Water level

by Mark Airey in General Tech Discussion 13 years ago

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Re: Water level

by Roger Lee » 13 years ago

Roger Lee

126 5.14k 4.58k

Having a higher mix of glycol does raise the boiling point, but it also reduces the heat transfer to the coolant. A 50/50 mix has a boiling point of 270F where Evans waterless coolant has a boiling point of 370F. The problem with Evans is it reduces the heat transfer and which cause the temps to increase aprroximately 25F-30F. Many tight cowled Rotax engine would then be over or close to a max temp of 266F. Kind of defeats the purpose and may just be masking a boil over problem that could be fixed. A 50/50 coolant with water transfers heat more readily, but because the boiling point is 270F it is too close to the 266F max and may allow vapor spots to be created in the head and cause no cooling to that affected area. So Rotax reduced the max temp to 248F for 50/50 coolant use. You usually still get a bigger benifit from the 50/50 mix. Evans is a good coolant for certain applications where temp isn't as criticle on the higher end. The cost of Evans is $25 a gallon plus a gallon or prep fluid. Then you can never add just water because Evans is waterless.

So if you are already getting too hot then Evans will make things 25-30F hotter. Better to address the root of the problem. I would personally use the 50/50 and then evaluate and modify my cooling system to do a better job.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Water level

by Andy Buchan » 13 years ago

Andy Buchan

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Mark,
Agreeing with what Roger has said:

An 80% mix has a higher boiling point than a 50% mix so localised boiling is less likely to happen (but it also has a lower heat capacity so has less cooling effect). In a PFA (now LAA) magazine of the last century there was a good article on coolant mix ratios - and their conclusion was that an 80% mix was best.

In UK Evans coolant seems to have vanished. At our airfield we have a wide range of machines - CTs, Dynamics, Ban-nis, trikes - all with rotax 912 or 912S engines - and all OK on an 80% mix. Owners have tried the 50% mix but found colant overheat problems.

Andy Buchan

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Re: Water level

by Kevin Stewart » 13 years ago

Kevin Stewart

5 184 0

Under normal operating conditions the pressure cap should not open. Since you are loosing coolant from the main circuit into the overflow bottle then you are either running too hot, have a pressure problem or your cap is not holding the correct pressure. The cap is designed to draw coolant back from the overflow bottle if there is spare volume in the main coolant circuit as the engine cools.

The level in my 912UL coolant overflow bottle never seems to change. I don't think that I have the Evans type coolant, I believe it to be a water/anti-freeze blend.

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