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Marathon H Air Tank
My Marathon has it’s own 3 gallon air tank independent of the Prevost aux air for the purpose of supplying air to the various Marathon options like pocket doors, gen air bags, etc. This tank is supplied by the aux compressor as long as the valve in the steering bay is in the correct position. I drain this small tank often to keep the supply free of moisture because when I bought the bus it had water and rust in the tank. When I got the bus home, I flushed the tank best I could without removing and over the next 8,000 miles I would get a little water from the compressor as normal. I found a small air leak on the drain discharge and pulled the tank to sort it all out.
Bottom line, is if you have one of these, take it out and throw it away! I started cleaning the tank out and found nothing but rust. The tank has deteriorated inside to the point it’s junk. Hooked up the garden hose just to see how bad it was and after 4 full flushes looking like chocolate, the rust just keeps coming. I’m replacing with aluminum. Nothing upstream was harmed, I’ve had many pocket door fittings apart, the gunk was all on the bottom of the tank.
Another good example of draining your air tanks, you HAVE to drain them completely and let out all the air. When you crack the petcocks your just blowing past the water and crud.
This was after 4 full 3 gallon rinse flushes.
This will be the replacement.
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38 Replies
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Where was this mounted in the bus?
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On
my H, it’s in the 1st bay, curb side behind a panel with the 2
cruiseairs and gen radiator. In my steering bay there is a yellow air
cutoff valve that combines the aux air with the Marathon air. Mine
originally had a separate 12v compressor just for the Marathon air,
but it is removed using just the aux air compressor for both systems.
As originally setup from the factory, you could turn the yellow valve
and isolate the two air systems. The Marathon would run off the 12v
compressor and the aux air off the aux compressor. -
Are you going back to the factory setup ?
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Yes George, I will be putting a new 12v compressor back inline.
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Tom
Please give us the scoop on the new tank. Brand, model, where you got it, etc.
Thanks!
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Grizz,
I haven’t received it yet, but ordered on e-bay here: Tank
Actually I’m considering eliminating the tank all together. I have a perfect source of clean dry air from the aux tank, so not sure this other small tank is worth all the aggravation. I could eliminate the tank and the 12v compressor I was thinking about re-installing. Most of the previous buses I’ve owned used the aux air for all the accessories. It would be a 2 minute fix, just connect the 2 lines with a coupler instead of going through an air tank. Volume of air isn’t a factor for the accessories, most are 40psi regulated.
Anyone have any thoughts on that?
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Tom:
If you would, please let us know how the new tank worked out as a replacement for the original. I haven’t checked mine yet, but since its a 2001 Model Marathon, its probably is due for a replacement. It can’t hurt to change it out as a preventative maintenance operation.
On your thought of eliminating the tank and related compressor: I’m thinking if the coach has HWH automatic level system and/or if AUX air bleeds down some when parked for a few days, etc. it might be missed under some conditions.
I wouldn’t eliminate it in my coach. My opinion: if it wasn’t needed Marathon wouldn’t have spent the money installing it.
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I know big Al has discovered the same problem with his tank. You have a good point, with HWH leveling, the volume may be needed for air bag leveling while parked. Other than that, I see no reason for the added complexity to run various 40 psi accessories.
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Tom told me about his rust water in the aux tank . With a rattle located in the same area as the Aux tank access ….get the toolbox
Pancake style tank was flushed at Marathon after finding a plugged drain. Now we’ll give it more attention.
Drain was plugged again so in order to get at the tank, remove driver front fender. Next a weather
panel. With access now to this 4 gallon tank pretty straight forward to remove. With tank out I can hear water and something loose inside.
Located a tank at Grainger late today. With some isopropyl alcohol to flush lines this should be much better.
Tank was dated mfg9-98.
Truk4u….As to removal / bypass your tank I would keep tank as installed by Marathon. Prevost clean air will not be refillable unless
engine runs. I’am with Grizz on this one.
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What vintage buses are we talking about that have this setup guys?
Do we know?
Later
bv -
That is incorrect. When the engine is off, your air is coming from your Prevost aux air and compressor. The Marathon added air tank is nothing more than additional air capacity.
