KV6 - Oil emulsification / coolant loss.

[Yorkshire GOC]

Originally Posted by Yorkshire GOC

I would advise the OP to do the T-Cut test - take her out for a good thrash at motorway speeds for 10 miles or so. Leave the car till next day and open the expansion cap - if silent then good - however if there is the hiss of gas this is a clear indicator of exhaust gases in the coolant system - there should be no pressure in a cold system.

I would also see if exhaust gas can be smelt in the expansion tank itself following a good thrash and when the system is cold ie next day - again a pointer to exhaust gases being in the coolant system.

[T-Cut]

Originally Posted by kaiser

Again careful. You can have differences in ambient pressure (barometric) or even a lazy relief valve, which could cause a small differential in pressure between a cold system and ambient.
Not much, for sure, but a small "pfft" or a "sigh" when opening, is quite normal.

I've tested that theory over several consecutive days. My own car never gives any obvious sound whatever. If there is a sound, it's extremly faint. There's no significant hiss that could be mistaken for exhaust gas overpressure. I've tested the method using a pressure tight polyester pop bottle which don't expand significantly when pressurised and had with a similar free volume to the header tank. I wanted reasonably controlled conditions. So, I recorded the atmospheric pressure in millibars at the start of each test (bottle top open), then screwed the cap on tight and then left it at the same room temperature until there was a significant difference in the weather and the atmospheric pressure (at least 20mb and preferably much more). This could take several days to a week. With an ear close to the bottle cap, a barely discerable sigh can be heard. Unfortunately, the UK weather rarly varies as much as 20mb or more in 24 hours, so I believe the residual pressure test is valid. By hiss I mean exactly that.


TC

[SD1too]

Hello Sebastien,

As you've hinted, claims like these that your garage ...

Originally Posted by Sebastienclement

... found a leaky radiator, that was "pulling air into the cooling system and over-pressurising it".

And that ...

Originally Posted by Sebastienclement

their 'diagnosis' is a "cracked engine block".

... suggest to me that they don't know what they're doing. It's therefore a pretty good guess that, when working on your cooling system, they did not refill and bleed it according to the recommended MG Rover procedure. Here is that procedure. I'd suggest that you do it yourself now as it's not difficult. It will ensure that there is no air in the cooling system which can cause symptoms easily mistaken as something more serious.

The lumpiness is, of course, a separate issue. Did the garage charge you for new inlet manifold gaskets? You won't know if they bothered to use a torque wrench on the manifold nuts, but we can guess!

Simon

[Sebastienclement]

Used the car yesterday, covered about 50 miles. Still pressure in the cooling system this morning, thick mayo under the oil filler & approx 500ml of coolant gone.

I bled the system yesterday & these are the results after.

Sent from my SM-G960F using Tapatalk

[T-Cut]

Originally Posted by Sebastienclement

Used the car yesterday, covered about 50 miles. Still pressure in the cooling system this morning,

Yesterday and today have similar barometric pressure (warm weather around 1040mb). A clearly audible hiss is abnormal overpressure and doesn't sound good. A 500ml loss is rather worrying. Has the sump level increased? Before the run, did you eliminate any trapped air using the official bleed? If not, why not do the bleed routine and repeat the run?



TC

[Sebastienclement]

Originally Posted by T-Cut

Yesterday and today have similar barometric pressure (warm weather around 1040mb). A clearly audible hiss is abnormal overpressure and doesn't sound good. A 500ml loss is rather worrying. Has the sump level increased? Before the run, did you eliminate any trapped air using the official bleed? If not, why not do the bleed routine and repeat the run?



TC

Yes, system was bled properly - plenty of experience of doing this on my own KV6 motors.

The mayo is now thicker under the cap than John's photo above shows.

No noticeable rise in oil level, but oil was changed approx 500 miles ago and is dark, rather than the light golden colour it stays in my other cars.

Sent from my SM-G960F using Tapatalk

[T-Cut]

Originally Posted by Sebastienclement

No noticeable rise in oil level, but oil was changed approx 500 miles ago and is dark, rather than the light golden colour it stays in my other cars.

It does look worrying. Coolant can become incorporated into synthetic engine oil to produce a viscous dark/black fluid. I guess the bulk of the water part is being evaporated off, which increases the mayo formation at the top end

TC

[minimutly]

Originally Posted by Yorkshire GOC

I would advise the OP to do the T-Cut test - take her out for a good thrash at motorway speeds for 10 miles or so. Leave the car till next day and open the expansion cap - if silent then good - however if there is the hiss of gas this is a clear indicator of exhaust gases in the coolant system - there should be no pressure in a cold system.

Apologies for quoting this from the first page, but I feel this needs saying:-
This hiss could just as easily be air going in as coming out!
I have a coolant joint leaking on my zt v6 at the moment, its just a few drips a day, but after 3 days opening the lid gives me the same pssst, then the tank level drops as the water re-levels itself, with bubbles emitting from the bleed holes near the cap.

Also, just reading back up this page, the v6 (well all mine anyway), do not empty enough to give a clean oil after a change, even running on lpg, which is supposed to reduce contaminants in the oil.

[T-Cut]

Originally Posted by minimutly

This hiss could just as easily be air going in as coming out!

The pressure cap has a hair spring vacuum relief valve to prevent this.


TC

[minimutly]

Indeed it may have, but all these have a set pressure (depression) at which they open.
Do I need to record it?
I guess the only way to prove it would be to plumb a compound gauge into the bleed line - I'll have to see if I have one...