Dexcossie

Hi All


After some help relating to a overheating problem I have on my sierra sapphire 4x4 1992 cosworth.


When I first noticed the problem I found the two fans on the radiator weren't kicking in. My first thoughts were the radiator thermostat failed so I replaced it. This didn't fixed the problem so I changed the engine thermostat and this didn't solve the problem. I've checked the fuse in the fusebox under the bonnet and found it to be good. I then checked the wiring from the fusebox down to the radiator thermostat and found I only have one 12v supply to one of the fans when I short circuit the radiator thermostat. The other fan doesn't come on unless I swap the wires around at least I know both fans work but not at the same time.


Can any one provide some feedback reference how the system is wired and is there any special way the coolant system should be re-filled in case I'm encountering issues with air locks. Any help would be very much appreciated

martysmartie

iTrader: (1)

Yes the two lives come from a relay which is located in the fuse box (Yellow one) the rad switch trips the relay (Switched earth) when it closes and hence powering on the fans. Either you have a bad connection at the relay or a break in the live wire to that fan someone along the line.

TBH the fan circuit is sub standard to start with and many have been wired as the fuses etc melt due to the fans staying on for to long etc, you could either do a rewire (Plenty of info and diagrams on here or trace the live for the fan that is not working back to the fuse box and try to repair it, or run another new live back to the fuse box.

As for the overheating is it only happening after sitting stationary (In traffic etc) for a while? If so then the fans not working would cause this, if it's when it's moving then it's not going to be a fan problem!

Another bit of advise if you haven't done so already the fuel pump power also needs checking UNDER load, the wiring degrades over the years and builds up resistance and so the pump cannot draw the power it needs under load and so you can end up with an engine meltdown. Again many have been rewired for this very reason!

Martin

tabetha

What makes you think it is overheating ?, don't go by the very inaccurate gauge fitted to these.
Radiator thermostat ?, I assume you mean fan switch.
The fan circuit is dead simple, and unfortunately dead shit tbh.
If bridging the switch contacts show a fan/s working you know the switch is ok.
The thing you need to do is to first rewire the whole circuit, by using the original ford fan wiring and fuse, you are risking potentially a fire at worst, or a melted engine.
The fans only come on when sat idling for a long period.
It's not even worth trying to sort out the crap wiring ford put on these for fan control, rewire using the switch to switch another relay with a seperate loom for the fans, either buy one of diy your own, very easy.
tabetha

Dexcossie

Hi Martin and Tabetha



Thanks for your feedback very much appreciated.


Spent most of the day belling out the circuitry to have clearly understanding as how the system is configured. It would appear after testing the wires I have broken blue wire near the fusebox. Can't get underneath the fusebox as the people at ford didn't leave a enough slack in the cable to be able to check the underneath terminations. Therefore I will go with your suggestion to re-wire the circuit.


Couple of questions reference the re-wire

1. Would you recommend using the same 40amp relay and cable sizes.
2. Where can I purchase the relay and base unit, would I be able to purchase these items at a normal car spares shop, or would it be maplin / rs.
3. Is there a need for a relay if I wire the rad switch wiring to the same cable size as the fans.

As per your question was the car overheating when driven, I can confirm yes. I noticed the temperature gauge had gone up plus the rev counter needle was bouncing all over the place which leads me to think I have another problem apart from the broken blue wire to one of the fans. Any suggestions ?

tabetha

Hi,
A 40 amp relay would be fine, with some cable like 28/030, these bits can be purchased from www.vehicleproducts.co.uk
amongst others.
Yes you absolutely MUST use a relay, as the fan switch contacts are not heavy enough to carry the fan's amount of current.
Wire the relay as follows,
30 = battery live(fuse in line near to battery, 25 amps)
85 earth
86 live from fan switch(other side of the switch must of course have a live to "pass on)
87 output LIVE to fans,
when 85 and 86 have a earth and a live supplied it bridges internally the 30 and 87 together so the power can flow from the 30 to the 87.
85 and 86 can be the other way around, and it would still work perfectly.
The rev counter bouncing sounds like a search and clean of earths on the car would be a good idea.
Don't go by the gauge re the temp, is it using water, pushing it out of the rad cap, has oil in water, do the rad hoses go rock hard and scalding hot ?, can you see steam anywhere.
tabetha

martysmartie

iTrader: (1)

I concur, the temp gauges are inaccurate the difference between say the O and the R can be just a few degrees and the next minute it's down on the M again! Unless it was right near the red as there not that bad! Although you could have a dodgy sender.

Where abouts in Kent are you from btw?

Martin

Dexcossie

Hi Martin

I know what you mean reference ford gauges being inaccurate but the gauge has always displayed the same figure once the engine reaches temp.

yes, was thinking of changing the sender once i re-wired the fan circuit if the temp is still displaying a high level then before

I live in tonbridge

Dexcossie

Hi Tabetha

great site with all the bits i need many thanks

will let you know how i get on