After warm-up, the temp. guage will climb to normal operating temperature and the heater will blow hot air when it's sitting still idling, but as soon as you start driving again the temp. guage drops back down to cold and the heater starts blowing cold air.

Any ideas, I'm having trouble getting a consistent answer?

Thanks.

 

How long does the engine take to warm up and the gauge read normal?

The heater (a small radiator) uses engine coolant as its source of hot water.

Cold coolant as indicated by the gauge equals cold air coming out of the heater, hot coolant equal hot air.

At engine idle, with the car standing still, the coolant would be circulating slower through the engine regulator plus no air is going through the engine radiator. Eventually the coolant will get very hot.

When the engine RPM and cars speed increases, coolant flows faster through the radiator plus air is now flowing through the it. Both will cause the coolant temp to decrease.

Might be a stuck open or slow responding thermostat. The thermostat's job is to regulate coolant temp.

 

Doesn't take long for the engine to heat up, maybe a couple mintues... I haven't noticed any difference in that.

It's like when it's sitting still it gets warm circulation (it's obviously getting very hot just sitting there) and when you drive it, it just cools down too much (like you point out, now it's flowing faster and the radiator is cooling it down too)?

I was thinking a funky thermostat, but the Toyota dealer parts guy said the 1997 didn't have a thermostat? He said it was controlled with a heater core or something?

A thermostat would certainly be a cheap simple thing to try first though?

 

Is the heater and AC system automatic, meaning you "dial in" the temp setting and the climatic system maintains the temp? If so the climate system would be controlling a valve that adjusts the engine coolant going to the heater.

However, the gauge temp going back and forth between hot and cold is not normal and not related to how the climate system works (automatic or manual as in you adjust the temp).

The gauge shows the engine coolant temperature. It should typically stay just below the middle line and be rock solid regardless of driving conditions.

This engine does have a thermostat, perhaps the dealer was confused as they should know this.

Suggest you start with the thermostat.

The location of the thermostat depends on the engine model, V6 or 4 cylinder.

On the 4 cylinder follow the lower radiator hose to passengers side of the engine. The thermostat would be inside an aluminum housing the hose attaches to on the engine.

On the V6, follow the upper radiator hose to top of the engine. The thermostat would be inside the housing the hose attaches to. Between the housing and cylinder head.

For more info might look at the AutoZone website in their vehicle repair guide sections. The site requires membership (free) and contains a lot of specific car repair info.

 

I'll give that a try.

Thanks!

 

A new thermostat fixed the problem. The temp. guage climbs to normal and stays there and it now blows hot air while driving.

Thanks!