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Just so everyone is clear, in most cases aux air as supplied by a converter installed air compressor is usually inadequate for coach leveling with the engine off.
As stated above house air pressure needs are usually much lower pressures than that needed to level a coach so the aux compressors are usually set for cut-in and cut-out pressures lower than typical bus aux air pressures.
The only benefit of the additional tank is for added volume which will increase the time between aux compressor operations, but which will also increase the time required for the compressor to run.
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In my coach there is a rather large AUX air compressor that keeps the air supply up when the engine isn’t running. It is mounted on the back of the generator and has ample power to keep the AUX air pressure up, level and keep level the suspension when the engine isn’t operating. It makes availalbe a supply of air for the HWH to adjust the suspension every 30 minutes as/if needed. It is plumbed directly into the AUX (green) tank in the Cruiseair compressor bay. I suppose that tank is there for additional supply, but it also functions as a primary seperator of moisture and dirt. It pre-cleans the air before it goes into the chassis aux system. As far as I know, there is only the engine compressor and this one Marathon installs. I could be wrong, but I know of no other AUX compressor installed by Prevost.
I’ll be very happy to have the Marathon AUX compressor someday should the engine or engine compressor give out. It may take a while, but it’ll air up the chassis in an emergency. I think of it as insurance!
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This
is tough, wish we were sitting under the awning….Your
aux tank came from Prevost, supply air comes from the engine
compressor to handle your suspension and engine air bag bellows. The
aux tank is typically plumbed to the steering bay from Prevost with a
line going to the Norgren filter that has the drain on the bottom.
This is the last defense for water in your system.The
Converter adds the aux compressor and in most cases, that provides
all the air needs for the chassis side as well as the Converter side.
The aux compressor has a regulator and when parked, that’s the source
of your air with the key off since the engine compressor isn’t
running. The aux air from the compressor also goes through the
Norgren filter. When the engine is running, the air pressure is high
enough so the aux compressor won’t cycle.So
you stop, turn off the key, your aux tank is full and with the aux
compressor turned on, when the air bleeds down it automatically
builds air back up to the cut-off pressure from the regulator. This
keeps all accessory air items going, but has nothing to do with the
brake air.Now,
in my case, Marathon added an air tank along with a valve that
isolates the air for the pocket doors, step slide, seat and gen air
bags. This air tank gets it’s supply from the aux compressor, the
same one that’s feeding the Prevost aux air tank only when the
Marathon valve is in the open position.So,
when I’m parked and the Marathon valve is closed, the aux compressor
feeds the Marathon tank for all the Marathon accessories. If I
have a leaky Prevost aux air system, my Prevost aux tank falls to
zero. Remember, the Marathon valve is closed. The only way to get air
back into the Prevost aux tank is to open the valve and the
compressor will now fill both the Marathon tank and the Prevost aux
tank. Or, leave the valve closed and start the engine, but that makes
no sense.Now
I have a second air tank to maintain that needs drained often because
Marathon fed this tank direct from the aux compressor and it makes
more water than Jon at 3 am. And that’s why I’m considering
eliminating the Marathon tank and using Prevost aux air, just like it
was done on my Liberty. At least then there is only one drain point
for moisture, the Norgren filter in the steering bay. And when driving, it’s getting clean dry air.That’s
my story…… But, your’s may be setup completely different. -
Tom:
I’m not contridicting your statements. My comments were about not removing the aux (Marathon installed) air compressor, and it seems you are talking about removing or not removing the Marathon installed air tank.
In my coach with HWH leveling, the Marathon installed air compressor does supply air to the Prevost aux tank when parked – engine stopped. It maintains aux air pressure constantly. The HWH system checks the coach leveling every 30 minutes and makes adjustments as needed. Obviously, without the electric (Marathon installed) compressor, the aux supply would become depleted. The compressor is mandatory (in my coach) for this reason.
In addition, should compressed air be needed in an emergency to up the suspension or release the parking brake, the Marathon compressor makes a nice backup.
Perhaps I misunderstood some of the comments to mean Prevost aux air COMPRESSOR.
However, if the green tank collects a lot of water – that’s a good thing, because it’s stopping that water from getting into the rest of the system. More frequent draining would seem (to me) like a better plan than removing.
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