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Zeitgeist 13
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Joined: March 05, 2009
Posts: 12115
Location: Port Manteau
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 Posted: Thu Jul 09, 2020 5:29 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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The only stress an aluminum tank causes is the kind felt by your bank account.
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?Waldo?
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Joined: February 22, 2006
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| Posted: Thu Jul 09, 2020 6:01 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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| Marital stress? |
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ALIKA T3
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Joined: July 30, 2009
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Location: Honolulu,Hawaii and France
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| Posted: Thu Jul 09, 2020 6:31 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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I`m no engineer, I didn`t take physics or chemistry classes besides the main ones taught at high school but common sense would tell me rubber would expand at a greater rate than the plastic tank no matter what, it`s not like it`s equal. For the tank to expand, you would have to reach the expansion limit of the rubber hoses first since they are quite different material.
Next subject! 
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vanis13
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Joined: August 15, 2010
Posts: 3097
Location: ABQ NM USA.... Except when not
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| Posted: Thu Jul 09, 2020 7:40 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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| ALIKA T3 wrote: |
I`m no engineer, I didn`t take physics or chemistry classes besides the main ones taught at high school....
Next subject! |
Next subject is Home Economics...please be quiet and no rough housing in the hall on the way there 
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vwhammer
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Joined: May 20, 2006
Posts: 998
Location: Boulder CO.
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| Posted: Thu Jul 09, 2020 8:16 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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I am also technically not an engineer but my major in college was mechanical engineering and I did take physics classes and what not.
The pressure acting on the mostly curved walls of the plastic expansion tank is much less likely to distort any part of that tank unless it is trying to blow it up like a balloon.
This is not likely at the pressure levels we are dealing with in a typical cooling system.
Whereas with the rectangular expansion tank it's a lot more likely to see deflection or expansion in the middle of each panel than near the corners.
This is primarily why you don't see a whole lot of square or rectangular air pressure vessels.
That uneven deflection can lead to fatigue at weld joints and such resulting in a rupture.
Anyway I call bs on the theory in the original post.
The only way I will buy that is if a VW engineer jumps on here and tells me otherwise.
As has been stated, there are many other parts of the cooling system that would expand well before any expansion tank.
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dobryan
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jimf909 
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Joined: April 03, 2014
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| Posted: Thu Jul 09, 2020 8:42 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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| djkeev wrote: |
Your mechanic means well I’m sure, but he is just another example of the overall caliber of workers in the auto repair field today.
Kids really need a better grasp of physics and general knowledge today.
Dave |
Funny. My guess was that this mechanic was older than 50. Perhaps at some point when he was younger and the plastic tanks were introduced a creative tech rep was hearing objections about "plastics being the downfall to us all" from a then old dude (now 100 years old) and the rep pulled out the "magic of plastics is they expand and relieve the rest of the system from stress" and the kid bought it and has been saying that for decades.
@oceanair, thanks for bringing this here even if it's been challenged. Lots of ideas. I'm sure a plastic chamber can be made to change not at all under 15 psi or more than any sort of hoses and components depending on design criteria.
The idea of changing the tank AND all of the hoses on a maintenance schedule seems wasteful. I'll rely on lifetime durability of my tank and replace the hoses regardless every so often.
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MayorMcCheese
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Joined: October 07, 2009
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Location: Lancaster PA
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| Posted: Fri Jul 10, 2020 2:11 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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Abscate
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| Posted: Fri Jul 10, 2020 2:47 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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ThatAl tank is crazy over-engineered
There must be a million aftermarket tanks that could be adapted to this application. Ok, a million is probably hyperbole.
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Jake de Villiers
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oceanair
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| Posted: Fri Jul 10, 2020 8:07 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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| Quote: |
This is primarily why you don't see a whole lot of square or rectangular air pressure vessels.
That uneven deflection can lead to fatigue at weld joints and such resulting in a rupture. |
Is this a cause for long term service?
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vwhammer
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| Posted: Fri Jul 10, 2020 8:17 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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| oceanair wrote: |
| Quote: |
This is primarily why you don't see a whole lot of square or rectangular air pressure vessels.
That uneven deflection can lead to fatigue at weld joints and such resulting in a rupture. |
Is this a cause for long term service? |
If your asking if the RMW tank might be failure prone I am definitely not suggesting that.
At these pressures and with the right material thickness and proper welds I don't see a problem.
If it were fluctuating between 75-100psi and atmosphere I would be more concerned.
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jlrftype7
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Joined: July 24, 2018
Posts: 3580
Location: Chicago
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| Posted: Fri Jul 10, 2020 9:27 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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| Jake de Villiers wrote: |
| MarkWard wrote: |
I'd be more concerned about the dissimilar metals and electrolysis through the coolant. |
Bad Mark, bad!   |
Ohh, I see what he did there, Missed that the first time I read it... 
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fxr
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| Posted: Fri Jul 10, 2020 5:30 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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| oceanair wrote: |
Thoughts? |
Utter bollocks. As others have noted, the pressure cap releases at the same pressure - there cannot be any extra stress on the hoses.
A worrying lack of logic from a mechanic...
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ALIKA T3
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| Posted: Sun Jul 12, 2020 1:06 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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| fxr wrote: |
| oceanair wrote: |
Thoughts? |
Utter bollocks. As others have noted, the pressure cap releases at the same pressure - there cannot be any extra stress on the hoses.
A worrying lack of logic from a mechanic... |
Far too common!
I’ve been fixing an SVX swap for a customer here in Hi, done by the previous owner, a mechanic with his own business on the mainland, no recovery tank. LOL! it was just pissing off from the Golf/Jetta expansion tank cap pressure relief valve ( the same as Vanagon but no nipple), Vanagon expansion tank
His explanation was that there are not any recovery tanks on the SVX ( oh yeah?  )
It’s physics, fluid expands when hot, pressure gotta go somewhere and the volume of coolant in the Vanagon is much bigger!.... well, not surprising when I saw the level of bodge of everything else on this van.
