Overheating Question

[Troys]

A friend of mine recently purchased a 1995 D90 ST. It has about 130,000 miles. The truck's temp gauge goes to the red when he is pulling a grade or if left running and sitting still for longer than 15 minutes or so. When the truck is being driven around, the operating temp regisiters fine. I do think the gauge is working because when it registers hot, it's very hot. All appearances are that the truck has had a water pump installed and the previous owners says that a new themostat was installed. Any idea what to look at? I haven't taken a good look for mysef, but I had a few moments and thought I would post a thread.

Troy

[Mike Hippert]

Viscous fan! when the engine is hot shut her down, then try and turn the fan by hand, if hard to turn then it is working ok, if it is not hard to turn then you know whats wrong.

[chrisvonc]

As I have had to do just about the whole works on our Defender I would say check the following:
- Viscous fan as Mike described
- Double check the thermostat and water pump
- Make sure the system does not have air pockets in it
- Check the radiator. We replaced ours with a 4 core radiator and it never had a problem until out viscous fan gave out. If its questionable you could take it to a shop and have them check it out with a heat gun,
- Check for gases in the coolant. This would indicate a head leak if I am not mistaken.

[loykd]

Troy, Several guys have had to replace or recore their radiators too. Mine was done at about 105k miles.

[Glenn_Guinto]

Mike, by saying "hard to turn", do you mean great resistance or "some" resistance? I've always been puzzled by this viscous fan thingy. Thanks!

[Mike Hippert]

Well there will be a little resistance even when it is cold, so acctually one way to compair is to try turning it after it has been stiing over night (engine is cold), then try turning it after say 15 min of driving so the engine bay is nice and warm. There should be a good differance, sometimes it will get easier to turn when hot! Thats what mine did when it died.

What Troy described is just like a clutch fan. If you are going over 35 mph and it is the temp outside is below 70* F you don't need any fan to keep the engine cool in most cases. But even if it is 30* F out and you are not moving or moving slow the engine will overheat fairly quickly.

[Troys]

Thanks for the info guys!! I will try and sort it out in the next day or so. I will report what i find out.

Troy

[BarryO]

Our Disco did this -- low coolant and no pressure in the system. It was caused by a leak in the coolant reservior. You could fill the system up cold, and it would look fine. What I didn't know was that when the system heated up, the level would rise until it hit the seam in the reservior, where there was a leak. Coolant would just leak out. So check for leaky reservior, and for a cap that won't hold pressure, besides the stuff already mentioned.

[gearco]

Although it goes without saying, don't let this aluminum block motor overheat!!! My Discovery 3.9 did when I pulled a 7,000 lb trencher up a hill. That was the end of the motor. I've heard from reputable sources that when you heat them enough to get a head gasket, they are never the same, even after line boring, facing the heads, etc. At this point, if my Defender temp gauge gets a little over to the right, I'm trying to figure out what to do to lower the temp. You probably didn't need this post, but it made me feel better. LOL