Mercruiser Oil Question

My 4.3l calls for 25w40 also I've read that Merc has updated to 20w40 syn as recommended oil with other alternatives as 20w40 or 20w50. Came across 20w50 in store but was labeled as Heavy Duty Oil and/or for Diesel engines. Would this oil be okay or is it specifically made for diesel engines? Asked the clerks and they had no idea as a cross reference to marine application. Priced very well and was going to purchase for future use.

Re: Mercruiser Oil Question

If the oil is the right viscosity but a diesel oil/HD. use it. Not going to hurt anything, and the extra ZDDP and other anti wear agents will only help.. Keep in mind, if 20W50 is on the oil chart in your manual with 20W40 as normal recommendation, than it's probably for temps 32* and higher.

Re: Mercruiser Oil Question

20W/50 is too heavy for use in your location. When starting the engine in cooler temperatures it will take a little longer to circulate through the engine, and those first few seconds are where the most wear occurs!
As mentioned, OK for use in hot weather, but I would stick with the Merc recommendations.

Re: Mercruiser Oil Question

Any 20-50 syn oil made for automotive is sooo much better oil than that 4.3 was designed to use... will be all you need. I will ask just for the sake of change...Why 20/50 in a cold block or 15/50 sounds nutty as hell...But the golden rule here...MFG and Moderator's why ask...

Re: Mercruiser Oil Question

Is the synthetic oil just for the newer engines? Because my 2001 mercruiser operation manual states in bold... synthetic oils are not recommended. I just keep using the regular oil quicksilver 25w40 from walmart at $5.50 a quart. I keep looking at the 20w50 Castrol but merc wants 25w40 so thats what it gets...

EDIT.... did a little research and found this link. I guess they have updated the requirements as oil has evolved...

http://www.mercurymarine.com/servic...ntenance/faqs/mercruiser/?category=fuel#MCOil

Re: Mercruiser Oil Question

Alot of it I see rides on the temps you are at. The temp range here for my boatin is from 32*f to 90*f so that leaves me stuck with an all-around weight oil. I change oil only once a year (b 4 winterizing). I've always went with the original recommendation from merc and that is 25w40 Quicksilver (i believe that is not a synthetic though). Since recently, merc updated to recom 20w40 full synthetic, I guess due to catalyst engines??? I'll most likely stick with the orginal 25w40 quicksilver plus they always carry it at wal-mart. It is sorta mind boggling though about the diff weight ranges of these oils. Tow vehicle has a hemi that calls for 5w20 with a 195*f tstat.....go figure?!? lol.

Re: Mercruiser Oil Question

90stingray said:

Is the synthetic oil just for the newer engines? Because my 2001 mercruiser operation manual states in bold... synthetic oils are not recommended. I just keep using the regular oil quicksilver 25w40 from walmart at $5.50 a quart. I keep looking at the 20w50 Castrol but merc wants 25w40 so thats what it gets...

EDIT.... did a little research and found this link. I guess they have updated the requirements as oil has evolved...

Click to expand...

Must have been posting at the same time.

Re: Mercruiser Oil Question

tahoejag said:

It is sorta mind boggling though about the diff weight ranges of these oils. Tow vehicle has a hemi that calls for 5w20 with a 195*f tstat.....go figure?!? lol.

Click to expand...

Boat engines are working A LOT harder than vehicles... thus the higher weight.

Re: Mercruiser Oil Question

Yes, the new merc 20/40 weight oil was formulated more for their newer catalyst engines but is safe for all their past engines if desired. It's probably more cost efficient to stay with the older version though.

tahoejag said:

Since recently, merc updated to recom 20w40 full synthetic, I guess due to catalyst engines??? I'll most likely stick with the orginal 25w40 quicksilver plus they always carry it at wal-mart. It is sorta mind boggling though about the diff weight ranges of these oils. Tow vehicle has a hemi that calls for 5w20 with a 195*f tstat.....go figure?!? lol.

Click to expand...

One of the main reasons your hemi uses the 5w20 is so that the "multi displacement system" which is similar to GM's active fuel management system will deactivate four cylinders much more efficiently to help reduce fuel consumption under light throttle loads.
Engine-Cylinder Deactivation Saves Fuel | J.D. Power