Lotus Elan

otter switch accuracy

PostPost by: checkrail » Thu Oct 18, 2018 2:44 pm

Hi this is my first enquiry since joining. My plus 2 new to me from Paul Matty has the normal electric fan in front of the radiator and was coming on just before 1/2 way on the temp.dial even on normal open road running, the gauge then stayed steady at 1/2 way with the fan running constantly. I was expecting the fan to cut out on a normal 60/70 mph run.
I queried this with Paul? in PM's workshop, he said the otter switch could be suspect and sent me a replacement.
This has not made much difference, if anything the fan starts up earlier.
As I understand it the engine is running at the correct temp but why is the fan not cutting out? There is a manual overide switch fitted, and the heater is working perfectly.

Any ideas? Thank you
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PostPost by: Bigbaldybloke » Thu Oct 18, 2018 6:03 pm

Need to know what the actual engine temperature is, I was always taught don?t assume anything, so I?d check the temperature gauge is reading correctly as my next step, if it is, there are alternatives to the otter switch, have a search in this section for fan switch and you?ll find lots of info. If the gauge is out, check the sensor and gauge are matched and also the voltage stabiliser for the instruments is fitted and working correctly. You can remove the sensor and put it in boiling water to see if it reads 100 deg C, probably not worth checking zero with icy water as the gauge is not that accurate, ambient should be fine for the bottom of the gauge range check.
I?m assuming the override switch isn?t causing the fan to run all the time otherwise you would have noticed and two otter switches giving the same (or very similar) fan operation would tend to indicate it?s something else, but using my don?t assume motto, two otter switches could both be faulty although it?s unlikely!
Cooling on a plus 2 can be marginal, you need to check that the blanking plates and sealing foam are in place around the radiator to ensure the full flow of air goes through the radiator and not around it. Also check the fan is going the correct direction. Lots of things to look at good luck and welcome to Lotus ownership.
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PostPost by: Chrispy » Thu Oct 18, 2018 10:59 pm

Could have a hotter thermostat installed as well.
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PostPost by: 512BB » Thu Oct 18, 2018 10:59 pm

Whilst rebuilding the engine on one of my cars recently, obviously the radiator was out of it. The engine rebuild took longer than I had planned, over a year, and in that time the rubber grommet on the otter switch dried out. So much so, that when the rad went back in, got hot and pressure built up, coolant pissed out from around the grommet.

Bit of a faff, as the otter switch was nicely wired in, but I just replaced the grommet and used the old otter switch, as that had been working perfectly. Now trying to get the old otter fitted to a new grommet was a struggle, to say the least, even with a bit of grease on it, and took much swivelling back and forth. Fill up the rad and away we went. Except that all the swivelling buggered up the 30 year old otter switch, which failed switch the fan on at any temp.

Oh well, drain the rad again and fit the new otter switch that I had taken the grommet from, a brass looking affair, as opposed to a zinc / cadmium plated old school one........aahhhh.

And the crux of the story. The new otter, switches the fan on at about 86 degrees, whereas the old otter switched the fan on at 90 degrees, and therefore, with the summer we have just had, the fan was running most of the time...........very annoying.

So I suspect Checkrail, that there is nothing wrong with your engine temperature, its the new brass otter switch that is turning the fan on early. Doesn't hurt to check out the rest of the system though, to be sure.

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PostPost by: nigelrbfurness » Fri Oct 19, 2018 9:39 am

Having the fan running all the time is only of concern if the engine is overheating. If the dashboard gauge shows a constant temperature once warmed up and assuming its working correctly it means the engine cooling system is doing its job. What you do not want is the temperature going up and down by a large amount whilst driving. This shortens the head gasket life considerably of any aluminium head/cast iron block engine as the head expands and contracts more than the block does. So if your cooling system is maintaining the engine at thermostat temperature - 88c is fine - then that is a healthy situation and no cause to worry. A simple test for the hysteresis of the otter switch is to run the engine up to temperature, with the fan controlled by the otter switch, then turn the ignition off. Leave it to stand for ten minutes then check the engine temperature again and see if the fan comes on when you turn on the ignition. If it comes on, then the otter switch is sticking. As others have pointed out, all Elan cooling systems are marginal, the later cars being worst. I've not had many Elans where the fan didn't run most if the time in summer when the engine was warm.
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PostPost by: checkrail » Fri Oct 19, 2018 5:59 pm

Thanks for that info. Nigel, when I switch off at home after a run the fan is always on which is to be expected living where I do in busy Lincoln. Because the fan keeps running for so long----- will it ever stop!----- as I have a battery master switch I just kill the electrics. Although I have plenty of history with the car I don't know how old the battery is.
After a good poke around I realise there are no side valences on the rad which I guess is not helping.

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