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Old 02-08-2018, 06:43 PM
JPalese's Avatar
JPalese JPalese is offline
Join Date: Apr 2011
Location: KHXF
Posts: 136
Default Coolant Leak AFTER 5 year hose replacement

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.

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.
John Palese
1) AAL Captain & Check Airman
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2) Adjunct Professor-Aviation Science, Carroll University.
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Last edited by JPalese : 02-17-2018 at 04:41 PM. Reason: typo and material omitted.
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Old 02-08-2018, 07:29 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
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Location: Hinckley, Ohio
Posts: 781

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.
Jim Stricker
Hinckley, Ohio
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80 hrs Flying Aeronca Chief 11AC
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Old 02-08-2018, 07:47 PM
rgmwa rgmwa is offline
Join Date: Feb 2010
Location: Perth, Western Australia
Posts: 1,567

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.
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Old 02-08-2018, 07:55 PM
MMiller MMiller is offline
Join Date: Oct 2010
Location: Babylon NY
Posts: 48

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.
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Old 02-08-2018, 08:17 PM
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RV6_flyer RV6_flyer is offline
Join Date: Jan 2005
Location: NC25
Posts: 2,837

Originally Posted by MMiller View Post
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.
Gary A. Sobek
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Building RV-8 S/N: 80012

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Old 02-08-2018, 08:18 PM
newamiga newamiga is offline
Join Date: Jan 2011
Location: Barneveld, NY
Posts: 178

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.

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Old 02-09-2018, 03:02 AM
crashley crashley is offline
Join Date: Jun 2009
Location: hazelwood north vic
Posts: 160

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

Last edited by crashley : 02-09-2018 at 03:06 AM. Reason: spelling
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Old 02-09-2018, 04:36 AM
BillL BillL is offline
Join Date: Sep 2007
Location: Central IL
Posts: 4,143

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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Last edited by BillL : 02-09-2018 at 04:38 AM.
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Old 02-09-2018, 05:21 AM
lewy lewy is offline
Join Date: Nov 2009
Location: Jackson Ohio
Posts: 131
Default 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.
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Old 02-09-2018, 06:48 AM
John-G John-G is offline
Join Date: Jan 2012
Location: Northeast Ohio
Posts: 477

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.

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