914F3 coolant leak/sticking wastegate

NOTE: TOPPING UP THE OVERFLOW BOTTLE DOES NOT FILL THE COOLING SYSTEM. (Especially if the bottom of the bottle is lower than the hose coming from the expansion tank.)

The coolant must be added to the expansion tank (spider), filled right to the ledge upon which the pressure (radiator) cap seats.

I just inspected a 3rd case where not understanding how to fill plus a bad cap has resulted in likely ruined 912 engine. The bottle was full, the expansion tank had nothing in it. Some genius had "fixed" the coolant mess by adding a barb to the bottle cap and running a tygon line overboard.

The bottle is there to accept hot coolant when it expands. When it cools, it's supposed to get sucked back into the cooling system. If there is air between, this doesn't happen. A bad cap means blowing coolant out the line and usually out of the bottle and "topping off" the expansion tank with air.

Sean/Jeffry:

Thanks for the info.  Regarding the cooling system: we flew today for 30 mins, to a local airport, ran it up pretty well.  Landed and hung out for about four hours.  No drops, no leaks.....no signs of any leakage.  On the return flight - same thing.  So....either the new radiator cap, new hose and/or new routing appears to have fixed the problem, or contributed to the fix.  The real test will come with a longer high altitude flight - which is forthcoming in about a week.  But so far....all promising.

The wastegate is another issue.  I lubed it up again prior to takeoff, but it didn't do the job this time - the turbo overboosted, had to throttle back on takeoff, and for the entire 30 minute flight (with the exception of descent and landing) the MP varied all over the place....it was never constant, always moving back and forth +,- 2 inches....sometimes it even moved all the way in the yellow.  Landed, hung out for those four hours....and on the flight back, everything was perfect.  Absolutely perfect power on takeoff, no "variable" MP at any point....the entire flight back, absolutely no problem and everything worked perfectly.  And I didn't lubricate the wastegate prior to takeoff. Very odd for sure.

I've been using Mouse Milk for lubrication, and it has worked well in the past (at least for several flights), but I will now try the 8151.  Adding a lubrication hole sounds like a great idea to me.

I’ve been flying my 914 for 21 years now off and on, replacing a cracked crankcase, cylinders and pistons. Not once have I lubed the wastegate or needed to. Just my experience in a Europa airframe.

"...........using Mouse Milk for lubrication"

I Googled "Mouse Milk" -  its a light weight penetrating oil - likely to "flash off" something as hot as a waste gate, within moments of start up - completely useless!

My earlier comment -  "The wastegates I am familiar with are not lubricated."

Sam Purpura's comment - "Not once have I lubed the wastegate or needed to." 

If you insist on lubricating the wastegate:

"I have often drilled a hole in a hinge that would benefit from lubrication. I use a 2mm drill bit, finish off with a brief countersink to make a small conical top to the hole. Using a chainsaw grease gun (they have a pointed application end) pump LB 5151 or any other high solids content, high temperature lubricant, into the hole until lubricant appears around the joints."

My earlier comment   

"Sticking" is usually caused by misalignment due to mechanical damage and or wear..........

The only durable solution is to find out why your wastegate is sticking & fix it."

Thanks Sean.

I found Rotax SI-914-003 R1 which seems to exactly address the problem I'm having. Ironically, they propose Mouse Milk as one of the lubricating options for the wastegate. But to really get into the shaft/bearing, I may have to remove the muffler.  Definitely need to figure out why its doing what it's doing, and drilling a hole is something we have to consider here, even if the problem is identified.  Next step is to find a certified mechanic to go after this with me.  The SI is pretty clear on the process, and offers a suggestion as to why it sticks in the first place.  But this must certainly be, or was at one time, a common problem in the Rotax 914 units in the field.