M44 Pistons

[bmwz3tower]

Got an endoscope today (unrelated to the car) and thought I'd use it to have a look at the tops of the pistons. They seem to be quite shiny on the exhaust side. Is this normal? Or is it burning coolant, signalling the head gasket is leaking?

 

[Duncodin]

Not sure abour coolant. When the engine is swirched off fhe cooling system is still hot and under pressure for a while which would continue pushing water into the cylinder. That water would find its way down past the piston rings into the crank case which would result in the creamy 'mayo' mess in your oil filler cap. Got any Mayo in your filler cap?

Burning water you'd also get white exhaust smoke.

Interesting to see other people's pictures though. My 80,000 mile M44 looks pretty clean.

 

[bmwz3tower]

Not sure abour coolant. When the engine is swirched off fhe cooling system is still hot and under pressure for a while which would continue pushing water into the cylinder. That water would find its way down past the piston rings into the crank case which would result in the creamy 'mayo' mess in your oil filler cap. Got any Mayo in your filler cap?

Burning water you'd also get white exhaust smoke.

Interesting to see other people's pictures though. My 80,000 mile M44 looks pretty clean. View attachment 357017

I've not got any mayo thankfully. My M44 is also at about 80,000 miles as well. I do get quite abit of white steam on cold start but I'm almost certain that's down to the weather. Plus the smoke/steam doesn't smell at all like coolant.

 

[Duncodin]

I've not got any mayo thankfully. My M44 is also at about 80,000 miles as well. I do get quite abit of white steam on cold start but I'm almost certain that's down to the weather. Plus the smoke/steam doesn't smell at all like coolant.

Oh. hang on. The M44 has, IIRC, a pre-heated throttle body upstream of the intake manifold. Water could, I suppose, leak past there and collect upstream when the engine isn't running. ie not dripping down into the cylinder. On start up that would all get sucked in and burned. No Mayo in the oil cap but would give that white cloud on cold start and the 'steam cleaned' appearance of the piston crown.

The thing I'd be checking is the Throttle Body gasket. If I'm not mistaken the throttle body is at the end of the fat rubber intake. No major surgery involved except for gettingpast that fat rubber pipe and some vacuum tubes.

 

[Stevo7682]

Pistons can look different from car to car depending on usage.
But a lot of Piston have a hot and cold side due to the combustion process where the inlet side injects the cooler fuel air mix . You get a swirl effect on combustion the the hot gases exit on exhaust side so that side of piston can be hotter so therefore less carbon build up.
Lynne's M44 zed had catastrophic gasket failure when i bought it ran lole a bag of nails was using coolant and pressurising coolant system oil side ok.

When head was off gasket blowing between 2 and 3 and slightly between 1 and 2 .
Piston 2 and 3 were spotless due to steam cleaning effect of coolant in combustion chamber nuber 1 slightly also number 4 had carbon build up

Based on your single piston picture looks ok.
Stephen.

 

[bmwz3tower]

Pistons can look different from car to car depending on usage.
But a lot of Piston have a hot and cold side due to the combustion process where the inlet side injects the cooler fuel air mix . You get a swirl effect on combustion the the hot gases exit on exhaust side so that side of piston can be hotter so therefore less carbon build up.
Lynne's M44 zed had catastrophic gasket failure when i bought it ran lole a bag of nails was using coolant and pressurising coolant system oil side ok.

When head was off gasket blowing between 2 and 3 and slightly between 1 and 2 .
Piston 2 and 3 were spotless due to steam cleaning effect of coolant in combustion chamber nuber 1 slightly also number 4 had carbon build up

Based on your single piston picture looks ok.
Stephen.

Thanks Stephen and Dunconin,

I'm pretty sure I'm not losing any coolant at the moment and the engine runs pretty smoothly, maybe a slightly lumpy idle but ive heard thats usual for the m44. All the pistons look like those 2 which I posted photos of.

As for coolant leaking in through the throttle body heater plate, I recently put new metal gaskets in, as I had to remove the intake manifold to fix the starter. But the gaskets have been unclamped and retightened a couple of times, so that could affect the sealing.

 

[bmwz3tower]

Oh. hang on. The M44 has, IIRC, a pre-heated throttle body upstream of the intake manifold. Water could, I suppose, leak past there and collect upstream when the engine isn't running. ie not dripping down into the cylinder. On start up that would all get sucked in and burned. No Mayo in the oil cap but would give that white cloud on cold start and the 'steam cleaned' appearance of the piston crown.

The thing I'd be checking is the Throttle Body gasket. If I'm not mistaken the throttle body is at the end of the fat rubber intake. No major surgery involved except for gettingpast that fat rubber pipe and some vacuum tubes.

I think this theory is correct, I got the boroscope in through the disa valve and could see puddles of liquid collecting at the lowest point.

I presume this is coolant mixed with oil from the inside of the manifold. I'm pretty sure it's not just oil as I can't see how that would collect in the manifold whilst the engine isn't on.

 

[Andyboy]

It looks fine to me.

The lumpy M44 idle is normal and you can cure it by adjusting the exhaust cam timing - I forget which way but there was a BMW technical bulletin for it years ago.