Engine Oil Weight for 5.0L Mercruiser

[RegalBoater]

Hey fellow boaters,, I was just wondering what you guys that have a 350 5.0L Chevy Small Blocks run for Oil Weight? I have heard straight 30 or 40 weight but I wanted to clarify this here.<br /> <br />Thanks for the info

 

[KaGee]

Re: Engine Oil Weight for 5.0L Mercruiser

SAE30 weight would be correct, I believe. I've read of others using 20W50.

 

[RegalBoater]

Re: Engine Oil Weight for 5.0L Mercruiser

cool thanks,, I was thinking so.. I was going to try some new synthetic oils and the viscosity for the 20W-50 oils look to be good for marine applications

 

[KaGee]

Re: Engine Oil Weight for 5.0L Mercruiser

Is the Avitar your boat?? Looks a little like my Regal. I have a fishing cuddy though.

 

[LubeDude]

Re: Engine Oil Weight for 5.0L Mercruiser

My choice for you would be a 15W-40 HDDO, (heavy Duty Diesel oil) They have great additive packages and hold up very well to the beating your engine will go through, very high TBN, and a great storage oil. I myself would use a synthetic, but if you are not going to run an extended drain program, you are paying three times the price for oil that you need to.

 

[MFG197]

Re: Engine Oil Weight for 5.0L Mercruiser

I use SAE 40 as recommended in all my manuals.<br /><br />BTW 5.0 is 305 CID, 5.7 is 350 CID<br /><br />LubeDude is the man though. I'm sure following his advice may be also correct, or better.

 

[Scaaty]

Re: Engine Oil Weight for 5.0L Mercruiser

I run the 15w-40 diesel too (350GM). Lubedude nailed it right. The straight weight is from the old daze. Standard viscosity oils and temps under 180 are tough on the pump/bearings/rings etc, and as these motors run at only 140 degrees or so their oil really never gets up to a decent operating temp...just my nickels worth

 

[RegalBoater]

Re: Engine Oil Weight for 5.0L Mercruiser

KaGee,, yea that is my boat.. bought it last winter used it all summer no probs.. it is an 1982 245 Regal Ambassador Cruiser.. Been alot of fun in party cove.. Just putting it up for winter..<br /><br />LubeDude thanks man,, I will heed your advice.. I know this engines take a beating even when just cruising pushing about 5500 lbs..

 

[RegalBoater]

Re: Engine Oil Weight for 5.0L Mercruiser

Robby,, that was my exact thinking on the operating temps... Thanks for reinforcing my thought

 

[rodbolt]

Re: Engine Oil Weight for 5.0L Mercruiser

why not just consult the owners manual? over the years all the manufactures have flip flopped on oil. some 7.4 volvos and 5.7's require straight 30 wt and some mercs use 25w-40. the owners manual will tell ya.<br /> good luck and keep posting

 

[crazy charlie]

Re: Engine Oil Weight for 5.0L Mercruiser

RB you will enjoy the Regal.I am on my third one and have loved each boat more and more.I currently have twin 5.0s and I stick to the manual reco of straight 30 weight and I run 40 weight in July and August.I was tempted to try synthetics as I did in 2 of my vehicles.A honda I owned worked great with synthetics and my Jeep immediately began an oil leak with the synthetic so I drained it and went back to conventional and the leak subsided but stayed as a small leak.That made me apprehensive to try it in my boat for fear of a leak.Charlie

 

[Don S]

Re: Engine Oil Weight for 5.0L Mercruiser

Never have quite understood why people don't like a manufactures recommendation on oil. The manufacturer has to warranty his engine, so they choose the oil that works the best for their application.<br /> Cars run at 1500 rpm for long periods and run hotter than boat engines. Boat engines run at 3500 or higher for long periods of time but run at cooler temps and higher loads.<br /><br />Here is what Merc recommends for their engines.<br /><br />