Have a 2001 Montero Sport 3.0 that is overheating on uphill grades after 20 miles or so.

Have already replaced all belts, radiator hoses, water pump, thermostat, temperature sensor. Did a coolant flush and running new coolant. Not losing coolant and appearance is normal.

After 20+ miles going up moderate grades (CO front range) the temp gauge slowly heads up from the middle of gauge to the max. Bought a dongle to plug into computer to get an accurate temp readout using OBD Fusion on a Kindle Fire. It is hitting 240 degrees and up to 250 degrees on steep hills. This is with ambient air temperatures of 60-85 degrees. So it isn't the temp gauge issue.

Pulley driven fan behind the radiator seems to be functioning correctly. Electric fan in front of radiator comes on with A/C when parked.

Any ideas on what to check next? Radiator? Fan Clutch?

 

I have the same issue with my 1999 Montero sport. When driving up grades temperature goes up. Mechanics say radiator and water pump are ok. Thinking about changing radiator anyway. Have you solve this on your Sport?

 

I replaced the thermostat, radiator cap and temperature sensor and it didn't fix the issue. Finally took it to the shop and they said it was the fan clutch. Seems to have fixed the problem. They said the fan clutch was freewheeling. I had tried spinning the fan clutch earlier by hand and it stopped within half a revolution like you would hope.

 

I replaced the Fan Clutch even though it was not free wheeling, and have done a coolant flush, nether one helped. On advise from the mechanics did not replace radiator or water pump (Was replaced at 50,000 miles when timing belt changed) . Did not think about thermostat as it does not get hot idling or in stop and go traffic. Maybe I will take to a different shop to get another opinion. How many miles did you have on your Sport when the problem started?

 

137,200. Radiator would have been next on my list if it hadn't been the fan clutch.

 

I really love the Sport but do not want to take it on the road until this heating issue is resolved. Guess I may have to spring for the new radiator. Thanks for your help JasperCO1956.

 

Thermostat would not be my suspect. There are two malfunctions for thermostat - stuck Closed (you'd be overheating as soon as you start any driving), or stuck Open (you'd never reach proper engine operating temps, since it would bypass all coolant all the time). I think it's something else. The suspects are - air bubble in the cooling system, bad water pump, radiator with some flow restriction. Did you ever have any sort of StopLeak put into the system? If so, you could have internal cooling passages clogged up thus restricting heat exchange.

 

Have not used StopLeak in the system. Water pump was changed at 50,000 miles when timing belt was changed (Now at 80,000 miles). Still has original radiator almost 20 years old. Used the Lisle Spill free Funnel when I flushed the coolant , hopefully got all the air bubbles out. No leaks from water pump or other hoses in cooling system. So even though I have not used StopLeak could the radiator still be restricted?

 

Yes, it is possible to have restricted flow in the radiator. If you used tap water instead of distilled when mixing with coolant, it's possible that you have developed calcium deposits that restrict flow inside of the radiator or at the very least reduce efficiency of heat exchange. If radiator is not leaking, there is no reason to replace it with new one. You can take it to a radiator shop and they can treat it to remove deposits from inside and get it back to peak efficiency.

 

Hopefully should not have any calcium. I purchased it from dealer when it was a year old, and have not used tap water in radiator only distilled water 50/50 mix with coolant.