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Q: High Thermostat Temp on 2000 Mitsubishi Montero Sport

I have a very odd problem with my M. Sport. The temperature gauge goes up when I travel at high RPM's (highway) and I have the A/C on. Also the weather has to be hot (90+ degrees). These are the conditions for my temp gauge to go up. If it's above 90 outside and I drive without the A/C on, the temp gauge doesn't move a bit. If I drive around with the A/C on & it's city driving, the temp gauge does go up but not as fast. I also noticed that the secondary fan turns on when the A/C is turned on, but it's constantly on. I thought those fans only turn on when the temp goes up. Any idea's on what's wrong with my Sport?
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First of all, the fans run continuously when the a/c is on - I would consider that to be normal. The air flow is needed across the a/c condenser in order for the system to function correctly. The temp gauge rising when the a/c is on could also be considered normal depending on how much it rises - it could also mean a fault wit the cooling system. Low coolant level, poor coolant flow, or restricted air flow across the radiator for example. One easy check would be to make sure all the air deflectors and duct work around the radiator is in place and functioning correctly. Next make sure the coolant level is full. If these checks are OK and the temp approaches the red zone then I would suggest you have the cooling system inspected by a qualified technician. If the gauge just rises slightly but does not go near the red zone the you may be OK just keeping an eye on the gauge and take action if things get worse.
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