Nissan overheating mystery

Is this video an accurate representation of what is supposed to happen when I run my truck with the cap off?

All that bubbling that happened when the fans came on, am I supposed to see that? My fan comes on as soon as I start the motor, its always on. But even when the truck reaches opperating temp and after watching it for several minutes after that, I never see ANY water flow or movement in the radiator.

 
With the radiator having a different temp in that out I'd say you've got coolant flow. All that bubbling you are getting is air coming out. Try squeezing the upper radiator hose a few times to force coolant flow. (It might also get a bit more air out.)
 
Every time I squeeze the upper hose quickly, air bubbles come out. I think when I release the hose it sucks air back in through the top of the radiator.
 
I took a garden hose and sprayed water into the upper hose port toward the motor (pictured) and then the lower port.

I sprayed water for about 3 seconds into the upper port before it backed up and started shooting back at me, and only about 1 seconds when spraying it in the lower hose. Is the thermostat blocking the passage?


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You've definitely got air in the system. Try squeezing the bubbles out and adding coolant as you slowly release the hose. (Got 3 arms?)
 
Man, I've bled the system 2 dozen times and last night I let the truck run with no cap for 40 minutes. Nothing helped. I did build a lower shroud today and close off some of the gap at the top from my body lift I put on 4 years ago.




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find someone in your area with an air lift. it is a tool you put on the radiator and it vacuums the system with compressed air and then you stick a tube in your coolant and it fills the system with the coolant by releasing the vacuum and sucking the coolant. i don't know if the auto parts stores carry them or not, i got mine off of the tool truck.
 
I know this will sound strange, but has the fan ever been changed? I had a jeep once with the same symptoms. I chased it down for weeks changing water pump, thermostat, radiator, pressure checked the cooling system and everything else I could think of. It ended up being that the fan had been damaged during a bump up and someone put a fan from a 4.2 instead of a 4.0 and they were set up to turn the opposite direction. Double check to make sure the fan is pulling air through the radiator and not pushing it back out of the radiator.
 
The fan does not keep spinning a lot after I cut the motor off buMt it is easier to spin when it's real hot, but I think it's supposed to be like that.
If the fan was the problem it wouldn't overheat on the highway, right?
 
the fan is basically at "idle" at highway speeds because more air is being forced through the radiator.

ok, here is the real test. get it up to operating temp, roll up some newspaper, and stick it in the fan with the truck running, if you can stop the fan with ease it's no good.
 
Im starting to think it may be the coolant temp sensor. I bought a laser thermometer today and went for a drive. When the needle got to this position....



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I pulled over and with the truck still running I took temp readings from the radiator, upper hose and lower hose. The upper hose and top of the radiator always read the same temp, and that was 185. The lower hose read 165.





I drive home and with the the truck idling and the AC blasting I took a reading when the needle got to this position....



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I took several readings over about a 10 min period and got temps between 173 and 185 at the upper hose, and between 149 and 155 at the lower hose.


The temp of the top of the motor where the bleeder screw is was 177.



Also, here is a video of me starting and turning off the truck. You can see how the gauge changes.





 
OK. Here's where it get fun. Get out your trusty multi meter. Ohm out the sensor at cold and at operating temp. Then check at the back of the gauge. (the wiring with the temp sensor plugged in.) They should be the same at both ends. I.E. 4ohms at the sensor when cold and 4-5 ohms at the harness end at the back of the cluster. If they aren't the same you've got a wiring issue. IF they are odds are the gauge is the problem.
 
A buddy came over with a scanner today and we went for a drive. We went up the highway in 97 degree weather with AC on. The needle started to creep up from the normal position as the scanner got to about 215. It peaked at 221 before getting off the highway, then with the truck idling with the AC on full blast it settled at 222 with the temp gauge needle pretty close to the warning zone.
When we turned the AC off and turned the heat on the temp dropped down to 195 where it settled. With the laser thermometer, we took readings of around 180 in the left (hose) side of the radiator core near the top, and 135 degrees in the same spot on the right side of the radiator. Does this mean the radiator is blocked?
 
No, that means the radiator is working. Remember this. A radiator takes the heat (180 degrees) out of the engine (in the coolant) and transfers it into the air coming through it. It then cycles the cooler (135 degrees) coolant back into the engine to remove more heat from the engine. A 45 degree temp difference through the radiator is pretty damn good. Usually you only get 20 to 30.
 
I changed both sensors, and taster changing the cheap gauge sensor it seemed to help a lot, but not solve the problem completely. The needle no longer pegs in the warning zone but it did still creep up to 222 on the highway with the AC on when it was 97 outside. The needle starts creeping up from the normal position at 215, and at 222 it was getting pretty close to the warning zone.


However, driving around without the AC on the temp never got over 197. So, it appears the cheap $4 sensor was bad, but that I still have an issue causing the truck to run hot, but not extremely hot.
 
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