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otter switch position


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looking at my 1985 s3 I see the otter switch being located in the back close to the engine, however on the later cars they are up front very close to the rad.  what is the best position?   on my (custom) europa I made an otter switch with 2 tempetures settings, the lowest switches on the first fan and the higher switch sets the second fan. (otter switch is up front in the rad (hot side)  thinking to do the same on the esprit with the 3rd fan operated by a dashboard switch. 

 I am rewiring the esprit with all new copper so I can go both ways (that doesn't sound straight LOL) 

thanks, Rick

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  • Gold FFM

Interesting question. Purely theoretical, I'd say the fans are there to control the temperature of the radiator output, so it would make sense to put the otter switch there. This can be either at the radiator side or at the engine side. So if the radiator doesn't provide enough cooling (assumed because of lack of air flow an no other problems like internal blockage or such), the fans should come on for extra cooling.

On the other hand, the objective is to keep the engine temperature within limits, so you'd want to monitor coolant temperature at the engine and apply extra cooling when needed. So the switch needs to be were the temperature is highest, i.e. near the thermostat. This is were the temperature sensor is. The later Esprits with electronic fan control use a sensor in the same water rail, be it at the other side of the engine. Similar in most (if not all) other cars with engine management controling the fans, always on the hot side. Some Range Rovers were equiped with an additional sensor in the radiator output hose as well, to verify operation of the thermostat and radiator (used purely as backup and for diagnostics).
By monitoring the hot side, you get the complete picture, both heat generation in the engine and cooling in the radiator, so seems the most logical.

In your specific case, it makes sense to have the otter switch at the radiator, as that is where the fans are, so less wiring needed. Temperature should not really differ from that at the engine output. Unless the thermostat is closed, but in that case turning on the fans wont be much help anyway. I would use relays to switch the fans either parallel or in series rather than one by one. And use a manual switch to operate all three (in parallel), so you have maximum cooling available if needed. I have such a switch in my Esprit as well.

Filip

I have made many mistakes in my life. Buying a multiple Lotus is not one of them.

 

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@Filip, nice Idea about switching them in series.  on my spitfire the otter switch sits on the cold (outlet) side but the engine is directly behind the rad so no long delay in water temp drop, on a mid engined car you want the otter switch in the hot side so when the water is too hot the fans go on before entering the rad to avoid a hot peak in the system returning to the engine but if the rad is big enough one does not need fans at all?  but looking at various mid engined cars I just copy what they do.  (otter switch in the hot side)   looks like I am going for the front mounted otter switchs, it keeps the wires short and simple and clears the engine bay. 

btw where about are you located in flanders, I have a few customers and family menbers in flanders. 

Rick

 

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  • Gold FFM

Very true about temp variations due to the length and volume in the pipes on a mid engined car like the Esprit. If I pay attention, I can see a drop of a few ° when the thermostat starts to open and the cold water enters the engine.
The idea of switching in series or parallel also comes from the Range Rover. Only 2 fans (auxiliary only, main fan is a big viscous one) so easy to switch. I should take a piece of paper and do some drawings for 3 fans.

My Workshop is near Leuven (Holsbeek), otherwise I'm with my better half near Brussels (Tervuren). My roots are near Antwerp, spent some years closer to Gent as well.

Filip

I have made many mistakes in my life. Buying a multiple Lotus is not one of them.

 

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thats only half an houre away from one of my customers in heist op den berg, family is around Antwerp (hoevenen/kapellen/essen)  In the near future I'll be back there for a machine rebuild, this will take a week or so. can visit and talk lotus if you like.   

Rick

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  • Gold FFM

I'm originally from Schilde, so not far from Kapellen.

You're most welcome to visit the Workshop for a chat and a pint if you're in the area. 🍻

We should probably continue this via PM, en in het Nederlands.

Filip

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I have made many mistakes in my life. Buying a multiple Lotus is not one of them.

 

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