Merc Mark 55E fuel/oil ratio still 25:1???

[John Reynolds]

I'm working on restoring a 1956 Mercury Mark 55E; got the lower unit overhauled now and I am learning as I go. Will eventually paint, and replace most fuel and ignition parts. Powerhead is in great shape. Got me a service manual, owner's manual, and parts list. Owner's manual tells me that the fuel/oil ratio is 25:1; is it still 25:1 with modern TC-W3 oils after nearly 50 years??? Thanks a lot

 

[alcan]

Re: Merc Mark 55E fuel/oil ratio still 25:1???

Hi John<br />Your engine was designed to run 24/25:1. So the answer is yes. Don't by into that using less than recomended oil deal.

 

[MartyTn]

Re: Merc Mark 55E fuel/oil ratio still 25:1???

Hi John,<br />I've seen a lot of friendly discussions and story swapping over this one. I've heard a lot of folks say they run the old needle bearing Mercs (and I think that includes the 55E) on less oil than the original 24:1 ratio - up to and including 50:1. I've also seen discussions where racers - and they do still race these Mercs - say they use more oil because it seals better. Some at 24:1 and some even down to 12:1 or so. A bunch of these old Merc guys can be found at John's old Merc web site at<br /> http://www.pfs-ware.com/kwast/mercboard/index.htm <br />and that would also be a good place to pose your question. Good luck, Marty.

 

[John Reynolds]

Re: Merc Mark 55E fuel/oil ratio still 25:1???

Thanks Alcan.<br /><br />I've heard here and there that with modern oils, you should be able to go to something like 32 or 40 to one. But common sense tells me that if too much carbon-build-up wasn't a problem back in the old days with the oil back then and at a 25:1 ratio, then deposits certainly should not be an issue now with modern oils, plus have plenty of lube available for the engine at the 25;1 ratio.

 

[ODDD1]

Re: Merc Mark 55E fuel/oil ratio still 25:1???

John, think of it this way...that motor is a 44 CID 4 cylinder that merc used well into the '90's...same pistons, rings, bearings and basically the same rods and crank.....and for 30 years we have been using 50:1 in them...I dont think it will be a prob in yours.

 

[John Reynolds]

Re: Merc Mark 55E fuel/oil ratio still 25:1???

Thanks ODDD1, I had no idea that basically the same engine was produced for so long, into the 90's. Design was one thing, but what about the metals? Alloys, heat treating, and all of that stuff. And someone mentioned needle bearings; i wonder what that has to do with it?