Radiator fan didn’t come on

[265bhp]

So engine got somewhat hot....Which caused something of an expulsion of coolant...!....as I took the car for a short test drive up and down the lane this evening....

I have checked the wiring to fan motor and fan relay
I have 12v supply reaching the relay via the green wire
I know the fan motor works as I connec6ed it directly to the battery
I wondered of the (new from Fosseway) thermostat was faulty so I thought I would try and test by bridging between the positive and negative supplies for the thermostat

Nothing happens...

I realise I may have committed a school boy error but surely this should work...and activate the fan motor...?

Best
Jonathan

[abowie]

Has it ever worked?

It's a pretty simple circuit. Switch connects to earth to actuate relay.

Relay wiring or fault would be my guess. If you bridge the switch does the relay clunk?

Depending on the relay you're using you may need a skip lead to power both circuits.

[265bhp]

Hi Andrew

The relay is an old stock..beleive ..W1/C1 and C2....it it the correct type...and from memory yes it clunked when tested...on the bench....but I can certainly try that again...forgive the simplistic question...but when you say bridge the switch do you mean bridge across the 2 spade connectors on the thermostat ?..and see if that makes the relay clunk..?

Best
Jonathan

[265bhp]

And sorry...no ..not worked before as the original relay was missing

[Simonpfhc]

Check all those fuses Jonathan - those fans draw a lot of current on startup.

Don’t ask me how I know

[chrisfell]

I’ve said this before, and it is worthwhile repeating. Our cars are old. All of the components are old. We are taxing these components way beyond their design or expected sunsets. We should treat them accordingly.
My car has its original design otter switch, and a Kenlowe switch, and a manual override switch.
I test each regularly.

[mgcjag]

Hi Jonathan...so is the clutch now sorted as you've been driving up/down your lane? Re fluid expulsion....have you just refilled your system.......is the main thermostat working.....Steve

[abowie]

I've got my car in bits at the moment so can't show the whole wiring. Don't ask....

With some replacement relays you can connect them as per the wiring diagram but you don't get power to the switching circuit.

You need to add a skip cable.

See pic.

Maybe this is your problem.

[abowie]

This is my 3.8 roadster.

[MarekH]

Dear Jonathan,

For a three pole c1,c2,w1 relay, c2 has a double function:- it's the 12v supply which will come back out of c1 and go to the fan when the relay is activated AND it is one of the w terminals for the relay coil. That means w1 goes to the Otter switch and the other side of the Otter has to be securely grounded to the chassis. The other side of the fan from c1 needs to be securely grounded.

If you earth w1 directly, the relay should clunk and the fan come on.
The resistance from w1 to c2 will be about 65ohms. If it is infinity, it's not connected somewhere due to corrosion or a break.

You sound like you are describing a wiring problem. The resistance of the earth side of the Otter should be zero to the frame; the resistance of the relay side of the Ottter should be zero to c1 of the relay, so yes, bridging the Otter contacts should activate the relay.

kind regards
Marek

[phoenix]

Have you tested the Otto switch .Remove it connect a continuity meter to it and dip in hot water similar to testing a thermostat.

[steve3.8]

Jonathan--
Is the temp gauge reading high ?.
Electrics aside ,have you also checked and proven the operating temperatures of both the engine thermostat and the fan otter stat with a thermometer? . I have seen engine thermostats being sold specifically for the 6 cylinder E Type rated at 88 deg --bearing in mind that is the opening temperature not the fully open-- 74 deg thermostat is standard
The original 3.8 otter was 72-80 deg- the fosseway is 78-85 deg .

[265bhp]

Hi guys
Sorry for the delay in replying...have just come back in

Thank you for all the input...appreciate the help

Hi Steve
Thanks for the chat on Sunday...the clutch as I had mentioned is slightly better...a small amount of air was teased out..and I will try once more....so I thought to cheer myself up I would try another t4st drive rather than spend all the time looking at the car...plus as the clutch does work it couldn’t really do any harm..!

So....to double check and do some diagnostics...drain coolant and......Main thermostat checked out as moving in a pan of boiling water...should do it was new from Ken Jenkins when he bored out the aluminium housing...then I checked the otter switch...also works...as it should as it was new from Fosseway

Wiring is all good, and earths also...and having checked the relay directly off a battery ....it also worked...thanks Marek...your descriptions helped clarify what was going through my head....what I do need to do is get a replacement multimeter however as mine is playing up...and I do need to check the quality of my earth connections....

Drove myself almost mad checking and double and triple checking the wiring to the relay...and testing

I also checked the fuse..yup..it had blown but when I replaced it somehow all still didn’t work....

I don’t know...test and re-test...and then...success

I don’t have a rational explanation but with a 25amp fuse the fan comes on when I connect the spade terminal on the back of the otter switch to ground...with the relay making a satisfying clunk

So I think what I need to do is get the car up to temperature and just keep an eye on things....but I will also get a new multimeter to be extra satisfied.....

[MarekH]

Two points:-
Your new wiring loom has very good male connectors, but quite a few of the female connectors (to my touch) were very subtly oversized (or perhaps some of the aftermarket male bullet connectors were undersized). This means they all fit, but are not as tight as could be. When the opportunity lends itself to it, I would get a pair of pliers and delicately squeeze the female bullet connectors so the male connectors are a tighter press fit. You'll know which ones are suspect because it ought to be pretty bloody impossible to make them move without quite a bit of force. Anything which isn't a totally airtight seal will corrode and volts will be lost en route to where they are needed.

Fans are an inductive load. Without going into physics too much, the current drawn at turn on is infinite, but drops very down fast exponentially to its average current drawn. Basically a fan that only draws a steady three amps will likely blow a five amp fuse at turn on. A multimeter set to ohms wouldn't have quite told you what you needed to know.

kind regards
Marek

[Polse7317]

Hi Marek , i always learn something about electric issues when i read your post....
all my electric problems have been solved with one or many of your posts.
I am very grateful to your knowledge

[265bhp]

Two points:-
Your new wiring loom has very good male connectors, but quite a few of the female connectors (to my touch) were very subtly oversized (or perhaps some of the aftermarket male bullet connectors were undersized). This means they all fit, but are not as tight as could be. When the opportunity lends itself to it, I would get a pair of pliers and delicately squeeze the female bullet connectors so the male connectors are a tighter press fit. You'll know which ones are suspect because it ought to be pretty bloody impossible to make them move without quite a bit of force. Anything which isn't a totally airtight seal will corrode and volts will be lost en route to where they are needed.

Fans are an inductive load. Without going into physics too much, the current drawn at turn on is infinite, but drops very down fast exponentially to its average current drawn. Basically a fan that only draws a steady three amps will likely blow a five amp fuse at turn on. A multimeter set to ohms wouldn't have quite told you what you needed to know.


Sure willl.....I look forward to the day when all I have to do is crimp my Bullet connectors

kind regards
Marek

[eddiecross]

Many thanks for this thread.
Great tip to take the relay "+" feed from the fan supply.
I was going to run the "+" feed from the coil

btw cheapest prices for the Lucas relays (one advantage of having a Commando). Andover Norton supply them for Mk3's.

Eddie