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ayglass ayglass is offline
Registered User
Join Date: Aug 2006
Location: Cleveland, Georgia
Posts: 149
Hey Marty,

So how do you explain the coke found in the post-turbo screen that I installed? Are you suggesting that the coke was created somewhere else and passed through the close-tolerance turbo bearing to get to the strainer?

I'll let Dave speak to his "thermal excursion". My engine has not been extremely hot and has not been shut down after a hard run without a cool down period so I would say that my coke formed within normal operating parameters.

I can't argue the broad case that coke isn't found under other circumstances. I can only argue that in my case it was found post-turbo and that coke is implicated in the lubrication problems with my engine. Looking at the oil flow diagram, oil returning from the heads passes through the oil filter before returning to the tank and oil from the turbo doesn't. My theory was that this was a design flaw with this unfiltered tank and return so I put a screen inline with the turbo and collected coke bits.

Simply put, I can't rule out the universe of other ways that coke could have arrived in my cam spray bar. I can only point out a likely source that does indeed create coke bits. I've addressed this source, but of course I will continue to look for any indication that I have another source.

As to the synthetic oil, I was using synthetic at the time of the incident. I realize that the coke could have been formed before I switched to synthetic and then broken loose, but all of us (excepting those who have done a complete rebuild and replaced oil coolers etc) have used dino oil in our cars because that's what was available and factory recommended when these cars were born. My car is proof that synthetic oil, later in the engine's life does not make one immune to issues with coke. As you suggest, I may go synthetic from the beginning with a new rebuild. That seems prudent given that turbo engines are more "thermally challenged" than NA engines.
Andy Glass
'86 930 Kokeln IC, K27-7200, SC cams, GHL headers, Fabspeed muffler, Short R&P , misc other mistakes made...
Old 12-08-2007, 04:25 PM
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