My second-hand microlight, Rotax 912-powered, came with Evans NPG+ coolant. As I read the internet, this is good stuff, especially in hot climates, but I find it very expensive.

I should like to switch to the usual water + glycol. The Rotax engine can certainly stand that, but of course I have to check with the manufacturer if the rest of the cooling system can work on water plus glycol too.

Meanwhile I should be glad for opinions: is the Evans stuff worth its price? for someone who can't stand hot weather anyway, and is therefore unlikely to venture into hot climates?

The main thing to check if you are switching to 50/50 coolant is the pressure cap. From memory, the Evens one is 0.8bar and the 50/50 has to be 1.2bar. Radiator cap is around £50. The LAA recommend you have a coolant temp gauge as well as cylinder head temps. Cylinder head max temps change when you change coolant.

Most of the people I know who switched to Evens switched back complaining of overheating and expense. My 192ULS has only ever used 50/50 and I have had no issues even in southern Europe in summer.

Good luck!
Rod1

Thanks, Rod1, much appreciated. I'd never have thought of swapping the filler cap. 50 quid seems quite hefty, though, will think twice.

One of the aircrafts I use to fly is Rotax912 powered. Due to the engine itself, or to the installation, the fact is that this engine runs always very cold. We've switched to Evans from 50/50 and now we fly with CHT reaching 120ºC everytime. So perfect for us.

If you don't have this 'cold engine' problem, maybe you don't need Evans. But if you have it, Evans seems indeed a good solution. Maybe if you try and switch to 50/50 'traditional' coolant, you will find out your Rotax runs very cold.

Thanks for thinking along - but weren't thermostats supposed to deal with "cold engine" issues? Or, alternatively, some duct tape around the water radiator, as we do around the oil radiator in winter?

The thermostats usually installed on Rotax engines are only useful to get 70ºC quickly on cold weather. But since they open the circuit to the radiator at only 70ºC, you still have the same problem to get temp over there.

The duct tape "solution" works, but is no controllable at all during flight. I've had to land several times to remove part of the duct tape because in every climb I was getting close to red line. Other times I should have put more duct tape and I've made the whole flight with only 60-70ºC. The advantage of Evans is that keeps consistently a good temperature.

I would recommend using the 50/50 coolant only if the aircraft is equipped with cowl flaps actuated from the cockpit, to have full control of the engine temperature in changing conditions.

I have been wondering about controllable flaps, both for the oil and water radiators. Funny one never sees them, though there is a recent thread on a German forum.
(( Jalousie für Ölkühler P92 - Technik & Flugzeuge - Ultraleicht Forum - ulForum.de (http://www.ulforum.de/ultraleicht/forum/2_technik-und-flugzeuge/2504_jalousie-fuer-lkuehler-p92) ))