Mercruiser oil consumption during break-in

captsls · 05-28-2007, 10:10 AM

I just bought a dual inboard boat with one completely rebuilt Mercruiser 7.4L MPI Horizon engine. I know oil consumption is high during break-in but what is normal. I have about 3 hours on the engine and have used at least 2 1/2 quarts. Is this normal or did the re-build company do something wrong? The underwater exhaust is putting out a lot of white smoke over 2000 RPM while the other engine is smokeless Thanks for the help
captsls

Edward R. Cozzi · 05-28-2007, 07:29 PM

2 1/2 quarts in three hours sounds excessive to me.

Check for blowby at idle. If you have any, they may have broken a piston ring during assembly. A compression test is next whether you have blowby or not.

captsls · 05-29-2007, 07:02 AM

Thanks for responding. I don't know what blow-by is but the white smoke disappears when I am at idle or low RPM. I am going to run it today for an hour and see exactly how much oil is consumed.
captsls

Edward R. Cozzi · 05-29-2007, 10:44 AM

Blowby is crankcase pressure that is compression that is "blowing by" your piston rings.
Easy check is to remove oil filler cap while engine is idling. With the back of your fingers feel over the opening for puffs of air coming out of the hole. If you feel nothing you're in good shape pertaining to blowby.

ghittner · 05-30-2007, 11:46 AM

Too much oil use.

captsls · 05-31-2007, 09:18 AM

After speaking with mechanic and Surveyor I overstated oil consumption. We actually used 1.5 quarts during first 4 hours. I ran 1 hour yesterday and used NO oil. Still on Full.

Only pending issue is some (but less white smoke) on rebuilt engine in underwater exhaust. Ocean Water temp is still in low 50's but the other engine has no smoke. Both are FWC. Operating temp is the same 175 deg. First 4 hours it smoked at all RPM except idle. Now, it only smokes over 2500. Will this go away after break-in???

Thanks for the help!

Edward R. Cozzi · 05-31-2007, 08:29 PM

Are you sure that "white smoke" isn't light blue?

If it's white it's probably steam. Check your exhaust system for hot spots with an infrared heat gun.

If it's light blue it could be normal oil burning before your rings seat themselves. If that's the case it should go away by itself.

Keep us posted.