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View Full Version : Need Advice on Engine Oil for older Mastercraft


Tom Padukiewicz
05-12-2010, 01:16 AM
Just purchased an 25 year old mastercraft (1985) with about 850 hours on the engine. Previous owner states he has used conventional 5w-30w motor oil routinely. He also said he just re-packed the wheel bearings and greased the rudder & steering unit but all were as dry as a bone. I had always used Mobile-1 synthetic in my 93 Pro-Star 190 S&S with very good results. I'm not a mechanic so I am asking for advice on whether there might be any problems with switching from conventional oil to synthetic in a boat this old?

Kyle
05-12-2010, 01:28 AM
It should not damage anything switching oils. I would run a viscosity break down fluid or an engine flush thrould it before I changed the oil. I believe you can add a can of the fluid and run the engine like 5 minutes and then change the oil and it gets all of the crud out. DO NOT run the engine longer than the instructions on the bottle. It makes your oil very thin and it will eventually quit doing its job. I have used this kind of stuff before when I worked at a cadillac dealership as a tech and it works well if you follow the directions. Most people think that if you run it for a few minutes longer that the engine will be cleaner but the reason why there is a time limit is because the oil will quit working and you will eventually damage something by adding time to it. I use a stop watch and shut the engine down exactly at the time period required. I have also never had to replace a customers engine or any of my own from using the flush. Key is to use it properly.

03 35th Anniversary
05-12-2010, 01:29 AM
Just purchased an 25 year old mastercraft (1985) with about 850 hours on the engine. Previous owner states he has used conventional 5w-30w motor oil routinely. He also said he just re-packed the wheel bearings and greased the rudder & steering unit but all were as dry as a bone. I had always used Mobile-1 synthetic in my 93 Pro-Star 190 S&S with very good results. I'm not a mechanic so I am asking for advice on whether there might be any problems with switching from conventional oil to synthetic in a boat this old?

Once you go to synthetic your not suppose to go back, but to answer your question. No it shouldn't hurt anything.

Tom Padukiewicz
05-12-2010, 01:36 AM
Thanks guys, I was hoping that would be the case. I just want to get everything up to snuff so I know where I am starting and can keep it up from there. I spent a few hours pulling the motor box and floors today so that I could scrub all the 25 year old crud out of the bilge. Greased the steeing unit and rudder.... Looks much nicer down there now!

east tx skier
05-12-2010, 10:26 AM
Thanks guys, I was hoping that would be the case. I just want to get everything up to snuff so I know where I am starting and can keep it up from there. I spent a few hours pulling the motor box and floors today so that I could scrub all the 25 year old crud out of the bilge. Greased the steeing unit and rudder.... Looks much nicer down there now!

Welcome, Tom. There's a been a fairly good discussion about Oil, ZDDP reduction, and flat tappet cams on 351 Fords over the last couple of days. Probably worth checking out. Enjoy your boat!

thatsmrmastercraft
05-12-2010, 10:36 AM
The only concern about switching to a synthetic is potential oil leaks. There will be the possibility of a rear main seal leak if the tolerance is at its max where with the petroleum based oil it may not leak. Also, some oil may make it passed the rings if they are worn enough. Shouldn't be a problem, unless the 750 were particularly 'hard' hours. Sometimes that synthetic can be too slippery.

Once the either of the engines on my F150 hit about 160,000 I ended up switching to petroleum based oil to combat some oil consumption issues.