engine cleaner/degreaser works pretty well. My only experiences are with gas engines, but I imagine it would be the smae. The only problem is the stuff can get pretty priidy if you byu it by the gallon. The napa near me has it in bulk but it is also a distribution center, so not sure on availability either.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth