DonkeyDave Posted March 25, 2001 Share Posted March 25, 2001 I thought this was probably the thermoswitch in the radiator header as they do seem to fail regularly. So I got a new one but guess what the fan still doesn't come on. So I removed the thermoswitch, short circuit the fan terminals - fan comes on. Check the thermoswitch cold, switch open, heat it up and the switch closes. So with switch still hot and closed reconnect terminals - no fan. Short circuit terminals fan comes on. I'm stuck now! Any help gratefully received... Link to comment Share on other sites More sharing options...
Peter Carmichael Posted March 25, 2001 Share Posted March 25, 2001 In the meantime wire the terminals to a manual switch. It sounds like you have done exactly the right things, but the thermoswitch would appear to be the only culprit. Maybe the mechanical force of spannering it into the radiator is causing some problem? Link to comment Share on other sites More sharing options...
Tony Martyr Posted March 25, 2001 Share Posted March 25, 2001 All automotive problems that tend to defy logic have dodgy earth connections as the answer. Link to comment Share on other sites More sharing options...
DonkeyDave Posted March 25, 2001 Author Share Posted March 25, 2001 The earth is fine, I can get the fan to go on by shorting it. I have 3 thermoswitches lying in the garage, they all close at temperature, when closed none of them operate the fan - tis very strange. Even my Dad the electrical engineer is baffled. Am wiring a manual switch using the fan switch for the heater to keep things sensible in the meantime, I will be able to run the fan off the MBE ECU but will need a new loom and was going to wait until the off season to do this when I get a rebuild. Any bright ideas?! Link to comment Share on other sites More sharing options...
tony isherwood Posted March 25, 2001 Share Posted March 25, 2001 If the switch is in the top of the radiator (some rads have them in the side). It could be that you have air in the top of the rad and there is an air pocket @ the switch. I.e. the air temp never gets hot enough to swith the fan on. Failing head gaskets tend to cause this problem ( to my cost). the repetitive circle of air, running too hot, more air, running hotter ! See Peter's post on filling the cooling system. I jack the front up so the front rad is well above the heater and then fill the system making sure the alan key plug in the radiator (about 8mm ?) lets all the air out. TonyIsh Link to comment Share on other sites More sharing options...
CHRIS CLARK Posted March 25, 2001 Share Posted March 25, 2001 D.D. I wired a 'Kenlowe' fan stat. into the system so I could adjust the 'kick in' temp. To date, it has worked perfectly. Cost was about 23 UKP. It's adjustment range is from 30* to 120*. Mine's set to kick in at 90* and kicks out at 85/86* (indicated). Link to comment Share on other sites More sharing options...
DonkeyDave Posted March 25, 2001 Author Share Posted March 25, 2001 thanks for the replies, I have checked the coolant level and been topping it up as of course every time I take out a thermoswitch I loose some coolant. I have also had the switch in boiling water attached to the fan terminals - no fan. Yet I know the switch is closed, and I know the fan works, I seem to have two perfectly working systems that are refusing to work together. Total resistance across the switch when open is 0.02 ohm, hardly anything to get excited about. Still baffled. Link to comment Share on other sites More sharing options...
CHRIS CLARK Posted March 25, 2001 Share Posted March 25, 2001 "two perfectly working systems that are refusing to work together". Sounds like a marriage!!!!!!!!!! Link to comment Share on other sites More sharing options...
Graham Sewell Posted March 26, 2001 Share Posted March 26, 2001 If you want to have a manual over-ride switch, use a relay as the fans draw upto 10A (peak 15A when starting) and the heat generated in a wire passing through a bulkhead may not be desirable. I located the relay next to the rad, powered it from the existing switched live to the thermoswitch and sent the earth signal to the switch. Cheers, Graham Link to comment Share on other sites More sharing options...
Marius Posted March 26, 2001 Share Posted March 26, 2001 I once had this problem with my rev-counter. Guess what, the cable had broken without any cause (car just 6 month old). Maybe you should measure the cable from the switch to the fan. Just a guess. Marius Link to comment Share on other sites More sharing options...
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