Going to do a compression test on this engine:



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I took out the spark plugs out of the boat yesterday and now I got to find something to spray in the cylinders . I heard that Marvel Mystery Oil works good for cylinder lubrication.

Should I use that product or is there something better?

Thanks!


BTW: The engine is a Mercruiser Bravo 7.4 V8 w/ thunderbolt ignition & power steering...anyone know what year it would be?

Sam,

Did you get a new boat?

...And marvel mystery will work very well for cylinder lubrication. Has the engine not been run for a long time?

I'll go pick some of that up this weekend.....and its not my boat, yet, but the boatyard manager is offering it for sale to me, if I sell my Mini Hawk. Engine has been sitting for 3 years.

IF it is the original block, the year can be determined by the casting numbers. If it's not the original block, casting numbers can help tell you that also. Lots of resources on the web to locate / decode GM casting numbers.

I would do a leak down test. I just bought a boat that had been in storage, the mechanic said the compression was fine, but when I did the leak down 2 cylinders were at 50%. The bores had rusted too much and the rings wouldn't seal.