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Aqua-Hot coolant mystery?


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Hi All,

I've got some puzzling behavior in my aqha hot AHE-100-02S 

Last year I repaired a leaking coolant reservoir and replaced the coolant. I monitored the system closely for a couple months with reference marks to make sure the levels were consistent between hot and cold and the level wasn't dropping. All good, so out of sight/out of mind... It's normally turned off unless we're travelling.

Then last week we got back from a trip and I looked at the reservoir and it was empty. So I filled it about to about 1/2 and watched it for a couple-days and determined that the reservoir wasn't leaking again. No signs of a leak. Hmmm.

So I turned the unit on and let it heat up, with the assumption that the level must be low, and it would expel some air and then slurp in the coolant when switched off, and I'd use a couple heat/cool cycles to top up the level in the tank back up (getting to the cap to directly check level is REALLY a pain).

Apparently the AH coolant level was not low because the unit expelled a pretty normal amount of coolant when it heated up. Which put the level right near the High mark in the reservoir.

So far so good, but where did the missing coolant go???

And here's the part that really confused me: when I turned the unit off and let it cool down, the level in the reservoir only dropped about 3/8".

About the only thing I can figure could cause this would be a small leak somewhere in the coolant overflow line. If it's pulling air into the system instead of sucking coolant out of the reservoir, that might explain it. If it was a leak in the pressurized part of the system it wouldn't have forced coolant out into the reservoir, right?

But so far I haven't found any coolant dripping anywhere.

Can anybody think of another plausible scenario that might explain this or where to start looking for a leak?

Thanks,

Walter

 

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I have had somewhat similar experience some time ago and after experimenting it turned out to be a crack in the brass radiator neck. I could not definitely explain why it would be pushing coolant out and not sucking it back at the same rate but settled at an idea that heating cycle is faster than cooling cycle and that changes behavior of the leaky crack. That's after multiple changes of the cap, overflow hose and closely watching it through the heating cycle. The neck crack was at the back side that I could not see and coolant was seeping into the housing through the not so tight rubber seal and absorbing into the tank insulation. It could have been a number of other possibilities like an internal leak into the engine cooling loop or heating registers. My hot water loop is external so I knew that wasn't a suspect. I would start with a new cap, check the hose and go from there. Hope you have a better access than I do...

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10 minutes ago, Ivan K said:

 turned out to be a crack in the brass radiator neck. .. Hope you have a better access than I do...

Thanks Ivan. I'll try and investigate that area. I've read of other cases of corrosion at the filler neck.

My access is pretty bad! I can barely get my arm in there to remove the cap...

Walter

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Walter, you may have multiple things causing what you have described.

My advice is to replace the back half of the coolant overflow hose with an automotive fuel line with the same ID and a new clamp. Install a coupler on the other end of the new opaque hose and then a section of clear tubing on the front half of the hose that connects to the overflow tank. That clear section can be replaced easily anytime it's needed. While you are working at the filler, replace the radiator cap with a new one but make sure the tank is full of coolant before installing a new cap.

The overflow tank level should be near the cold point of just above it. Then start up the Aqua-Hot diesel burner and watch the level in the overflow tank go up. Make a mental note as to where the level is when the Webasto turns off or place a piece of tape there on the side of the tank.

Now you know exactly where the level should be when the coolant is stone cold and where it should be when it is HOT and at it most upper level. If those points change while using the Aqua-Hot then it's time to start looking where the coolant might be disappearing.

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15 hours ago, wamcneil said:

Thanks Richard.

If I can't find any obvious issues around the filler neck I'll go ahead and replace the cap and hose. I sure hope it's the overflow hose...

Walter

My clear tubing overflow hose would get very hard from the heat of the coolant and eventually crack near the filler neck. Replaced it TOO many times so I eventually replaced it with tubing that would NOT harden up and crack, hence the reason for the fuel line near the filler neck then clear near the overflow tank.

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4 hours ago, Dr4Film said:

My clear tubing overflow hose would get very hard from the heat of the coolant and eventually crack near the filler neck. Replaced it TOO many times so I eventually replaced it with tubing that would NOT harden up and crack, hence the reason for the fuel line near the filler neck then clear near the overflow tank.

We ended up doing the same thing. That plastic clear hose is just not the correct one for that application. I also changed the cap to 7#. 

Paul A

On 8/31/2020 at 12:08 PM, wamcneil said:

Thanks Ivan. I'll try and investigate that area. I've read of other cases of corrosion at the filler neck.

My access is pretty bad! I can barely get my arm in there to remove the cap...

Walter

You may want to try using a mirror , one like the dentists use. They are cheap at harbor Freight. Check it when you start it up when the unit is cold.

Paul A

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  • 2 months later...

Just following up in case anybody is chasing a similar problem.

Thanks again for the great advice.

With cooler weather approaching I got motivated to look at it again and found the hose clamp loose at the radiator cap. I don't remember messing with it, but I must have taken it loose last year when changing the antifreeze. Maybe the hose clamp was in the way and the cap was hanging up on it.

The clear hose appears to be intact and not hardened so I'll defer replacement for the time being...

I've been through 4-5 heat/cool cycles and it appears to be acting normal.

Cheers,

Walter

Edited by wamcneil
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  • 1 month later...
Posted (edited)
On 8/31/2020 at 11:55 AM, Ivan K said:

I have had somewhat similar experience some time ago and after experimenting it turned out to be a crack in the brass radiator neck. I could not definitely explain why it would be pushing coolant out and not sucking it back at the same rate but settled at an idea that heating cycle is faster than cooling cycle and that changes behavior of the leaky crack. That's after multiple changes of the cap, overflow hose and closely watching it through the heating cycle. The neck crack was at the back side that I could not see and coolant was seeping into the housing through the not so tight rubber seal and absorbing into the tank insulation. It could have been a number of other possibilities like an internal leak into the engine cooling loop or heating registers. My hot water loop is external so I knew that wasn't a suspect. I would start with a new cap, check the hose and go from there. Hope you have a better access than I do...

