electrical/overheating

[jod]

Hi,
i am in need of some guidance.Rad cap has been lifting and dumping coolant,fans not coming on.
1.Cylinder head gasket tested ok
2.Radiator recored ok
3.hoses checked and new clip's fitted ok
4.new thermostat fitted from leven ok
5.new otter switch fitted from leven ok
6.new fan relay fitted ok
7.override switch fitted ok
8.system refilled and bled ok
9.still dumping and fans not cutting in
Now here is the thing that i am stuck with,when the ignition is turned on,(engine not running) and the override fan switch is operated the fans come on then when the engine runs the fans shut down as soon as the engine starts idling.When checking the temp range the fans do not come on and the car overheats and boils,but if i turn the engine off and just turn on the ignition the fans come on.
Any advice or guidance would be appreciated,otherwise i am stranded i was supposed to be taking the car to Bristol classic car show tomorrow !

[tvrbob]

Are you certain that you have primed it completely? Sounds like airlock to me.

[jod]

Thanks bob,
I,m pretty sure that it's not air,if it were why then are the fans not operating as soon as the engine runs,but run when only the ignition is turned on?

[tvrbob]

I was thinking that if air is locking the pump then you would have overheated water in the block and cooler water at the fan switch. With very poor water movement you will soon boil and the fans would not have recieved a signal to start, fan switch still cool. It's possible you have two probs. The electrics of your override could be iffy.

I experienced boiling and steaming without fan switch activation. That was poor circulation because a slug of air kept finding its way to the pump. Things get worse then because steam stops the pump too.

If you have air or are generating steam then don't expect the fans to start. The hot water may not be getting to the switch.

[jod]

Once againt thanks Bob,
What you are saying makes sense but after the problem occurred i placed a thermometer inside the swirl tank and the temp was in the 90's.i've also bled the system as per the owners manual which gives a good description.Can you give me any tip's how you managed to get rid of the air in your particular case.I've also removed my override switch and the fan's still only cut in after the ignition has been turned off and then on.Cheers

[GreenV8S]

Are you saying that with the fan override on, the fans run continuously when the ignition is on engine stopped, but after you start the engine the fans stop even when the override is still on?

Is your override just shorting across the otter switch or is it trying to do something more clever?

[jod]

Hi green v8s,
you've got it in a nut shell,but with my override disconnected the problem is still there.
The temp rises and boils,turn the engine off and immediately turn the ignition on and the fans cut in.

[GreenV8S]

That sounds like a wiring fault. Should be fairly easy to track down since it is repeatable. Just make sure you don't let the engine overheat along the way or a trivial problem could turn into a very expensive rebuild.

I suggest you start by confirming normal operation of the fan when the ignition is on with the engine stopped, and then see what changes when you start the engine.

You should have 12v to one side of the otter switch and earth on the other. When the otter switch goes over temperature it closes, pulling the 12v down to earth. Do you get this? Also identify the fuses and relay used to drive the fan, you'll need to know these for the next step.

[jod]

What is the next step.
i thought about checking the earth connection on the front under the rad?

[GreenV8S]

After you've tested the otter switch wiring, the next step will be to measure the voltage of each wire at the fan. There will be a plug close to the fan, unplug the fan and this gives you access to the two wires to test them. One should be permanently earthed, the other should have 0v when the fan is off and 12v when the fan is on. It is also worth checking the continuity of the earth by using it to earth a test lamp. Incidentally, you don't need to bring the engine up to temperature to test the wiring to the fan, just short together the two wires at the otter switch.

[jod]

Hi v8s,
thanks for the help so far,this is where i have got to.
Power at otter switch
11.9 with override switch off & ign on.
6.3 ----------''-------- on -----''-
13.5 ---------''-------- off & engine running
9.7 ----------''-------- on -------''------

Fan connections
12.46 on both connections with override switch on & ign on

Zero -----------------''----------------------- &
engine running.
It seems that there is no power at all to the fans when the engine is actually running.I have replaced the otter connectors and the fan connectors look good.I have looked everywhere for the earth connection but i must need an appointment at specsavers because i cannot find it.I am now clutching at straws and would again appreciate any help

[david beer]

The 12v ish at the otter should go to 0 when either the otter is "closed" or the fan over ride is on. I would run a new "earth" to the otter switch.

[GreenV8S]

Those readings at the otter switch show there's a poor earth on this circuit. Don't understand the readings at the fan though. Why would you be getting 12v on both terminals? One of them must be earthed for the fan to work, and we know the fan does work when the engine is stopped! Maybe they're sharing the faulty earth and what you're measuring is back-feed from the other circuit?

Don't see the problem yet but it does look as if you are looking at an earth fault, possibly in two circuits (otter switch and fan). Sanity check, you should be able to bring the fans on by earthing the otter switch wire that normally has 12v on it. The body of the alternator is a good earth point, just stay clear of the terminals at the back. At the very least you should be able to hear the relay cutting in and out as you do this. If the fans don't come in too, we need to look for a fault on the fan circuit too.

[spend]

Pull out the fan relay and see whats going on at the relay terminals.

switch circuit: 85 & 86 - 1 is live with ignition on, other is switched to earth by otter &or override.

fan circuit: 30 & 87 - 1 is permanantly live (via fuse) other direct to Fans.

YMMV if you have twin relays, but similar idea.

HTH Dave

[4lf4-155]

my advice. buy a clio cup Tee hee!

[jod]

Hi v8s,
Just to update you,i slept on this problem overnight and rechecked all my volt's etc.
The earth on the otter switch had continuity when just the ign was on and also when the engine was on fast tickover but when on normal idle earth was lost.
Must have been a short in the cable,anyway i have run a new good earth to the otter switch and everything works perfect.
The fan's cut in and out as they should and fitting a recored rad and overhaul of the cooling system is excellent.
Thanks for all the help and guidance that was readily forhcoming from you and the rest of the lads/lasses?
Cheers