Coolant leak - otter switch

[rbgosling]

I don't think I share Peter's philosophy on the thermostat/fan switch strategy.

My view is that the engine normal operating temperature is more of a (narrow-ish) range, not a single target temperature. The thermostat is there to prevent the coolant dropping below the bottom of the range, and to ensure the engine heats up to the target range as quickly as possible. The fan is there to prevent the engine exceeding the top of the range, and in most cases should not be needed at all (forward motion through the air should be sufficient), only kicking in if the car is going slowly/stopped or ambient temperature is very high. There's no need for the fan to keep running until the engine is bought down to the thermostat temperature, it only needs to bring it down to within the target temperature range.

Peter mentions the slowing coolant flow making it easier for the fans to drop the radiator temperature to the target value. But radiator temperature is not what is important here, that's not the parameter to be focusing on. It's engine temperature that is important, and if we slow coolant flow rate through the radiator, we will be extracting less heat from the engine.

"...the rad fans will have a drawn-out fight against the incoming faster-flowing hot water passing through the rad..." Yes, that's exactly what we want if the engine is hot, because that is what will extract the greatest amount of heat from the engine itself.

[Lotus-e-Clan]

"...the rad fans will have a drawn-out fight against the incoming faster-flowing hot water passing through the rad..." Yes, that's exactly what we want if the engine is hot, because that is what will extract the greatest amount of heat from the engine itself.

Yes I agree that more absolute heat is extracted when there is a larger delta between coolant and air temperature. But why allow the engine to overheat just so you can remove more absolute heat?

If that was universally good a thing then you might fit higher thermostat values in hot climates just to achieve a greater coolant to ambient air delta? The Service Notes hot climate fan switch make/break range quotes 82/72C.

[rbgosling]

"...the rad fans will have a drawn-out fight against the incoming faster-flowing hot water passing through the rad..." Yes, that's exactly what we want if the engine is hot, because that is what will extract the greatest amount of heat from the engine itself.

Yes I agree that more absolute heat is extracted when there is a larger delta between coolant and air temperature. But why allow the engine to overheat just so you can remove more absolute heat?

If that was universally good a thing then you might fit higher thermostat values in hot climates just to achieve a greater coolant to ambient air delta? The Service Notes hot climate fan switch make/break range quotes 82/72C.

I'm not suggesting letting the engine overheat, so you can remove more heat. I want to keep the engine within the target temperatures; if that means the radiator gets a bit hotter, so it can reject more heat, then that is what should happen. Remember, what we are trying to control here is engine temperature, not radiator temperature, and they are not the same thing.

[Lotus-e-Clan]

I see where you are coming from but I still consider 95C as an unnecessary overheat in crawling traffic (when the fans are likely to be used).

Also I agree, 82C is the temp at the thermostat, not the radiator. The even lower rad coolant temp (I agree with you there) is to be seen as a reserve of cool water used to keep an efficient lid on system temp when it's called upon.

With an 95/86C switch I'd expect the fans to kick in more frequently because rad temp will eventually equal system temp and you've allowed the oil temp to rise too, perpetuating system heat. Ideally I want my rad temp below system temp if possible and no extra heat lurking in the oil.

[rogbmw]

I am going through the Excel SE, and this summer will be replacing the thermostat with the Hot Climate one. Since we live in Florida, I do this on most of my cars. I am also replacing all hoses with a new hose kit, and will be changing over to Evans. I have had good luck with Evans Coolant in the past. I also have a new Aluminum radiator from SJ.

[Lotus-e-Clan]

Hi rogbmw. Shortly after converting to Evans on both the Clan and Excel, I carried out a simple, reproducible experiment comparing Evans to tap water as a heat buffer. The predictable outcome was that water is a superior heat buffer (gains and loses heat slowly, comparatively).


What Evans detractors tend to overlook is that Evans, as opposed to water as a coolant, gains heat quickly and releases it quickly (poor heat buffer compared to water). The oversight is that you can take advantage of this fact within your cooling system design.

I found that a key cooling system consideration is that Evans works better with an electric water pump (EWP) where you can increase the coolant flow in order to cycle through the water jacket and rad quicker using a programmed EWP than with a OE system optimised for water. This is most beneficial compared the OE systems at low engine speeds in traffic. That's not to say the original WP is useless compared to an EWP using Evans, but you can make it work better, especially in slow traffic.

Will be interested to hear about your own experiences after converting the Excel to Evans.

[Lotus-e-Clan]

The fan switch is an M22 x 1.5 thread, readily available on Ebay.
FWIW, Car Builder part Numbers were MOIN32 and FANSW5, but will be cheaper on Ebay.

Tony, thanks for that Car Builder heads-up . However, a quick browse through the range of Car Builder fan switches comparing to Service Notes values, has given me exactly what I want to fit to mine, but it's not the M22 FANSW5 item.

The M22 FANSW5 makes/breaks @95/86C.

I'm going for the M14 FANSW which makes/breaks @87/82C.

Please challenge my thinking on this in case I'm missing something , but the logic behind my thinking is that in the Excel Service Notes, the latest Otter switch values are 92/82C for temperate climates.

I bought and fitted the 87/82C fan switch. Now I've given it a proper test on a trip into the deep south fro Yorkshire, I can report that it works brilliantly. I particularly like the 5C delta as the fans don't run for too long. And the lower fan switching range just above the thermostat value of 82C prevents heat soak escalation. Oil temps were good too.

[DavidOliver]

I have recently replaced the otter switch and rubber seal (SJS supply)
I dobted the electrical part of the switch, no leaks.

The old seal was hard and fell apart on removal. (there were no wires securing the switch)
i cleaned up the metal pipe surfaces, installed the seal and switch with high grade silicone sealant.
I then applied silicone to the inside of the pipe where the seal protrudes intending to seal the inside joint (where the water starts from)
i left the unit 24 hours for the silicone to adhere (cure) to the metal surfaces and then fitted.
I used ordinary galvanised wire to control the switch from popping out of the housing/seal to avoid a recovery vehicle scene.


Dave the cog