heyadamhey

I've read this how-to guide and don't fancy taking that on because I think it's excessive in my situation. The reason I want to do this, is that I just took delivery of an '87 S4 that's been sitting for several years and the fuel is bad. Smells like varnish.
I want to make sure that the tank is free of any old fuel and any sludge that may have formed i.e. as clean as possible. I'll drain the fuel as described in Step 5 in the above guide and then use a boroscope to look inside via the filler opening.
I was told there could be "congealed ethanol" at the bottom. Would it be safe to use something like acetone to dissolve this and then repeat the above drain process?

Alternatively, is there a better way to do this?

Thanks in advance

Andrew Schauer

If "several years" is around three, I'd drain everything you can from the tank, check for any obvious issues inside with your 'scope, fill the tank and drive it. Add some quality injector cleaner for a few tanks and you'll be just fine. If several years is 10 years, you'll probably want to go a bit farther.

Shirah

If you carefully remove the level gauge sender (in the back) wouldn't you have a 2 to 3" diameter
hole to suck up the old fuel (using a manual suction pump, of course)?
That's how I would do it if I had to.

Speedtoys

Dude...why

Remove the in tank sock/filter, and replace it. Then you can drain the tank and rinse it out easily.

Shirah

OK, OK. I thought I read he didn't want to do it the normal way ..........
That's what happens when I take my meds after work, instead of with breakfast

Rob Edwards

I'd drain the tank, put a clamp on the rubber outlet hose, put rubber plugs on the filler neck and top vent, pour a gallon (or two) of lacquer thinner in the tank, installed the fuel level sender, rent a pickup truck, strap the tank down on some soft supports in the bed, and drive around in stop-start traffic for a week. I recently rescued the bottom of a fuel level sender that had a half inch of gluey varnish on it. Sender cap + lacquer thinner in a glass spaghetti sauce jar dissolved the varnish in a week of soaking. Agitation (hence the pickup truck) probably would have sped it up.

gbgastowers

If you have a baby monkey hand like me you shine a light in there and wipe up grime. Then put some acetone in there and swish it around and dump it out. Put a new screener in and don’t mess up the threads on your tank insert. They can spin in the plastic which is bad. I also did remove my tank. Probably need to replace the specially shaped hose that goes through the frame

Speedtoys

.

He needs to do it the right way...which is remove the tank, R&R the sock, R&R the vent hose...but...

Petza914

Drain it, remove it, and use a pressure washer wand inside then let it thoroughly dry

drkekar

+1 on what Petza914 said. That is what I did on mine with new strainer and breather hose.

heyadamhey

Thanks for the input everyone.
If I understand the above correctly - there is a strainer on the inside of the outlet of the tank where it feeds into the pump and filter, which should ideally be cleaned and replaced. Maybe I can get my 9-year-old to reach in there and do that (KIDDING!). My wife is quite petit though hahahah

One thing I was curious about was whether the plastic tank could safely handle something like acetone to dissolve any congealed fuel. Seems like that would be ok, but not the most thorough method.

Just thinking about it - maybe it's better to pump it out through the fuel-level-sender hole (like Shirah suggested) to suck out any crap that's in there, so it doesn't end up stuck on the strainer. "Just do it the right way!" I hear some of you thinking

I'll post a reply once I've looked in there with a scope after I've drained it.

gbgastowers

Your strainer is probably dust by now. Let us know

heyadamhey

Ok, so I went in through the fuel-level-sender opening and didn't need the scope - the torch on my phone was fine.
To my eyes, it didn't appear too bad, but I did end up getting a fair bit of gunk and dirt out. I bought a little battery-powered pump and pumped out the gas. Worked a treat!
I brushed around the inside with an extra long paint brush and there was a bit of tar-like stuff on the end
I then poured into about half a gallon of lacquer thinners and brushed around the inside with said paint brush and the thinners went from clear to brown. Drained and repeated. Then I was our of thinners, but I was satisfied that the tank itself was clean. I poured in some fresh gas and pumped that out. x3.

I did unfortunately damage the strainer with the pump, so I'll have to address that at another stage. I also realised my fuel level sender is faulty. Only reads half a tank.



Battery operated pump



Pumping out the dirty thinners




After draining the gas



Old gas.


The brush after brushing the inside, but before using the thinners



Dirty thinners



Cleaning the inside using the long paint brush



Looking good



The last bits of crud to rinse out, but I got it all

I put in 10L of gas and some fuel system cleaner. Next job is timing belt, water pump and porken tensioner, so I'm not going to be running the engine until that's all done

So all-in-all, I'm pleased with the result. For now... The sender needs replacing and that strainer does too. Those will have to wait a bit though.

Can the strainer be replaced from underneath without dropping the tank? The top access hole is way too small for my hand

Rob Edwards

Nice work!

The strainer _has_ to be replaced from underneath, it is removed using either a 36 mm socket or a 36 mm spanner. It makes access somewhat easier to remove the bolts that hold the rear two straps of the tank cradle so the cradle can be dropped down to give you a straight shot at the hex fitting on the end of the strainer:

EDIT: And you may want to find a hose clamp that you can install over the circumference of the opening that the strainer threads into- the threads are part of a metal insert that's molded into the bottom of the tank, and you don't want to cause the insert to spin within the opening, as you'll have ruined the tank (There is a repair for a spun thread insert but you want to avoid that....)

Petza914

There will be a fair amount more of that crystallized stuff under the white cap of that in tank assembly that the fuel sender resides in. The top isn't supposed to come off, but will and as long as you have it lined up well enought for the sendwr to go down through the center of it, it won't cause any issues.