Defender 200tdi Overheating Issue

[chip.daniels]

Hi all, I have a 1992 Defender 110 with a 200tdi which over the past 12 months has slowly increased it's 'operating temperature', to the point now where the needle is just below the black blank area below red hot.

It doesn't get hot very quick, takes about 15 minutes of driving fairly quick to come up to this temp, and then stays there when stopped and idling or when driving.

I have replaced the thermostat and the temperature sensor to no avail. I tested the gauge and wiring by hooking up the in wiring to the old sensor which I then put in a pot of water at around 88-90 degrees, which reads straight up and down on the gauge.

I have used an old laser thermometer to get the temperature when hot of a couple components: top coolant pipe = 80, bottom coolant pipe = 60, and thermostat housing = 84. These seem like pretty standard measurements and not particularly indicative of overheating to me.

However, when I turn the hot engine off, the fan spins with very little resistance, and when the engine cools, the fan become very firm and hard to turn. From what I understand this is the opposite behaviour of what you would want so, I am fairly certain that it needs replacing at some point. But, I am not sure that it is the source of the problem here, given it gets hot when going 100 on the highway, where I would assume the fan becomes redundant.

Having already done the thermostat and temperature sensor, I was hoping someone could provide me with some advice on what they think the problem is, rather than just continually replacing components until it works.

Thank you for your help.

[shack]

What happens if you run it until the gauge is that far up, then turn the ignition right off for 10 seconds, then restart.

What does the gauge do then?

[dero]

I would replace the viscous fan coupling .

[AK83]

I would replace the viscous fan coupling .

Yeah, me too.

Had the same trouble with the D1(300tdi).

Did some pre prep stuff to it for a week away, and of course on the way up to high country at about 95-100 on the fwy, it's running hotter than normal.
Usually sits on 83-85 on a warm day, but out of the blue it's now at 95-ish. I knew as soon as we hit slower hilly roads it'll race up and over 100's so had no choice other than to slow down as much as I could and fall behind(the bro, in his TD5).

Still made it, and on really slow tracks in the high country, didn't really heat up at all. Only at speed on fwy with hill climbs.

Got home, changed viscous, went for test drive up the same fwy as first day of trip ... no problem now.

[chip.daniels]

What happens if you run it until the gauge is that far up, then turn the ignition right off for 10 seconds, then restart.

What does the gauge do then?

Tried that this morning, but the gauge just returned to the same hot mark

[shack]

Tried that this morning, but the gauge just returned to the same hot markOk, I have seen where either the gauge has failed or there's an earthing problem and the gauge will keep climbing, but an ignition cycle will reset it.

As others have said, the viscous hub on the fan may be failing, although the temp figures you have quoted seem fine to me.

[Fattima]

When you replaced the temp sender did you get the correct one? I recently had an issue after an engine swap with what looked like over heating. I was supplied the incorrect sender for the 300tdi, there is a difference between the ones for the Discovery and the Defender. Might be the same with the 200tdi.
300TDI water temp sensors - two types (https://www.aulro.com/afvb/90-110-130-defender-county/81839-300tdi-water-temp-sensors-two-types.html)
But the viscous coupler sounds crook too.

[AK83]

Also: a quick and easy test to see if the hub is working properly or not. If you have a heat gun of some kind! you said that when the engine is up to temp, the hub turns more easily. If you can get it off, use the heat gun on the small coil at the front of the hub.
Heating up this coil activates the valve in the hub to allow the silicon to lock it.
One it's hot, the coil will unwind itself(you will see it) and if it was originally free it should then be hard to turn again.

[chip.daniels]

Okay thank you very much for your help guys, I have a fan hub on order and will give that a go next.

[123rover50]

Also: a quick and easy test to see if the hub is working properly or not. If you have a heat gun of some kind! you said that when the engine is up to temp, the hub turns more easily. If you can get it off, use the heat gun on the small coil at the front of the hub.
Heating up this coil activates the valve in the hub to allow the silicon to lock it.
One it's hot, the coil will unwind itself(you will see it) and if it was originally free it should then be hard to turn again.

How much heat does a heat gun put out compared to the temp that the air through the radiator gives the fan hub.?
When should the fan hub start to lock up ? 90C perhaps ?
That test would show its working but not perhaps at the right temp.
Just a thought[bigwhistle]

[AK83]

I used an IR temp gun to watch over the temps.

Mine started to open in the high 80's.
Was hard to control an exact temp, and being the impatient type I did have the heat gun at the highest setting.

And to be sure, I did test it in this manner off the car.

[AK83]

Hi all, I have a 1992 Defender 110 with a 200tdi which over the past 12 months has slowly increased it's 'operating temperature', to the point now where the needle is just below the black blank area below red hot.

.....

Also:

I had similar issues with my old '79 RRC many years ago.
I was out on a 3 day drive and on the 2nd day the RRC did exactly the same thing. At the time I had twin electric fans on the car, removed the VC fan. Temp gauge showing at the red line suddenly. No problem on the first day, just started the next morning ... 'out of the blue'.
I checked temps by hand, there was basically no pressure in the hoses, could put hand of them for a few sec, i.e. not massively hot, but more importantly it didn't actually feel like it was at the temp that the gauge was indicating.

I changed all manner of stuff, even removing electric fans and replacing VC fan too, tempo sender, etc. Not being able to work it out, it ran like this for a couple of years, as I just couldn't figure out what was wrong ... even though nothing actually felt wrong.
One day I was working on (I think) harmonic balancer, to do the front seal .. and I rubbed against the radiator and it crumbled into dust.

pulled rad, turned out it was just old and rotten, replaced and bingo .. temp gauge back to normal.
For the two years it ran at the redline, it never once felt it actually ran hot, never ran with high pressure on coolant hoses, and just 'felt' normal.
RRC of this era had an oil temp gauge, and this never showed excessive heat in the oil either, always ran in the low zone. One time, just to confirm this I ran the car at higher speed for a few minutes and oil temp did rise to about the middle range on the gauge.