Mercury 25 fourstroke stroke oil weight?

[Sealbilly]

Mercury only has 2 weight rating available, 10w30 & 25w40. I fish year round and was wondering if I could use a 5w40 diesel oil since I fish and duck hunt in the winter? Where I live it gets into the single digits in january. I always have some T6 rotella that I run in my bikes and ATV and also my truck. I rarely fish in the summer until after dark to get away from the heat which is usually in the high 90s. What are your thoughts?

 

[JavierH19]

Many people do and I would too. The thing about hdeo rusting or causing foaming in boat engines is baloney. So many people use nothing but hdeo for the life.

P

Thread 'Thinking of switching from Merc 25w40 to 15w40 HDE'

Jul 4, 2008

Thinking of switching my searay twin 7.4L Horizon engines to a HDEO from Merc 25w40. What do you all think? Which one is best?

• PT1
• Replies: 31
• Forum: Boat/PWC Lubrication

 

[nwjones18]

I think 5w-40 T6 would be a fine choice year round.

 

[PontiacHO]

https://www.basspro.com/shop/en/qui...eRcaq2IHsb2mpf9ka6qGixM4Ok63xl5BoCWoIQAvD_BwE

Why not use what Mercury advises?

 

[JavierH19]

https://www.basspro.com/shop/en/quicksilver-25w40-4-stroke-marine-engine-oil?hvarAID=shopping_googleproductextensions&ds_e=GOOGLE&ds_c=BPS|Shopping|PMax|Boating|General|NAud|Google|NMT&gclsrc=aw.ds&gad_source=1&gbraid=0AAAAAD1Tgtcf1tydVN4GbWNa3lrteUy-g&gclid=CjwKCAiA5pq-BhBuEiwAvkzVZU4vI6sGCGClS2Vu4aecgTeRcaq2IHsb2mpf9ka6qGixM4Ok63xl5BoCWoIQAvD_BwE

Why not use what Mercury advises?

He stated that he goes out in single digit weather. A 25w would make that engine struggle in the cold. 5w-40 would be a good year round oil.

 

[4WD]

Mystik makes an NMMA 10W30 synthetic with a very low Noack

https://www.oreillyauto.com/detail/...-marine-motor-oil-10w-30-1-quart/mys1/jt41030

 

[Ride_Red]

The marine engine oil has extra corrosion inhibitors for the wet environment. So, that's a nod in the marine oil direction.

On the other hand... If you trailer your boat and store it in a dry garage, and use it on fresh water, then the extra corrosion protection may not matter much over normal oil.

 

[Sealbilly]

I do fish fresh water and store it in the dry.

 

[4WD]

The marine engine oil has extra corrosion inhibitors for the wet environment. So, that's a nod in the marine oil direction.

On the other hand... If you trailer your boat and store it in a dry garage, and use it on fresh water, then the extra corrosion protection may not matter much over normal oil.

They also test for foaming since boats do WOT allot …

 

[Sealbilly]

https://www.basspro.com/shop/en/quicksilver-25w40-4-stroke-marine-engine-oil?hvarAID=shopping_googleproductextensions&ds_e=GOOGLE&ds_c=BPS|Shopping|PMax|Boating|General|NAud|Google|NMT&gclsrc=aw.ds&gad_source=1&gbraid=0AAAAAD1Tgtcf1tydVN4GbWNa3lrteUy-g&gclid=CjwKCAiA5pq-BhBuEiwAvkzVZU4vI6sGCGClS2Vu4aecgTeRcaq2IHsb2mpf9ka6qGixM4Ok63xl5BoCWoIQAvD_BwE

Why not use what Mercury advises?

My motor has no sticker with recommendation. And Im not about to use a 25w during duck season. I used the 10w30.

 

[4WD]

My motor has no sticker with recommendation. And Im not about to use a 25w during duck season. I used the 10w30.

Merc has always been anti viscosity modifier - and you can bet that 25W40 plays a mono somewhere else …
Not a good winter lube …

 

[userfriendly]

Owners manual says 10W30.
Delvac 1300 meets CK-4/SP.
40C 80
100C 12
150C 3.6

10W30 M-1 is an option and what my son put in his 25 with the jet drive.