P38 overheating ( maybe )?

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Neil.ms

Member
Posts
48
Location
Goring on Thames
2001 4.0L reconditioned engine fitted last year ( new water pump, radiator , thermostat and hoses fitted at the same time ) and only done about 300 miles since then. Have recently noticed that when getting back home after a drive that the air con fan is running. Had a look, and the air con radiator had been damaged by what looked like a large piece of gravel getting caught in the fan blades ( reducing air flow to the top of the radiator ). New air con rad fitted as well as temperature gauge. Using the instrument menu on my nanocom it still sometimes flashes up overheating when it hits 105c. When the nanocom says the engine is running at 99c my infrared thermometer says the temperature of the gauge is 90c ? Engine not losing water and the top of the radiator is 30c warmer than the bottom. Am I being paranoid ( it’s hard not to be when you own a p38 ).
 
Sounds like your radiator is fine, a 30 degree drop is good. Unfortunately the Thors run hot for some reason. My GEMS runs at 85-88 normally and 92 in traffic on a hot day with the AC on.

I’d be inclined to trust you IR scanner as to temperature. That having been said, remember that most of them have a wide cone of projection, so you need to be very close to whatever it is you are scanning, unless what you are scanning is very big. Most have something like a 30cm cone at 50cm, so at 20” from your target, you are scanning a circle of a foot in diameter.

The hottest part of the engine is us ally the rear of the cylinder heads. For this reason I have an Engine Guard gauge/alarm bolted to the spare threaded hole on the back of the LH cyl head. It works well. In addition it is giving you information as to the actual head temperature and not the water temp. Advantage here is, if you lose your water, you lose your temp gauge reading as well.

All in all, you seem to have a hot thermostat in place. I’d be more comfortable with the engine running around 88 deg. The origins Buick/Rover spec for these engines was 180F or 82C. Higher temps are all about trying to get engines to meet pollution standards.
 
As far as I know there is only one thermostat, but given the variations on temp reading you see, I’m going to guess that there are “versions” of it for cooler running. Now, finding one!

What I have seen done is to drill a couple of 4-5mm holes in the thermostat plate. that allows circulation of some water even if the thermostat is closed, so allowing some cooling. You would be surprised how much water two 5mm holes will pass.
 
Marshall8hp said:
As far as I know there is only one thermostat, but given the variations on temp reading you see, I’m going to guess that there are “versions” of it for cooler running. Now, finding one!

What I have seen done is to drill a couple of 4-5mm holes in the thermostat plate. that allows circulation of some water even if the thermostat is closed, so allowing some cooling. You would be surprised how much water two 5mm holes will pass.
Click to expand...
My old thermostat had the 2 hole hack. It never got above 80 and in the winter was cooler to 60, the cab was freezing, even with the heater set to max.
 
Is your viscous fan working, you should here it roar when it cuts in ( they spin all the time but lock up and spin a lot faster when working)
get it hot all up to temp and try and stop the fan with a rolled up news paper, if you get confetti its fine if it stops its goosed
 
Update on the issue. Viscous fan not engaging when the engine is hot. Replaced and cooling seems a lot better ( air con fans not switching on now ). Still not sure why the temperature sensor is reading too high, but I may have a colleague at work who can help me with that? Have also ordered an engine guard sensor, as i want to keep the engine sweet ( just in case the p38 tests my patience so much that I decide to buy a Morgan plus eight ). Thanks again for all the advice.
 
Thor runs slightly hotter for efficiency reasons, but again anything above 98c is getting too hot.

The A/C fans should kick in on a thor at 105c to assist the airflow..

The idea being the viscous fan pulling and the A/C fans pushing...

;)
 
Henry_b said:
Thor runs slightly hotter for efficiency reasons, but again anything above 98c is getting too hot.

The A/C fans should kick in on a thor at 105c to assist the airflow..

The idea being the viscous fan pulling and the A/C fans pushing...

;)
Click to expand...
Thermostat doesn't fully open until 96, which is crazy!!
 
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