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kevin77westy
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| Posted: Fri Jul 17, 2020 5:32 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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Hogwash. I'm chugging the cool aid! Installed this little beauty today.
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khughes
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Joined: July 13, 2013
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Location: Phoenix AZ
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| Posted: Sat Jul 18, 2020 11:26 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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| ?Waldo? wrote: |
The max pressure of 14-15psi is what the entire system will see once the engine reaches normal operating temperature and the entire system is designed to withstand that maximum pressure for an indefinite period of time.
It is impossible for the aluminum tank to cause additional stress on other components in the system vs. a plastic tank because the material of the expansion tank is neither what is creating the stress, nor is it what is regulating the stress on the entire system. |
The easy way (IMO) to understand it is that the only thing that the minute expansion of the tank can accomplish is to increase the system volume. So that tiny expansion would decrease the overall system pressure (infinitesimally) only as long as it takes for system pressure to stabilize - it's a dynamic system as ?Waldo? describes. And as soon as the expansion stops - which it obviously does as the pressure and temperature stabilize (controlled by the cap vent as well), then it becomes a fixed volume again (as the aluminum tank mostly is) until you stop running and it cools down.
What the mechanic said could only make sense in a static pressurized system, and then only in the context of how much air/water volume it would take to reach failure of the expandable components, never in dynamically pressure controlled system like we're talking about.
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Wildthings
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| Posted: Sat Jul 18, 2020 5:14 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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When recovery tanks were first being added to cooling systems I remember hearing that because the top tanks of the radiators no longer had an air pocket the there were increased pressure spikes in the cooling system that could harm the radiator causing it to leak. This actually seemed plausible, but I don't think I ever actually noticed any increase in failures, in fact if anything the opposite happened, failures went down. Even when I added coolant recovery tanks to earlier vehicles, which I did to quiet a few rig of various natures, I did not see an increased failure rate for cooling system parts. I will admit that I often dropped the cap pressure at the same time I added the recovery tank though in an effort to protect old radiators and other aging cooling system components.
All that said, getting rig of the OEM style pressure cap is for me a real plus as it is known to fail and allow the cooling system pressure to climb above the design pressure. I really like being able to waltz in to any autoparts and buy a new cap if I think I need one. I have RMW aluminium tanks on both of my Vanagons, one a 83 1/2 with a 2.1L cooling system and the other a 91 with a 2.2 Subaru. |
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khughes
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| Posted: Sat Jul 18, 2020 10:39 pm Post subject: Re: Got a lesson about aluminum expansion tanks |
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| Wildthings wrote: |
When recovery tanks were first being added to cooling systems I remember hearing that because the top tanks of the radiators no longer had an air pocket the there were increased pressure spikes in the cooling system that could harm the radiator causing it to leak. This actually seemed plausible, but I don't think I ever actually noticed any increase in failures, in fact if anything the opposite happened, failures went down. Even when I added coolant recovery tanks to earlier vehicles, which I did to quiet a few rig of various natures, I did not see an increased failure rate for cooling system parts. I will admit that I often dropped the cap pressure at the same time I added the recovery tank though in an effort to protect old radiators and other aging cooling system components.
All that said, getting rig of the OEM style pressure cap is for me a real plus as it is known to fail and allow the cooling system pressure to climb above the design pressure. I really like being able to waltz in to any autoparts and buy a new cap if I think I need one. I have RMW aluminium tanks on both of my Vanagons, one a 83 1/2 with a 2.1L cooling system and the other a 91 with a 2.2 Subaru. |
Actually, with air in the system the pressure will be higher than if it's purged and all liquid. For any given temperature, the pressure will be the sum of the partial pressure of the liquid, and the partial pressure of the air. Seems odd, but it's easily seen in heat sterilization of liquid filled containers (something I've done for decades).
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Wildthings
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| Posted: Sun Jul 19, 2020 5:13 am Post subject: Re: Got a lesson about aluminum expansion tanks |
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| khughes wrote: |
| Wildthings wrote: |
When recovery tanks were first being added to cooling systems I remember hearing that because the top tanks of the radiators no longer had an air pocket the there were increased pressure spikes in the cooling system that could harm the radiator causing it to leak. This actually seemed plausible, but I don't think I ever actually noticed any increase in failures, in fact if anything the opposite happened, failures went down. Even when I added coolant recovery tanks to earlier vehicles, which I did to quiet a few rig of various natures, I did not see an increased failure rate for cooling system parts. I will admit that I often dropped the cap pressure at the same time I added the recovery tank though in an effort to protect old radiators and other aging cooling system components.
All that said, getting rig of the OEM style pressure cap is for me a real plus as it is known to fail and allow the cooling system pressure to climb above the design pressure. I really like being able to waltz in to any autoparts and buy a new cap if I think I need one. I have RMW aluminium tanks on both of my Vanagons, one a 83 1/2 with a 2.1L cooling system and the other a 91 with a 2.2 Subaru. |
Actually, with air in the system the pressure will be higher than if it's purged and all liquid. For any given temperature, the pressure will be the sum of the partial pressure of the liquid, and the partial pressure of the air. Seems odd, but it's easily seen in heat sterilization of liquid filled containers (something I've done for decades). |
The pressure cap will take care of what you are talking about, what the pressure cap may not be able to handle is shock waves running through the system, a hydraulic system with a 15 psi relief valve may momentarily actually see pressures many times the pressure of the relief if there is nothing to absorb the pressure spikes. As I said I never noticed any actual problem with this on an automotive cooling system. |
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