Mysterious coolant loss in a Rotax 912 85hp

[matt walsh]

Hi all, Gladys, our Skyfox Gazelle, is experiencing a loss of coolant but with no obvius signs of a leak. She will empty the overflow bottle after a 2 hr flight in current coolish temps. We have poored over the engine whilst running it but nothing obvious. we've replaced the expansion tank cap and tightened all clamps but stil nothin. The Rotax 85hp has done 2100 hrs and no loss has been observed dueing last 250 /3 years operation.

 

Your collective wisdoms on possible causes etc will be greatly appreciated. I have discussed with gary Flood who could only suggest possible leak from exhaust ports if the exhaust pipe were loose and has "worn" a hole in the head through to the coolant passages( seems a most unlikely event). Cheers Matt Walsh and Neil Sidwell, Gazelle 3478, Penfield Aerodrome, Sunbury Victoria.

 

 

[Ultralights]

is the coolant cap the right rating? i had a similar issue when the cap seal wore out, i mistakenly replaced it with the wrong rated cap, and lost coolant slowly through the cap. got a new cap, and all has been good ever since.. i do have the ULS100hp though.

 

 

[mothra]

Its amazing how many ways coolant finds its way out.

 

A cooling system pressure tester lets you pressurise the cooling system while cold and not running so you can spot those tiny leaks at hose clamps, rad header tanks, gasket surfaces etc. They are a reasonably standard auto workshop tool if you have a friendly mechanic. Stant do a good one Ive seen occasionally at the usual auto stores.

 

 

[MarcK]

I can only compare to automotive but if it has a proper pressurised radiator remove the cap and see if you get bubbles in the radiator. Classic signed of a combustion leak. If you have this leak it will allow water in the cylinder and blow it out the exhaust. Also check for oil in the radiator another sign of trouble. A sign of water in the oil is white gunk under the filler cap for the oil.

 

The things you learn driving junk heaps.

 

Marc

 

 

[bushcaddy105]

I have seen pinhole corrosion in an aluminium head bore a tiny hole from the coolant passage into the exhaust port. Discovered by slight coolant stain at the exhaust flange. Caused by some tiny bit of foreign material being included in the head casting at manufacture, and setting up electrolytic corrosion. It took years to eventually break through.

 

 

[facthunter]

I've seen plenty of corrosion in cylinder heads sometimes in vehicles 18 months old. You have to bandsaw the heads apart to find this. Sometimes it goes into the exhaust port. How old is the motor and how well has the coolant been looked after?. If there is a small perforation it will get bigger so sort the matter out. If you are getting a leak at a port the colour of the exhaust pipe internally will change but you won't build up pressure as you will if it is in the combustion chamber. Nev

 

 

[cscotthendry]

If you have air trapped in the system and are using a water/glycol coolant there is the possibility of steam occurring and pushing the coolant out. Also check that the coolant is not escaping from the water pump past the seals. With 2100 hrs on the clock, it might be worth poping the water pump cover and renewing the gaskets and seals around the bolts especially the bottom bolt (I think) has a compression washer on it.

 

Not to contradict Floods, but I think youwould see some evidence of coolant leakage around the exhaust pipe if the pipe had worn through the cylinder head at the exhaust port.

 

 

[matt walsh]

Thanks all above replies. We did another run up and noted some small coolant on underside of water pump. Spoke with Gary Flood who also suggested the rotary seal on the water pump shaft maybe allowing coolant to escape past and leak out via a small inpection/venting hole in the engine casing about 20mm forward of the waterpump houseing/main engine casing.

 

Suggestion on pressure testing is sound and we are arranging this. This may identify any coolant escaping past the seal. Will check the exhaust pipe colour also although havent noticed any change aas I always rub the inside of the pipe to see that sh'e burning clean/brown.

 

 

[Camel]

Thanks all above replies. We did another run up and noted some small coolant on underside of water pump. Spoke with Gary Flood who also suggested the rotary seal on the water pump shaft maybe allowing coolant to escape past and leak out via a small inpection/venting hole in the engine casing about 20mm forward of the waterpump houseing/main engine casing.Suggestion on pressure testing is sound and we are arranging this. This may identify any coolant escaping past the seal. Will check the exhaust pipe colour also although havent noticed any change aas I always rub the inside of the pipe to see that sh'e burning clean/brown.

A simple test is with engine warm squeeze the radiator hoses by hand causing the system to increase pressure and observe any leaks.

 

 

[facthunter]

It is very easy to get something that will pressure the system. Re the exhaust colour It will only be noticed if the pipe is removed and inspected close to the head. You would have to know what you are looking for. Water pump seal is one of the first places to look. Coolant usually dries to a whitish powder. Nev

 

 

[matt walsh]

morning all, Nev, I agree that the rotary seal is probably the culprit here. Unfortunately its a costly item to replace because of need to remove engine fom plane then the altenator stuff to access the water pump, as I understand the water pump (and hence seal) can't be removed whilst engine is in place. So significant labour costs involved and estimates in the $2-3,000 range. At this stage we will continue to monitor rate of coolant loss but expect this work will need to be done in near future. I would be interested to hear from others who have replaced the seal or water pump in their Rotax. Thanks all Matt Walsh

 

 

[bilby54]

morning all, Nev, I agree that the rotary seal is probably the culprit here. Unfortunately its a costly item to replace because of need to remove engine fom plane then the altenator stuff to access the water pump, as I understand the water pump (and hence seal) can't be removed whilst engine is in place.

Matt, you do not have to remove the engine from a gazelle to replace the water pump.

 

It probably looks daunting but it is really easy once you have done it a couple of times

 

 

[geoffreywh]

I would be talking to somebody else! $2-3K is a LOT of hours............. who takes 20-30 hours @ $100 p.h. to re and re. a motor?. I would Guess. 3 hours out and 6 back plus replace parts and hoses. @60p.h. for an L2.... 2 days would be an enormous time frame to do that job.