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Old 01-03-2011, 01:22 PM
Kkrose Kkrose is offline
Join Date: Dec 2003
Location: CA
Posts: 216
What is wrong with the heater/temperature gauge in my car?

I have a 2004 Mazda Tribute that I adore. It has never caused me any problems and other than routine maintenance has never cost me anything in repairs. I guess it's about time, but I am hoping this is a relatively cheap and easy fix (that I might be able to do myself?).

So here is the deal, whenever my car is driving, the temperature gauge stays low (near the bottom) and the heater blows lukewarm air at best. If I come to a stop it will raise a bit. Today I pulled into a parking lot to make a phone call and while I was idling in neutral (it's a manual transmission) the temperature came back up to normal and the heater blew hot air. As soon as I got back on the freeway, the gauge and air temperature dropped again.

I am mostly looking for easy things I can have my semi-car savy friend look at before I take it to an actual shop (which I will do if it is at all complicated). I am extremely broke right now, so if it is something I can fix on my own, that would be great. Any ideas?
Old 01-03-2011, 01:27 PM
running coach running coach is offline
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Probably the thermostat is stuck open.

Paging Rick, Gary T., Greasy Jack
Old 01-03-2011, 01:27 PM
dolphinboy dolphinboy is online now
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Location: Bigfork, Montana
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I'm guessing you need a new thermostat... you can probably replace it yourself.

Last edited by dolphinboy; 01-03-2011 at 01:28 PM.
Old 01-03-2011, 01:37 PM
The Surb The Surb is offline
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Check your anti-freeze / coolant level.
Old 01-03-2011, 01:39 PM
Joey P Joey P is online now
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Originally Posted by The Surb View Post
Check your anti-freeze / coolant level.
Second that. It's easy to check. If it's not the case, no big deal, if it is the case, better that you caught it sooner rather then later.
Old 01-03-2011, 01:41 PM
Philster Philster is offline
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T-stat. Missing or stuck fully open.

Not good for the engine at all. Results: Fuel/air mix is not ideal, and this is not ideal combustion for your engine/emmission control. Doesn't help that the oil isn't fully warm fast enough either.

Easy to fix/replace on most cars.
Old 01-03-2011, 01:52 PM
Kkrose Kkrose is offline
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Location: CA
Posts: 216
I just went and checked the coolant level and it looked fine. What explains the temperature rise when I am in nuetral? Would a stuck or missing thermostat do that? I would think it just wouldn't move at all. I will admit though that I don't know much about cars...
Old 01-03-2011, 01:55 PM
Gary T Gary T is offline
Join Date: Mar 2002
Location: KCMO
Posts: 11,189
My first thought is an air pocket in the cooling system. Check the coolant level in the surge tank with the engine cold (it may be necessary to remove the pressure cap to get a good look). If it's low, top up the coolant to the maximum mark indicated on the surge tank and see if you now have consistent heat. If this was it, the next thing is to find and fix the leak that allowed the loss of coolant and ingress of air.

While a faulty thermostat is not impossible, it is unlikely -- it's rare for a thermostat to go back and forth between poor heat and normal heat. However, if the cooling system is full when the symptom is present, that would be the next thing to check. It's probably quicker and easier to replace the thermostat than to test it.
Old 01-03-2011, 02:02 PM
Gary T Gary T is offline
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Location: KCMO
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I should have previewed before hitting submit. If you're quite sure the coolant level is okay, replace the thermostat. The airflow across the radiator at highway speeds will remove heat from the system quickly. At idle it has a chance to build up some heat, though I suspect it would be below specs (~150 F) with the blower on high.
Old 01-03-2011, 02:48 PM
UncleRojelio UncleRojelio is offline
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Originally Posted by Kkrose View Post
Would a stuck or missing thermostat do that? I would think it just wouldn't move at all. I will admit though that I don't know much about cars...
You are conflating the gauge you are looking at on your dashboard with the thermostat installed on your engine. The gauge tells you the temperature of the coolant circulating in your engine. The thermostat controls the temperature of the coolant.

Last edited by UncleRojelio; 01-03-2011 at 02:49 PM.
Old 01-03-2011, 04:50 PM
automagic automagic is offline
Join Date: Oct 2010
Location: Palmdale, Ca
Posts: 296
As I recall Mazda's typically have pressurized overflow tanks. If there is air in the system the best way to remove it is to let the car cool down. With a large rag over the cap remove the pressure cap on the tank and add coolant up to the full line and let the engine run with the cap off. If there is air it just might bubble up through the tank and the level of the coolant will go down. Add coolant as necessary.

Do this for a maximum of 10-15 min. Since there is no pressure in the system the water will evaporate out messing up your water to coolant ratio. After replacing the cap drive it around and repeat the process. This way you can be sure all the air is out.

After all that is done check under your car for any leaks since coolant should only escape if there is a leak. Although if for some reason you make large elevation changes while driving your car the lower pressure at a high elevation may force a lot of coolant out and when you get back down to lower elevations you will be lower on coolant. If this happens frequently eventually you will lose a lot of coolant.

If that does not help your heating situation, I recommend replacing your thermostat.

I used to have a 2004 Mazda RX-8 which I replaced a radiator on. It took me 5 or 6 tries to get all the bubbles out of the cooling system.
Old 01-04-2011, 11:23 AM
Maus Magill Maus Magill is online now
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Timely thread. My 2004 Passat just started doing the same thing. Time to start looking at new thermostats. Maybe I can replace that myself. Unlike the fscking headlights and airfilter.


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