Coolant pump.

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Coolant pump.

Postby Tommy J » Thu 26.03.2020, 15:34

Can anybody shed light on why my coolant pump is switching itself on when the engine is cold. I have just inherited a lovely car with very low miles. It has been dry stored for the last 11 years or so. I fitted a new battery and the coolant pump sprung into action. I have had to pull the plug out to stop it spinning and wearing down the battery. Has anyone any suggestions of the best way to test what is wrong? I am assuming there must be a thermostat somewhere controlling this. If so where is it and does it go to ground to complete the circuit? If so I can simply do a continuity test to check if it has failed. Thanks in advance
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Re: Coolant pump.

Postby GeoffSmith » Thu 26.03.2020, 16:23

Do the radiator fans run when the ignition is on?

The radiator fan switch controls both: http://wikilec.com/view/Radiator_Fan_Thermal_Switch

The relevant circuit diagram is here: http://wikilec.com/images/e/e0/MJ25-18_Cooling_Fans.gif

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Re: Coolant pump.

Postby Tommy J » Sat 28.03.2020, 09:15

I have tested it today and the fans spin up for a second when I first switch the ignition on then stop but the coolant pump carries on going.
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Re: Coolant pump.

Postby nigelpen » Sun 29.03.2020, 13:04

Hello,
I wonder how you are getting on with your coolant motor problem. I expect you are aware that the sequence of events should be; when you switch on the ignition and start your car, neither the fans or the coolant pump should be activated.
Once the car is hot and the temperature rises to about the 3/4 mark on the temperature guage the coolant fans should kick in. If you switch the ignition off now, the fans will stop and the coolant motor should operate pumping cooling fluid around the engine in the 'reverse' direction to that of the water pump until the temperature drops down.
Obviously if the coolant pump is going at the same time as the water pump (engine running) they are working against each other!
If you look at the diagrams aready posted hopefully you will be able to follow this through from the temperature sensor and operation of relays.
My guess is that a relay or the temperature sensor is suspect. On the M100 I have found the odd relay failing with time so that may be the cause.
Perhaps the 11 year lay up has affected the smooth opeartion of the electrics etc.
Having said that on my SE Turbo I know my coolant pump works (they sometimes seize up) yet it doesn't operate as I have laid out above, even though I have replaced the odd relay.
In my case this is not a major problem as I dont drive the car hard enough for the coolant fans to be running when I switch off the ignition, although I would like one day to cue this anomaly!
Best of luck.
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Re: Coolant pump.

Postby Tommy J » Sun 05.04.2020, 08:06

nigelpen wrote:Hello,
I wonder how you are getting on with your coolant motor problem. I expect you are aware that the sequence of events should be; when you switch on the ignition and start your car, neither the fans or the coolant pump should be activated.
Once the car is hot and the temperature rises to about the 3/4 mark on the temperature guage the coolant fans should kick in. If you switch the ignition off now, the fans will stop and the coolant motor should operate pumping cooling fluid around the engine in the 'reverse' direction to that of the water pump until the temperature drops down.
Obviously if the coolant pump is going at the same time as the water pump (engine running) they are working against each other!
If you look at the diagrams aready posted hopefully you will be able to follow this through from the temperature sensor and operation of relays.
My guess is that a relay or the temperature sensor is suspect. On the M100 I have found the odd relay failing with time so that may be the cause.
Perhaps the 11 year lay up has affected the smooth opeartion of the electrics etc.
Having said that on my SE Turbo I know my coolant pump works (they sometimes seize up) yet it doesn't operate as I have laid out above, even though I have replaced the odd relay.
In my case this is not a major problem as I dont drive the car hard enough for the coolant fans to be running when I switch off the ignition, although I would like one day to cue this anomaly!
Best of luck.



To date I have not had time to look. I have simply unplugged the pump so it doesnt run the battery down. I am trying to re align the drivers door and fit a new guide that connects to the winder motor. Wow. These cars are tricky
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Re: Coolant pump.

Postby Tommy J » Thu 23.04.2020, 13:36

nigelpen wrote:Hello,
I wonder how you are getting on with your coolant motor problem. I expect you are aware that the sequence of events should be; when you switch on the ignition and start your car, neither the fans or the coolant pump should be activated.
Once the car is hot and the temperature rises to about the 3/4 mark on the temperature guage the coolant fans should kick in. If you switch the ignition off now, the fans will stop and the coolant motor should operate pumping cooling fluid around the engine in the 'reverse' direction to that of the water pump until the temperature drops down.
Obviously if the coolant pump is going at the same time as the water pump (engine running) they are working against each other!
If you look at the diagrams aready posted hopefully you will be able to follow this through from the temperature sensor and operation of relays.
My guess is that a relay or the temperature sensor is suspect. On the M100 I have found the odd relay failing with time so that may be the cause.
Perhaps the 11 year lay up has affected the smooth opeartion of the electrics etc.
Having said that on my SE Turbo I know my coolant pump works (they sometimes seize up) yet it doesn't operate as I have laid out above, even though I have replaced the odd relay.
In my case this is not a major problem as I dont drive the car hard enough for the coolant fans to be running when I switch off the ignition, although I would like one day to cue this anomaly!
Best of luck.



Very strange. I have now had the time to do all the engine servicing and started the car. I have reconnected the electric fan. It has got up to temperature and the fans have kicked in and out to keep the temp correct. The electric fan has not come on after switching the car off ever since. I have only been able to run the engine in neutral because I have no brakes at the moment so suspect engine temperature for the electric fan has not been reached. But all good to date. I have visually inspected the wiring and nothing looks chaffed or damaged so I wonder if it was just the sensor having a wobbly.
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