Turning Down The Heat


The worst thing that you hear when setting out on a 4WD trip are those dreaded words, “my car’s overheating!” Receiving this panicked message from a travel companion is sure to cause a sinking feeling in your stomach.

Well, this is exactly what happened on our last trip into the Victorian High Country. Coming into Mansfield, one of the Nissan Patrols in our group started to overheat. The owner of the vehicle had previously had problems with the engine, and had recently fitted a new radiator, water pump and thermostat, but was still having issues.

Luckily it all happened just as we pulled into the BP service station. The 4WD was fitted with thermo fans, so we ran the fans for a while to cool the engine temperature. Once the pressures in the radiator hoses had dissipated we were able to undo the radiator cap. With the radiator cap removed it was clear that there was no water in the system.

I should mention here that a hot radiator is a radiator under pressure, and a radiator under pressure is dangerous. You should not remove a radiator cap without making sure the engine has cooled enough to relieve the pressure in the system. If removed too soon the radiator can spew out boiling water and steam and can result in serious burns. Trust me after 20 years in the business I still did it not all that long ago, and it really hurts.

The 4.2 petrol engine has a bleeder on top of the inlet manifold. We unscrewed the bleeder, started the engine and slowly filled the radiator back up again until water came out of the bleeder.

Now when filling an engine that is not completely cold, it is best to start and run the engine while filling so as to circulate the water and mix it as evenly as possible. Just adding cold water to a hot engine can also cause damage and be dangerous as it can steam up out of the radiator.

Once full we then checked for any water leaking under the vehicle in case a hose had blown, and we also turned on the heater to make sure the water was circulating throughout the entire system. With everything checked the radiator cap was put on and we kept going.

At the time it wasn’t evident that there could be a further problem, but with about an hour to go to get to our camp, we pushed on and kept in contact with each other over the UHF. The Patrol was fine, it didn’t seem to run hot.


Removing the bleeder screw to make sure that we don’t have any trapped air in the system.

Removing the bleeder screw to make sure that we don’t have any trapped air in the system.

The next morning we double checked the water level and found it to be low again, then it became clear that there was a deeper problem. We refilled the water level and checked again for leaks and again there were none evident. This narrowed down the possibilities, and made a leak in the head gasket seem very possible.

After a quick test, one which we call the crank test, we were able to see that there were clear signs of a blown head gasket. This made it all the more obvious for the owner, as he had been chasing this problem for a while now.

In this case it didn’t mean that we had to trailer the 4WD home, it just meant that we had to manage the problem all the way home and set out stops along the way to allow the vehicle to cool, recheck and refill the system. During the drive home another related problem showed itself. At some point the 4WD wouldn’t run on gas. As the gas system on a vehicle works, it runs very cold and the system relies on water to pass through the gas components. With no water in the gas components, the converter simply freezes up to the point that the engine will not run, as the gas will not flow.

The problems almost did not stop there, as the driver of the affected vehicle didn’t have any petrol left. We were lucky enough to limp to the service station where he could fill up with petrol, but after refilling the water in the engine he ended up being able to continue to drive on gas.


As you can see in this photo, once the water level is full water should trickle out of the bleeder hole. This indicates that the water level in the engine is full and has pushed out any trapped air.

As you can see in this photo, once the water level is full water should trickle out of the bleeder hole. This indicates that the water level in the engine is full and has pushed out any trapped air.

Is it a great idea to drive a vehicle with a blown head gasket? NO! Further damage can occur and it can also lead to a seized engine. In this case we were confident that we could manage the problem along the way and get the vehicle home safely.
To give a couple of tips if I may, my Patrol also runs on petrol and gas and I have also been caught with a water problem. I now always travel with too much water. Not for drinking, I take extra in case I or another vehicle has a problem along the way.
I also drive my vehicle on petrol and gas but I like to swap between the two while out on the tracks. I will often drive it on petrol and use half the tank, then swap to gas and use some of that, leaving some petrol in the tank. If I am carrying a jerry or two then I will use that up before I go back onto gas, but I will never empty one completely before using the other, just in case I have a problem with the other fuel system.
Hope to see you out there, don’t be shy come say hi.


Qualified motor mechanic Adam Adler has spent half his life under the bonnet of a 4WD and has worked for some of the top accessory companies and workshops. He knows what it takes to get your vehicle out there and back home in one piece. He runs the online aftermarket store www.nutsabout4wd.com.au.



This article was originally posted by 4WD Touring Australia.

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Comments 3

  1. I have seen this problem many times over the years, not just patrols, and not just petrol engines. I fit low water level warning devices to my trucks and 4X4s. When caught out, especially when extra water is not at hand, I fill the radiator ( if I have water) and only do the radiator cap up to the first click, not down tight. this relieves the water pressure and more than doubles the travel distance. BUT you MUST keep a very close eye on the temp gauge as the boiling point has now been reduced to atmospheric pressure which is much lower than when under pressure with a fully locked cap. hope this helps.

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