Lately I have run across a difficult to diagnose problem with my 2001 Infiniti I 30. It seems that the cooling fan runs from the time the engine reaches operating temperature and it never cools the engine down such that the fan stops running. In addition, if I drive the car for about 1-2 hours nonstop on the highway it begins to overheat. The last time this happened I turned my heater on full and I was able to reduce the temperature enough to make it home without causing further damage(I hope!). I have replaced the thermostat twice and flushed the radiator, but the problem persists. I had a mechanic perform an engine diagnostic test, but he found nothing. I love the car, but I can’t drive it very far for fear of damaging the engine or getting stuck in the middle of nowhere. Can you offer any suggestions?

Highway driving shouldn’t overheat a car. Logically, the radiator should be cooling the coolant plenty . . . enough to keep it from overheating. Even though this seems obvious, is there anything blocking the radiator? Next thing I’d think about is circulation of the coolant. Let’s assume that the radiator is not blocked and is doing it’s job (the constant running of the fan bothers me though), is the coolant actually circulating fast enough to cool the engine? Water pump? Although it is somewhat dangerous to view the hot coolant via removal of the radiator cap, you can do it if you’re careful. Watch for the collant running through the radiator. Be careful! Check the thermostat again (I know, you’ve done it 2x). They can be bad from the box. Installed properly? This sounds like a circulation problem to me. BTW . . . how many miles? Any front end damage ever? How’s the radiator look (fins bent?) Just my two cents, but I know you can get this solved by elimination if you go through it logically. Good luck! Rocketman

When was the last time you changed the coolant? Are you using the right mix? How is the water pump, is it the original? How many miles on the car? Have someone check the radiator and hoses. A good radiator shop can use a tool to check for blockages easily. Has the thermostat ever been replaced?

Car has 128xxx mi and no front end damage. Fan blades are straight and both fans run constantly. Will check the water flow. My thoughts were centering on the water pump as well. Thanks for your thoughts. Will keep updated.

Coolant changed in April along with flush. 2 thermostat changes since then. The temperature does not begin to overheat until I drive it for 1-2 hours at 60mph. The constantly running fans are troubling and I feel as though the water isn’t running as it should or there is a blockage as you suggested. Thanks for your thoughts! Will keep updated.