At those speeds, it sounds like your radiator is blocked.

Be cautious about removing anything from a cooling system if its not working as it should do.

In addition to the other checks already mentioned I'd consider the condition of the coolant, too much water in glycol based cooling systems can cause overheating. Are you losing a lot of coolant?

The rad cap may fail which reduces the pressure in the cooling system and fools the temp sender into thinking the engine is boiling.

Another thing can be seeds/vegetation/mud blocking the fins of the radiator - not easy to spot with plastic shrouds around the rads.

Most viscous fans have a manual locking tab which can be pushed/pulled/bent to lock the fan on, if the fan is at fault.

Thanks for all your messages:

The thermostat is out; we have a long drive down to the Mauritanian border so if we still have a overheating problem I will re diagnose before the dessert proper:

Thanks again:

Ps: What is the best tyre pressure for sand: the recommended pressure for off road - info found on the inside of the door - is 1.75 front 2.1 rear: Ive been told i should go 1 in front 1.5 at the back:

Thanks

What John says is correct. In case of thermostat trouble it is better not to remove the entire thermostat but only remove the internal moving part and put back the housing. The housing with a reduced internal diameter works as an orifice and limits the coolant flow through the engine!

In case of visco coupling trouble; open it up and put a few screws in or two half old piston rings orso and close it again. With the debree inside it will be mechanically locked and rotate at engine speed.

Cheers,

Noel
www.exploreafrica.web-log.nl

Some good cooling advice on this thread.

One final thing that hasn't been mentioned - electrical problems can give you a false reading on a temp dial. We've had several phantom overheats that have been traced back to loose earths or other such electrical voodoo.

Flicking lights, or other devices, on and off to see if they affect the dial is one way to check this, though it sounds unlikely to be the culprit if the problem is speed-linked.

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Pictures, Mauritania 2011

Richard,

Sounds you are driving a Landy! Poor earting lead on the chassis results in high temperature reading in the gauge on Landies

Cheers

Noel

Thermostats don't just help the engine heat up they keep the engine at a constant temperature.

Without them every time you tax an engine (up hills, over dunes) it will run warmer and then cool down a bit as you go back down the other side, then warmer again at the next hill and so on...

These constant cycles of heat/cooling (which you can see by a few degrees on the temperature gauge) expand and contract everything, and importantly fatigue the head gasket bond with the head and the engine block. While this wont effect the performance in the short term it will reduce the life of the head gasket in the long term.

it's also worth noting that in any car, the radiator and fan combination are designed to be able to over-cool the engine they go with, and the role of the thermostat is to regulate and control that overcooling effect. Without it your engine will always be running cooler, not just while you are warming the engine.

The bottom line is that Landcruisers are designed to run in hot climates over dunes fully laden with a thermostat. If your thermostat is faulty chuck it and by a new one. It will cost you less than a £5 (and in morocco probably less still) It take about 3 minutes to change it, and top up the water.

Testing it in hot water is practically it's hard to do. Thermostats generally fail cos there was no coolant in the radiator (which prevents rusting on the inside), so they get cacked up with rust and don't close or open any more.

If your engine is still running hot with a new Thermostat, there is another reason, find that other reason and fix that (most likely the viscous coupling, they dry out when they get old and don't couple as much so the radiator doesnt "overcool", or alternatively overloading). Dont bodge it by taking out the thermostat which will just disguise the problem.

As an emergency measure it's fine, and on a landrover sure (cos there's no spiritual beauty in the engineering ethos of a LR engine, which is doomed to premature failure from the minute it leaves the factory). But if you found out your mechanic had done it to your everyday commuter car to hide the fact something else was broken you'd be pretty angry so why do it to your overlanding Landcruiser?

An easy(and safe) way to check if the coupling needs the silicone gel is to let the engine run and someone turns it off. the fan is suppose to stop after another 5 turns or so. If the fan doesn't stop wuickly once you've turned the engine off, then it could be the gel. I had this problem with a Hilux, however it was fine when travelling at speed (the faster the better) because the airflow cools the engine. it only became a problem if the car was idling.

Once that was fixed, it was running fine except when going a bit faster (being faster than 100km). when the engine was heating up a bit and especially on long hill or on hot days. First thing to do is switch off the aircon (if you have one). In my case, the aircon condensor sits in front of the radiator and the blades were bent etc, so the airflow wasn't coming through. Check it out and see if it can be straightend with a gentle nudge. After all that, I also had to replace the radiator because of lots and lots of corrugated roads I travelled on here in Oz. there was a crack in one of the corners.

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