Overheating/Gauge Puzzle

My new (to me) 2001 Gen 3 XLS is running well all things considered. I'm still amazed at the overall capability and quality given what I paid for it. However, I have had fits with overheating (and possibly faux overheating). Ever since we got the vehicle the needle would bounce up to the highest level on the gauge after just a short drive. The first couple of times it happened I immediately pulled over and spent time letting it "cool down." The next time it spiked I drove by a local shop and asked them to check the temp of the belts and block and everything was cool/normal. So, after some research I began to believe that it was the well-documented problem with a faulty circuit behind the dash that needs to be re-soldered. Problem is, once in a blue moon it would actually feel too hot under the hood, the hoses would be very hot to the touch and I could hear coolant bubbling/boiling. Hmmm. Was it possible that I had both a bad gauge AND a legit overheating issue? Regardless, I took these steps:

- installed new radiator hoses
- installed new thermostat and o-ring
- deep flushed radiator
- refilled radiator and overflow tank with fresh pre-mixed coolant

The very next day the truck registered hot after a short drive, the hoses felt hot and the coolant could be heard boiling again. Grrrrr. So now I begin to suspect air bubbles in the system. After some online research I found an article on an Australian forum where a Pajero owner suggested:

- jacking the front of the truck up high
- removing the radiator cap
- squeezing the top radiator hose to burp trapped air out of the system
- filling radiator and overflow tank again and reinstalling cap

The forum member noted that this was a common problem with Pajero/Montero's following coolant changes on flat ground. So I followed that procedure and...boom. Temp gauge falls well below the halfway mark and has remained there rock-steady for a week now. Figured I'd share this procedure with others here in case it comes in handy.

Unfortunately, I now have a concern that the operating temp is TOO low. When driving it the last few days it has hovered at the point between the bottom and middle of the gauge:

785Tduh.jpg


From what I've read a too-low temp means that the (new) thermostat I installed may be stuck open somehow so the engine is constantly cooling. Is it possible that I installed the thermostat wrong incorrectly or that the brand I used does not play well with the Montero?

Thanks in advance for any helpful input.
 
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What brand of thermostat did you use? I always prefer using OEM thermostats.

It's possible that if you used an aftermarket one that it will open at a lower temp which would cause your issue, or it could be stuck partially open.
 

nckwltn

Explorer
Did you put in one of those fail safe thermostats that when they get too hot they stick open?

Also, if you can, plug something into the OBD2 port that can read the engine coolant temp. The gauge will read almost dead in the middle between like 190 and 230.... that's a lot of range, and something in the OBD2 will give you an exact number. My preference is an UltraGauge, but there are smartphone apps and blue tooth dongles that will get you the same.
 
Thanks for the replies. I installed a
Motorad Failsafe thermostat. I understand the assumption may be that the engine is overheating and the new thermostat remains open but I’ve watched the gauge carefully the last few days and it has never crept above the halfway mark. Of course, that could indicate that it’s been stuck open from the moment I installed it. Regardless, I’m convinced that burping the system made a big difference.

My paranoid side is also wondering about the old water pump...which will be replaced shortly. Thanks again.
 
When I had a motorad thermostat on my RX7, it would take forever to get up to temp, and would always read a little low. (previous owner installed it)

When I went to an OEM thermostat, the car warmed up much more quickly and the temp gauge read right in the middle.
 

Igorskiy86

Observer
That's a pretty good find on raising front end of the truck to bleed the system. I think my vehicle has a similar problem, not as extreme as yours, but when going up a hill and parking afterwards I can hear boiling noise from the coolant system. Will give a method you described a try.
 
Hope it helps you, Igor. Sure did the trick for me...though truth be told the bleeder screws likely accomplish the same thing.

I'm still juggling the "too good" thermostat function, though, so I'll likely spring for an OEM thermostat per suggestions above.

lift.jpg

thermo.jpg
 

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