Oil mix ratio

[doors67us]

Hey all, wondering how much oil i should add to my gas/ratio my outboard is a 55 Evinrude fleetwin 7.5 I've seen 32:1 ,16:1 not sure what it should be mixed to,also read that with the invention of newer 2 stroke oils there's more protection,so there's not a need to mix it as strong as OMC called for with old 2 stroke back in the day

 

[saltchuckmatt]

Hey all, wondering how much oil i should add to my gas/ratio my outboard is a 55 Evinrude fleetwin 7.5 I've seen 32:1 ,16:1 not sure what it should be mixed to,also read that with the invention of newer 2 stroke oils there's more protection,so there's not a need to mix it as strong as OMC called for with old 2 stroke back in the day

Pretty sure it's 24 to 1 but you should plenty of opinions on this one.

 

[racerone]

Mix at 24:1-----But you will get many different opinions on oil and lubrication.----No needle bearings so they need oil for cooling.----Need oil to set up the " hydrodynamic wedge " in these bearings.

 

[doors67us]

What about the newer oils?2stroke oils have come a long way since 1955 ,read others saying it's not necessary to use the old ratio?

 

[racerone]

Use 24:1 on that motor.------I often say it ---" oil and lubrication in 2 strokes is not well understood "------Or perhaps post here in what you know about bearings and what happens to the oil that is mixed with the gasoline.

 

[F_R]

Actually, it is supposed to get 16:1. 24:1 would be a minimum IMHO.

 

[stwaller]

I believe I have the same motor and this is on the inside of the cover. It calls for a half pint of oil per gallon.

 

[saltchuckmatt]

I believe I have the same motor and this is on the inside of the cover. It calls for a half pint of oil per gallon.

So there you have it....16 to 1 when they built it. Your call it looks like.

 

[jimmbo]

What about the newer oils?2stroke oils have come a long way since 1955 ,read others saying it's not necessary to use the old ratio?

That may apply to engines with Anti Friction Bearings throughout, but not engines with Friction Bearings(Bushing). Lots of Oil is needed as Racer explained. Less than 16:1 and you are at risk of Metal to Metal contact in the Connecting Rod Bearings, as there will not be enough Oil to maintain separation of the Crankshaft and Connecting Rod after Ignition of the Fuel Charge and the Piston is being pushed

 

[ct1762@gmail.com]

its almost funny as the pistons/rings are fine even at 100:1. its just the bearings that all that oil is needed!

 

[jimmbo]

its almost funny as the pistons/rings are fine even at 100:1. its just the bearings that all that oil is needed!

Not much different in an Auto/Truck engine, lose Oil Pressure/Flow, and the Connecting Rod Bearings or Camshaft are the first things to fail.

 

[doors67us]

That makes total sense,like one said, there's going to be lots of opinions on this subject

 

[oldboat1]

7 1/2 was 16:1, while other OMCs in the line were 24:1. Difference in bearings, I suppose -- Racerone or F_R (or some others) might be able to clarify.

 

[racerone]

Rod bearings were bigger on the 7.5 HP compared to the 5.5 HP.-----There also was some issues with the smaller pressure tank and ability of folks to understand mixing.-------One quart to the 6 gallon tank or 1 quart to the 3 gallon tank.