Mark 25 fuel oil mix

[dave-bernard]

gear lube is grease not oil on these. I use John deer corn head grease.
25-1 originally but in 63 when merc came out with 50-1 they recommended it with all there motors. I use it richer. 1 can to 5 gallons

[amuller]

quote Cheetahgod:

Will these coils work?
http://www.rockauto.com/en/moreinfo.php … 14&jsn=257

That looks like a REPCO (or Tecumseh) coil, and the price is good. But the description is wrong in the Standard catalog and I couldn’t find any specs or application information.

I’ve had good luck with Rockauto.

[jw-in-dixie]

With modern oil, I use 40:1 and run WOT most of the time, with no problem. Not saying YOU should do that. 🙄

[billw]

I think the factory said you could run 50:1 with their at-the-time-modern oil. However, I run all my Mark 25s at 24:1 and they just seem to love it. At the end of the day, I just disconnect the fuel line, let it run out of gas at idle and consider it winterized. (After then changing the gear oil, of course.)

Long live American manufacturing!

[jpatti75]

quote BillW:

I think the factory said you could run 50:1 with their at-the-time-modern oil. However, I run all my Mark 25s at 24:1 and they just seem to love it. At the end of the day, I just disconnect the fuel line, let it run out of gas at idle and consider it winterized. (After then changing the gear oil, of course.)

+1

[outbdnut2]

I don’t totally buy in to the idea that modern oils are that much better to allow cutting use in half. I buy house brand TCW3 at places like Walmart or Fleet Farm by the gallon and go with original manufacturer’s recommended mix.

Some manufacturers may have been happy to see motors only last 10 years instead of 20+….so they can sell more new ones!
Dave

[cheetahgod]

There is a yellow oil in my mark 25 lower unit. Is it supposed to have grease instead ?

[dave-bernard]

Yes

[ryanjames170]

I used to run 32:1 but I now run 24:1 in my green motor.. oil is cheap for what it’s worth.

[billw]

quote Cheetahgod:

There is a yellow oil in my mark 25 lower unit. Is it supposed to have grease instead ?

Like Dave said, it was supposed to have a thin grease, but NOT regular automotive grease. 99% of old Mercury lower units out there today don’t have the seals or shaft surfaces capable of holding in oil. Consider yourself gifted to find one that WILL hold gear oil. I reseal all mine and use 90W oil all the time. It works fine and is very easy to change fresh after each use, which in my case is once about every eight years. If you choose to keep using oil, just remember to check it and change it after each use. (You should be doing that with grease, too, anyway, given the history of old Mercury lower units.)

Long live American manufacturing!

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