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What could be causing my 85 6.9 to get hot (on the high side of normal)? It doesn't do this all the time, just every now and then. The coolent is full. One time it got warm and after 10 min it dropped to the middle of normal. Some times if it gets warm, if I shut it off for 5 or 10 min, it cools down. It is doing it more often now. Would this be my rad. cap or thermostat or something else. Please help. Also my overflow does not fill up (or if it does, it is not much). Thanks.
I would change my thermostat first off, but DO NOT get anything but an IH or a Ford thermostat, the universal thermostats built for gassers will mess your cooling system up. I would also flush the rad real good, maybe you have something plugging a few of your cooling tubes
could be you have a lot of debris between the ac. condensor and the radiator and it has the air flow restricted enough that it dosn't take much to start over heating..Looking at the radiator or condensor it is impossible to see the stuff between them with out moving one of them enough to look between them and you will need access to clean this area anyway..It is a common area missed often for plugging.
What really comes in handy for diagnosing problems like this is a small pocket infra red thermometer. But the other way to get some clues is to CAREFULLY feel the top of the rad and then the bottom to see if coolant is really flowing through.
Also, sometimes the cluster gauge reguator can also go goofy and cause high temperature readings, then go back down when you tap the dash.
it gets warm on any kind of driving. I don't pull anything. When it does cool down it goes pretty quick. between the rad and condenser is clear, already checked that. I bought the truck from a farmer so it could be possible that he put the wrong t-stat in.
Thanks for the info everyone, Figured out the problem. I bought a new motorcraft t-stat, and went to install it. When I got the old one out I found it was a cheap gasser t-stat. Put the oem in and it hasn't got close to overheating. Thanks again.