JohnM Posted May 7, 2007 Share Posted May 7, 2007 I'm going to Le Mans in my R300 and thought it might be worth adding an override switch to the fan - just in case ❗ How is it best to wire this, without upsetting the fan's normal operation? Thanks John Never too old...... Link to comment Share on other sites More sharing options...
NevDyson Posted May 7, 2007 Share Posted May 7, 2007 John, You can run a lead straight from a live feed, through a switch and then run a feed wire and spur into the positive on the fan. You may however want to put an inline fuse for protetion. Link to comment Share on other sites More sharing options...
Myles Posted May 7, 2007 Share Posted May 7, 2007 If you've seen my recent thread about fan voltage, you'll be wanting to minimise your losses. Chris W's famous Electrickery articles are on my site - the relevant one is here - with permission. I've just rewired my fan and relay with 1.5mm 2 thinwall cable and a new relay - I've got the voltage-drop down to just a 1/3rd of an amp - seems to work fine. 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7s Equipe™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Bricol Posted May 7, 2007 Share Posted May 7, 2007 "voltage-drop down to just a 1/3rd of an amp" Now even I, as a mechanical engineer, know there is something not quite right there . . I am bemused by the need for over-ride switches - how many of you have fitted one to your tin-top? Bri Link to comment Share on other sites More sharing options...
Myles Posted May 8, 2007 Share Posted May 8, 2007 Doh! Perhaps we fit them because we've lovingly-crafted our engines and can't see why they should have to cycle through any greater temperature range than necessary. You'll be wanting us to tape over the OP gauges next... 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7s Equipe™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Colin Mill Posted May 8, 2007 Share Posted May 8, 2007 I worry that the over-ride switch could actually increases the thermal stressing of the engine. If used while the engine is at tick over the residence time of the water in the radiator is long so the exit temperature from the rad is low. This is then pumped into the engine. The thermostat response time (and the bias towards sensing the bypass flow) will, I think allow this to happen. I believe that the system is somewhat awry anyway in having the stat in the top of the rad. Other cars (including a Rover 200) I have looked at all seem to have the fan switch in the outflow of the rad. If you use the over-ride I think it would be sensible to keep the revs up when you stop to make sure the circulation through the system is kept up preventing the exit temperature from the rad falling too low. If I hear the fan is on when I come to a halt I hold about 2000 rpm till it drops out. Colin Edited by - Colin Mill on 8 May 2007 09:01:07 Link to comment Share on other sites More sharing options...
MartinWoodham Posted May 8, 2007 Share Posted May 8, 2007 AFAIk the main purpose of an override switch is in race cars where the airflow can reverse and go forwards out of the rad when slipstreaming another car. (yes really!) Where this is likley to happen you preempt the rapid temp rise (even with no thermostat as per most CC race series) by switching the fan on manually. Mine is wired through the heater swicth - heater not fitted. I've set it so that the light in the switch comes on if the fan is on, and both positions are wired the same ie i don't have to worry whether I moved the switch 1 click or 2, either puts the fan on. Also you can then use the heater wiring, only running a (suitably rated) wire from the heater terminal to the rad. Of course if you've got a heater you'll need to run a wire/ wire and relay etc. as long as your override switch is wired in parallel with the temp switch, you won't change the normal operation. Martin Aero'd supersported ex-Roadsports B...anyone got a cheap LSD? Edited by - mwoodham on 8 May 2007 10:00:44 Link to comment Share on other sites More sharing options...
JohnM Posted May 8, 2007 Author Share Posted May 8, 2007 Seems that there's some question as to whether an override is a good idea or not - will have to ponder that one. But thanks everyone for the responses, all very useful John Never too old...... Link to comment Share on other sites More sharing options...
Colin Mill Posted May 9, 2007 Share Posted May 9, 2007 I just found this article here which may be of interest in considering the fan switch. Link to comment Share on other sites More sharing options...
Mick Day Posted May 9, 2007 Share Posted May 9, 2007 The overide switch is needed as a backup for when the fan thermoswitch fails. TADTS Link to comment Share on other sites More sharing options...
Colin Mill Posted May 9, 2007 Share Posted May 9, 2007 Where do Caterham source them from? - it must take real talent to buy ones that fail as I have never yet had one fail on any make of car. If I felt the need for a backup I would put a clip lead in the toolkit. Link to comment Share on other sites More sharing options...
Mick Day Posted May 11, 2007 Share Posted May 11, 2007 it must take real talent to buy ones that fail as I have never yet had one fail on any make of car.Neither have I until the thermoswitch in my 7 failed after 18 months use in 1995. It's a VW part so I fitted an override just in case. My fan is now switched via the ECU but the override is still there just in case. A mate of mine has a TVR & lot's of bits go wrong; mainly electrical. All these items come from other production cars where they survive quite happily until the car's scrapped. Specify a part for an original installation then test it to death in that installation & it'll work for yonks. Take it out of that environment (in a Caterham or TVR?) & the shape of the envelope changes leading to premature failure. Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 11, 2007 Share Posted May 11, 2007 Is there anything wrong with just wiring a wire from each terminal on the switch in the radiator and connecting the other end to a switch that connects them, hence turning the fan on? Save rummaging around for a positive feed and it's already fused. Link to comment Share on other sites More sharing options...
Mick Day Posted May 11, 2007 Share Posted May 11, 2007 Alex That's what I did for a few years but the voltage drop at the end of this now very long wire is quite a bit. Also the fan works on a 15 amp fuse so current flow is quite high. In the end I fitted a 30 amp relay & sited it by the fan: Terminal 85 is a switched earth (override switch &/or ECU) Terminal 86 is 12v supply (I used the green feed to the now redundant fan switch) Terminal 30 is 12v supply (again green feed) Terminal 87 is black/green to fan Link to comment Share on other sites More sharing options...
Bricol Posted May 11, 2007 Share Posted May 11, 2007 I must have a rarity - an original, supplied by Caterham, fan switch still switching the fan after 5 yrs . . . 😬 Mind you, three temp senders, two oil pressure senders, one speedo . . . have been replaced. 😳 I have had them go in tin-tops before, but I would be wary of relying on the over-ride - the one time you miss the guage climbing 'cos the road is so much fun and . . . Bri Link to comment Share on other sites More sharing options...
oilyhands Posted May 11, 2007 Share Posted May 11, 2007 John, You can trigger the fan directly from your ECU using a relay and just one additonal wire, this can be spliced to a dashboard switch so you can have a manual override. Oily Link to comment Share on other sites More sharing options...
CharlieD Posted May 11, 2007 Share Posted May 11, 2007 Oily, Have you got a little more detail for us not so competent electricians? Charlie Link to comment Share on other sites More sharing options...
Sootysevener Posted May 13, 2007 Share Posted May 13, 2007 Simple fix using the Chris W article. There is often - particularly in heavy traffic too much temperature variation if the thermo switch cuts in and out and i prefer to switch on earlier using manual over ride if the thermo switch has recently activated. Also need to watch heatsoak which can reverse back into the head if you've got headers wrapped - the tendency to warp metal should not be encouraged so a mix of manual and auto contol should catch normal overheating early. Myles - did you cut the article from the pdf version of LF about which all seems to have gone quiet recently 😬 *wink* David 1989 1700XF SS clams with carbon webshots here Link to comment Share on other sites More sharing options...
Myles Posted May 14, 2007 Share Posted May 14, 2007 pdf version of LF Shhh! They'll all want one! In seriousness, no - it was all done with permish and Chris W eventually took up my offer to host the rest of his articles. He sent me the .pdfs (available on the site) - but I also retyped(!) them for html use. 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7s Equipe™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
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