912 ULS2-01

[arizonarotors]

I have a new 912 ULS2-01 installed in my Gobosh. The mechanic who installed my engine used Evans Waterless coolant.

I am going to drain it and fill with an approved coolant.

1. What is the optimum coolant?
2. Do modern coolants have surfactants?

I've heard horror stories about how critical it is to "purge" the cooling system when refilling. Any tips? I've searched the Rotax website but can't seem to find the SI that details coolant installation.

I'm aware these questions have probably been answered again and again. I appreciate your patience. I have decades of Lycoming and Continental experience, but the 9 series Rotax engine is still a puzzlement to me.

Jim

[3Dreaming]

Dex-cool 50/50 premix, or Dex-cool mixed 50/50 is the way to go. Make sure you get all of the Evans coolant out, as the two coolants will not play well together. I have never had any issues with getting air out of the systems I have worked on, but I have never worked on a Gobosh.

[arizonarotors]

Thanks, I appreciate the help.

Jim

[drseti]

Going from Evans waterless coolant to Dexcool is fairly easy - just drain the system at its lowest point, seal it back up, and then add the new mix. (If you mix your own Dexcool, remember to use distilled water - tap water has minerals that can promote corrosion in the heads).

Going the other direction is a little trickier, as you have to purge all the water from your cooling system before adding the Evans. This can be done by draining the system, refilling with alcohol, and then draining out all the alcohol (which will have absorbed all the water) before refilling with Evans.

I find the Dexcool 50:50 H2O mix ideal for these engines. I have one customer who uses Evans, and I've been trying for 3 years to convince him to switch over to Dexcool. Not sure why he is so resistant.

[arizonarotors]

Thanks Paul,

Going to switch this week. The mechanic that installed my new engine put in Evans because that was the only "approved" coolant in the POH of my 2009 SLSA Gobosh.

It seems clear to me that, here in moderately warm Phoenix, the reduced thermal transfer capability of waterless coolants is not good for me.

My question about surfactants was just curiosity about their benefit.

Jim