Otter switch earth?

[Stevemorris]

Hi all,

I have a silly issue that's bothering me as I cannot remember from the days I was working on these cars how the header tank is earthed?

The wiring diagram shows the cooling fan system in very simple terms, Ignition switched live to the motor, earth to motor supplied by otter switch when the engine reaches N.O.T.

My question is, how is the header tank earthed? It is rubber mounted to the picture frame, and the stay brackets go to the top of the radiator, which is also rubber mounted?

I have changed quite a few header tanks over the years, but I have never seen (unless my memory is failing me!) a separate earth wire from the tank to the chassis/frame? Was there one and have I forgotten about it??

Thanks, Steve.

[40GT]

There has been a thread recently about this and the possibility of corrosion due to the earthing, I haven't had a problem though, I'm sure bad storage, not being driven etc would contribute.

On an opposite tack I have some heavy duty spot welders, which are water cooled, the factory recommend not using de ionised water, as it reduces the electrical flow, they recommend tap water and if needed no more than 5% antifreeze as this impairs current too.

[Stevemorris]

Thanks Sean.

The diagram isn't much use, I did look at some other threads related to this but there isn't an answer so far.

Surely Jaguar never expected the earth to be via the coolant? It doesn't work! I have a 50/50 bluecol mix in my car, and like you said it won't work above a certain %??

Anyway, Ive made up a separate ground wire and am fitting it between the header tank mounting bolts and the picture frame, at least I can guarantee it is always going to be a decent earth!

Thanks again, Steve.

[mgcjag]

The wireing diagram shows an earth at the otter switch..the manual refers to removeing 2 wires when removeing the otter switch..you should have an earth wire in the harness...Steve

[mgcjag]

Sean where are you getting the information....the Jag service manual calls for water as soft as procurable an approved inhibitory may be used...winter months strongly reccomended to use antifreeze in proportions specified be the manufacturer....Steve

[40GT]

Steve, from a Spot welding manual, I was just showing the opposites to a system in a car.

[Stevemorris]

Thanks chaps.

Steve, my wiring has been messed about with as it has had a manual fan switch fitted. I have run a temporary earth from the header tank fixing bolt to the picture frame and it all works correctly now. I think I will leave the manual switch in, in case I need it one day! I'll leave the extra wiring there so if the otter switch fails at any point all I need to do is switch the bullet connection at the fan wiring and were back to manual.

I do recall (faintly) there was an earth wire on one of the 3 otter switch bolts, I'll look for the wire in the loom and see if I can get it back to standard though.

*EDIT*

Yes, here you can clearly see a male lucar on one of the 3 bolts.



Thanks chaps, Steve.

[Allrand]

The 3.8 has a separate earth wire attached one of the otter switch attachment screws.

[Heuer]

The wiring loom should have two wires going to the Otter switch, one of which (black) is the earth. This is a 3.8 which has the Otter switch on the top of the header, 4.2 cars have it on the front of the header tank.


You can see the two spade connectors on the Otter in the above drawing:

[abowie]

Hi all,

I have a silly issue that's bothering me as I cannot remember from the days I was working on these cars how the header tank is earthed?

It doesn't need to be. The otter switch circuit is in itself an earth. One wire goes to the motor and the other wire is an earth. The otter switch completes the circuit.

[Allrand]

Yes but the header tank itself needs to be earthed because, as the OP mentioned, it's rubber mounted.

[mgcjag]

Hi Steve....I forgot to ask....do you have a relay for your fan....some cars don't....its a good idea otherwise you will have high current running through the otter switch...the relay reduces the current and you wont have a problem with the otter contacts burning out.....Steve

[johnetype]

Yes but the header tank itself needs to be earthed because, as the OP mentioned, it's rubber mounted.

No, Andrew is correct, the header tank doesn't need to be earthed, it's the body of the Otter switch that needs be earthed and it's connected to earth by the lucar under the bolt head as shown in the illustration above.

That the same connection may earth the header tank through the stud welded to it that the Otter switch mounts on is a happenstance but not a necessity.

[Stevemorris]

Hi Steve....I forgot to ask....do you have a relay for your fan....some cars don't....its a good idea otherwise you will have high current running through the otter switch...the relay reduces the current and you wont have a problem with the otter contacts burning out.....Steve

Hi Steve, I am currently contemplating replacing the fan, and may well go down the CoolCat or Fosseway route so I will decide on relay then although I will probably just stick one on anyway.

I am also considering a standard motor with the flymo style blade as I do love originality as I said before. For everyone that says the standard set up is poor, there are people who say it's good! The latest Lucas 3GM unit has uprated electronics as well.

I know the arguments for a modern style fan are sound, but I would say the amount of times I am going to go anywhere in the car where I get stuck in bad traffic (we live out in the 'sticks') is going to be pretty low. So, I may opt for the OE stuff. But for now, the fan is working as it should and I am happy to do a few miles in the car to find out how it is generally, then make the decision later down the line.

Thanks to all who have contributed to this thread, some good answers. I know the original loom at the front will have both wires in it somewhere but the additional earth wire I added does the same job, plus I have probably made it a bit heavier/more substantial. Attached is a diagram of the new wire position shown with a red arrow.

Steve.

[Stevemorris]

Yes but the header tank itself needs to be earthed because, as the OP mentioned, it's rubber mounted.

No, Andrew is correct, the header tank doesn't need to be earthed, it's the body of the Otter switch that needs be earthed and it's connected to earth by the lucar under the bolt head as shown in the illustration above.

That the same connection may earth the header tank through the stud welded to it that the Otter switch mounts on is a happenstance but not a necessity.

Theoretically, if the otter is wired as per factory, the header tank IS earthed.

[johnetype]

Yes, but that's not the point. Allrand said the header tank had to be earthed because it is rubber mounted and that is simply not true.

[bitsobrits]

[quote
I am also considering a standard motor with the flymo style blade as I do love originality as I said before.
[/quote]

The standard fan blade is fine if you like the 'originality' of overheating on hot days and in slow traffic. Otherwise hang it on a wall.

An XK engined E type with a standard cooling system in fine fettle and with a multi blade aftermarket fan doesn't overheat. The fan motor/blade is all but invisible when installed, so the modification is very discreet.