They answer is that no, you should not be using TCW-3 in your seadoo, run the recommended API-TC but the 720 and smaller engines don't need full synthetic or even semi-synthetic, mineral oil is fine.
The long answer is......
The following is from a Rotax Aircraft engineer but applies exactly to our 2-stroke Seadoos aslo powered by Rotax.....
There are many TC-W3 rated oils out there that are also APC-TC rated. API-TC OK, TC-W3 not OK, what about the ones rated both?
Hi Larry, you’ve asked a great oil question that really stirs up a lot of two stroke pilots. I have spent a lot of time researching to stroke oils. If I ask about engine oils when presenting a seminar, it seems like I’d get a different favourite oil from each attendee. Ok, here goes my opinion on the great oil debate.
Our Rotax aircraft engines operated at high load, high rpm and high piston temperature for prolonged periods. For our application the correct oil specified is API -TC (low ash) rated oil, period! This applies to to the aircooled (503) as well liquid cooled (582) aircraft engines equally.
A boat or watercraft engine is cooled by cool lake water and this engine application experiences much lower piston temperatures. These craft use TC-W3 rated oil.
A boats engines exhaust exits under the surface of the water. This reduces the exhaust sound level, however the products of combustion enter the water directly. TC-W3, (ashless boat oil) has an additive (detergent) package made up of organic substances to reduce water pollution. TC-W3 organic additive package will not withstand the much higher piston area temperatures our Rotax aircraft engine experience.
Our API-TC (low ash) oil for use in our aircraft Rotax aircraft engines has a additive (detergent) package made up of metallic substances (heavy metals) . This additive package is what allows piston area protection at much higher temperatures.
True API-TC oil users make up up a small percentage of the market, so oil companies have reformulated TC-W boat oil to also pass the minimum API-TC test standards. This fits all engines oil blend is like a “one size fits all” piece of clothing. I believe this dual purpose oil blend must contain the low temperature operation organic additive package or it couldn’t be used in a watercraft.
I would recommend you use only a specified standalone API-TC oil to protect your Rotax aircraft engine. Rotax has documents referring to correct operating fluids, including two stroke oil.
Regards John Baker iRMT 3852
Finally, will your engine blow up using TCW-3? No, probably not but it is not the correct oil, does not lubricate as well and has been known to cause the rotary valve and inner crank seals to leak.
In the end it is up to you to decide if you want to save a couple bucks and try an oil that isn't rated for your Seadoo.
You can get the Lucas for $25 a gallon.
