I have a 1999 Discovery II. I have replaced the thermostat, upper and lower radiator hoses. Heater blows hot. Running universal 50/50 green cooant. Starts running hot when a/c is blasted. Granted it was 98 degrees on the thermometer in the car. No leaks that I can see. Anybody Aden any ideas what I should troubleshoot next?

Thanks.

Phil

 

1. If you define "hot" as anywhere above the 50% spot on the gauge then we agree you are running hot. If you define hot as the end of the gauge or red light on, then you have been running hot for a while. The gauge is built to point at 50% from about 130 - 240F. Running hot starts at 215 - 217. 235 is beginning head gasket damage. Normal should be 195 or less at 60 mph.

2. Check the following -

radiators for coolant, oil, and transmisson fluid are free of leaves and trash and mud so air can flow

main fan clutch - test when warmed up, engine off, spin and release - should stop in under 1 revolution - impacts slow and parked cooling

electric fan - should have heard this come on, blades should spin freely when tested, fuse in underhood box should be good.

radiator - could be internally clogged - use an IR thermometer to "shoot" the fins top to bottom. If bottom is more than 10F colder then rad is not passing a lot of water down there. Flush won't cure, should have been done every two yeras along with coolant swap out.

There is a 180F stat that can lower your temps some, only buy the real Rover one, not Motorad.

 

As disco mike will probably reiterate, try a new expansion reservoir cap. I just sprung the $40 for a new genuine cap today. 96, in denver and never broke 200 in traffic with the ac blasting. Yesterday I hit the 210-220 range while gridlocked. And I have a young radiator and 180 degree t-stat.

I threw the new cap at it as an easy long-shot before throwing down for the brass impeller high perf water pump. Glad I followed DM's advice, even if it took me a year to get around to it.

As the coolant gets closer to boiling it expands, thus becomes less effective... cascade reaction. Here at 5000' msl, evaporation occurs at lower temps because of less ambient air pressure.

Try a new cap.

 

Oh, and X2 on the electric fan. They get trashed out there on the front of the vehicle. If you're blowing fuses you may need a new motor(s), there are many threads on cheaper Denso replacements from more common vehicles.

Mine was so toasted that it finally cooked the wiring.

 

Excess pressure is the head gasket allowing combustion gasses into the cooling system probably.

If you are 50/50 coolant to water, you probably don't have boiling to make such pressure.

replace

Fan clutch
T-Stat to a 180 degree rover t-stat. Not motor-rad.
Radiator - replace it with a new one from RockAuto Parts Catalog About $230 shipped.