Hi,

My 91 3.9 runs hot when towing. It mostly sits just over the half way point but then rises to about two thirds for no apparent reason. I have managed this by turning the heater on full blast to cool it down which seems to work.

It also happened last week without towing but in a long traffic queue, again cooled it down with the heater. Yesterday though when towing again, it got warm but I decided to leave it to see if it would manage itself as the temp was moving up and down by a few mm every few minutes. To this point it had never got to any where closer than 2-4 mm from the red zone and never into the red. It got to just before the red zone yesterday before i blasted the heater to take some heat out.

So, they are the symptoms.

The viscous fan works fine, the electric fans seem to be cutting in ok and there is no water loss from the expanion tank. It hasn't boiled, no steam etc. The rad looks in decent order but there is some crud gathering along the bottom which i'll remove today

Towing a horsebox with one horse so not an excessive load. I had no problems in the summer but the increase in temp has been present while towing from my getting the RR in May.

I know this is a old topic but as it mostly runs bang in the middle of the gauge that it might be something different/simple

Thanks

I'd be checking the Water Pump (impellors have been known to work loose) and see if the Rad is blocked....

A refresh of the Coolant to ensure there are no airlocks wouldn't go a miss either.

Thanks, will check those things out.

Hoped to do so today but got sidetracked decorating (dull!)

Mine doesn't like standing still either and it is quite common. Coolant or coolant sensor are worth checking.

Feel the rad for cool spots as its possibly blocked. I was told they can be almost impossible to back flush and clean properly.

Thanks chaps, I'll have a proper look this weekend.

Double check the viscous fan when hot.