This happened to me last year and did it again the other day. Car warms up normally to just under half on the gauge. Sometime later when i'm sitting at a light i notice that the air coming out of the vents gets cold. It's more noticible on VERY cold days, but i noticed it cool off a bit when it was 40 degrees outside the other day. The second i start driving again, it gets hot.

I replaced the water pump with the timing belt about 8,000 miles ago and the coolant level is full. The temperature guage does not fluctuate either which led me to rule out the thermostat, but maybe im wrong.

Anybody had this problem?

 

i had that problem in my old car, but the temp gauge would fluctuate, it was the head gasket.

 

um...my car does that. nearest i can figure (just my logical theory) is that the air is comming in cold when the thermostat is closed cause the water isn't passing through the heater core. So, when idling the car isn't running as hot, thermo closes and your air is just comming from outside. I dunno, makes sense to me but perhaps im just completly clueless lol.

 

So could it be a problem with coolant circulating? I have a VERY small pinhole leak in the top radiator tank but it doesnt leak unless i have been running it for a long time. Could that allow enough air to get in the system even with the radiator full and the proper level in the resevoir???

 

I doubt it would be that, I have the same problem and it takes alittle bit for my car to heat up.

 

Do you put your climate control on fresh air or circulate air? That makes a big difference.
I notice my car stays warmer when it is on circulate.

 

I usually have it on fresh air unless im using the A/C in summer. I still dont think it should cool off when i stop and warm up right as i start moving again (like 2 seconds after i hit the gas).

 

THE SYSTEM HAS TO BUILD UP PRESSURE TO CREATE HEAT FIX THE LEAK POWER FLUSH THE HEATER CORE