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Radiator cooling fan thermostatic switch location


Guest wunntenn
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Guest wunntenn

I dont want this to be a viscous V electric fan argument - I'm aware of the pros and cons. And I've got an electric one fitted.

There was an informative thread some time back about correct location for the thermostatic fan switch. I've searched but cant locate it. If I recall correctly it stated that it was better to locate the fan switch in the lower pipe, the radiator>engine, rather than the top hose, engine>radiator.

The logic being that the fan will consider the ability of the radiator to provide sufficient cooling and switch the fan on when appropriate, rather than located in the top hose where it will trigger the fan on the basis of the heat of coolant coming straight out of the engine. In the bottom location it takes account of the temperature of the coolant leaving the radiator and entering the engine, which is arguably more important.

Am I right with this?

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wunntenn,

I put mine in the top hose because it already had a joint in it rather than cut the bottom hose, however I feel the fan comes on too early and too frequently because the switch I've got (came with Si's excellent X-switch kit) ideally should be sensing outflow temperature bringing the fan on when the rad alone can't cope.

If I did it again then I'd put it in the bottom hose. I now need to experiment with higher temp switches to compensate for the switch being in the top hose.

HTH

Mo

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Guest wunntenn

To add to the puzzlement, I have the X-fan switch/pipe fitted (top hose, but intending to move to bottom hose) and only the day before yesterday was it warm enough to trigger the fan.

It came on in traffic, and the indicator light came on in the cab to alert me. The fan was buzzing away merrily, engine temp stable and correct, and I got home and parked, let it sit idling for a moment and shut off the ignition. The fan continued to run, so I waited, but it would not go off, even as the engine cooled.

I disconnected one of the two red wires to the switch and it shut down. Next morning I reconnected the wire, and despite the fact that the engine was stone cold, the fan still triggered, with or without the ignition being on. I thought perhaps there was a 'reset' in the switch so pulled off all the wires, but it still continued to run when reconnected. I ran the van all day yesterday, and tried several times to reconnect the switch but it still triggers the fan. I have an overrride switch fitted in the cab so I can run on demand and test operation, and it was off, and triggers correctly when switched on.

I'm a bit puzzled by this - the wiring setup may be to blame, but that aside I'm curious as to what could cause a thermostatically switched circuit to trigger even when cold. Any suggestions?

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Guest wunntenn

I didn't do the wiring - it was part of a larger renovation and engine overhaul (all well done I should add, by Barttec Engineering in Airdrie), and the wiring diagram they supplied for the new wiring setup went awol in the handover so I'm still trying to figure out where everything is going, and how, but I did specify a relay for each the main switching components - spots, Eberspacher and electric fan, so I just need to get in about it and sort it out. - have just become a dad a few weeks ago so time has not been freely available to fiddle with stuff! But you're probably right - a duff switch sounds like the culprit. Cheers.

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Guest WALFY
wunntenn,

I put mine in the top hose because it already had a joint in it rather than cut the bottom hose, however I feel the fan comes on too early and too frequently because the switch I've got (came with Si's excellent X-switch kit) ideally should be sensing outflow temperature bringing the fan on when the rad alone can't cope.

If I did it again then I'd put it in the bottom hose. I now need to experiment with higher temp switches to compensate for the switch being in the top hose.

HTH

Mo

Mo

Not sure if it was on Si's site or in a post but he has a list of all the senders in the range, showing both twin circuit and single circuit with all the cut in and out temps. HTH

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Yup, I've seen that Walfers, what I need to know now is how to tell the temp difference between top and bottom hose using stuff in the garage to work out what temp the new switch should work at.

Mo

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Guest WALFY

Ah. Sorry I misunderstood your post then. Do you not have 1 of those laser thermometer thingys then. Can take a reading of the pipes at the top and bottom and of the rad core itself. With and without the fan helping things along. HTH more than my last post

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