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Coolant Leak AFTER 5 year hose replacement

JPalese

Well Known Member
Your help is needed.

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.

RV-12-Coolant-Leak


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.

All suggestions appreciated.
 
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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.
 
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.
 
So I was watching a good two part video on YouTube of a Rotax Maint class done at Lockwood recently. One of the items they discussed and that I hadn't heard of before are two seals in front of the water pump. They said that coolant leaks can develop at one of these two seal points. Just a guess.

Here is a link to part one of that video.
https://www.youtube.com/watch?v=DFfxHbaU_Bs



Carl
 
take it for a good fly and the pull the cowls and start searching with a good torch
four bottom head hoses four top head hoses four top head elbows water pump in and out radiator in and out header tank to radiator connection
look carefully for coolant residue
Mine developed a tiny leak where the top hose elbow comes out of the head you couldn't see any coolant only greenish powder type mark near the leaking fitting
 
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For those pesky leaks in coolant systems I use the dye from the autoparts store. Then look with a black light to find the leaker. I have found it very helpful. Actually, some coolant is also illuminated with black light, just not as vivid.

Hose materials can creep with elevated temps and a fixed diameter hose clamp will allow the connection to loosen with time. Either just keep tightening the clamps, (but not over tighten) or get constant force clamps of some type for the job. Thankfully, they are widely available these days.

Rarely there can be an o-ring connection that will leak at zero pressure, but not vacuum or pressure. I had on that would drop a few drops as the unit cooled down when ambients were below 32F. Every time.

You are right, no cooling system should leak, zero.
 
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Leak

We had a similar leak to what you described. When we changed the hoses I took the radiator to a shop and he found a leak on the bottom hose neck of the radiator in the weld. They pressurize the radiator and submerge it in water and air bubbles will show where the leak is. Hope you find it.
 
John -

I would be curious to know if the hose clamps were changed at the time the hoses were replaced. The factory Rotax hose clamps are a constant tension type that expand and contract with the hose assembly ... perhaps those were changed out to the standard worm drive type ... which don't tend to expand and contract in unison with the hose assembly unless they are the type with the spring on the screw drive.

As previously mentioned by others, check the hose between the reservoir and expansion tank (it is prone to splitting) and check the tiny weep hole on the bottom of the water pump for drips.

Please let us know the cause(s) of your issue.

Happy flying,
 
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.

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.
 
The Dye / UV Black Light will find the source of your leak...

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.
Bill
 
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.
 
Hose Springs missing?

John,
What do you recommend for our A&P to avoid this problem?
Something about leaving out two radiator hose springs?

Tim
 
I had a tiny leak develop after hose change out - about 1/2? overflow bottle level in 50 Hours. The fluorescent dye didn?t show anything except around the weep hole on the bottom of the water pump. After about 80 Hours and tightening hose clamps at oil change (I replaced most spring clamps) the leak seems to have disappeared. My engine has about 700 Hours on it. Changeout was at about 590 Hours.
 
Leak stopped (for now?)

Now that the ambient temperatures are no longer in the deep freeze, my mysterious leak just stopped.

Coolant level in the overflow tank is visually unchanged, and out of curiosity I topped off the expansion tank .... about 1/2 ounce of coolant was needed to top off the expansion tank.

IF I find the cause or have further info I will advise the group.
 
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