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Re: My 1994 2litre-non turbo Subaru Legacy travelled 250,000 km's.

The engine appears to overheat after about 20 mins driving. The temperature gauge climbs particularly in 5th gear at about 100ks.

I can reduce this by changing down to 4th gear for a time but as soon as I change up to 5th it will climb again. I have stopped and checked the water level in the top up reservoir by the radiator but this is full.

However, when the engine cools and I check the level the next day, I need to fill the reservoir up as it is almost empty.

I have had the radiator checked several times and to date have not been able to trace the source of the water leak.

I am confused as to why the overheating occurs when to my eye there is plenty of water in the radiator top up reservoir.

Comments please.

Maurice

From the "Ask Jack" archives - 22 August 2009

An overheating engine is bad on any vehicle but in my experience a major overheat on a Subaru can be hugely expensive.

The reason for an expansion tank or reservoir is to allow for natural expansion within the cooling system as the engine temperature rises. As the engine cools the water level should drop in the reservoir as the water is drawn back into the radiator. This level should stay constant however if there are no leaks or problems in the cooling system.

For this system to work, the cooling system must be sealed and retain pressure which is controlled by the radiator cap (allowing the pressure to be release at a certain temperature).

In a nutshell, the water is moving from one chamber to another based on temperature and controlled by the radiator cap.

You have a problem which needs to be addressed immediately. The cooling system needs to be pressure tested for internal as well as external water loss. An internal leak can be from the head gasket allowing water to enter the combustion chamber and pushed out through the exhaust. Have a look for steam from the exhaust tail pipe or sometimes a miss fire when cold is a sign of internal water loss.

To pressure test a cooling system is not a huge job and at the same time the radiator cap should be tested to ensure it can hold the required pressure.

The thermostat may also need to be looked at.

I don't have a specific answer for you, but don't drive the vehicle too far until the problem is checked thoroughly and sorted.

I can supply the name of an AA Licensed repairer in your area if you wish. Just let me know where you currently reside.