Swapping oils

I happen to be an oil rep and a racer. I would flush the engine out as stated. If you have had PAG oil ( Polyalkylene Glycol) and PAO ( Polyalphaolefin) those 2 do NOT like each other at all and needs to be throughly cleaned as stated. Some oil lab coat guys even say you shouldn’t ever even switch them however I will admit to doing so.

There seems to be a 50/50 split of both kinds of oil that are “kart oils” so chances are Very high of having one or the other previously in there.
 
When we have had to switch oils I just take a can of brake clean and spray from the oil fill hole and let drain. Spray at least twice and let drain again we have never had a issue doing it this way.
 
The only time I lost an engine after I changed oils was when I flushed with mineral spirits. Was it related? I really do not know, but any other time I all I did was change the oil, run it for a short time and change again. Lubrication failure most always shows up in the big end of the rod. I would make sure that any oil that was removed from there, by flushing was replaced before starting. Perhaps by letting it soak in the new oil while at BDC and turning the motor by hand before starting.
That's interesting. Every engine that comes through our shop for a rebuild is thoroughly washed in mineral spirits. I wonder if you didn't get it all out or let it dry long enough? A couple liberal shots of Brake Clean or acetone will help it evaporate quicker.
Almost every engine we rebuild goes on the dyno before shipping, so we would surely catch something if there were a problem with cleaning/rinsing the bottom end with mineral spirits.
 
I'd say there's a bit of difference here between rebuilding the engines and flushing them to change oils. During the rebuild the parts are cleaned, dried, inspected or replaced, then lubricated and reassembled correct? In my opinion flushing with mineral spirits without lubrication for initial startup is a bad idea, because likely the fluid film of mineral spirits in the bearings will not dry, and if it does then you have a dry bearing until enough oil is slung around which I imagine would be too late. Just an opinion and looking to discuss further, although I have no plans to be switching oils.
 
That's interesting. Every engine that comes through our shop for a rebuild is thoroughly washed in mineral spirits. I wonder if you didn't get it all out or let it dry long enough? A couple liberal shots of Brake Clean or acetone will help it evaporate quicker.
Almost every engine we rebuild goes on the dyno before shipping, so we would surely catch something if there were a problem with cleaning/rinsing the bottom end with mineral spirits.
Not saying it is a bad thing to do, just relating my experience. Don't remember the details, it was long ago. It was before the 4T was out. I was "probably" swapping out one refrigerant oil for another.
 
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I'd say there's a bit of difference here between rebuilding the engines and flushing them to change oils. During the rebuild the parts are cleaned, dried, inspected or replaced, then lubricated and reassembled correct? In my opinion flushing with mineral spirits without lubrication for initial startup is a bad idea, because likely the fluid film of mineral spirits in the bearings will not dry, and if it does then you have a dry bearing until enough oil is slung around which I imagine would be too late. Just an opinion and looking to discuss further, although I have no plans to be switching oils.
Yes, on a complete rebuild...but on the LO206, you cannot disassemble the bottom end. We DO, however, clean and flush the bottom end (ie shortblock) with mineral spirits on every 206 rebuild, regardless of what oil is going back into the engine. (Been doing this for 10 years or more now.)
 
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