RV8 cooling fan modification
Some time ago Peter Garton had a problem for a short while in the engine bay of his RV8 - the header tank overflowed after switching off the engine. He found that it was due to airlocks in the cooling system which were removed and then the system settled down. In mid-August he was in touch saying "temperatures can easily reach 37°C in Germany during the Summer and recently temperatures in mid-August have been exceptionally high". Peter found that when he returned from a run in his RV8 on a hot day and then parked in an underground car park, the heat from the engine bay was considerable and was very noticeable even though his car park is airconditioned. Peter decided that a modification which allowed the cooling fan to run after the ignition was turned off would be a useful improvement. This note describes this modification.
(Aug 12)

Wiring modification which allows the fans to run when the ignition is off
Peter went along to his local Bosch workshop and they made a change to the wiring which allows the cooling fan on his RV8 to continue to run for a few moments after switching off the engine until the engine temperature comes down to the lower level when the thermostat turns the fan off. If the heat from the hot engine then transfers more heat to the cooling system and the temperature rises again, then the thermostat can cause the fan to kick in again.

The modification to the wiring is shown alongside as a mark-up on a copy of the wiring diagram in the RV8 Repair Manual - see a page with the heading "Cooling fan" which is page 5 in the Wiring Diagrams section at the back of that manual. When Bosch made the wiring modification they joined up W (the feed to the relay coil) to the live feed from the battery N. This ensures permanent power to the fan so that it does not necessarily switch off when the ignition switch is turned off. It is essential that the original ignition feed wire W is disconnected otherwise you would have put a bridge across the ignition switch which will mean it is always on.

Now with Peter's RV8 the cooling fan will usually run for 5 to around 20 seconds after switching off the ignition depending on the ambient conditions and the length of the run made in the car, but on a cool day when the engine is not so hot then the fan may not run after the ignition is turned off. On one occasion the fan has come on after the car has been parked up and then gone off but then it has switched itself on again but only for another 8 seconds or so.

In reviewing Peter's report of this useful modification, Bob Owen notes "the feed to the relay coil - W in the mark up diagram above - should be transferred to the live feed. It is essential that the original ignition feed wire W is disconnected (as shown above) otherwise you would have put a bridge across the ignition switch which will mean it is always on."

Peter heard from the Bosch engineer who carried out the work that relay number 2 on his RV8 was replaced with a Bosch 30amp relay part number 0332 209 151 which is a standard part available from several sources. This relay is a standard relay and does not have a delay feature. To the extent the fans can run on after the ignition has been turned off, that delay in their turning off is achieved by the wiring

Source: marked up copy of the wiring diagram for the cooling fan showing the wiring modification - RV8 Repair Manual AKM7154ENG

modification and controlled by the thermostat switch and not by a "delay" feature in the relay itself.

Consequences for the RV8 alarm system
Peter refers in his note to this as a possible issue saying "it has never bothered me personally but it might happen that the fluctuation of the current when the fan is activated after the alarm is set could set off the alarm. This has not happened to me so I would advise not provoking this and simply to wait for a few seconds before activating the alarm itself to make sure that the fan won't suddenly start going again."
Peter Garton undertook a series of tests with his modified cooling fan wiring arrangements.

Tests to check the RV8 alarm system is not triggered by the cooling fan coming on after the alarm has been set
Following the tests (full details are on the detailed illustrated version of this note), Peter concluded "that the wiring modification can be made to an RV8 without creating a problem with the alarm fitted as a Factory feature on the RV8 model. However as a precaution I would "pause" after turning off the ignition when the engine is very hot, in case it cuts in a second time, before setting the alarm after cutting the ignition because from my experience the cooling fan runs on after the ignition is cut off when the coolant is very hot. I suggest the "pause" might be around 20-30 seconds maximum after ignition switch-off before activating the alarm."

Caution for RV8 owners with non-standard alarms or immobilisers
Where an RV8 has had an alternative alarm systems fitted as a later addition (for example a Thatcham rated immobiliser), owners should check with the supplier of that equipment about possible effects of the wiring modification described in this note. A year or so after the RV8 was produced a new classification of car alarms was introduced in the UK called "Thatcham" and a significant number of RV8 owners have, at the unfortunate insistence of a couple of insurers, had a Thatcham immobiliser fitted so there is the possibility that the wiring modification described here by Peter Garton might cause those Thatcham systems to throw a wobbly when the cooling fan starts up after the ignition is turned off and the immobiliser is set!

See our more detailed and illustrated version of this note. More
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