coolant pump

[jgbff7]

My coolant pump does not work. So I did the trick of earthing the plug on the thermostat housing. With ignition on, the main fans work. With the igntion off, nothing.

So I disconnected the pump and put 12 v across it. Nothing. So pump is broken.

So I got a new pump which is known to work and connected it up and did the earthing trick again. Nothing.

So it looks as if I have two problems. First the pump is broken and secondly 12v are not getting to the pump.

The truth is that I do not really understand why the earthing trick works, but given that I cannot get the new pump to work (which does work with 12 v directly on to it) where do I look next please? Relay? Would a faulty relay stop the earthing trick working?

Sorry to be dim.

Thanks

John

[Saltire]

Not dim at all, John

Here’s the wiring diagram for that bit of the car:

E0BB2D8D-57E9-45D2-87D4-39985CF0E7C7.png

The pump is the bit at the top of the diagram. For the pump to work normally on the car, three things must be true:

1. Ignition is off (sensed by the cooling fan relay)
2. The cooling fan temperature switch is closed (ON). Note: this switch is specific to the fans; it’s a different switch from the one driving the temp gauge and the one sending info to the ECU
3. Fuse C4 is sound

The “earthing trick” that you refer to just gets over the hassle of needing the cooling fan temperature switch on (just a thought: you are earthing the right switch, aren’t you? It’s the red one in this diagram. There are three of the b***ers):

9D5B41FE-1B45-47BB-98CA-C2E05CBC7817.png

From the symptoms you describe, I’d be inclined to suspect that either you have a bad earth (often an issue on the Elan), or the fuse has blown, or you have a faulty cooling pump relay. Both these last two are under the removable cover on top of the dashboard in front of the steering wheel, and both are cheap to replace. You can find details of exactly where they are in the Electrical Manual, which is available through the “Manuals” link at the top of this and all the forum pages, assuming you’re logged in.

If you’re coming to Castle Combe at the end of May, I’m happy to have a look (assuming you’ve not fixed it by then), or there may be another more local member who could give you a hand.

Hope that helps!

[jgbff7]

Thank you very much for going to so much trouble for me.

I think I have the right connector (single wire) so I shall investigate the fuse and relay.

I am very grateful

John

[Hector2021]

I have the exact same issue and had a look into it today but ran out of light and time as i was also replacing the O ring on the the cam bung. This was successful.
I know that the pump must have been replaced by a previous owner as the wires running from it are brown and blue (not matching the wiring diagram) and go to a non lotus looking connector. My pump fails to run with 12v direct to it but when i ground the temp sensor with ignition off, although i can hear the relay energise i dont get 12v at the connector. The radiator fans do run with the ignition on however if i test them this way and also if i let the car stand with the engine running long enough.
Im suspecting a duff pump and possibly a blown fuse.

[Simon_P]

Brown and blue wire with a horrible hard black plug on q 3 inch lead - sounds original

You can try rebuilding the pump it probably just needs the motor cleaning but if the spring keeping the magnets in position is rusted it is scrap.

[jgbff7]

Brown and black with a horrible black connector is what I have. The connector is madness. It has four parts and only comes apart with a small screwdiver forcing the clips to undo. As you say, nothing like the wiring diagram.

The fuse is number 4, bottom right. The relay is G bottom row two from the left, all under the cover in the dash.

I am waiting for a relay removal tool to arrive. Again really difficult to get out. Needle nosed pliers would not grip adequately.

My fuse was ok so I suspect the relay, which I cannot hear energising.

But compared to replacing the cambelt, this is a doddle!

John

[Hector2021]

Looking again i suppose the colour of the wires could be correct. The diagram doesn't show the colours from the pump to the first connector, but they are black and black/slate from the other side of the odd 1950's black 2 pin connector. Im going to remove the pump next weekend and see if thats the culprit.

[Tuga2112]

there is probably something of value in my video of the pump replacement.

honestly. i would be unplugging the wires from the pump and put the multimeter on voltage, short the temperature sensor with the car switched off, and check if theres 12v or not.

then follow the circuit diagrams backwards. which from a glance to the whole thread, sounded like the pump's relay are likely to be burned out.

if my recollection is right. the pump relay is on the top of the dashboard, its a standard 40amp cube relay and needle nose pliers should be perfectly adequate to remove it.

[Hector2021]

John, this was your post originally so apologies for my almost hi-jacking it. Did you manage to sort your pump out?
I have spent today fiddling with a few small fixes. The pump being one of them. My C4 fuse (5A)had blown for some reason, so once I replaced it i got 12v at the pump connector when i shorted the temp sensor. I removed my pump to find that it had been leaking slightly, probably over many years and the internals of the motor were totally wet and corroded. The motor was still free to turn but wont work on 12v.
Looks like i need to source a new pump then.

[jgbff7]

Please do apologise. I am always glad to hear from you.

My starting point was that the main fans worked with the sensor wire earthed and the ignition on. With the ignition off the pump did not work.

So I checked the fuse which was intact. I then had the relay out. I put 12v across it and got nothing so I thiought I had found the issue. But as I tested again I heard the click. So I put it back and found then that I had 12v at the grotty black connector with the sensor earthed.

By this stage I was satisfied that the cables were fine but the pump was at fault. So I bought a new pump. It worked with 12v from a battery connected to it on the bench. I fitted the new one which worked with the earthed sender wire.

My conclusion is that I had a faulty pump and a stuck relay.

I took the old pump to pieces . The impellor was very clean but the windings were corroded and I could not get the pump to work.

So the issues are solved! The bit which surprised me was that the relay started to work. I suppose I ought to replace it out of a sense of caution but it is very accessible and can wait for now.

John

[jgbff7]

PS Both SJSportscars and PNM do replacement pumps, at a price.

I have read that a Mercedes one fits with the correct orientation.

J

[Tuga2112]

PS Both SJSportscars and PNM do replacement pumps, at a price.

I have read that a Mercedes one fits with the correct orientation.

J

i think the one i fitted was the mercedes one. But the wiring needed extending. extending the wiring VS paying the "lotus" brand extra is a decision you need to make before buing, but i know some people got the same mercedes unit and the wires were already extended. i guess mine was the cheapest option without extentions

[Jamie N]

If anyone is in need I have a spare OEM pump here in perfect working order, 35 plus postage.

[Hector2021]

If anyone is in need I have a spare OEM pump here in perfect working order, 35 plus postage.

This is just typical timing on my part. Having finally established it was the pump that was shot i bought a similar spec replacement off ebay yesterday - (0392020073 Bosch Auxiliary Additional 1J0965561A)

Im pretty sure its the right one but it doesnt have the flying lead. I'll need to get a fuel injector connector and make a jumper lead to join the original socket.
However i would much rather keep all original. If you are 100% sure that your spare works and there is no sign of leaks from the impeller. Then ill buy yours and return the ebay one. Ill send you a PM