John Gaines Posted July 5, 2003 Share Posted July 5, 2003 My radiator can be used with the fan switch at the tpo or bottom. Am I correct to assume that it is better to sense the temprature as the coolant leaves the radiator rather than as it enters? Any thoughts? Link to comment Share on other sites More sharing options...
DrivRich Posted July 5, 2003 Share Posted July 5, 2003 Are you sure 🤔 ❗ I felt a bit of a twit when I presented my Roadsport at post build inspection with the radiator upside down 🙆🏻 The air bleed is horizontal on the top of the radiator. The drain plug is vertical on the rear of the radiator at the bottom - I thought the drain plug should face downwards to drain that leaves you with only one choice, the fan switch at the top of the radiator on the rear vertical face 😬 Oh - and with the drain plug incorrectly pointing downwards it fouls with the nose cone which was a losey fit anyway. Dave Saw a 7 Hitched a ride in a 7 Ordering a 7 - Done that now ❗ Will Own a 7 😬 - First Week of 2003 - Got Her Now 😬 😬 Up to the elbows in cardboard and bits 😳 passed Post Build now - SVA in 2 weeks SVA was a breeze (except the driver side door hinges ) 2 weeks and 4 visits to DVLA just to get the registration On the Road At Last 😬 😬 Membership Number 6640 Link to comment Share on other sites More sharing options...
Mick Day Posted July 5, 2003 Share Posted July 5, 2003 The fan switch needs to sense the temperature at its hottest point so put it in the top of the rad. Mick Link to comment Share on other sites More sharing options...
michaelw Posted July 6, 2003 Share Posted July 6, 2003 Mine is at the top and if you get any air in the rad then the fan won't come on. I know there shouldn't be any - just a comment. Michael. Link to comment Share on other sites More sharing options...
John Gaines Posted July 7, 2003 Author Share Posted July 7, 2003 My thought was that it seems more sensible to trigger the fan if the temperature had not dropped enough after it had passes through the radiator. Am I missing something simple? My radiator has bleed holes at both the top and bottom. Link to comment Share on other sites More sharing options...
I.Mupferit Posted July 7, 2003 Share Posted July 7, 2003 Definitely at the top of the radiator to read the engine temperature at its hottest and switch on at the pre-set (88 deg I think) temperature. If you mount it at the bottom of the radiator, it won't switch on until the engine is way, way too hot due to the temperature drop across the rad. core. Brent Link to comment Share on other sites More sharing options...
Mick Day Posted July 8, 2003 Share Posted July 8, 2003 Spot on Brent, but I think the standard (VW Polo part) switch operates at 92 - 95 deg. Considering the unreliability, in a Caterham installation, of this part make sure you have a manual switch for when it doesn't work. Or better still get the fan switched from the ECU. Mick Link to comment Share on other sites More sharing options...
Peter Carmichael Posted July 8, 2003 Share Posted July 8, 2003 Everybody is right, but for all the wrong reasons. The fan only switches on when the return temp from the rad has risen. If you switched the fan on the basis of the exit temp it would switch on at much the same time, however the fan's effect on the exit temperature would make sure it switched off far too soon. The switch has some built-in hysteresis but this would not be enough to keep the fan on long enough to cure a bulk temperature increase. Rigged as John suggested the fan would cycle on and off more rapidly. Link to comment Share on other sites More sharing options...
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