temp gauge puzzles

millsy

4x4 Earth Contributer
Puzzle #1;
About 9 months ago I noticed the temp gauge needle changed from sitting near the middle of the to much lower down the scale - on the first, and only, mark up from cold. On my MQ that's just about 1/8 around the dial. I had put a new bottom radiator hose in around that time.

I was wondering if the new radiator hose and the change in the gauge was just a concidence. Or maybe the old hose was thin enopugh to be collapsing under the suction of the water pump.

But I also noticed that even after a good drive you could hold the bottom hose quiet firmly with no fear of burning your hands. It was just luke warm. It is a heavy duty, 2 year old radiator, and a small motor ( 2.8L ).

I put a new thermostat in, but it made no difference. So do those temp sensors in the thermostat housing finally go off with old age, and as a result give a low reading? Or is there any other explanation?

Puzzle#2
An interesting observation, that I cannot recall seeing on any of my other cars, is that this old Patrol seems to know when the sun is setting. Even on a hot day the temp needle drops to the left by about 3mm on the scale, just as the light fades at the end of the day. This even happens on a warm day, but when I drive off in the coolest part of the day, early the next morning, after sunrise, there is the gauge sitting in its normal day position! Does anyone else also have a car that seems to be light sensitive? Its got me stumped!

Its up to its old tricks again, now that I have put it back on the road. But its a bit of a worry to see the gauge read nearly zero after sunset. I think its dropping back a bit more than it used to!
 
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russell789

Member
for puzzle #1 i'd be checking the fan, assuming it is viscous maybe it is sticking on and over cooling? to check this when it is cold it should spin relatively freely, if it is very hard to turn, its is staying on and possibly causing your problem.

for puzzle #2 i have no idea.. thats very strange

i know you have already replaced the thermostat but it sounds like the thermostat, another good idea would be if you have an infra red temp gauge to start looking at temps around the engine bay, (thermostat housing, top hose etc)
 

croozza

Active Member
Could be the thermostat, some after market ones have a different opening temperature, see if you can get the opening temp of a genuine one and match it with an aftermarket one, as the one you have now could be opening too early causing the low temp.
It could also be the ambient temp that has dropped causing the temp drop in the cooling system in the evening.
 

millsy

4x4 Earth Contributer
I might try another thermostat, even though this new one is just a few months old.

But why should the temp gauge change even if the air outside does cool down outside? I thought that was the whole idea of a thermostat. Unless of course it is stuck open! Aaahhh! I see!

Might make sure I get a different brand. This new thermostat was doing the same thing from the day I fitted it! Not good enough. But still wondering whether the actual sensor might be the problem. First I will try another thermostat, and see what happens. The temp gauge used to sit near the middle of the scale, as the manual points out in various sections.

Thanks for your help guys.
 
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Big Rig

4x4 Earth Contributer
This may sound like a silly question but are you having any issues at the same time with your fuel gauge. Reason I ask is in the older cars like yours most had a voltage stabiliser which was common between the temp gauge and the fuel gauge. These often played up and made their owners go into a mad panic. It was just a simple fix to change this as they are generally behind the instrument panel.
 

frosty

4x4 Earth Contributer
This may sound like a silly question but are you having any issues at the same time with your fuel gauge. Reason I ask is in the older cars like yours most had a voltage stabiliser which was common between the temp gauge and the fuel gauge. These often played up and made their owners go into a mad panic. It was just a simple fix to change this as they are generally behind the instrument panel.

Also, does it drop when you turn the lights on??
 

millsy

4x4 Earth Contributer
I think the fuel gauge is working Ok Big Rig.

And Frosty, that's a good point about whether its when I turn the lights on. Will have to check that one out before I rush off and buy another thermo. But the fact that it moved from sitting near the centre of the scale for the first 18 months I had the car, to right over at the left side is also part of the puzzle.
 

russell789

Member
you could always fit an aftermarket gauge too, thats what i did, before i bought my car it ran on 1/3 and that was boiling (had a blown headgasket) and rather than stuff around i put in a speco gauge, less than $50 and its far more accurate than a factory gauge, or if you really want to splash out get a VDO gauge
 

millsy

4x4 Earth Contributer
Hi frosty. I tried that lights check today. Your'e right! As soon as I flicked the lights on, the temp started dropping. And of course the reverse. So yep - the car IS light sensitive!

Now I am thinking why? Is it that temp stabilzer that Big Rig mentioned. Or is it a 'bad ground' effect in the thermo housing, where the sensor is screwed in. Maybe I just need to unscrew the sensor, give it a clean up by unning a die acoss its threads, and tap out the thermo housing to get rid of any gunk that is preventing a proper current when the supply voltage drops?

I guess that's what that stabilizer thing does, since the voltage will probably drop every time the lights are turned on, and that would affect the temp sensor. Just have to try one, then the other if necessary I suppose.
 
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