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Overheating issues

i own a 2001 nissan xterra (bought used last year) it has 107k miles and has recently started overheating.

My mechanic (has been for 3 years now) first changed the thermostat - it overheated again - the garage it ook it to (i was two hours from home when it happened) found a cracked hose near the heater core and clamped it, allowing me to drive home just fine the next day with no issues. a week or so later, it overheated again after the spark plugs were changed out. mechanic couldn’t find anything and sent me home saying it was probably just an air pocket. No overheating issues until a week later - then we replaced the radiator. two days after i got it back, it overheated again.

what the heck is going on?? now i’m wondering if the car isn’t actually overheating at all!

i had a friend (NOT my mechanic) look at it and he saw these possiblities:

1) fan clutch - the fan is very easy to move after the engine has been shut down.

2) possible temperature sending unit (?) problem - (the haynes manual has it running(?) at lower ohms than it is actually running at

i’ll be driving around with an infrared thermometer to test the radiator hose internal temperature if the car ‘overheats’ again and will be picking up a new sending unit at an auto parts place.

what else can i look for! this is making ME overheat and i’m not made of money!

  1. fan clutch - the fan is very easy to move after the engine has been shut down.

The fan clutch should be easy to move. It will only engage when the engine is hot. At highway speeds the fan shouldn’t even be running…The air from just moving should be enough to cool the engine.

Check the sending unit…Oh heck…just replace it…cheap enough.

If that’s not the last part you haven’t changed yet is the waterpump.

Has it been loosing coolant?

as i understand it, RIGHT after the engine has been running for some time and shut off, the fan clutch should provide SOME resistance as it had just been locked up - when the car engine is cold it should be freely moving.

at least that’s how i what i was lead to believe. is that incorrect?

picking up a new sending unit tomorrow.

i’d like to know how the water pump can be TESTED BEFORE i go to the trouble of replacing it. i simply can’t afford to play the trial and error game at $500 a pop.


to be completely honest, i don’t even know if the car is ACTUALLY overheating. all i have to tell me that it is overheating is the temp gauge and the idiot light (Service engine soon) - wouldn’t there be a lot of steam and such coming from the hood if it overheats?

update - with the infrared thermometer mentioned above - anytime the temperature gauge starting rising to the top today, i pulled over, popped the hood and checked the temperature of the radiator hose - while it was hot to touch, it was not ‘melt your skin hot’ - the temperature i read on the hose was never more than 190 degrees. isn’t that generally a “normal” temperature that would have my temperature gauge needle sitting in the middle of the gauge like it normally does?

the last time the needle rose, i left the engine running, hopped out, popped the hood and took another reading. 175?. i drove away and the needle slowly lowered back to the regular spot - just below halfway up the gauge.

s i understand it, RIGHT after the engine has been running for some time and shut off, the fan clutch should provide SOME resistance as it had just been locked up - when the car engine is cold it should be freely moving.

It’s going to take a little time for the coil to get hot enough to engage the clutch. To check the clutch out…Run the truck at idle, just sitting in your driveway. That should get the engine hot enough to engage the clutch. After about 10 minutes (OR when the gauge says it’s getting too hot)…turn the truck of and try to move the clutch. If it’s engaged it’ll be hard to turn.

we replaced the fan clutch. it’s still overheating.

not the issue.

The radiator hose, in it of itself, isn’t measuring the temperature inside the block where the sending unit is located. You mentioned that after you drove away the needle on the temperature gauge began to lower. I would rule out the water pump at this point. I’m not familar with the type of pump in the Nissan’s, but it’s possible that when the engine is turning rapidly (as opposed to idling), the pump will function. This would explain why sometimes the temperature rises and no apparent pattern is recognized.

good point ebko87.

have you changed the temp sender yet? that is the cheapest (excepting the thermostat) thing to replace.

have you removed the rad cap (when cold)? see if the coolant is flowing? that is a pretty basic check of the water pump. although you have stated you had the hose clamped; upon return home did you replace it? if a hose needs an extra clamp it is an indication it is collapsing. i would replace the hoses first, then the temp sender.

we had a new sending unit switch, but when the SES light came on with an overheating engine condition code, (and the temp of the water in the radiator hose was measuring at 205 (meaning in other spots it was higher) we didn’t bother to replace it) - planning on testing the thermostat (and possibly replacing) on sat as well as backflushing the system to look for blockage.

I am wondering if your overheating issue was resolved. I too own a 2001 Xterra that has had overheating issues for over two years. I have chased the problem down with lots of money to no avail. We have replaced all of the major elements in the cooling system, radiator, water pump, clutch fan, thermostat, sending unit, etc. until my mechanic doesn’t want to see the problem or my SUV again.

Just a thought here. If the vehicle isn’t actually overheating, could it be a gage or instrument panel malfunction. My '87 Mustang had been giving me a devil of a time with the gages reading funky until I discovered that the “Instrument Resistor” was faulty. No help from the Haynes manual, here. They don’t even list it in the index.

Try Cappy’s suggestion to change the radiator cap. If it’s intermittantly not holding pressure, the boiling point of the coolant will be lower (at those times).

Also check the coolant for the presence of hydrocarbons. Since it may have been repeatedly overheated this would be a prudent (and inexpensive) check.