I can idle my car for 20 minutes. I can drive the kids to school, but I don;'t get heat until i rev the engine up over 4k rpm. I've replaced the radiator, and thermostat after i found a leak in it last year. i now notice sometimes the temp gauge goes to hot before it comes back down to a medium range. (does that make any sense?). I've also recently replaced the Heater control valve in an attempt to fix this temperature issue. before the HCV was replaced, i would never have cool air as the old one was "stuck", or so i believed.

any idea why my car won't blow out hot air until I race the engine for a while? It's plenty hot before that.

 

probably a bad thermostat or you have a pocket of air in the system that needs to be burped.
a late opening thermostat will do what you describe or air will get stuck in the cooling system like the heater core. try burping the system with the heater on max when the car is cold again. don't open the cap while hot obviously.
It could be something more complicated but those are the areas I would start. If you bought the right thermostat then try burping first for the temp gauge rising and falling issue. for the no heat issue it could be related to that or the heater valve was not replaced right, but it is just a valve a vsv and a vacuum line so its not that hard to mess up or check.

 

Have you checked to see if the valve moves when you turn on and off the heat? You can make sure the valve is working by giving it vacuum and removing it. Also check your coolant level.

 

My car did that when the head gasket was failing. It would mysteriously lose coolant, and occasionally the temp would climb, and fall. When this happened, my heat would go luke warm or cold. Finally, the HG failed in dramatic fashion and I swapped in a GTE

 

yeah it can be a symptom of a slightly blown head gasket. that is what I meant by something more complicated, but no one wants to hear they possibly have a blown head gasket till the simple stuff is sorted. you may not even have oil or coolant mixing to give it away either, you sort of know its starting when you fill the overflow and it mysteriously dissapears every week. over time it will get worse if thats the case. leak down test should show it if this is the case.

 

hmmm. Interesting.

I'll try the burping thing. I really hope that;s it. maybe i'll even get a thermostat replacement again. it was fairly cheap

When i replaced the HCV, i tested it by turning the head up and down, on and off. The valve moved.

It doesn't leak coolant. level stays constant. (i think). I'l double check that.

I hope to heck it's not the gasket.

Thanks guys. I'll check back in with updates.

 

what's that?

 

UPDATE:

I was able to stabilize the temp gauge. Turns out the coolant level was low. Like somebody said earlier, I fill the reservoir tank bi weekly and it mysteriously disappears. I was actually overheating a little bit last week. That is better now.

I am still having intermittent heat issue, however. I think i burped the system correctly, but i cannot be certain. Today I going to replace the thermostat again, and attempt to burp the thing again.

Any other ideas? Somebody mentioned to me it could be water pump. sound realistic?

 

if you are mysteriously losing coolant and it is not leaking onto the ground then you really need to start looking at the head gasket(s).. i had the exact same issue with a leaky radiator (no heat). as long as the radiator is topped off, heat works fine.

 

how does your exhaust look, smoky and a bit sweet? you could have a small headgasket leak into the combustion chamber. usually happens after an overheat the head will warp some and the gasket wont seal right anymore. you may be due for a compression test or a leakdown test to confirm.

If its not the thermostat or an air pocket causing the heat problem, then its either a bad waterpump or a headgasket or a bad radiator. you would probalby notice a bad radiator, and the bad waterpump would not cause the coolant to actually disappear. now if it was just low and an air pocket and took a couple times to fill/get the air out, then it should go back to normal after filling a few times, but if you have to keep on refilling it, you know its going somewhere its not supposed to, and its probably the headgasket. another test is to run the car up to temp where its fully hot, shut it down and pull the plugs and look for the pressure washed one from the coolant.

 

exhaust looks normal. i'll chime in after the thermostat replacement. Thanks guys.