I have a 2002 Range Rover and have had no problems with it until Sunday night. After driving for about 2 hours on the highway I had to stop at a red light in a small town, my temp gauge jumped up to red and coolant started boiling out the cap. After I let it cool down, I added more coolant and drove another hour with no problems. The next day I changed out the t-stat thinking that was the problem. Drove it around town for 2 days, no problem. Wednesday, after driving about 1 hour on the highway, stopped at a red light and overheated again. Same as before, cooled down added coolant another 2 hours down the road no problem...I am lost as what to do next. Each time it was s stop from about 65mph but only those 2 times.

 

Try replacing the reservoir cap, it regulates the pressure in the system. If it is faulty, it can cause the coolant to boil out.

 

Also check fan clutch. If you have no fan, you can drive at freeway speed and the rad is cooled enough by 5280 feet per minute of wind. When you pull off, and there is almost no air flow, the rad will promptly overheat. The fan clutch, when cold, should spin maybe a portion of a turn, feel like peanut butter inside. When engine is warmed up, spin and release it again. The clutch should stop in less than one revolution. A clutch with low or no silicone fluid inside will freewheel, and does not provide much air flow. Foolish mechanics can also install fans backwards, and there will also be low air flow. A proper fan will suck air thru the grille, hold a paper towel against the grille and it should not blow reversed and push the paper away from the grille.

Also check your electric fan, it provides extra cooling at slow speed.

 

I'll put my money on Savannah's diagnosis, something to do with the cooling fan.

 

I a 2000 RR wife ran it hot one day a year ago. I replaced the thermostat heart valve below the radiator, no fix, replaced res cap, no fix, repair shop tokk me for 3500 on a head gasket etc., no fix, well you might get block before it gets hot, repair shop said radiators clogged, i removed had local rad shop clean, still no fix, fans working. After much frustration and head scratching it seems that when it gets hot the upper radiator hose gets very tight. My local repair just wants more money. How can i diagnose the problem. If I did not replace the stat i would say that was the problem. I also evacuated air from the cooling system.

 

This sounds like exhaust gas getting into the coolant. It will make coolant extra hot, and the pressure will make upper hose very hard. There is a chemcial test for this you can buy at parts store for about $60. It will do maybe 15 tests, so you can check it many times after various repairs. The liquid changes color if it senses products of combustion in the hot coolant.

Now for the bad news. It could be a bad install of the head gaskets (warranty?), especially if they did not do machine shop work to "plane" the heads back to flatness before putting in the new gaskets. The spec of flatness is .002 inch, your printer paper is .0038 inch, pretty tight. But it could also be a cracked block or head, which when heated allows the exhaust gas to get into the water jacket of the engine. Heads could have been pressure tested when head gaskets done, block can be pressure tested with some dismantling.

There is a product called KSeal, which can in some cases provide some relief, it goes in the coolant, and when exposed to high temp it forms a glaze and seals the leak. Because your cooling system is already cleaned out, it should not cause much other problems. This is an emergency "get me home" trick for some, and a "last thing before engine replaced or rebuilt" for others, or something tossed in just before vehicle sold. Length of "fix" varys.

 

Thanks very much I will try the gas test. I was told the machine work etc. was done. I now understand the shop mentioned some kind of gas test to determine it needed a head gasket job in the course of getting to where i am now. I will up date soon.