range corresponding with finally a blast of heat from the heating system. The problem has progressed to the point where the needle almost reaches the red line before shooting down madflame , and as such I am not driving it anymore until I fix it. I am suspectecting that the thermostat is faulty and not opening on time and I have read the SHOtimes instructions for changing it (easy), however from the searces I have done it has been indicated that it normally fails open. Based on the symptoms, would people tend to think that this is indeed the problem?

 

[NetNinja]

I was having the same problems. But a blast of heat from the heating system? Hmm

All I did was change out the thermostat and all is well now. Took about 1 hour including filling up my cooling system. I had to watch the cooling levels for 3 days until I had it filled back up to normal levels.
Make sure the jiggle valves are at 12 0clock when you put the new thermostat back in.

 

[SHOZ123]

If you are getting hot then cold out of the heater with the temp gauge reading high you have air in your cooling system. The air gets trapped in the heater core and will quickly cool off. The lack of a completely full cooling system will allow the pocket of air to stay in the heater lines as there is not enough coolant to displace all the air.

Another thing, unless you just filled your cooling system the only reasons you would have air in there is a leak or a bad pressure cap. A properly functioning cooling system will purge and keep itself free of air.

<small>[ December 25, 2003, 12:32 PM: Message edited by: SHOZ123 ]</small>

 

[Electric Frost]

Sorry, maybe I was not clear with my "blast of hot air" comment. What I meant was that I had the heater on full blast the whole time, yet it blows stone cold until the gauge goes up to the red and then sharply and abruptly drops to normal, and this is when you get the heat all of a sudden.

 

[projectSHO89]

You were clear enough the first time.

Follow Paul's advice.

Steve

 

[Rob94]

Yup. Sounds like an air pocket. You get heat once the gauge drops to normal cause the thermostat opens and lets a gush of coolant flow, displacing the air.

 

[AutoSHO]

One of my friends was having this problem (i.e. thermostat sticking) but his wasn't accompanied by the heat problem. Replacing the thermostat solved his problems.

 

[Electric Frost]

Thanks guys, I appreciate the replies. I'll check for air in the system tomorrow morning and if need be I'll venture out into the boxing day chaos and find myself a t-stat. Enjoy the rest of your holidays everyone...

 

[projectSHO89]

Buy a radiator cap instead. It is easier to change and is more likely to be the culprit. You can always keep the t-stat in reserve.

Steve