Sim Posted August 16, 2020 Share Posted August 16, 2020 Leave the heater valve open all the time when filling and running - Ive not seen an airlock at that end - (especially with a bleed tee)Is the bottom hose from radiator getting hot? if not, then either an airlock or thermostat is not opening ( rather than a fan problem)i don't think fan will come on unless there's flow of hot coolant through the radiator and that won't happen until thermostat opens and bottom hose is hot.( if you search the archives, another long term solution is to drill a small hole in the thermostat, so it is permanently passing a small amount of coolant through radiator and helps with airlock removal. The downside is it can overcool in cold weather)Simon Link to comment Share on other sites More sharing options...
goodcoffeecode Posted August 16, 2020 Author Share Posted August 16, 2020 I think we have a winner! Unscrewed the cooling fan switch (and lost about half a cup of coolant). So, firstly, this does seem to now be submerged in the fluid. Disconnected both wires from the switch and shorted them together. Turning on ignition starts the fan. Connected wires back to switch and then submerged it in boiling water for a few minutes. Fan did not come on.So, on the assumption that it doesn't take longer for it to get up to temperature, it looks like the switch has failed.Also, because all the hoses got nice and hot on the second start, I think I'm happy that the thermostat is OK. I'll test that hypothesis (once the new switch is fitted) by started the engine with a little gap in either the hex screw or bleed tee. Link to comment Share on other sites More sharing options...
goodcoffeecode Posted August 16, 2020 Author Share Posted August 16, 2020 In the meantime, I'm pretty pleased with this. It's a bit Heath Robinson, but I've fitted an override switch. I saw a post detailing relays and lights, but that's way beyond my current electrical abilities! I just added a couple of piggyback spade things to the cooling fan switch, passed some 17A wire through an existing hole in the bulk head, drilled a new hole in the dashboard and put in a new switch. Works like a charm Link to comment Share on other sites More sharing options...
Bricol Posted August 16, 2020 Share Posted August 16, 2020 I never understood the over-ride switch idea - does your tin-top, which I assume does more miles more often in more traffic, have one? Just make sure the radiator switch works - if you rely on the over-ride, one day you will forget it . . .Its more complication to go wrong or cause problems. My original fan switch failed after 16-ish years, and I've had one stat fail (the Land Rover modification one) which didn't get noticed on the road, but did on Dave Walkers rolling road.On my trials car, which spends all day when competing mostly idling, with bursts of revs, and sometime really high revs, on test sections, I just have the fan switched on all the time, able to be switched off if the trial section goes through deep water. Link to comment Share on other sites More sharing options...
goodcoffeecode Posted August 16, 2020 Author Share Posted August 16, 2020 Yeah, I know what you mean. I think there's real benefit, however, in getting the relay installation with the "on" light. I really need to be able to drive this on Tuesday, and I'm not sure the new switch will arrive in time. This is a sub-£10 fix Link to comment Share on other sites More sharing options...
TomB Posted August 17, 2020 Share Posted August 17, 2020 This is a sub-£10 fix well it would be, but now you need to find £200 for a new Carbon Fibre dashboard Link to comment Share on other sites More sharing options...
goodcoffeecode Posted August 17, 2020 Author Share Posted August 17, 2020 TomB - ha! It went in perfectly. Clean, drilled hole and new switch lines up with existing controls in order to satisfy my OCD Link to comment Share on other sites More sharing options...
John Vine Posted August 17, 2020 Share Posted August 17, 2020 Re #52:...and then submerged it in boiling water for a few minutes. Fan did not come on.If you simply poured off a cup from the kettle, and dunked the switch in, there would likely have been a significant heat loss, such that the temperature sensor in the switch never reached its (92C?) threshold.To test it reliably, you need to rig up a small test circuit with battery and bulb, and then dunk the brass bit in continuously boiling water (in a saucepan, say). Better still, measure both heating and cooling from/to 80C with a thermometer. That way, you'll establish the actual operating range of the switch. So, it's by no means certain that your switch is faulty, although your symptoms suggest it may well be. JV Link to comment Share on other sites More sharing options...
420R Posted August 19, 2020 Share Posted August 19, 2020 It makes little sense to drill a hole in the dash to fit a switch for what is a temporary lash up.You could have cable tied the switch underneath the dash onto something accessible.Of course it's your car... Link to comment Share on other sites More sharing options...
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