I was just visiting my machinist yesterday and he was just getting ready to run the block and head cleaner on a small block (Corvette) engine that had Mobil One used in it from day one. I wish I had my digital camera with me; incredible sludge build-up!:eek: He's been doing block and head work for over 30 years, and was very surprised himself.
Jim

Castrol 5w50 Synthetic in boat and synthetic blend in the old Toyota 4X4:D

valvoline racing straight 40 weight

Merc 20-50

I can understand not using Merc oil, but why do some of you prefer the multiviscosity over the straight weight? Merc seems to reccommend the straight weight as the next best thing to their own oil.:confused:

Straight from the Merc website:

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What type of oil should I use? Can I use synthetic oil?

To help obtain optimum engine performance and to provide maximum protection, we recommend the use of Mercury Precision 4-Cycle 25W-40 Marine Engine Oil. This oil is a special blend of 25-weight and 40-weight oils for marine engines. If not available, a good grade, straight weight, detergent automotive oil of correct viscosity, with an API service rating of SH,CF/CF-2 may be used.

In those areas where Mercury Precision 4-Cycle 25W-40 Marine Engine Oil or a recommended straight weight oil is not available, a multi-viscosity 20W-40 or, as a second but less preferable choice, 20W-50, with API service ratings of SH,CF/CF-2 may be used.

IMPORTANT: The use of non-detergent oils, multi-viscosity oils (other than Quicksilver 25W-40 or a good quality 20W-40 or 20W-50), synthetic oils, low quality oils or oils that contain solid additives are specifically NOT recommended.
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'02 575SC's running Mobile 1, 15/50. Still running Mercruiser HP gear lube in XR drives. Combination doing great. Tried Redline in bravo drives in previous boat, Redline found every weakest seal point and leaked; mostly inside the bilge area, some outside. I know Redline is a good syn oil for the drives; may try again in my XR's.;)
'02 Cig 42 Tiger TS

Valvoline VR1 straight 40.

Mercruiser 25/40

Valvoline VR1 straight 40

do you realy have to run a drive oil in the drives or are they just worried about an enviromental thing