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Water-cooled engines... Good or bad?


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I read a negative-sounding comment on the forum a few days ago about water-cooling... Something about carrying boiling water on your back. Many of the paramotor community over here also talk negatively about water-cooling, but most comments seem to start like "Many people have problems with.... " or "I've heard that.... ". Though they all have bad things to say, none seem to be from personal experience. I wondered how the people on the forum feel about water-cooled engines such as the Sky 100. Has anyone had any bad experiences with them?

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Water cooling is another maintenance item which can be neglected, but general longevity to time before overhaul is a nice tradeoff. I'd fly one if it weighed what the mini2 does with cooling system and made the same power at the same price. Looks like its convection based cooling...

@ 18hp though, she's just too puny to push my cheeseburgers around.

Only 13kg with liquids tho.

Don't see a TBO listed.


Wish I had some exposure to them, but I'm just goofing off at work...

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i have had no experience of water cooled on a paramotor . the comments that carrying hot water on your back you said people have said?

well we carry petrol and a spinning prop, and people are fussed about hot water? i cant figure it out but you are right a lot of answers come from people who really dont know what they are on about.so listen but dont always believe what is said .

there is some very experienced people on here who will give good advise if you ask them.

i am guessin that your worry is if it ruptured?

i would be happy to use one without worry if there was a rupture and it sprayed at ya back it has a lot to get through before it gets to the skin and i think it would have cooled a bit before it did.

there will always be what if or ah but.

sometimes its better to listen to what yourself thinks

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The biggest benefit is stable head operating temp. With that should come longevity of internals.

While I'm not sure how that is accomplished with simple convective heating on engine mentioned, I understand the intent is to maintain operating temps for extended full throttle, where air cooled engines may suffer heat soak and/or meltdown in the worst ambient conditions. Also to retain heat on idle.

This engine is equipped with an overflow bottle, so expect the cap would vent if it over pressured giving a controlled boil over which should be pulled downwind by prop. If neglected though, it's not outside the realm of possibility that a hose could pop off and internal pressure direct boiling coolant in the pilot's direction. I expect that's what the original concerns were.

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Was just thinking about liquid cooling. Something I've come across in the past has been an air cooled barrel and water cooled head. With this in mind, I don't think it would be difficult to covert a standard head to liquid cooling. However, as T Andrews has suggested, it's possible that simple convective cooling wouldn't be sufficient to provide enough flow through the radiator. So my mind is wandering along the path of using a small water pump, driven by a fan, in turn driven by airflow.

This isn't a million miles away from some early aero engines without electrics, where battery charge facility has been added by the use of a small turbine.

An extra benefit of liquid cooling, is that a small proportion of waste heat can be easily diverted to the carb to prevent icing.

I'd use liquid cooling any day as long as the weight penalty wasn't prohibitive.

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There's a lot of folks out there copying others and still others trying to forge their own brand.

The Kobra snake looks an awful lot like the engine that started this thread, just rebranded as a Kobra engine.

Not surprising since sky engines make engines to be sold for use in paramotors...

They offer an air cooled engine too, the "Rocco" based on the mini2 plus.

It all makes me question how valid any of their literature is, when I see the Kobra Rocco using the mini2 "Kobra" version, detuned to 24Hp, with a 2.7:1 redrive, and a WB37 yet still using the mini2's factory pipe generated hp and torque curve map just like the full factory pipe.

This is either very very impressive getting what looks like much more out of less, or a big fat lie they're hoping no one will call them on.

Marketing embellishments make me bitter because they prey on the uninformed and work to keep folks misinformed at least until a sale has been made.

I'm not bashing the brand, just calling it like I see it. They have really cool branding. 8)

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Fresh Breeze and Kobra make significant modifications to make a superb engine much better still (probably the best out there). They trade a small amount of the excess performance for the reliability we need as demonstrated very admirably this summer! Perhaps we should thank them rather than knock them.

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This was my point.

I appreciate a detuned engine if it improves reliability and extends time before overhaul (which it does indeed).

My point was, if it is indeed detuned, then the factory hp/torque map is no longer accurate, yet seems to be happily presented as factual.

I'm not knocking them as much as questioning whether they should be knocked.

Compared to the WJ RR mini2 implementation, the Kobra is much more a "daily driver" but for the multi-cheeseburger pilot, more is better.

Nothing is ideal without the circumstances it will be used in.

To re-rail the thread, see aixro xr-50 'rotron engine' listed @ 15.4kg liquid cooled on parajet's site:


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  • 4 weeks later...

hi. Air cooled engines work well. Why have the added complexity of a water pump that'll need parts sevice and is a steaming kettle as well. the rad is also delicate too as are the rubber hoses, something you don't need on a paramotor. The Sky is a cool looking thing tho but unnecessary imo.


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