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Fan thermostat temp setting


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Ive fitted a Merlin fan thermostat, its fitted into the top pipe from the rad.

This has a thermostat in it, thats settable from 70-120, but Im struggling to work out what temp it should be set at.

The manual says the thermostat opens between 72-83, but thats just to allow water flow, not when the fan should come on/turn off.

This is on a SD1 3.5 V8.

I have found that shutting the engine down and restarting when the fan is ON blows fuses though :rolleyes:

So I guess what Im asking is.... Whats the working water temp for a 3.5 V8?

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Hi I know it's not a V8 but on my 300 TDI I use a X-fan switch from Simonr and use the higher switch point on it which is 92C and the fan hardly ever gets switched on. The lower setting on the switch is 88C. So I would go for that on yours and see how it goes.



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The early SD1’s run the temp lower stat…….... this was later replaced with a 88C stat . IIRC this was due to the oil not reaching the correct temp on the early RR’s ………….you may find it better to replace the stat with the 88C

With an 88C stat the fan should come on at about 95C …………………..

I have my twin fans set to come on at half speed @circa 95C and full speed @circa 100C.

100C is only about ¾ on a normal C/N/H gauge……….



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After a bit of faffing about with the power supply I seem to have got it running properly.

Ive set the fan at approx 95, but it will need a bit of roadrun to check its set a the right temp :)

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I have found that the V8 should run below 90 deg Celsius. Your thermostat regulates the engine temp to a minimum temp. Your fan switch is there to regulate your water temp. The most common fan switch is a 92-87 which is on at 92 and turns off again at a reducing temp of 87 deg. I would set your fan switch for on at 90 - 92 deg C.

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