Hypothetical.....I have a 2000 250hp yamaha. Say i ran out of Yamalube and all i had to put in was regular car oil just to limp in for a half mile or so. Would this cause any serious harm to the engine? Only for a half mile or so...
You don't say what weight or type of motor oil it was but most likely no harm. It used to be that all outboards were run on a mixture of gas and 30 weight automotive oil. I would however, pump out ALL the auto oil and replace it with 2 stroke oil. The properties of todays 2 stroke oil is quite different from automotive oil.
You should be fine. I would take compression readings to be sure though and listen to the motor closely the next time you run it...after purging the oil system of the 10W-30.
Besides, doesn't the motor still run in "limp" mode even when it detects no oil in the tanks? If it can survive that for a little while, I would think it's chances get better even w/ 10W-30.
Did you remove the cowling, flip the toggle on the ECU and pump some more oil from the main tank to the engine tank, then run out? This will allow you to run at full speed again if not.
If not, that would be the preferred method.
As and aside, I ran an outboard for hundreds of hours on the cheapest 30 weight oil I could find for pre-mix.
Would not hurt the engine, would increase carbon build up. Keep the rpms under 2K. Not recommended for long term use. Some of that really cheap oil out there is not much more than motor oil with a anti-corrosion additive to make it TC3.
I can see stranded at sea, someone happens along with some fuel and regular engine oil to get you back to port.
I would throw a quart of 2-stroke oil in the bilge somewhere just in case.
When I rode 2-stroke dirtbikes in the woods I would carry a 3-oz pinch pack of oil in my backpack. If I ran out of gas all I needed was a gallon of regular to get me back to camp. I never ran out. 8)
That's what happened CJBROWN.....I radioed to see if anyone in my area had any oil at all and a guy came up next to me and threw me a half quart of motor oil..