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MG MGB GT V8 Factory Originals Technical - Temperamental Fan temperature switch.


I'm currently having some trouble with my thermoswitch (otterswitch?) on the rangerover V8 thermostat housing.
This is the range rover air conditioning switch and switches itself on at 94 degrees C. This worked perfectly for the last three years, suddenly it took to not switching itself off until the engine was cold. The hysteresis function out of whack. Not Every time, just every now and again, with increasing frequency.
OK I thought, switch failing. I put in my spare. This one did not switch on at all.
I shorted the switch connector to keep the fan on all the time while I went to buy a new switch.
Fitted the new one at the shop ($65 !!). This did not work. Changed the new switch for another one they had. Same problem.
Four in a row! The odds are about 99.99975 to one against. I have my moments of paranoia and angst, but even I am not that unlucky.
The switch operates a relay. Power from ignition through the otter switch to the relay thence to relay earth.
Relay works fine and ignition power supply OK, shorting demonstrates that.
I even stuck a couple of these switches in a pan of boiling water. The resistance was infinite at 100 degrees. They should switch at 94 degrees C.
I'm mystified, these switches are supposed to be trouble free.
I'm going to go fit a Davies craige switch (like the Ken Lowe one), but I hate leaving the problem unsolved and I rather liked the neat use of the Rangerover switch. The adjustable one is messy.
If I'm having trouble with this switch some one else also will, eventually.
Any thoughts anyone?


Peter

SU Burlen do a replacement for the factory V8 Otter switch (so-called becasue it switches on when the water gets 'otter). It seems to have a slightly lower switch-on than my old Otter, no bad thing, but that could be because mine was on the way out. It also has a wider and more variable hysteresis, sometimes it doesn't switch off until the temp gauge is practically down on N which means the fans are running longer than they used to. At others the temp gauge hardly varies between on and off and the fans only run briefly but frequently.

The odds of getting a succession of faulty parts from the same supplier are actually quite high these days, especially if they come from the same batch. Replacement parts are rarely as good as the originals unless you can get OE or NOS, and AFAIK genuine Otters haven't been available for years.

The Otter in the factory V8 is a single terminal device i.e. when it operates it puts out a ground picked up from its physical mounting and that is used to operate a relay which is backed by a fused ignition 12v supply. Two-terminal thermostatic switches were used in the 4-cylinders cars and operated the fans directly i.e. no relay.

The air conditioning only comes on at 94C? Is that the economy version? :o)
Paul Hunt 2

Hi Peter,

You might be able to get round your problem, or perhaps identify it a bit more, by using a switch from one of the Kenlowe electric fan kits. This switch has a temperature probe - an expanding fluid in a tube, rather like the mechanical temperature gauge common to many MGs - which can be fitted into one of the radiator hoses. There is a special seal which helps keep the joint waterproof. At the 'cold' end of the tube is a cunning linkage to a pair of contacts used to control the fan. There is also a mechanical adjustment which allows the switch to operate at different temperatures.

I've recently moved house into smaller premises but in a box, somewhere, I've got a spare switch unit complete except for the special seal. I might be able to find it, given some notice. Alternatively both Brown and Gammons and the MGOC shop are only a few miles away; I could investigate sourcing the bits for you, if you wish.

Perhaps you could contact me off line. My email address is still good but I'll have to contact the webmaster to see how to change Gloucestershire into Cambridgeshire!

Regards

Peter Hills
P L Hills

Yes Paul, we are soooo.. tough in Australia that only a girly wimp would even consider turning on the air conditioning at less than 94 degrees Celsius!
Re reading my post I believe I was mostly looking for confirmation that the switches were bad (which seems to be the case) and partly hoping someone might have a miraculous solution.
Peter,
Very kind of you to offer. If you've emailed me I can't get at my emails at the moment, I've run out of Gig for this month (too much VEOH) and have been slowed to snails pace.
I've installed the local version of the Kenlow switch. I was trying to ovoid that because I really hated the under the hose stainless capillary concept, Makes taking off the radiator hose potentially expensive. Also when I tried it was hard to get on and it leaked copiously, in spite of the rubber "seal" provided. No matter how hard I did it up. You'd need a very thick rubber hose for that to work. The installation instructions suggested that silicone be used to deal with persistent leaks (as opposed to the more usual intermittent leaks I guess!). I really didn't like that.
Obviously this is a common problem as Davies Craige have now just (March) produced an installation kit for $30 ex tax.

http://www.daviescraig.com.au/documents/Thermal_Switches/0409_instructions.pdf


http://www.daviescraig.com.au/main/thermal_switches.asp?prodid=4

Obviously I could buy a tap and install the compression fitting into the thermostat housing by either using a 22M plug/bush, or getting a blank housing. This I'll almost certainly do at some stage, in the mean time it works very well, it was quick and doesn't look too bad. The sensor points down and is more or less out of sight.
If someone had time and didn't want to buy the kit, they could easily source and buy the compression fitting body, compression nut and 6mm brass olive. or quarter inch depending on the sensor. The brass olive is the type that has concave ends. Longer in the center, receding to the outer edge. <ZZ> It squeezes the olive evenly around the sensor over about 5mm in length. It doesn't pinch the sensor. A search on the net pulled up a variety of suppliers. However I was in a hurry and I wouldn't have saved too much from $34 what with all the driving around.



Peter

PL - click on 'Customise' in the menu bar at the top of the page.
Paul Hunt 2

Paul,

Thank you. Now done.

Peter
Peter Hills

Hi Peter (in Melbourne, Aus)

The Kenlowe seal works quite well and should be easy to send - it might even work with your local switch variant. If you need one, send me an email - I don't have your address.

Regards

Peter (in Melbourn [Note no 'e'] Cabridgeshire!)
Peter Hills

Good of you Pete, But I've installed the "installation in line" kit which works quite well.
Peter Sherman

I had the leaky seal issue quite bad - a smear of vaseline around the seal and it was fine.
Liam H

This thread was discussed between 25/09/2007 and 30/09/2007

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