Fuel tank sealer questions - PeachParts Mercedes-Benz Forum

Demothen · #1 05-19-2016, 02:39 PM

Hi all,
My '85 300D has been producing a bit of rust in the clear filter (I've put maybe 1000-1500 miles on the current filter, but when I move it I can actually see the rust sinking). I can't imagine that this is helping the engine produce power easily, and I'm not really the type of person to just deal with the effect without fixing the cause. I haven't looked in the tank recently, but from what I remember the sides looked new, so it's almost certainly rusting out around the bottom below the fuel level.

I was thinking about using POR15's fuel tank sealer, and was wondering what sort of results people have had with it? It looks like I'll need to plug the fuel screen area, the sender area, and the fill area in order to slosh the fluid around properly?

Are there any other seals, etc, I should replace while I have it out? I already have a new tank to fuel line hose that I've been meaning to install. Should I expect to have troubles cleaning the tank? It seems like I might want to use some cheaper degreaser, followed by the cleaner/degreaser and prep in the kit. I was thinking about using some threaded rod with some light chain on the end chucked into my drill to help break loose any scale at the bottom of the tank, as well as probably some nuts & bolts when cleaning it to help more. I don't THINK the tank is so far gone as to have pinholes, though apparently the sealer will help with that anyway. (Unfortunately, the you pick style yards around here like to use the forklift to pierce the tank, so getting a good used one is not likely).

I've also been having problems with my fuel sender sticking at 2/3 full lately. One of the first things I did when I bought the car a year and a half ago was to pull the sender, de-gunk it, and repair the reserve light wire. It had a bit of rust on the metal shaft that I sanded off - I suspect this is what's causing the float to stick. Now I have access to a small metal lathe, and was thinking about dismantling the sender and either using the lathe to smooth the surface again, or possibly mill a new piece. I'd think that I would want to spray some por15 on the piece to prevent it from rusting again.. That or I need to pony up the $$$ to buy a new sender...

Diesel911 · #2 05-19-2016, 03:53 PM

An internet search for Diesel Fuel Tank Sealer will likely bring up more then on product.

I would think that for all of them you would need to remove and clean the Tank according to the Sealer Makers instructions.

For sure the Tank Gauge Sending Unit needs to be removed.

The POR15 Website would likely have more detailed info on the subject.

charmalu · #3 05-20-2016, 12:45 AM

Why don`t you look around for a 300D that some guy is parting out?
Probably pick up the tank for less than $50. Maybe less if you pull it.

I seen tanks on CL and E-Bay listed for around $150 which is crazy.
You can pick up a whole car for $300 or more.

I lucked out and actually found one in PNP they forgot to poke holes in.

That is impossible to find for sure. Think I paid $39 and got the sender too.
And then later bought on from a forum member for $40 - $50, don`t remember.

The fuel tanks are 21 gallons except for the 80- 83 240D which is 17 gallons.

Charlie

tjts1 · #4 05-20-2016, 12:59 AM

How is the moisture getting in to cause rust? Is this indicative of a faulty vent valve?

Sugar Bear · #5 05-20-2016, 08:26 AM

Is it definitely rust and not algae/fungus?

If it is rust, it could be the fuel line from the tank to the injection pump instead of the tank. This could be diagnosed by placing a small inline filter prior to the fuel line at the tank exit to see what it collects.

Good luck and keep us posted.

funola · #6 05-20-2016, 10:01 AM

I would never consider sealing a tank. You will not be able to surface prep the inside well enough for the sealant to stick and last. It may flake off in due time. Buy a used tank if yours is rusted out, which is hard to belief.

I had a W123 tank from an 83 300D sitting outdoors for 2 years and there was not a bit of rust on it. The tank is well made out of quality steel. It has a coating of lead and tin (called terne) which is highly rust resistant. I have no need for that tank anymore so had it cut open to have a look and there was not a bit of rust inside either. The only place rust can come from IMO is the fuel cap, which unfortunately is not made out of quality materials. I would suggest drain the tank, wash it out and look inside with a borescope and see what you find. If it is indeed rusted out, buy a good used tank.

vstech · #7 05-20-2016, 10:30 AM

more likely the sediment in the filter is fungus/bacteria/asphalt, etc...

I would get a bottle of starton diesel treatment, and pour it in...

Demothen · #8 05-20-2016, 12:02 PM

I have the treatment on order. But its red and silver flakes in the filter, and i know the sender at least has rusted some. Havent checked with a magnet yet but i am pretty sure thats rust and flakey steel

Diesel911 · #9 05-20-2016, 09:13 PM

Water gets into the Fuel Tank by way of the Vent because water is in the Air. It later can condense inside the Tank as liquid Water.

There is also a claim that there is some water content in the Diesel Fuel. Like regular Brake Fluid, Diesel Fuel can absorb water from the air.

Both rust and water are also common contaminates that you can get as you pump it into your Fuel tank. That is more a problem with smaller out of the way Fuel Stations then it is with busy truck stops.

Fuel contamination is a big problem with ships and boats and hot humid costal areas.

Graham · #10 05-21-2016, 10:03 AM

Home heating oil is similar to diesel fuel. Corrosion of storage tanks does occur and can be a problem for home owners. Caused by condensation in tanks.

