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Hairline crack in fuel tank at hose bib joint

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Hairline crack in fuel tank at hose bib joint

Post by pbierre »

This first appeared 4 months ago as a P0456 EVAP System Leak. There were also P0442 EVAP System Small Leak, and the "Missing or Damaged Gas Cap" alert on the console. When I filled the gas tank 100%, raw gas drips came down, about 1 drop (25 uL) every 30 seconds, coming from rear of tank on passenger side. When the fill level worked down to 7/8, the drips stopped, but the DTCs continued.

The drip behavior indicated that the leak must be high up on the fuel tank / hose system on passenger side.

I went under the car, looking for the telltale "gunk" trail. I found gunk where the filler vent hose attaches to the tank hose bib, but this had me erroneously conclude the hose clamp had gone "lazy". No improvement after replacing hose clamp.

I next removed the rear seats to inspect the fuel pump seal, which is 3" right above the filler hose bibs. It looked clean. So, with mounting frustration, and the seats removed giving a slim view of the top of the tank, I took it to an indie shop for a fuel system pressure smoke test. They reported back "smoke leaking from top of tank", which was too vague to be actionable. (They quoted me 8 hours labor to replace the tank + $1400 parts). The tech who did the smoke test forgot to remove a plug stopper he had put over the EVAP Vent Air-Filter during the test, so when I went to refuel, I couldn't pump any gas in. I knew enough to check for this test plug, and went back to the indie demanding a retest at their expense, this time pinpointing the leak location.

The 2nd smoke test showed that there was a hairline crack in the joint between the blue plastic vent hose bib and the tank body. Who would have thought?....altho I've now seen this specific failure mentioned on the Brickboard. I consulted two other Volvo shops, and they gave the same advisory..."we can only replace the fuel tank...$3200".

Long story short, I started researching plastic welding and decided to try saving this ice white '04 XC70 that way.

I went to the piknpull, and sawed off a 6" x 6" piece of fuel tank from the same MY, thus assuring a compatible plastic to make a weld patch. A cut out a donut shaped patch that would just slide over the hose bib and cover the original weld joint. I thinned my patch to about 2mm for good melting. I used the Chicago Electric 80W Plastic Welding Iron, which I judged safely underpowered...no risk of burning through the fuel tank by accident. I popped the hose off to slide on the patch donut, then put the hose back on to isolate the welding work from open gas tank / fumes. The welding was messy, and the blue hose bib plastic did not blend easily with the black patch, but the patch welded nicely to the tank body.

With this inexpensive repair, the EVAP codes have stopped. The weld seems to have done the trick.

Total cost: $140 for smoke test
$95 at Volvo dealer to clear the SRS "airbag urgent service needed" code, thrown driving with seats removed
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Re: Hairline crack in fuel tank at hose bib joint

Post by abscate »

Please tell us you took some pictures and let's post them up

Awesome repair and saved car

$3200 buck repair from dealer, seriously?
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