8 replies to this topic

[Darwinism]

Hi all,

 

Due to some pressure issues I need to run compression test (expansion tank expanded and blew coolant everywhere),  I removed and checked the water pump and thermostat, the thermo was stuck closed in boiling water so I ordered a new one and a new water pump for good measure.

 

In the mean time is it still safe and accurate to run a compression test or should I wait until I've fitted the new parts and refilled the antifreeze?

 

I ask because the Haines manual says to get the engine warmed up, with no thermo, pump or coolant I don't know if that's possible...

It say's to remove the fuel pump fuse to depressurise the fuel system, no issue, but to disable the ignition system I was wondering if disconnecting the battery would do the same thing as disconnecting the multiplug from the DIS, or should I do both?

Total noob as you may have guessed.

Thanks for any help.

 

[Carlos W]

You can't do a compression test with the battery removed, as you can't turn the engine over on the starter.

[nicklouse]

what Mini is it?

 

does not matter about getting it warm as you are looking for a failed head/gasket it will show easily,

 

yes remove plugs. and disable fuel and spark.

[Darwinism]

what Mini is it?

 

does not matter about getting it warm as you are looking for a failed head/gasket it will show easily,

 

yes remove plugs. and disable fuel and spark.

Thanks, so I don't touch the battery? It's a '99 MPi

 

How about without the pump or therm removed etc..

Edited by Darwinism, 27 July 2016 - 03:41 PM.

[Carlos W]

 

what Mini is it?

 

does not matter about getting it warm as you are looking for a failed head/gasket it will show easily,

 

yes remove plugs. and disable fuel and spark.

Thanks, so I don't touch the battery? It's a '99 MPi

 

How about without the pump or therm removed etc..

 

The water pump and thermostat wont affect compression test results.

 

And you'll need the battery to make the starter motor turn over

[Ethel]

Removing the spark plugs disables the ignition, as well as putting less load on the battery and starter so your tests remain more comparable across all 4 cylinders, not spinning a water pump will also aid a little. I would imagine disconnecting the plug from the crank sensor will also stop the injectors and ignition coil from firing, perhaps an MPI owner can say if that's not a good tactic?

 

Compression tests will never simulate running cylinder pressures - a teaspoons worth of oil inserted through each plug hole for a second test will help to demonstrate if there's enough piston blow-by to be concerned about. By deduction, it can point the finger poor valve seats if there's negligible improvement in a poor pressure reading from dry to wet.

[Darwinism]

Lovely thanks very much. I'm hoping the faulty thermostat was the cause but I guess that would be too easy :)

[gazza82]

Disconnect the low tension wires to the coil or take the distributor cap off and the ht lead to the coil and it won't start or generate big HT sparks as you spin the engine!!

[AlexMozza]

Disconnect the low tension wires to the coil or take the distributor cap off and the ht lead to the coil and it won't start or generate big HT sparks as you spin the engine!!

On an mpi you don't have them
Disconnecting the coil pack plug will do it though