Low Pressure Fuel pump leaks / tank diesel leaks. Cracked pumps.


Two High Roof 118s
I've had an ongoing problem with leaks from my tank since buying one of my 2006 T1N 118"s. This one had about 240k on it at purchase.

Driving it home from LA to SF I noticed it would leak some diesel with the tank full. I would be doing the RV build on it for many months so I just kept it half full and it wasn't a problem.
Once the build was near done I dropped the tank to see what the problem was.
The fuel pump was simply loose, completely slack. I tightened it, reinstalled the tank, and the leak stopped.
One suspicious thing that happened, only once, was that I got a little "puff" of pressure out of the tank when I removed the fuel cap to fuel up.
I noted this, considered that there might be a valve falling in the tank, but I never noticed it happen again. I probably filled the tank 3 times before I started renting this van out, (and starting work on my second van) so I would not expect renters to report back such a minor thing. Anyway, about 15k - 20k miles and 10 months go by with no troubles.

I got interested in cleaning my fuel system and preserving my injectors so I bought some Opti-Lube Summer Cetane and had the next renter put 1-2 oz of it in per tank. Not saying this is the culprit, it could be unrelated, but it's worth noting because about 500 miles later my real troubles begin:

I get a call that there's diesel leaking from the tank, especially while it's full. Not being full seems to help the problem a lot, if not eliminate the problem. We take it in for service in Bend Oregon. Over the phone they tell me that sometimes these old Sprinter tanks "swell" and you can't get the pump to screw back on, then you need a whole new tank. They drop the tank. They suspect a failing low-pressure pump gasket (the big one at the fuel tank) and replace some fuel lines in the area for good measure. The pump screws back on, so they don't recommend a new tank. I got the feeling they didn't quite find a smoking gun, but anyways this fixes the problem for about ~6 weeks and ~4k miles.

Then it comes back from a rental and I detect a little leakage after I top off the fuel (essentially overfilling it, renter had it full enough). Found this problem around 10pm with a new renter picking it up at 9am so I advise the renters to fill it no more than 7/8 tank and keep an eye on it. Works fine that way, no leaking while parked, no smell, puts on about 3k miles with lots of elevation change out to Salt Lake, Tetons, Badlands, and finally Chicago. In Chicago, it sits for a few days, they start it and find diesel dripping fast out under where the tank, where the low-pressure fuel pump is. We take it in to another mechanic. Over the phone I ask that whatever it needs, it should get, I'd like to fix the root cause. I tell them about the "puff" from the fuel tank once. I say to replace any valves that could cause problems even if they don't appear to be broken. They find the fuel pump cracked and replace it (for ~$1100). They smoke test the system and find no problems, replace only the pump, button it all back up and call me to have it picked up.

It makes it back to SF from Chicago fine, and then up and around Bend Oregon for a while, sits for a while... within FIVE miles of the original shop that changed the gasket, then starts fast leaking diesel from the front of the engine (I don't know where yet, but currently I'd guess the high-pressure pump from a photo I have) while running.
It's now in the original shop's parking lot, waiting on service.

Maybe the hoses are just at the end of their life?
Does anyone have experience with this?
Do these tanks swell and crack apart fuel pumps?
Are there pressure relief valves involved that fail and pop the pumps?
Could a fuel additive embrittle plastic and rubber so fast as to start having problems within as little as 500, or even 5,000 miles?
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Two High Roof 118s
Okay, at first I thought the 3rd leak was from the tank, I'm just getting reports from the renter. (I edited my original post to reduce confusion) Knowing now that it's probably the high-pressure pump makes me feel less frustrated with recurring tank problems. Two leaks from the tank over 10k miles seems a lot more acceptable now than three.

I'm still curious as to what could cause a fuel pump to crack and whether there are problems with swelling tanks and such and if fuel additives could "add" to the problem.


'05 Snow Camper, '17 170 4x4, Adventure Vissionary
I have fixed many of loosely screwed on (gasket not sealed) low p fuel pumps.. and now have a com-back leak when I know the gasket is properly sealed. Or at least I know the pump is screwed on nice and tight.

I have not seen a low p pump crack, but sounds like the Chicagoland guys found that? did they happen to send you a pic or perhaps the pump itself with the vehicle?

Or, did they swap the gasket with new when they replaced the pump? Perhaps the gasket itself was failing?

I am interested in what actually fixed the issue... thanks for the follow up.


Two High Roof 118s

Nope, I didn't get a picture from either shop nor a dead cracked pump. Good idea though, I'll consider asking for such things in the future. Always a balance between stepping on their toes and letting them know you'd rather not be taken advantage of.

What fixed it?
Sounds like either re-tightening/new hoses / new gasket or some combination did fix the original issue. And a new pump fixed the second issue. I wouldn't be surprised if the first shop's work left a hose straining on the pump or something, thus causing it to crack, but I'm just making up wild guesses.

Why do you think these things loosen up? Is this something I'll need to do every 20k or something? I'd consider wiring it in or some type of epoxy fixation to avoid that job in the future!

The third issue was just loose screws in the high-pressure pump. I fixed that from 2am to 7am in the shop parking lot and was ALMOST out of there before opening.
After the ~500mile drive home I smelled/found still another leak. Imagine my relief when I traced it from the drain hose that seems to come from the back of the injector enclosure on top of the head. This leak seems to have been at the steel lines feeding each injector. (front 3 loose(ish), rear 2 tight) Have tightened them and awaiting some harder and longer testing than idling in my driveway to confirm.


'05 Snow Camper, '17 170 4x4, Adventure Vissionary
I get the balance; nothing worse than approaching somebody who knows wtf they are doing and throwing out that some guy on a forum said XYZ... but, there is something to be said for having some knowledge going into a conversation.

if i was to take a bet on what was going on.. gasket.. again! and i just dropped the fing tank again on this guys rig and tightened the gasket so will see.

service interval? nah....... if it leaks, it needs to be fixed!

yes ..... hpfp back bolts need servicing (i red lactate :).. along with replacing o ring separating the hpfp from the head (a very common oil leak)..

if you have diesel coming out of the tube out the back of the injector galley there are a few culprits

we are neighbors i believe.. hit me up if you would like! i bee busy... but like your biz

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