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


Tom Padukiewicz
05-12-2010, 02:16 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, 02:28 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, 02:29 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, 02:36 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, 11:26 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, 11:36 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.

jsonova99
07-23-2016, 09:52 PM
So the ZDDP discussion with flat tappets is interesting, the Mobil-1 15w-50 looks like a great option, but I'm curious if anybody has run into issues with leaky motors after switching? I've always been under the impression that older motors switched to synthetic are prone to leaks. My understanding was that it was due to the higher detergent qualities in synthetics removing a lot of deposits around seals that may have degraded over the years due to the deposits coating them (this may be BS, but I also own an older land rover so the flat tappet issue and of course oil leaks are a common discussion). When I switch my 2000 Land Rover Discovery to Mobil 1 around 30k miles, it was noticeable that a lot of the engine seals were showing signs of leaks. Now of course a Land Rover is not a great comparison since they all leak to some extent, at least the older ones. Anyway, I'm looking to switch away from Rotella, but wanted to see what others have experienced when switching to synthetics on the older 351 Fords in terms of any oil leaks.

stig
07-24-2016, 05:33 PM
My friends use Redline synthetics in their race cars. I looked at a bottle the other day and it said it had a higher ZDDP content which is what we like. Normal synthetics cannot use a high ZDDP content because it can foul up the cats on a car, which we don't have so win win!

jsonova99
07-24-2016, 06:29 PM
My friends use Redline synthetics in their race cars. I looked at a bottle the other day and it said it had a higher ZDDP content which is what we like. Normal synthetics cannot use a high ZDDP content because it can foul up the cats on a car, which we don't have so win win!

Right, I was looking at Mobil 1 15w-50 which has very high content, but I'm still concerned about switching over to synthetic due to the potential for leaks. Currently using Rotella 15w-40 like many, but it sounds like they have lowered their content. May just stick with this for a while.

curver900
07-25-2016, 11:03 AM
with 850 hours and no oil blowing and no leaks why go to synthetic? Oil that you change annually can be regular oil and no issues will follow you... don't change what works... and it sounds to me like you may be asking for issues by switching..

if it isn't broke... the saying goes...

mikeg205
07-25-2016, 11:10 AM
woo hoo an oil discussion! synthetic always better - better shear strength and you last protection in an over heat situation. also toss in a bottle of hyperlube zinc replacement - not snake oil -

M1 15w50 a great oil - plus it's inexpensive..

http://www.hyperlube.com/c3/zinc-replacement-additive-c7.html

sorry curver switching to synth will never cause leaks..