25w-40 or 25w-50

mnm99

Well-Known Member
Oct 2, 2015
2,445
Long Island
Boat Info
2004 340 SeaRay Sundancer
Engines
Twin 8.1 Merc
Ahhh. I always use Mercruiser 25w-40 in my 8.1's. I just noticed yesterday that I bought a gallon of 25w-50. I bought this around a month ago to keep on board for top offs. I shouldn't have a problem using this to top off here and there right? Can't find the receipt to bring it back.
 
I think you will be fine - the difference is minimal, without the label it would take a chemist to tell the difference - even if they could.
 
I would be reluctant unless they are the same brands. Mixing different additives could have an adverse effect on the oil. Not worth the chance for the price of a gallon of oil for me.
 
No issue using it at all. The 50 is just a little higher temp rating. Depending how early you start or how late you end your season, id consider something lower then 25 for cold starts.
 
Would be fine. I switched to 15w/50 synth last July and hasn't used a drop in those 12 months. As your experiencing, I also found the merc 25w/40 requires top offs and more so as the season went on.
 
I don’t see any problem with it at all. Never heard of a motor blowing because of the type, brand or multi weight oil used. Seen plenty go because of no oil, but none because of using a different viscosity like you’re talking about.
 
I use Mobil 1 15-50 in my 8.1. Seems to run fine.
 

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