Well, my saga continues... and I think I have the same problem as this...

After a number of cycles, coolant accumulates in the surge tank and then there's no overflow when the unit heats up. Apparently it's leaking a little around the filler neck and pulling in air as it cools. Eventually the level stabilizes with about 1/2 gallon of air in the heater tank when cold. I can see a little seepage at the radiator neck as it heats up.

Apparently coolant leaks out of the crack slower than the air is pulled back in, so some of the ejected coolant just stays in the overflow bottle each time the unit cools.

Ivan, what did you do about your leak? 

Unfortunately I don't think I have any better access than you do... it's really hard to even get a good look at the neck. Looks like there's a vertical tube coming up from the tank, and filler neck is brazed to that? 

I don't think I'm willing to pull the AH out to fix this. Is there any harm in leaving the tank 1/2 gallon low? Apparently it burps out the air as it heats up and then is pretty much full when the unit is up to temperature.

Thanks,

Walter

Edited by wamcneil
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I can't remember if it was on this forum or irv2, but I remember somebody mentioning they had a leak at the filler neck and somehow pulled the top off of the tube, then used hose and hose clamps to joint the two. Would that be practical to do without pulling the AH out?

 

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Walter, I know there is/was a repair kit from AH to do what you said, I think even a heat shrink tube to use but I did it my way, it just came up a couple of days ago as a followup to an old post so I just copied the link...

 

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Thanks Ivan. That’s exactly what I need. 
I thought of trying to make some kind of hollow expanding bung like that, but I didn’t realize I could buy a ready-made test plug!

How easily did your cap come off?  Since there’s already a crack started, I wonder if I can work it up and down gently to get it off altogether. 
Thanks

Walter

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Walter, glad you find it useful. If you definitely decide to remove the brass part, it should be very easy. It was for me. Wiggle and twist it a bit, the steel pipe is solid. You can see in my last picture that it sits in the pipe by less than 1/4 inch, the solder was only around its perimeter and in my case was mostly held in place just by rust. It came right off in one piece. And the workaround really works. I really don't see why the system was even pressurized given the thermostats settings. The only theoretical reason I came up with was the engine loop but I doubt anyone would run the engine past boiling point of the mix even with 100% heat transfer through the long hoses.

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  • 2 weeks later...

Just a follow-up.

The radiator cap brass filler neck is soldered to the top edge of a 1-1/2" OD steel tube coming out the top of the AH tank. Just the very top edge of the tube is soldered to the filler neck. It's not like the filler has a sleeve that fits down tight into the pipe and is soldered securely. It's just perched atop the tube and is soldered to the edge of the pipe only.

This solder joint had cracked. Very little coolant was escaping, but the crack mainly allowed air to seep into the tank when cooling. So coolant gets pushed out to the overflow reservoir, and then air gets sucked back into the AH tank.

I don't see any practical way to "fix" this with the AH in place, so I've plugged the tube with a 1-3/8" rubber expanding radiator test plug like Ivan did (1-3/8" is nominal. actual OD ~1.25"). My first attempt was to put a 1-1/8" test plug down through the filler neck and plug it with the filler neck in place, but that was a disaster. Plug got stuck in there and I couldn't get it back out. Thankfully I was able to pry up on the filler neck and get it to pop clean off the top of the tube.

Presently I'm running the system unpressurized, and I think this would probably work just fine. But I have ordered a 2.5 L pressurized coolant reservoir and plan to put this in place of the original overflow bottle. My system displaces about 2-1/4 L between hot and cold, so I think this tank will suffice. The new tank has a pressure cap on it, so the overflow hose from the AH to the tank will be pressurized and I'll run a new 5/16" coolant hose for it. 

I do remember reading a thread where somebody got a short piece of radiator hose over the tube to extend it up and put a filler on the other end of the hose. I think this might be a 'better' fix, but I figure the top housing of the AH would need to be cut back to make room for the hose clamp and a tool to tighten it. Which I think would be a nightmare in this confined space... Looks like the newer AHs have a tube that extend higher than mine (mine is flush with the top of the housing). In that case, the hose repair would be a LOT easier.

So, if you've got a leaking filler neck, don't despair. It's not that bad.

Cheers,

Walter

 

Edited by wamcneil
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Roger Burke offers a filler neck repair kit on his site. His site is: rvhydronicheaterrepair.com

and the part is called “no-solder-filler neck kit”

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Ok, now it makes sense. Somebody mentioned a repair kit using heat-shrink. He’s using some kind of Uber-shrink instead of trying to get a hose clamp down in there. 
If I ever wind up clamping to that pipe, I’ll use an elbow hose to turn it horizontal and use a remote filler cap outboard where it can be. accessed by human hands!

cheers

Walter

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42 minutes ago, Chargerman said:

Roger Burke offers a filler neck repair kit on his site. His site is: rvhydronicheaterrepair.com

and the part is called “no-solder-filler neck kit”

Certainly an option if you are willing to remove the whole AH from the rig. Impossible to install while in place in our rig, probably the same for most. Not mentioning $220 for a new neck vs. ~$20...

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I repaired a leaky filler neck with a piece of silicone hose, two clamps, and a flange welded to a filler neck. I drilled a small hole in Aqua Hot cabinet to access lower clamp to tighten. Very simple process and very economical. Hope this helps.

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41 minutes ago, Frank Bergamo said:

. I drilled a small hole in Aqua Hot cabinet to access lower clamp to tighten. Very simple process and very economical. Hope this helps.

Brilliant!

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