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I have a Mitsubishi Galant 2003, 2.4L engine with 234k miles on it. When I drive it the temperature gauge gets up to exactly midway, until exactly 30 minutes. Then it goes up to about 2/3 or 3/4 of the way up and then fluctuates between that point and midway after that.

What started all this was that I was seeing the temperature gauge going up and found a small radiator leak and small leaks in my radiator hoses. So I replaced the radiator, coolant temperature sensor, radiator hoses, and the thermostat.

Ever since I've had the car (I got it with 48k on it) I've never seen the temperature gauge read over the midway mark, until the leak, so I'm assuming it's not normal, even though it's not overheating.

I've also checked and the coolant level is up all the time and I do hear the radiator fans working. I also "burped" the system twice to ensure there isn't any air pocket causing this, but like I said, the one odd thing is it starts right at 30 minutes.

Any ideas as to what to check for next?

Update: I've run a vacuum gauge test and it was perfect, no fluctuations and it's within the normal range. No coolant leaks whatsoever, but I'm checking it once a week on the coolant level. No smoke from the tailpipe that I've observed.

So I'm not saying it's not a blown head gasket, but if it is, it has to be a very small leak. I'll check more today.

The problem is still there, but the temperature gauge range is about half of the fluctuations I had seen and now it's returning back to the normal temperature on the gauge or very close. When the car is heating up, both fans are running flat out and then the temperature goes down.

I did basic voltage/resistance tests on the radiator fan controller and everything was within specs.

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There are a handful of coolant/overheating related issues here, so you can search around. Since you've replaced the radiator, it is unlikely there is a clog. Thermostat replaced, so that should be good also. Here are a couple things to look at/verify.

Ensure you have fixed all leaks. Clean under the hood with engine degreaser, then after it overheats, look for signs of coolant spraying. If you can, look under the hood, with the engine running, while it is overheating. I've had leaks that wouldn't show up until the engine was starting to overheat.

The water pump could also be the cause of the failure. I had a similar issue, and the impeller on the water pump had cracked, and was not flowing enough coolant. It was worse when the engine was idle.

This could also be the sign of a bad head gasket. A couple other signs are: exhaust smells like coolant, bubbling in the radiator while the engine is running, one spark plug significantly cleaner than the others, and/or low compression.

A few questions for you. Are you loosing coolant? What are your driving habits city or highway?

  • It's been short trips to work, right at 30 minutes, but today I'm doing an hour on the highway. – James Drinkard Mar 12 '16 at 15:23
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I hope that you have not got a blown head gasket .Bubbling radiator water when cap is off and the engine is supposed to be cold .Odd smelling white smoke coming from the exhaust due to water and antifreeze getting into the cylinder[s] and burning in a very unclean way .Fiat puntos have a reputation for this .I would also check the water pump .Modern water pumps appear to do lower milages than thier 1930s counterparts.

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After thinking on this one I remembered when I had a Mazda 323 that would just die if I ran it at 60 mph or higher for about 30 minutes. It was a module in the distributor that was going out.

So I went and bought a new radiator fan with a controller and I thought that it resolved the issue, which was a fan controller that was going bad, but was still showing it was within specs with my limited testing tools. It helped some, but it wasn't the total solution.

I neglected to change out both radiator fans and the second fan was the intermittant issue. When the car started to overheat, I pulled over and actually saw the second fan start slowing down.

With the high mileage and things in pairs seem to go out together on cars, at least in my experience, I should have replaced both fans at the same time. The new second fan totally fixed the problem.

One other item I wanted to add, the quality of thermostats seems to be much less to me over the last 5 years. I replaced 3 on two different cars from two different local auto parts store chains. I ended up getting a Stant brand and I've not had problems since. The Stant brand was the same price as the Murray and Duralast thermostats I had been using that didn't last more than a year at a time.

  • Doesn't really seem normal to me. Unless this happens in really hot weather and/or car jams. – I have no idea what I'm doing Mar 22 '16 at 10:30
  • It stumped me as well, but like I said replacing both fans solved the problem. – James Drinkard Jun 1 '16 at 3:22

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