View Full Version : Back Pressure & oil

05-19-2008, 08:13 AM
Iíve got a 1993 Maristar 225. The boat runs great. However, there is pressure and oil coming out of the dip stick. It doesnít leak oil when on the water hose, but there is still back pressure. When at speed, on the lake, we have pressure and oil. Does anyone know or have an idea as to what might be causing this problem?

05-19-2008, 08:18 AM
going to take a wild guess as I dont even know if boats have this part, but bad/plugged PCV vavle?

05-19-2008, 10:16 AM
First check/replace the PCV (a hose running from a valve in the valve cover to the carburator or intake manifold that "sucks" vapors out of the engine). If it's plugged up, pressure will build in the crankcase and the easiest way out is up the dipstick tube.

If that's clear, it gets more expensive and difficult to troubleshoot in a hurry. Possibilities are:
Blown headgasket allowing compression gasses into an oil passage
Worn, glazed, stuck or broken rings
Cracked block

All three will show up as low compression. The only way to differentiate between a blown gasket and a cracked block is to pull the heads off and inspect. You may be able to diagnose worn rings from the other two by first doing a compression test, then sqirting a bit of oil (teaspoon or so) into the cylinder and repeating the compression test. If the compression improves, the oil helped temporarily "seal" the rings. A teardown is still necessary to "fix it right", but if it's a stuck ring, there is a (slight) chance it can be freed up - Shoot some PB Blaster, Liquid Wrench or other penetrating stuff into the cylinders and let it sit awhile, then run it with some engine cleaning oil additive.