Paul Ireland’s RV8 Cooling Fan Delay

Some time ago Peter Garton reported a problem in his RV8 – the header tank overflowed after switching off the engine. I had the same problem last year while driving in the Alps. I lost all the meagre reserve of coolant from the header tank when I stopped half way up one of the passes. I am sure you can imagine the difficulty this caused.

The problem is the same. In the RV8 the radiator cooling fan switches off when you turn the ignition off. Heat soak in the engine causes the water to expand and overflow the header tank. The solution is simple but not very practical. After stopping the engine, switch the ignition back on for 3 / 4 minutes to keep the cooling fan running.

Peter’s solution was to fit a manual switch (see RV8 notes). I have designed an, easy to fit, timer circuit (much like a modern car) that replaces the existing fan relay only requiring the addition of an earth strap. This keeps the fan running for 3 to 4 minutes after switching off the ignition if it is needed, which it often is!

Even though my car normally runs cool, since fitting this circuit, I have noticed how many times the fan stays on, especially after a short time manoeuvring in a car park.

Providing there is sufficient interest, I can get a batch of these circuits produced. Cost will be £66.00 plus P&P per unit.

If you are interested, please send your details to

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