Thread: 97 degree coolant temps - argh!

Originally Posted by 86mud

Hi All

I had noticed that my coolant temps had been reaching close to 95 on the highway recently (VDO mechanical temp gauge - 1998 300Tdi 130) and I thought my Defender was due for a cooling system update. The last time I had touched anything cooling system related was about 5 years ago.

So i ordered the whole shebang - new full alloy radiator, water pump, thermostat, p gasket, radiator cap, viscous fan hub. So I spent a Saturday replacing all the parts, draining all the old coolant (out of block) and filling up with fresh coolant.

Bleeding the cooling system in my truck is easy as I don't have a heater. I bypassed it many years ago as it was leaking (quick fix - joined the two pipes together). Don't need a heater in QLD - I'll replace the heater matrix once the Victorian borders open.

I have been driving the truck around town and temps have been sitting on 90 degrees.

Yesterday my boys had a MTB race on and we headed South West of Brisbane at 6.00am and settled in for the 1.5 hour drive. VDO gauge sat around 90 - 93. It would only rise going up a hill at 100km/h.

Coming home yesterday at about 1.00pm with outside temp about 32 degrees, the VDO was reading around 94/95 and would climb to 97 on hills.

This is hotter then before I do the cooling system update!!!!

So my brain started to go into overdrive trying to work why.

I had the air con running and it is running perfectly, with the thermo running as it should.

I don't have spot lights on the bull bar impeding air flow.

So all I can put it down to is a dud viscous fan hub.

Any other ideas?

I pulled over and checked under the bonnet at one stage. System was holding pressure properly and no sign of anything out of the ordinary. I have a low coolant alarm and it was not screaming.

I am going to order another fan hub now. Will go for a different brand like Bearmach. May be the Davies Craig branded unit is faulty?

Frustrating for sure.

FWIW. Why not put this query to Davies-Craig since it seems to be their hub currently fitted?

I have found DC to be most helpful in the past.

Have you checked the actual engine temp with a later thermometer to check the temp gauge sender unit? Sounds like it is the only part you didn’t change.
Did you check the new thermostat before you put it in? I have had a brand new one that didn’t open fully at temperature

Thanks for the replies.

Will try checking the engine temp first before blaming it all on the fan hub.

A bit late now, but you need to start testing things and stop randomly replacing and hoping.

Get an IR temperature gun and check that the gauge is reading correctly.

Test the viscous unit on the fan. When you are at 97, see if the fan is locked up. Use a rolled up newspaper and carefully try to stop the fan/ You should actually be able to hear it lock up. It is either on or off.

Do you have the correct thermostat with the bypass valve?

Like Phil B I had a new thermostat not opening. Boil it up and check the temp it opens fully. IR thermometer to check temps across pipe and radiator will also tell you more about what is going on.

Ok thanks everyone.

red90 - I installed a Waxstat thermostat with the little bypass valve siting at 12 o'clock in housing (can't go any other way)

I'll pull the thermostat tonight and test it.

Meanwhile I'll invest in a IR thermometer

I've only driven the Defender around town the last few days....all at 60km/hr and the VDO reads 89 - 90 no matter if I am sitting in peak hour traffic or giving it a boot full up a hill.

As you live in Qld, are you running plain water with anti corrosion/water pump lube. Water is much more efficient at transferring heat than coolant.
Unfortunately I don't have a link to the reference for this, I lost my old computer in the fires at Christmas.

Originally Posted by 86mud

Ok thanks everyone.

red90 - I installed a Waxstat thermostat with the little bypass valve siting at 12 o'clock in housing (can't go any other way)

I'll pull the thermostat tonight and test it.

Meanwhile I'll invest in a IR thermometer

I've only driven the Defender around town the last few days....all at 60km/hr and the VDO reads 89 - 90 no matter if I am sitting in peak hour traffic or giving it a boot full up a hill.

What is the temp that your new thermostat opens up at and is it the same temp as your previous one was??
If you hit a brick wall with this try using your old thermostat and see how that goes before you spend any more money