Cooling an Overheating Vehicle

Marco Antonello — 29 June 2015

I have spent a fair bit of time and money on my beloved 80 series LandCruiser in the past 12 or so months, which has resulted in a full engine rebuild, upgraded internals, rebuilt turbo and injector pump. The gearbox and transfer case also received attention, with all the bearings and syncros renewed. I consider it a long term investment, as this 4WD works for me and I plan to drive it for at least another 10 years.

Some parts were replaced because they were due and others because I wanted them new, but then one I didn’t want touched started giving me trouble.

Engine performance was sweet for a couple of thousand kilometres after the rebuild and I was thrilled with the way it handled the hills on my first high country ascent, but then the needle on the temperature gauge slowly began to rise. Clearly, the cooling system was being pushed to its limits.


A new water pump, brand new radiator and confidence in my recent engine reconstruction pointed to one conclusion: the fan clutch at the front of the engine was struggling. Now I admit, I’ve had few dealings with these fans and replacing it was not on my radar, so I phoned some of my mechanic friends to see if they had more of an idea than me.

I soon discovered this type of overheating under load is common in vehicles fitted with aftermarket turbo kits because the extra fuel consumption causes higher boost pressures, and the cooling system just can’t deal with the extra heat being made. I also learned from a Toyota dealer that silicon fluid can be added to a genuine clutch fan and that some units can even have the lock-up temperatures adjusted. Fluid levels may not be optimised for demanding conditions direct from the factory, so it’s worth checking if you’re experiencing issues under load.


Feeling more educated, it was time to test and remove the fan clutch. I checked for bearing play first by rocking the fan back and forth. I was pleased, as any signs of play would require an entire new unit. Once the fan clutch was on the bench, I unbolted the plastic fan so the clutch could be split in two. The tips of the fan blades had been damaged at some point: they weren’t that bad but it possibly could make a difference, so I ordered a brand new fan even though there were no signs of leaking fluid (without knowing the history, the fluid could have leaked long ago).

With the clutch in two pieces, I could see silicon fluid inside but the level was lower than the bottom of the holes, which is where I was told it needed to be. This clutch didn’t look to be an adjustable type so my only option was to fill to the correct level with extra silicon fluid. The fluid was readily available from my local Toyota dealership for only $12 per 15ml tube so I got two just to make sure I had enough. Adding the new fluid was slow-going as the silicon fluid was very thick and I wanted to make sure I didn’t overfill it. I ended up putting an extra 25ml into the reservoir.

While the clutch was apart, I blew hot air over the internal bi-metal sensor to see if it was working, and was relieved to see the attached internal metal strip turning to open up the different ports as it should. Before putting the clutch back together, I cleaned both mating surfaces and I also gave the O-ring a light coat of silicon to make sure it was 100 per cent sealed.


Once the fan clutch was reinstalled, it was time to take it for a test drive to see if my modifications had made a difference. The first thing I noticed was the needle on the temp gauge was sitting slightly lower than previously under normal driving conditions, which was a great start. Since then, I haven’t had any issues even when powering up a pretty decent hill and I believe the new fan blades have made a difference because the volume of the fan noise has risen.

If your 4WD is new and is pretty much stock standard then you shouldn’t have such issues, but performance modifications can place stress on other parts of the system because you are asking more of your engine. I might have been chasing my tail for a while if I hadn’t just rebuilt the engine, as the fan clutch would not normally be my first step in trying to fix the problem. All up it cost me around $60 and a few hours of my time for a problem that could have cost a lot more without actually being resolved.

Check out the full feature in issue #90 July 2015 of Camper Trailer Australia magazine.


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