11 replies to this topic

[Royale87d]

Hello everyone my name is Alfio and I'm writing from Italy.

Sorry if i disturb, but I have a problem with my 97 'Mini MPI: I completely rebuilt the engine, and I was testing the cooling circuit.

Once the fan started, I waited a few minutes and turned off the engine. But as soon as the engine was turned off, the water began to boil and level up in the expansion tank.

I have read a lot of discussions about it on the forum, but it seems that my problem has no solution.

All components are new (head gasket, radiator, thermostat and pump), but this "after boiling" phenomenon (should be caused by a loss of pressure in the circuit) persist.

If can help, the upper tube gets harder and harder as long the engine warm up and when the engine stops and water starts boiling the tube is very hot and very hard. Only after a few minutes (two or three) it becomes soft again and at the same time the water in the tank goes down and stops boiling (only few tiny bubbles).

Anyone can help me??? Thanks in advance

 

[Steve220]

Sounds like you need a new expansion tank cap.

[Quinlan minor]

Sounds like you need a new expansion tank cap.

Ditto on that.

 

Confirm by putting a polythene bag over the neck of the expansion tank (JUST FOR THE TEST!!) before screwing on your existing cap. If it doesn't boil up, it's the cap at fault.

DO NOT DRIVE THE CAR WITH THE BAG IN PLACE!

 

There are a lot of cheap, useless caps out there.

Get one of the BMW blue seal pressure caps.

[Royale87d]

Hi! Thanks to all, ok, i'll manage this test tomorrow!

Edited by Royale87d, 11 August 2020 - 01:27 PM.

[se7enmvu]

I think my caps at fault where can you source the bmw cap?

[Quinlan minor]

I think my caps at fault where can you source the bmw cap?

I got mine from Croydon Minis.

[viz139]

How long are you running the engine?  Have you left the engine running with the fan on? What is the temperature gauge reading when the engine is on?

[Royale87d]

Hi guys! Quinlan, i've put a polythene bag over the neck of the expansion tank and it doesn't boil up... so, are you of the opinion that it is the cap?

For Viz, the car is parked and the engine run for five minutes until the cooling fan switch on, the temperature gauge stay on half...

Thanks 

[Quinlan minor]

That confirms that your cap is the problem. Replace it with a good quality one and enjoy driving your Mini.

[viz139]

Does the coolant only boil when you stop the engine or if you leave it running for 15 min will the fan keep the temperature at normal?.  If the temperature gauge is staying at normal why are you turning off the engine?

[Royale87d]

Hi guys! Yesterday new cap arrived and today i’ve fitting it! No more boiling problem! Thanks Quinlan!

[Alice Dooper]

MPI expansion tank caps, a common storey!!  I keep one in my spares kit in the boot.  A lot of the caps on the market don’t seem very good quality.