I have an RV-12 S-LSA that is used in flight training.
When the 5 year hose replacement was needed it was performed by the FBO's A&P / Rotax Certified mechanic.
After the 5 year hose replacement a very small coolant leak has developed.
Coolant ONLY leaks after the engine has been run and is cooling down to the balmy WI winter temperatures.
Coolant does not leak when the engine is running.
Coolant does not leak statically.
Coolant does not leak when the cooling system is pressurized.
Coolant only leaks after the plane has been run and sits.
There are 2 small areas of coolant on the ground, both on the airplanes left side. The first leak is directly under the trailing edge of the fixed "cowl" flap. The second accumulation of coolant is directly under the leading edge of the left boarding step.
The forward puddle is about the size of a quarter. The aft puddle about the size of a silver dollar.
In the meanwhile anyone have any ideas or a similar problem?
I should add that I am not a great believer in coincidence. If the engine did not leak before the 5 year hose replacement but leaks after it, the common denominator is obvious, however, we can't see where the leak originates.
Last edited by JPalese : 02-17-2018 at 04:41 PM. Reason: typo and material omitted.
How can you be sure it isn’t leaking during flight? Perhaps it doesn’t drip down until it sits for a while. Is there coolant on the belly of the airplane? This would be most plausible explanation, as the coolant would most likely leak with heat/expansion/pressure.
When the engine shuts off and begins to cool the opposite occurs and vacuum begins to form and withdraw coolant from the overflow tank.
Maybe check the hose located under the filler cap to make sure it's seated properly and the hose end is not split. I had a similar leak a while back when the hose developed a split.
There is no coolant on the belly.
After the engine was wiped clean and dried, the engine was run for .6 with the Rotax mechanic observing. No leaks were observed during or immediately after the engine run.
LEAF, the local Rotax distributor, then directed the mechanic to pressurize the cooling system to 15PSI. No leaks were found.
We observed the engine for another .5. It was then re-cowled. The next morning the 2 small spots were on the ground as I initially described.
Also leave the cowl off, place white paper towels under the AC will help locate where its coming from same for oil leaks. Leaving the cowl on can cause problems as coolant will run off of it in a different place away from the leak.
John, I had a similar experience on a 912 uls in my Rans S-7S. For over two years I chased a similar leak as yours. The leak never showed up when running or right after flying. The engine was completely dry after flying or during a static run up uncowled. But, I would return the next day and there would be from a few drops to maybe half an once of coolant on the hanger floor. Seem to show up more on cool nights. Tried all manner of testing and repositioning of clamps no no avail. The coolant lost was minimal maybe adding 6 oz. between annuals.
Finally traced the leak by shining a light in a darken hanger and noticing a slight reflective trail from the top of right front cylinder, down between the heads onto an exhaust pipe and then to the cowl. The leak was from the coolant return elbow on top of the head. Held on by two screws and sealed by a small red o-ring (which looked to be in good shape) the leak disappear when I replaced the o-rinng.
Just my experience , but you might want to check. My symptoms exactly matched yours.
Right Front top of cyl, coolant elbow 'O' ring.
From my understanding there are 3 places that are common coolant leaks, but for different reasons.
After the 5 year rubber change this seems to happen if the spring clamp on the 17mm coolant hoses are too far back and not up by the flared end in the aluminum tube underneath the hose. Place the clamp just behind the flared end, but not on top of it. This makes a far better tight seal. Keeping the clamp to far back towards the end of the rubber hose can allow some oozing on some engines. After 25 hours of flight time take a few minutes and tighten up any screw clamps. The rubber will settle.
p.s. All clamps on the coolant hoses are better sealing up next to the aluminum flared ends on the metal tubing.
If you live where it gets really cold then you can see a few tablespoons of coolant at times back behind the rear tire on the ground. I learned in class that this happens because of different materials in the coolant pump. The coolant shaft setup is make up of stainless, two ceramic halves and the aluminum housing. Due to different expansion and contraction rates for these materials they can drip at times during cold weather and heating and cooling cycles and drips out the weep holes. It should be no more than a few tablespoons and if it's a large puddle there is another problem.
The last place a leak may show up, but may not always be real visible is up on top of the engine where the 17mm hose 90 degree aluminum tubes are. They can ooze around where they are threaded in. The air flow through the cowl can make this one a little harder to find. The give away is some tiny wet or dried residue barely seen around the base of the aluminum tube where it screws into the flat base. This is very easy to fix. Drain the coolant down past that high point. Take the flange off and heat gun it and the tube will unscrew. You can use either Loctite 243 or better yet Loctite 648 on the threads when you screw it back in. Do not forget to use a black magic marker to mark the tube and flange orientation so it will be in the alignment you want when you re-install it. let it dry over night without coolant to get the best seal. You can see this on YouTube videos.
John, I would start by checking all four worm drive hose clamps on both 1” hoses. It sounds like you have a leak at both the water pump and the radiator. Make sure the hose is pushed all the way onto the flange and hose clamps are clear of the barb on the flange.
Sounds like a 912 on an LSA at the airport I use to be based at. Similar issue after hose replacement. The owner found that the clamps were loose.
I have seen the same thing on my GMC. Not leak in normal weather temperatures but when it got cold, it would leak. Was a hose clamp not as tight as it should be.