Heater and temperature gauge not working properly

BUCKNHORSE

MEMBER
2006 DODGE CARAVAN
3.8L
6 CYL
2WD
AUTOMATIC
223,000 MILES

Hello. I've never ran across this problem before. I'm not a mechanic but I can do a lot of things myself. When I idle my engine temperature gauge works fine and my heater blows the right hot or cold air I want. But when I start going down the road my temperature gauge goes to zero and the heater blows barely warm air at best. But if I say stop at a red light, stop and idle at a store etc the gauge goes back to normal and I get hot air again. Don't know what to check first. Thanks

7 Replies

MASTERWRENCH

MECHANIC
258 POSTS

I would start with your thermostat. If it's stuck open, it's very possible it could be causing this condition. Attached below is the replacement procedure. Also, the attached link shows you how to test a thermostat for proper operation once it's removed from the engine.

https://www.2carpros.com/articles/how-an-engine-thermostat-works

Let us know what you find!

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Saturday, November 9th, 2019 AT 6:37 PM

BUCKNHORSE

MEMBER
4 POSTS

Thanks for the suggestion. I'll put in a new thermostat and let you know what happens. Thanks again.

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Sunday, November 10th, 2019 AT 6:19 AM

MASTERWRENCH

MECHANIC
258 POSTS

Sounds good!

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Sunday, November 10th, 2019 AT 6:27 AM

BUCKNHORSE

MEMBER
4 POSTS

Masterwrench, I thought for sure you had me good to go when I saw the old thermostat. I put in a new one and it's doing the same thing. What should we try next?

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Sunday, November 10th, 2019 AT 8:26 AM

MASTERWRENCH

MECHANIC
258 POSTS

That's very strange. A thermostat in that condition would have most definitely caused the symptoms you were experiencing. For the condition to have not changed at all by replacing it, seems very odd. Has it improved at all? I would double check to make sure all the air has been purged from the cooling system. Take a look at the video below for more information.

https://youtu.be/j8_MD76LbiQ

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Monday, November 11th, 2019 AT 7:49 PM

BUCKNHORSE

MEMBER
4 POSTS

Good morning Masterwrench. Everything is still the same since I've put in the new thermostat. I can start it up in the morning and let it idle and the temp gauge goes to about the middle and the air is really warm after a few minutes. But as soon as I start driving the gauge goes to zero and the air coming out is barely warm at all. I live in the country and even at a speed of 20 mph it does the same. It was 16 degrees here this morning and I don't have a garage to try to purge the system. It's supposed to warm up in a day or so and I'll try that. Do you think I may have got a bad thermostat? I didn't test it before I put it in but I also didn't check to see if it was rated for the temperature range I should have. And the box it came in is gone as well. Anyway thanks for your help. Clyde

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Tuesday, November 12th, 2019 AT 6:51 AM

KEN L

MASTER CERTIFIED MECHANIC
47,643 POSTS

It does sounds like the cooling system has an air pocket. I would try to raise the car in the rear as far as you can while the engine and heater are running (fan on high) then raise the front this "tipping" can dislodge the air. Make sure the cooling system is open and be ready to add more coolant. These guides can help:

https://www.2carpros.com/articles/jack-up-and-lift-your-car-safely

and

https://www.2carpros.com/articles/car-heater-not-working

Please run down these guides and report back.

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Thursday, November 14th, 2019 AT 11:18 AM