COOLING SYSTEM CARE

One cause of deterioration of cooling system coolant/inhibitor is air in the system. You may have noticed when checking the radiator water level that it is not always full to the brim, especially when cold. This is because as the water heats up it expands and is forced through the radiator cap to be lost down the overflow pipe.

When the system cools down it contracts and draws air back through the cap (or loose hose connections) which accounts for the drop in coolant level. Also be aware that the loss of coolant may be from any other part of the cooling system including cap, hoses, heater, holes crack, seals (especially the water pump shaft seal) and gaskets.

By fitting a radiator overflow catch tank (this is standard from 'L' '85 onwards), advantage is taken of the expansion/contraction of the fluid. You will also have to use a special radiator cap. On expansion water is driven across to the catch tank via a connecting tube. On contraction and cooling water is drawn back the other way thus eliminating air from the system which can operate at peak efficiency.

I recommend fitting stainless steel worm - drive hose clamps to ALL hoses to absolutely seal the system, as even the slightest gap or leak my prevent the system from drawing water back from the catch tank.

You should check the whole system for leaks, tighten/change the hose clamps and clean out the free-loading grass-hoppers frormthe radiator core. The latter is best done by removing the radiator and flushing the fins out from back side. Also flush the radiator internals out with a strong flow of water from the garden hose. Take care though with an old radiator as you may blow away a lot of the fins leaving behind only the cross cores! Let the radiator dry and give it a new look by painting with a can of gloss black paint which may help to hold some of those old fretted fins together for a few more years! Finally, you may be better off to go to a reputable radiator specialist- and have the radiator tested, cleaned, painted or re-cored. A bug screen of fly wire is a good idea fifted behind the grill.

The operation of the radiator thermo-switch can be checked by removing the grill and covering the front of the radiator with newspaper and running the engine whilst keeping an eye on the temperature gauge. The thermo-switch should turn on the fan/s when the gauge is somewhere between 1/2 way and red mark on the gauge; but this might vary from car to car. I stress that the car must not be driven with the radiator covered; and if the thermo-fan/s do not come on you should suspect the thermo-switch which is screwed into the radiator, that is assuming the wire to it is connected and the wiring and fuse is okay. It can be checked electrically with a 12 volt supply whilst immersed in a kettle of water which is brought to the boil. From 1985 'L' on, Subaru have wisely fifted a very good overflow tank as standard along with the special radiator cap, but the comments as above still apply, and particularly the last paragraph below.

It is not a bad idea to replace the thermostat every few years which will at the same time give you the opportunity to inspect the aluminium 'internals' of the thermostat housing. Make sure you re-fit one of the same opening temperature. This housing (on any make of car) is probably the first place to show signs of pitting. or scale through oxidisation of aluminium. These are warning signs and should be heeded as it probably means the inhibitor you are using is of/the wrong type/not enough/diluted/evaporated, or you did not put any in! If you are using Castrol Inhibitor (the best in my opinion) it should be fluoro-green, but should be changed every 12 months. Owners of pre-Liberty models should seriously consider fitting a manual override switch for the electric radiator fans.

One should not be lulled into a false sense of security by expecting the cooling system to look after itself just because you have an overflow catch tank. It is still necessary to periodically remove the radiator cap when cold to ensure the radiator is full of coolant; even if the coolant in the catch tank is at the correct level. A certain cause for concern is if the catch tank level is reducing (even if slowly and the radiator is full) as eventually it will be consumed and then the radiator level will also start to fall.

This article courtesy of Subaru 4WD Club of WA.

For more information on cooling system care see

Tech Talk Topic More Than Just A Coolant

Note: A concerned reader subsequently wrote to express a contrary opinion about using non-genuine coolants in Subarus. See Coolant Caution for details.

Disclaimer: Technical information given or disclosed in this website is given with the best intent and is advisory only. No responsibility is taken by the the Subaru 4WDrive Club of Queensland or its members for any damage or injury caused by any vehicle modifications made, or by the use of any products or the adoption of any procedures mentioned in this website.