4 stroke break in with premix oil/gas?

[jmoser]

Just got my new Tohatsu 4 hp 4 stroke and will be breaking it in this month.<br /><br />My last new 4 stroke was a 1995? Yamaha 9.9; I remember the manual stating to run the first 6 gal tank with premix oil/gas, I believe 50:1 ratio.<br /><br />The Tohatsu manual says nothing about using premix for the 10 hr break in, but premix seems to have some obvious benefits. I was thinking of using 100:1 or even 200:1 oil ratio for the first gallon of gas at least - does anyone know of any reason why this should be avoided? [besides 'cause the book doesn't say so!] <br /><br />I don't think a mild ratio like that should foul the head/valves, especially at low RPM break in speed and load conditions.<br /><br />I will change the spark plug and crankcase oil after break in - some plug insulators can get contaminated if not designed for rich/premix operation, the crank oil and gear oil should be changed regardless. And of course I will run the fuel system dry so the premix does not gum up the carbs.<br /><br />Any thoughts from the experts?

 

[JB]

Re: 4 stroke break in with premix oil/gas?

NO, NO!! Absolutely not, JMoser!<br /><br />4Strokes and 2Strokes are very different critters. 4Strokes are not intended to burn oil at any mix ratio. All you will do is foul plugs and carbon up the innards.<br /><br />Just burn gasoline, like the manual says.<br /><br />Good luck.

 

[TGuy]

Re: 4 stroke break in with premix oil/gas?

JB is absolutely right. DO NOT run pre-mix in a 4-stroke. Never, ever. Your Yammie must have been a 2-stroke model if you were running pre-mix. 4-strokes never require pre-mix. There is still a break-in period and your owners manual should cover the correct procedure.

 

[jmoser]

Re: 4 stroke break in with premix oil/gas?

I appreciate the replies.<br /><br />My Yamaha 9.9 was most certainly a 4 stroke and I would bet my house that the factory owner's manual clearly recommended running the first batch of gas with oil premix.<br /><br />It was either a 1994 or 1995 model 9.9 4 stroke.<br />Worth some research as a curiosity if anyone has this model to check the owners manual.

 

[khc1970]

Re: 4 stroke break in with premix oil/gas?

You can run premix in a 4 stroke, as long as the misture is very very light on oil.<br /><br />We very often add unused premixed from boat into car, if we know we won't be using boat for a little while otherwise the petrol will go off.<br /><br />All it will do is get a little smoky and will clear as soon as that batch of petrol is used up.

 

[JB]

Re: 4 stroke break in with premix oil/gas?

I have done the same as khc by mixing a quart or 2 of old premix at a fill up into a tank (3 gallons) on my riding mower. It smoked, but it was a low-tech, flathead engine with low compression ratio, AND, if it quit I would have just got off and had a beer. It was a way to dispose of suspect fuel.<br /><br />I would never do that to an outboard 4 stroke, and I wouldn't recommend it to anyone else.

 

[BillP]

Re: 4 stroke break in with premix oil/gas?

Except for the piston crowns and very top of cylinder wall, everything is already being lubed by the crankcase oil. I can't see what it will hurt or help except for plug fouling and that is a long shot for only a few hrs of break in. I've run a few hrs with 100:1 in my 96 carbed 50hp x 4s and couldn't tell the difference.<br /><br />If you look back at Snapper lawn mower 4 strokes (Briggs engine) years back they doubled the mfg warranty if you used premix. I think the reason was for mowing on hills where the oil pickup would sometimes grab air. I took the lead from that and used premix many years in an Ariens Techumseh engine...I blew 2 short blocks in 2 yrs before doing the oil. After adding the oil I went another 8 yrs and sold the mower. I run 100:1 synthetic premix in my Briggs lawn engine...10 yrs and no problems. That Tohatsu is a basic carbed engine just like the lawn gear so I can't see it hurting anything.<br /><br />That's my .02.

 

[TOHATSU GURU]

Re: 4 stroke break in with premix oil/gas?

Don't use pre-mix. It will only prolong the break-in time. You need a certain amount of friction to get the rings to seat to the cylinder walls. While it shouldn't cause any harm, you need to keep in mind that your engine operates on a open cooling system, not a closed system like land based tractors. Outboard 4-strokes have a problem with running to cool to begin with. You really do not want to make the situation worse.