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  #1  
Old 01-10-2017, 10:54 PM
Kevin23 Kevin23 is online now
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Default Mercury 25W40 Oil Temperature

Hi all, was just thinking about taking the boat out for some winter saugers this weekend and for some reason oil popped into my head out of the blue. Then I realized I have the factory 25w40 oil in my 90 4s since I wasn't planning on doing an oil change until spring. I've been doing some searching online and the only temperature rating I can find is to not use it below 40F stated on some forum. Is this accurate? Is that 40F air temp or 40F water temp? Am I safe at right around 40F air temp, as in low 40's, and 32-33 deg water temp?

Manual says:
Mercury or Quicksilver NMMA FC‑W or NMMA FC‑W catalyst compatible
certified SAE 10W‑30 4‑Stroke Marine Engine Oil is recommended for general,
all‑temperature use. As optional choices, Mercury or Quicksilver NMMA FC‑W
SAE 25W‑40 Mineral Marine 4‑Stroke Engine Oil or SAE 25‑W40 Synthetic
Blend Marine 4‑Stroke Engine Oil may be used. If the recommended Mercury
or Quicksilver NMMA FC‑W certified oils are not available, a major outboard
manufacturer's brand of NMMA FC‑W certified 4‑Stroke outboard oil of similar
viscosity may be used.
And in the manual it has a little figure that shows 10W30 okay from 0-120F but doesn't show 25W40.

The sticker says 25w40 recommended which is what i assume is in the motor.

Don't want to be doing an oil change in 20 degree temps, but I guess I could....
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  #2  
Old 01-10-2017, 11:48 PM
REW REW is offline
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Kevin,
If you are going to be running your motor in the cold, it would make sense to change it to 10-30 full synthetic oil.

You will have no temperature issues with that oil.

Good luck
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Old 01-11-2017, 04:22 AM
brigeton brigeton is offline
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For what it's worth the 115 I bought this year recommends 10-30 year around.
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Old 01-11-2017, 09:32 AM
Kevin23 Kevin23 is online now
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This is what i found on the motor today, didnt see it hidden under the starter. According to that, i am good in the cold with 25w40, right???
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Old 01-11-2017, 11:15 PM
Snowking Snowking is offline
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I would change it to 10w30. If the boat is stored unheated before you go fishing that 40 w oil will be pretty thick. It will make the starter work harder. If the 10-30 is a option for your engine. At least on my merc 150 you can run the lighter oil year round. You would not have to change back to the 40w in spring. For some reason I do not think Mercury likes full synthetic oil. They seem to like the blends. It might have 10w30 anyways. You could ask your dealer or whoever serviced it last. You might have an issue getting the 40w oil to drain all the way. if you cannot warm up the engine. You might have to let it drain for 20 minutes to try to get most of the oil out.

Last edited by Snowking; 01-11-2017 at 11:33 PM.
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Old 01-12-2017, 05:24 AM
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Bobby Winds Bobby Winds is offline
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Many small motors including some outboards don't have the proper seals for a full synthetic oil. You many notice seal leaking/seeping within a year.
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  #7  
Old 01-12-2017, 06:02 AM
25-40 oil
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Quote:
Originally Posted by Kevin23 View Post
This is what i found on the motor today, didnt see it hidden under the starter. According to that, i am good in the cold with 25w40, right???
Looks like the engine manufacturer states the 25-40 is good to about 10 degrees by your motor tag,you said the air temp is around 40.....load up and go,good luck catching winter eyes.
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Old 01-13-2017, 08:56 AM
Custom Eyes Custom Eyes is offline
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Quote:
Originally Posted by Kevin23 View Post
This is what i found on the motor today, didnt see it hidden under the starter. According to that, i am good in the cold with 25w40, right???
You should be fine as long as you let the engine get the oil warmed up a bit. Even the worst mineral oils will still flow down near 0F, but they're like sludge and very thick. Just don't go past idle until it's up to operating temp for a few minutes.

Last edited by Custom Eyes; 01-13-2017 at 08:58 AM.
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Old 01-13-2017, 11:26 AM
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Some outboard manuals specify a starting battery with higher MCA rating if the boat will be used below 32 degrees. Worth checking the manual and then your starting battery rating, especially if you decide to stay with the 25W40 oil
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Old 01-13-2017, 08:38 PM
Kevin23 Kevin23 is online now
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Quote:
Originally Posted by Custom Eyes View Post
You should be fine as long as you let the engine get the oil warmed up a bit. Even the worst mineral oils will still flow down near 0F, but they're like sludge and very thick. Just don't go past idle until it's up to operating temp for a few minutes.
Changed location, will only need the big motor for loading/unloading so I'm not too worried!
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