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My car keeps overheating. Any idea?


I have 2001 Nissan Xterra SE 3.3L V6. A few weeks ago my car started to overheat while going through the grapevine (mountain pass in SoCal). After filling it up with coolant, I took it to the shop. They couldn’t figure out what exactly was the problem. It passed the block test and such. They said the top hose was swelling up as if something was blocking it. They also said my car was going through about a gallon of coolant. They replaced the water pump, thermostat, and the top hose. they also replaced the timing belt.

After driving the car for an hour, it started to overheat again. This time, I took it to the Nissan dealership. They said the timing belt was off by 2 teeth and they think that’s why it overheated, so they fixed that problem. They also did a cooling system test and found no leaks.

I got the car back and it still overheats. After the turn off the car, I see coolant being bubbling back into the reservoir almost to the top.

Also, my radiator was replaced about a year ago.

Any ideas?


Start with a new radiator cap, you would be surprised how often this overlooked item is the culprit.

Thanks Keith, I will try that.

It sounds like the “block testing” they did was of brief duration and therefore maybe not accurate. A more accurate test is an overnight pressure test. Given the amount of coolant you’ve been losing, it’s possible you have a head gasket leak.

If a new radiator cap doesn’t do the trick, have an overnight pressure test done on the cooling system.

They can test for gasses in the coolant. A leak down test on the cylinders would also tell if the head gasket is breached.

Classic - head gasket.