I have read that tank corrosion has become more common in cars & trucks since the sulphur levels were reduced. I had the welds in an aluminum diesel tank on my boat corrode - don't know what caused that. Now have a nice poly tank!

This article talks about the bacterial corrosion caused possibly by teh drop in sulphur level.

https://www.bellperformance.com/blog/bid/111154/Diesel-Fuel-Tank-Corrosion-A-New-Culprit

DrLou · #11 05-21-2016, 11:03 AM

Quote:

Originally Posted by Demothen

Hi all,
My '85 300D has been producing a bit of rust in the clear filter ...

Demothen, as others have suggested, I'd make sure you're actually seeing rust as the primary problem. The yeast/bacterial flocculant/crud issue is statistically more likely to be causative, as these guys will accelerate any rust.

Additionally, along the way - as happened in my case - this crap can just about shut down fuel flow to the engine. Filters alone didn't cut it. Ultimately, pulled the tank, degreased/scrubbed it, and replaced the screen and both lines into it. Replaced the fuel lines while I was in there just for good measure. The tank itself wasn't significantly damaged by rust.

Was messy and time-consuming, but otherwise not a terrible job. And made a big difference in terms of fuel delivery.

Demothen · #12 05-21-2016, 08:36 PM

While I have the tank out for cleaning, should I be replacing the vent? Or is that something I can do at a later time in place if needed? Does anyone have a part number?
Also, I noticed after washing my car that its leaking into the trunk next to the fuel filler neck. Is the drain for the fuel neck steel, or rubber hose? Or is this likely from a bad fuel filler neck seal? Mine is pretty degraded, so leaking wouldnt surprise me. I will be ordering a new seal shortly.

Demothen · #13 06-13-2016, 02:18 PM

This weekend I pulled the fuel sender to recondition it (again). I had it out about a year and a half ago and cleaned the steel portion of rust and replaced it.

Recently the sender got stuck again, so I pulled it and dismantled it. Here's what I found:

The rod was rusted badly. There is no question that this is in large part rust, the metal is badly pitted. It looks like this piece was originally chromed. I was hoping to be able to remove the center piece and use a lathe to make a replacement, but the top of the sender seems to be press fit or glued together. Instead of spending 250$ for a new sender, and since my local junkyards are all out of w123's, I decided to try to refurbish this.

(There are some posts on how to dismantle the sender to clean it available online already, I'm not going to repeat these instructions. Google is your friend)

First step is to remove the wires. There are two wires that run the length of the sender. One is a standard copper wire that acts as part of a switch to turn on the reserve light. I marked both contacts where that wire goes with a sharpie to make sure I knew where it went. The other wire is much much thinner and appears to be a nichrome resistance wire. It loops from the contacts at the top of the sender, down through the float to the base, and back up to the other contact. You need to de-solder all these wires and place them aside somewhere safe. A tip to remove the heavily oxidized old solder is to wire brush it thoroughly (I use a brass wheel on my Dremel), then heat it up and add a bit of fresh solder. The new solder acts as a thermal bridge, and typically helps you re-melt the old solder. The copper wire probably has tiny hooks bent into it at the ends, so you may need to push it in the opposite direction you would expect to once the solder is hot to remove it.

Now you can remove the base. This is held on with a nut and washer. You may want to wire brush the threads before you try to remove it, depending on how badly rusted they are. The bottom piece should slip off.

Next there is a square "nut" - more of a spacer. This seems to be press-fit, and probably held up with some rust. Mine kind of fell off after some sanding.

Finally, you can remove the float. Let it drop to the bottom of the sender, then twist it a bit and it should come off.

Now it's time to clean up the central rod. Sandpaper works well, though for some reason I didn't think to use my bench grinder's wire wheel - which would have been quicker and easier.

Now the metal is relatively rust-free, and the float should work smoothly - but if you re-assemble it, chances are it will rust again in short order (sanding the rust off probably removed more chrome, making it more likely to rust again). Optimally, we'd have this re-chromed, or a new piece made and chromed, but since I can't figure out how to dismantle the top of the sender, that's not really an option. Instead I decided to use POR-15 to coat it. I am hoping that this will hold up in diesel fuel, but really only time will tell. There are certainly other products that might work, this is just what I had on-hand. Follow the instructions for your coating, and try to apply 1 or 2 thin even coats. If you coat the threads at the base, make sure you clean them up before the coating cures. I don't have a dye that's the right size, so before the coating cured, I ran the nut up and down the threads a few times to clean them out. Be sure to remove the nut and clean everything before it cures completely though. There is also a large washer/cap at the base of the sender that may be rusty, I coated that as well.

Tonight I will probably try to get some additional pictures and re-assemble the sender. I'm planning on letting it cure for a couple days before I put it back in the tank (it's too hot to drive my car right now without AC right now anyway).

Total cost to rebuild the sender so far was on the order of a few dollars for coatings and an hour or two of work. A new one is a couple order of magnitudes more expensive, so I'm happy to try to work with what I have.

I'll be draining and coating my tank shortly. I plan on pressure washing it with some heavy degreaser, shaking some chain or nuts and bolts in it, then using the POR15 kit with it's degreaser, prep, and coating. I've heard pretty good results with this, but if it doesn't work, I can always get another tank later.