I have a 08 GL320 that the wife drives. She uses it to pull a small 6x10 enclosed trailer to shows. I would guess it weights probably 2-3k lbs loaded. Anyway, it has about 245k on it now and I bought it with 207k. Right before I bought it all the air struts as well as the pump was replaced with Arnotts.. Not too long after I bought it the left rear started dropping overnight so I replaced both rear bags with Arnotts. Soon after, the pump went out. I attributed it to the air back leak and replaced it. She then started towing this trailer on occasion. No issues at first but then while she was 3 hours away she calls and says its on the ground. I drive up there and find the pump not running. Fuse blown. I replace it and it pumps back up. Soon that pump then goes out. I replace it again along with the valve block just to be sure. By this point everything in the system is pretty much brand new except the front struts which were replaced right before I bought it. Wife towed the trailer a few more times and guess what, pump goes out again sounding like its full of rocks. I replaced it for the 3rd time since I have owned it and the thing has been driven a little bit, but has been sitting in the driveway with the trailer attached to it for at least a couple of weeks and has not dropped an inch. No leaks anywhere. If it had leaks it would not stay at the proper height for weeks at a time.



Wife towed the trailer maybe 100 miles since the last replacement, then another few trips to town in the last couple of days. Yesterday she drove it 3 hours to a show and just called to say the truck is on the ground again. WTF? I told her to check the fuse when she can and get a replacement if blown, but who knows if this pump will be bad like the rest have been. It seems fine until you start pulling a small trailer with it. My assumption would be it has a leak, causing pump to run too long which blows the fuse, but as mentioned it stays up for weeks, no leaks. Perhaps there is a wire shorting to the pump, but again, how would that cause the pump itself to go bad? Are Arnott pumps just junk now days? What am I missing?

The relays contacts are known to fuse together its 40 amp current. I've also seen an extremely small hole in the line between the valve block and the reservoir which would only open up in colder temperatures. That's all I know.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

The relay has been replaced with each compressor replacement. Its possible it has some sort of small or intermittent leak to the central reservoir.

The system is a piece of crap. Owned an ‘08 GL450 and that system was nothing but trouble. Would never use that vehicle to tow even a bicycle rack. Just my own personal experience.

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Greg

Current
2005 E320 CDI (50k) W211 with OM648
1999 E300D Turbo (133k) W210 with OM606.962
1997 E300D NA (170k) W210 with OM606.912
1991 300D 2.5 Turbo (199k) W124 with OM602
1990 300D 2.5 Turbo (170k) W124 with OM602

My sister had a GL and the air suspension is the only problem she's ever had with it.

but it is a BIG problem

the third pump finally fixed it but who knows for how long

the other two would worked for a while then start sounding like a bearing was bad
or gravel in coffee can.

That is exactly the problem I was having with the bearing in a coffee can sound. Were they all Arnott pumps? Maybe they are having a bad run of them or something.

If you are frying pumps that quick, you need to check voltage drops when the pump is running, a semi bad grounding can cause the pump to fail. I had a BMW E39 wagon brought to me to fix a similar issue, its big power connector to the pump was not making good contact. A good cleanup and deoxit made it perfect again.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Disconnect the connector at the pump and inspect the female sockets CLOSELY! If there are ANY signs of discoloration replace the sockets. I'm betting there will be a noticeable difference between the two. These are readily available from your dealer. FWIW I've seen this many times.....

That is good info and not something I even considered. I will check it out.