370
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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