Piston Deposits - What caused them?

[603Racing]

Putting a shiny rebuilt head on my m20. Got the old head off and noticed this (sorry for the size, but wanted to retain resolution):



The other pistons had this buildup, but this was the worst one by far. The head leaked oil and coolant, but not into the clylinders. Any idea what this sh!t is? It was hard to get off and I'm pretty sure it wasn't carbon deposits.

Completely stock motor, headers, mark D chip, 17# injectors. Motor has about 150,00 miles on it, driven with spirit sometimes, but never raced. I do not put any additives in my oil or fuel. I run Brad Penn oil and always run 93 octate (mark d chip). I did have a bit of a vacuum leak at the bitch tube, but not a bad one. I usually buy my gas from Phillips66 or Quick Trip stations, not sure where Quick Trip fuel comes from.

[TobyB]

First guess is oil consumption.

I got a lot of that sort of thing running Shell gas a few years back-
switched to Chevron, and it got better. But that's a sample of exactly one...

t

[z122643]

Deposits like this are caused by poor fuel/poor tuning, coolant/antifreeze, or oil consumption. Oil consumption usually results in carbon build up on the piston tops. Where as poor fuel quality and coolant will result in pitting and higher burn temps.

This looks like a combo of all three...

[603Racing]

I did have a bad head gasket as well as a vacuum leak. I had very little or no oil consumption that I could tell, even with the leaky gasket I had to add very little oil every few weeks. Coolant was a bit more in the last few days before the head swap. And the vacuum leak had been there for a year or so.

[htown318is]

but.. chevron has WATTA IN IT.

[TobyB]

It all does, now...

t

[SpecM]

And the vacuum leak had been there for a year or so.

This

Lean fuel mixture = high combustion temps = erosion

May have contributed to you head gasket failure too