What engine oil? Oil & fuel cleaner additives?

[Ants]

Hi, just doing an initial oil and filter change on my (new to me) late 1970s Mercruier 140hp 3.0. It was left sitting around for a good few years so I am changing all consumables, fuel + water pumps etc.

Anyway what type of fuel do you think would be best for it? The (dated) Clymer service manual suggests 25W40 SE or SF API. I guess the modern equivilent would be a 15W40? Perhaps the bigger question is whether to go mineral or synthetic? I am not sure how much the engine has been used in its life, but left sitting prob didnt do it any good. A compression check was ok, they all averaged at approx 125psi, although they took a varying amount of cranks to get there, and one carried on to 135 with extended cranking, so certainly some varying engine wear there.

Also when I have it fully up and running do you think it would be worth using an oil cleaner additive, you know the one that you add, run engine for 30 mins, then change oil, to try to break down old oil build up, or might that cause more problems than it helps. Also what about fuel additives that likewise are supposed to help clean?

Many thanks,

Anthony

 

[180shabah]

Re: What engine oil? Oil & fuel cleaner additives?

If the temperature doesen't get much below 50degF during your season, I would run straight 30 weight and skip the oil additives. For fuel additives I like SeaFoam(also usable as a stabilizer for storage) and BG44K(amazing, but expensive and sometimes hard to find). I think SeaFom in the tank now(with fresh gas) and having a couple of spare fuel filters on hand would be a good start. Also, even if it runs good now, plan on a carb rebuild in the near future, it will probably get plugged up quickly.

 

[Ants]

Re: What engine oil? Oil & fuel cleaner additives?

I meant to say I am based in England, so only moderate temps in summer.

Also I think the carb was rebuilt shortly before it was left to stand (have removed carb top and looks clean in there, althougbt of course needles could still be built up), and I have the fuel tank removed to clean out and will replace all fuel lines.

Thanks Anthony

 

[180shabah]

Re: What engine oil? Oil & fuel cleaner additives?

I would still be concerned witha carb that has sat that long, although it be absolutely fine. Plus, your are removing/cleaning the tank and replacing the fuel lines, that should eliminate almost all issues with trash in the fuel system. No need for fuel additives, other than as required for stabilization.

 

[Gary H NC]

Re: What engine oil? Oil & fuel cleaner additives?

Also with a motor that old i would stick with regular oil,not synthetic.Any seals or gaskets that may leak very little now will leak a lot more with synthetic.
The straight 30w is a good idea too..