A two-year-old cooling problem fixed

Finally, after two years I figured out the cooling problem that was affecting my car's performance. It turns out the problem started with a bad fan clutch and I made it worse with a defective thermostat. Shame on me! This summer, I decided it was time to fix it and I did it! Here's how:

Bad fan clutch. Note the rusted bimetal sensory system.

The story starts with a 2004 Dodge Durango with a dead fan clutch. Actually not totally dead, but it wouldn't engage when the temperature was high enough, as it is supposed to do. It was running in "idle" all the time, which is fine for almost every day in San Diego weather. However, during the summer of 2009, weather got very hot and the fan clutch wouldn't engage so my car overheated a little bit, although it never got bad enough to turn the MIL light on, but it scared the hell out of me. At that time I didn't know much about car repairs, so the first thing I did, since it was the easiest to do, is to get a new thermostat in. I was obviously stumbling in the dark. Unfortunately, I got a defective thermostat from Autozone. This thermostat had a gasket that was not sealing properly and introduced a coolant leak. The leak made the cooling system unable to pressurize properly and that's why it kept overheating even more than that Summer 2009.

Close up of thermostat enclosure

So my car ended up being worse than it began, now we're facing a dead fan clutch and an open cooling system.

During these two years I never thought the thermostat could be the problem, as it was recently replaced, and I kept replacing stuff... replaced water pump, radiator hoses and clamps, changed coolant, flushed cooling system and even took out the radiator and had an expert clean it with rods. I also had my system checked for pressure by a couple of shops, and they weren't able to find anything wrong with my radiator or system. I even added a dye to my coolant that allowed for easy identification of leaks with a special UV light. But never had luck finding a leak.

New upper radiator hose and clamps

At this point, I haven't got the problem fixed, but I sure learned about car repairs, at least cooling system repairs.

This summer, when I was about to replace the radiator as a last resort, I thought I would try a pressure test myself. So I borrowed a radiator pressure tester from O'Reilly (by the way, great tool made by CTA Tools, highly recommended, very sturdy and well made) and voila!, as soon as I applied pressure above 20 PSI, I saw coolant dripping from the thermostat onto my garage's floor. It turns out the Autozone thermostat gasket was bad, but the leak was so small that it was not evident in any of the quick pressure tests they did to my car.

Replacing the thermostat

The cooling system was actually broken in an interesting way: it was working properly at low PSI pressures, no leaks, but when coolant was getting hotter and pressure rose around 20 PSI, the gasket couldn't hold the pressure and coolant started to leak. Note that I had no leaks in my garage floor whatsoever, which made it more difficult to diagnose.

But now I had found the leak and I assured myself I was going to get it fixed for good.

Fortunately I kept the original Chrysler thermostat - which by the way, tested ok when put in boiling water, and that allowed me to confirm the Autozone thermostat was bad. So if my original thermostat was good, what caused the initial overheating two years ago?

Fan removed for replacing the clutch

In retrospect, I figured out that the original problem had to do with the fan clutch, actually I never heard my fan "roar" and that's what made me look into it. I had a plan. I was going to replace:

• Fan clutch
• Coolant
• Thermostat
• Accessory belt - reaching End of Life at 100.000 miles

 

My car is getting all these

Once I had a written plan and the proper tools, it was very easy to get the job done. First I removed fan and fan clutch, accessory belt, drained the coolant, and got everything ready.

Replacing the accesory belt

Then I put the new thermostat in, put the new accessory belt and screwed the new fan clutch to the fan and got it installed.

Then I filled the cooling system with Zerex G-05 coolant and using the spill-free funnel by Lisle.

Filling the cooling system

The new thermostat showed no leaks and the new fan clutch engages when the temperature is high enough and makes a roaring noise, not convenient but keeps the engine cold. Hey it's a truck, after all.

The temperature of the engine is now a lot cooler than before, even when going uphill or in hot weather. I was getting used to seeing the engine temperature gauge touch the midpoint and even go above it. Now it stays way below the midpoint.

A look under the hood after work is finished

End of story.