Glycol Tank Cap Will Not Tighten

grassgd

The cap on the Alde glycol tank in my 2019 320S is always loose.  During trailing glycol splashes up to the cap and leaks out causing an unwanted mess with glycol always running down into the area under the rear.

I have used tape on the threads to try and get the cap to stay tight but that is not a very long term or 100%  fix.  

I would buy a new tank if I could be sure the cap would fit tight and seal. 

Do some owners of 320S' with the tank in the rear have tanks that the cap fits tight and seals?

Anyone buy a new tank and found the new tank cap seals?

bergger

I'm pretty sure the consensus is that the caps generally do not snug down tight as it is not a pressurized system.  The cap on our 400 will screw on a bit but if I turn it a little too far it will go loose.  It is kind of finicky.  But even being a loose fit we've never had glycol leak out of it.  How much glycol is in you expansion tank?  Maybe it's over filled a little?  Or it could just be the size and location of the tank.  I think the 400 uses a larger tank and ours is in the very front of the trailer not the rear where I believe yours is located.  Curious to see if anyone does have a tank with a tight cap.  

manyman297

Ditto what @bergger said for us. It has never tightened. I just snug it down.

grassgd

bergger said:

I'm pretty sure the consensus is that the caps generally do not snug down tight as it is not a pressurized system.  The cap on our 400 will screw on a bit but if I turn it a little too far it will go loose.  It is kind of finicky.  But even being a loose fit we've never had glycol leak out of it.  How much glycol is in you expansion tank?  Maybe it's over filled a little?  Or it could just be the size and location of the tank.  I think the 400 uses a larger tank and ours is in the very front of the trailer not the rear where I believe yours is located.  Curious to see if anyone does have a tank with a tight cap.  

My glycol level is not overfilled, and the tank only holds about 1/3 gallon at max fill level which is about 1/2 filled so as the trailer bounces on the highway it easily splashes on the loose cap.  It doesn't take much glycol to make a mess.

Even though the Alde system is not a closed system (it is vented to the atmosphere) it would be much better if continuous exposure to oxygen is eliminated.  That would increase the glycol life.  I am working to have the glycol tank vent to an expansion type of device and eliminate the vent to atmosphere.  Hence, I have two reasons to have the cap seal - stop the mess and close the system to constant oxygen exposure.

dragonsdofly

@grassgd-have a 2017 320S. 45,000 miles with reservoir in the back. We just snug the cap a little and have never had the cap leak. Hundreds of miles on gravel and first nation roads in some remote locations and no leaks. I wonder why the difference?

Maxcamp

Check the cap and tank for malformed threads if possible.  Common in plastic gas cans and other injection molded items.  Measure OD and see if you can transfer a cap from another object- gas can or water tank.  I've swapped out caps on gas cans all too often.

grassgd

Maxcamp8 said:

Check the cap and tank for malformed threads if possible.  Common in plastic gas cans and other injection molded items.  Measure OD and see if you can transfer a cap from another object- gas can or water tank.  I've swapped out caps on gas cans all too often.

The threads on the cap look fine.  The threads on the tank are not continuous (ie gaps without threads so I think it's not the cap that's the problem but I'll check again.

When I get the trailer out of storage again, I plan on measuring the tank opening to see if I can fit an End of Pipe Gripper or a Clean Out Plug Gripper or similar:

grassgd

The problem with the tank cap being able to seal is not related to the cap but the tank itself.  The threads are not continuous which allows the cap to pop loose when trying to tighten. 

Glycol Tank Threads

Also the very top of the tank is not flat which results in the rubber gasket contacting the top of the tank but it still has a gap on one side.  Without being able to tighten the cap enough to compress the rubber to make up the gap, the cap does not seal.

Here is simple solution which can be installed without removal of the tank.

Install a 3” stainless steel hose clamp on the tank opening/threads as shown:

3” Hose Clamp Installed

Only tighten until the clamp will not rotate by hand on the tank threads, do not over tighten. 

Install an Oatey 2” Gripper in the tank opening being careful to have the top of the tank opening roughly in the middle of the rubber expandable surface while tightening the wing nut to expand the rubber and seal on the top edge of the tank.

Oatey 2” Gripper

Positioning Of Gripper to Seal

To get an air tight seal, I had to tighten the wing nut about ¾ turns after it has some resistance.  Apparently this is because the gripper has to force the top of the tank to be actually round and seal on the gripper, which it is not actually round.  If you are not after a perfect air tight seal in an attempt to make a closed glycol system, the additional ¾ turn is not really necessary.   I would still install the 3” stainless steel hose clamp since the purpose of the clamp is to reinforce the top of the tank and hopefully prevent the force from the gripper causing damage to the tank.

If you are looking for an air tight seal to convert the glycol system to a closed system, there is another problem that needs to be addressed.  The vent and overflow tubing connection to the tank are made with a metal insert inside the tubing as it enters the tank. 

Oatey Gripper as Cap

These don’t make an air tight seal, especially as the tubing gets hard where it enters the tank.  Even with new tubing, it will leak if the tubing is pulled to the side in any way.

To remove the tubing with the metal inserts, you must twist it as you push it into the tank since the metal inserts are larger on the inside of the tank.

Metal Tubing Inserts

 Both holes in the tank are right at 5/16 “ so a 1/4” or 5/16” tubing bulkhead fitting can be used to provide a tubing connection that can be made air tight.

Bulkhead Tubing Fitting – note added large rubber gasket

 The overflow is the lowest connection and is right at a point where the tank curves from vertical to horizontal, hence challenging for the fitting to make a good seal.

OVERFLOW

 

 The vent connection is located on the horizontal top of the tank and provides a good seal for the bulkhead fitting.

Vent

Fitting Inserted into Overflow Hole (note tape on tank threads in old attempt to seal cap)

Fitting Installed – Note - Not Ideal Nut Contact & Fitting Angles Upward Due to Tank

If converting to a closed glycol system, both vent and overflow connection would not be needed.  The overflow would be the best connection to route to an expansion reservoir located below the level of the fill cap and the vent could just be plugged.  Bonding to the HDPE glycol tank is very difficult for epoxy, silicones, sealants, etc other than plastic welding which could be performed with a solder iron if you are capable of this type of process.  There are some products claiming to work on HPDE, but I have no experience with them. That’s why I describe bolted type connections below.

The vent could be plugged with a nut, bolt and sealing washer. Another option is to use a 5/16” counter sunk bolt, washer and nut to make a metal to HDPE seal since the HDPE is soft and would seal against the counter sunk bolt face. If you desire to keep the vent and drain connections, simply use two bulkhead fittings on the tank and the vent tubing line could be plugged at any time in the future to convert to a closed system later.

Sorry for this being so long.

Bayliss

Interesting read, @grassgd.  I appreciate all the photos and details on how you addressed the concerns you encountered.  You gave a thorough and thoughtful description of your approach to the problem.  Thanks!