Car Overheats While Driving But Not At Idle. I have a 1999 jeep grand cherokee 4.0 l6 147,000 miles that overheats when idle but when driving it goes back to normal. Maybe your coolant levels are not the problem.
Less when driving more when the car idles. There are a couple of possible ways that an air bubble could get into your cooling system. When your car overheats when idle, one of the prime suspects is the coolant.
The car is sucking in air some place, this is why the heater stops working, it fills with air, then starts the overheating process. Most common cause here seems to be the egr cooling leaking into the exhaust. But if the fan is working, consider the next points as the possible reasons why your car overheats in stop & go traffic.
The fan should spin freely and with almost no resistance whatsoever. You should see the temperature dip as the water pump spools up. If the electric fan doesn't come on when the engine reaches normal operating temperature, then you either have an electrical problem or the fan is malfunctioning.
However, if there is no heater switch in car, then there cannot be any leakage. Cars have a radiator to cool the engine, just like your home air conditioning system. No speed, you get full air flow (albeit hot air from the engine) across the radiator.
If your car overheats while idling due to a bad thermostat. You can test this by putting the car in neutral or park and revving the engine to about 1000 rpm under the redline for a few seconds. Tighten or replace the belts.
Low cooling liquid level ; Engine's drive belts may be broken or slipping. If your car comes with a heater switch, it may be possible that there is a leakage in the heater core which could cause loss of coolant and hence increase the engine temperature.