Underheating problem

Has anyone ever had a problem with a car underheating?

All of a sudden the temp gauge is lower than usual (about half way up, usually 3/4) and my heater is blowing luke warm air. There is enough coolant in the radiator, there are no leaks and the cooling fan seems to be working properly. The temp seems to actually go up if I turn on the heater. This is completely backwards from everything I know!

I have done no modifications to the cooling system or motor (recently) other than check the fluids, so what's going on?

I don't mind that it runs cooler, the only frustrating part is that now I can't defog my windshield! I will definitely need to fix this problem before winter!


Could it be ALIENS?

hey my d16a did that and it was a thermistat cuz what happens is it gets stuck open and it lets the antifreeze free flow before the motor is warm so it will never warm up so replace the thermostat and it will get warm and work normal.

yeah , just replace the thermostat and you should be good to go

Alright, But I still think it's aliens...

The only part about the thermostat solution that doesn't make sense to me is that even on the two 100 mile drives I've been on in the last week It still doesn't get hot, not even when I was stuck in stop and go traffic on my way back. Also why would the temp gauge go up when I turn on the heater? Normally the heater acts like a secondary radiator and will actually cool the engine a little. I've had cars where I've removed the thermostat alltogether and they would still come up to a normal operating temperature. Granted these were older American cars with V8's, so maybe 4 cylinder aluminum motors react differently(?).

Oh well, just another excuse to finish the "D16A1 build and swap" this summer.

I had the problem with the car never getting warm myself, and it was my thermostat... Stuck wide open. But I couldn't even get luke-warm air out of the thing, and it was the middle of winter... Anyways... At least pull the thermostat out to check it. It only takes about 10 mins. :)

Could be a bad temp sensor sending a faulty signal to your gauge. But i don't think that would affect the heater in not blowing out hot air.

haha,aliens.....

I cant get any heat and my fluid levels are normal. I did smell something burning before the heat went out but not sure where that came from. Did you get your problem fixed and how did you do it - as I may have the same thing. No heat and my car doesn't overheat. thx




Alright, But I still think it's aliens...

The only part about the thermostat solution that doesn't make sense to me is that even on the two 100 mile drives I've been on in the last week It still doesn't get hot, not even when I was stuck in stop and go traffic on my way back. Also why would the temp gauge go up when I turn on the heater? Normally the heater acts like a secondary radiator and will actually cool the engine a little. I've had cars where I've removed the thermostat alltogether and they would still come up to a normal operating temperature. Granted these were older American cars with V8's, so maybe 4 cylinder aluminum motors react differently(?).

Oh well, just another excuse to finish the "D16A1 build and swap" this summer.

Does the heater fan come on?
(located behind glovebox)

Is the heater bypass valve stuck in the closed position?
(located on firewall below intake manifold)

Part of my problem was that my heater blower fan was so packed with leaves and pine needles that it was no longer blowing air.