My disco 2 is over heating when I go for more than 15 miles. I have only had it a month.. has done it since i got it. Im assuming when it has had time to heatup. It has a new h2o pump new thermo. sometimes when i shut it off the fans run.. sometimes not..oil light flickers when it gets hot... if I keep the rps up doesnt flicker. I am wondering about fan /temp sensors.. or just the electric fans..Not a mech but have had to work on my own stuff all my life. Can somebody help me diagnose this??

 

What coolant are you using? Tell us more about your truck year, mileage? Radiator or head gaskets could be the problem and either way it sounds like you are going to need to be pretty mechanical real soon.

 

Do not continue to drive it or you may toast the engine.
If you want help with this, send me your number and I'll call you back today.

 

You are thinking the temp gauge works like other cars, and it doesn't. It will stay a 50% point if temp is in nomal range. But only when overheating starts does it move above mid point. Much easier to see with a digital scanner or Ultra Gauge.

If you also hear gurgles under the dash that is an indication of exhaust gas in coolant (head gasket). There is a $50 chemical test for that you can buy at parts store.

If new water pump the fan belt could be on wrong, fan blades reversed, etc. A paper towel should be held to the grille by air flow rather than blown away.

Radiator can be half full of sludge reducing cooling, this will show up slow overheating. Rapid "volcano" overheating is usually head gasket or worse.

You would also want to be sure you are not loosing coolant. It can leak making the overflow bottle low, and that leak could be external from a hose, etc.