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P80 Fuel tank - what type of plastic? [HDPE with Nylon additive] Topic is solved

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
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BlackBart
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Re: P80 Fuel tank - what type of plastic? [HDPE with Nylon additive]

Post by BlackBart » Tue Aug 27, 2019 10:41 am

ex-1984 245T wagon
1994 850T wagon
2004 XC70 wagon BlackBetty
Is it time for a 1964 122 wagon?

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matthew1
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Re: P80 Fuel tank - what type of plastic? [HDPE with Nylon additive]

Post by matthew1 » Fri Dec 20, 2019 12:55 pm

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1997 850 T5, MSD ignition coil, Hallman manual boost controller, injectors, R bumper, OMP strut brace [gone]
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Re: P80 Fuel tank - what type of plastic? [HDPE with Nylon additive]

Post by BlackBart » Thu Jan 02, 2020 11:42 am

Matt - sorry I didn't wrap this up very thoroughly! Here's some more info and pics on the steps I did.

I followed a good guide to tank removal, intended for replacing the hoses on top of the tank. The handiest part of it was jumping the fuel pump to empty the tank....

"Next drain the fuel tank to lighten it for removal. This can be done by siphoning, but since I had to get to the pump, it is easier to use the pump itself to push gas out through a length of 1/4″ ID tubing."

"First you depressurize the line by running the engine with the fuel pump relay (103) pulled. Then pull the yellow striped hose fitting up and off."

"Then connect the tubing and then hard-wire the fuel pump to run by bridging these two terminals of the relay with some needle nose pliers or something."

"Ignition needs to be switched on with a key to run the pump. Jump the pump until it starts to go dry (foam coming out).
Once the tank is empty, the four cables on top of fuel tank (fuel pump, pressure sensor, level sensor and something else) must be disconnected."

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850 - jump fuel pump.jpeg
850 - jump fuel pump.jpeg (84.46 KiB) Viewed 36 times
Last edited by BlackBart on Thu Jan 02, 2020 12:11 pm, edited 1 time in total.
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Is it time for a 1964 122 wagon?

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Re: P80 Fuel tank - what type of plastic? [HDPE with Nylon additive]

Post by BlackBart » Thu Jan 02, 2020 11:48 am

Frame is supported on jack stands, far enough apart and away from the tank so you can maneuver.
Disconnect the wire retainer that holds the rubber filler neck into the sheet metal.
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Unbolt the straps holding the tank up. I should probably have undone both front and back to make it easier. I just dropped the rear of the straps. The tank is not completely empty now, so be wary. There is a sump in the bottom that holds some fuel. But it was surprisingly light.

Support the tank with a flat board on a floor jack, wiggle the hoses at the front, and the straps, and the filler neck, and wrestle it down to the floor. Be cautious of old and brittle fittings and hoses. Here is the tiny one that broke - it was due and good thing I didn't put it back on with a slight crack.
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This plastic strap holds a group of hoses and wiring coming from the front of the car. Work it open with a flat blade and move the hoses out of the way.
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Is it time for a 1964 122 wagon?

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Re: P80 Fuel tank - what type of plastic? [HDPE with Nylon additive]

Post by BlackBart » Thu Jan 02, 2020 12:00 pm

The famous heat shield. It's on the left side of the car looking forward, shields against the heat of the tailpipe passing by. The fittings on the plastic tank for this shield are what leaks.
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I carefully drained the tank completely (there is a check flap in the bottom of the filler neck, so it doesn't just run out), and filled it with water to test. Here's the leak. You can just see a crack around the hub of this thing. It dripped surprisingly fast, at about 6 gallons. All other fittings remained dry.
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I acquired some HDPE plastic scrap from a local fabricator. You can buy little round and triangular rods as well, but only in pretty big quantities. I cut it into very thin strips.
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This is the tool I bought from Harbor Fright. It is not a very good tool. It is the second one I got - the first failed in 10 minutes. The second had been out of the box and was dirty - no doubt returned by someone. But I will use it once, and it was fine. There are videos on plastic welding, which were helpful.
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You heat the underlying plastic, and the "rod," stick the end of the rod, and slowly roll it down flat against the tank with the heat on the underside of the rod. The tank is relatively thin, don't hover in one spot and melt a hole in it.
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I'm not skilled at this, and this looks like a mess, but it is a patch over the cracks, and then a layer on top of that to encase it. It goes clear when hot, then cools back to white. Use heavy gloves, and long needle nose pliers and screwdrivers to handle it. Stay AWAY from that nozzle.
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Search Keywords - weld a plastic fuel tank, cracked plastic fuel tank, leaking fuel tank.
Last edited by BlackBart on Thu Jan 02, 2020 12:23 pm, edited 2 times in total.
ex-1984 245T wagon
1994 850T wagon
2004 XC70 wagon BlackBetty
Is it time for a 1964 122 wagon?

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Re: P80 Fuel tank - what type of plastic? [HDPE with Nylon additive]

Post by BlackBart » Thu Jan 02, 2020 12:10 pm

I filled it up with water again after cooling, and it sat for several hours to make sure it didn't drop any.
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Drain all the water and DRY THE TANK. It's black - I left it out in the sun for a few hours.


This is that little rubber hose that links a hard line to the pump. Different diameter at each end - buy the Volvo part!
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Lift the tank back up, wrestle it into the filler hole and straps, route your hoses through the strap, fight with the metal tank straps, and wiggle it up into place. Snap that wire c-clip into the rubber groove at the filler neck. I used a bit of vaseline to work it onto the sheet metal - mistake! Kept popping loose. Just work it onto the sheet metal lip by hand or with a dull trim tool so you don't cut it.
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I marked the inlet pipes so I got the connectors back in the right spots.
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Reconnect everything, check your hoses and electrical connections, replace the pump fuse, button up the lids.

Back to normal! No leaks!
IMG_4496.JPG
ex-1984 245T wagon
1994 850T wagon
2004 XC70 wagon BlackBetty
Is it time for a 1964 122 wagon?

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Re: Fuel tank - what type of plastic?

Post by erikv11 » Thu Jan 02, 2020 12:25 pm

BlackBart wrote:
Mon Aug 26, 2019 9:55 pm
No bushings that I can see yet. I’ve had it since 60k miles. It did start it’s life in Dallas, so....
Not putting the heat shield back on those bolts - I’ll figure out an alternative.
...
What did you end up doing about this? Looks like the shield is back on in your photos.
'95 854 T5-R, Motronic 4.4, 185k
'96 855 NA, 145k
'98 S70 NA, 220k (living out west)
'98 V70, T5 tune-injectors-turbo, LPT engine, 285k
'06 S60 R, 165k
'99 Camry V6 :shock: 125k
gone: '96 NA 850 210k, '98 NA V70 182k

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Re: P80 Fuel tank - what type of plastic? [HDPE with Nylon additive]

Post by BlackBart » Thu Jan 02, 2020 12:51 pm

It seemed very solid, and I wasn't sure how to build a bracket to hang it off the tailpipe, so I screwed it back on. Seems fine. The factory tank has thicker bosses where those plug mounts are melted in. It's not molded in one piece. It looks like they maybe missed in a couple of places, or the heat stress of melting and pushing them in and cooling caused the cracks. The crack went around the plug, not radially out.
ex-1984 245T wagon
1994 850T wagon
2004 XC70 wagon BlackBetty
Is it time for a 1964 122 wagon?

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