Cutting open a Mercedes R107 fuel tank…and modifying a non OEM tank

In this video, we cut open an old Mercedes R107 fuel tank and take a look to see what’s inside. Some of the R107 Mercedes fuel tanks which are for sale, have non-standard fittings for the fuel strainer and are not suitable for the early SL fuel sender units. This video shows you how you can potentially modify a new style tank and use it for an old SL.

[@rome288]

Wow. You are going through what I went through 5 years ago. What I did was have a radiator shop clean and coat the inside of my old tank. Their chemicals would eat up the plastic Venturi so I had a metal Venturi made. They cut open the tank, welded in my metal Venturi, patched the tank and then cleaned and coated it. This was still a lot cheaper than a new tank. I did not realize that there were two tank configurations so a new tank may not have worked.

[@MikesMercsandothercars]

Thanks for your comment. Interesting to learn that the chemicals would eat up a plastic venturi. I have just taken it out of the tank and will sell it on eBay just in case anyone need one. Still umming and ahhing about the fuel strainer issue. I am kind of loathe to cut into the new tank. All the best. Mike

[@TonyLiveTV]

Great video Mike!

[@MikesMercsandothercars]

You say the nicest things! Mike

[@martinowens5309]

I have a fuel tank strainer that is original fro pm early 1972. It has the internal thread on the strainer and the nut is flush without any protruding features. It comes with a brass tube that has external threads at one end with a small flange that when threaded into the strainer forms a seal. The other end is a tube with a flange for the fuel hose and clamp. Does anyone have a recommendation for the coating of the inside of the tank. I had the tank cleaned in a hot caustic. They did not do a thorough job and I had t rinse a number of times. If I take my finger I can see a very light reddish tinge of rust residue. The Venturi looks like it got eaten up a little on the outside but appears in tact. Should I coat the tank? Welcoming any thoughts.

[@bjornarhuse]

Using the smaller (and coarser) fuel strainer shouldn’t be a problem, the filters will still do most of the work anyway. As for the fitting I would make sure that it seals, possibly using something magic. The old one didn’t have a proper sealing surface except the metal-to-metal nipple which isn’t all that great anyways. For the sender I would weld the new one in place, I am sceptical to gluing anything on a tank…

[@MikesMercsandothercars]

I think you are probably right about the mesh size if the strainer...although on the earlier D Jetronic fuel pumps there is a built in check valve (spring and ball bearing) which could get clogged by fine debris. I am loath to cut into the new tank and modify it to fit the standard Mercedes strainer - the upside of being OEM doesn't outweigh the downside of the tank leaking or rusting prematurely. I have decided to use Permatex 'Aviation Form-A-Gasket No.3' Gasket Sealant to seal the threads of the fuel hose to pulsation damper. This is a non setting fuel resistant compound that should stop the threads leaking. I will use 3m Panel bond to attach the fuel sender fitting as this sits on top of the tank and doesn't come in contact with any fuel. Welding this fitting would burn off the primer inside the tank which is difficult to re-prime.... the inside top of the tank is constantly exposed to air and will eventually rust if not 100% sealed. Thanks for your comment - I appreciate you taking an interest. Many subscribers are far more knowledgeable and experienced than I will ever be. Mike

[@brittanywright9646]

I got anxiety watching him constantly rubbing his fingers around that rusted metal. Otherwise, great video! One other option that I don't believe you mentioned would be to just go and buy the proper fuel tank for the car instead of cutting up and swapping parts from 2 tanks just to make one. Economically, seems like the time and effort involved would cost more than just buying the correct part.

[@MikesMercsandothercars]

Thanks for your comment. Unfortunately, they dont make tanks for the early R107 SL's....and the Mercedes cost for a new tank was in excess of £1500+vat. Mike

[@jonnybigpotato4263]

Hi Mike. Another useful and really relevant video for me and my 1974 SLC. I need to replace the main fuel line from the tank to the damper cage as I’m replacing all the fuel hoses given their age. So I am about to try unscreewing that pipe from the tank strainer unit. I may also try to remove the strainer unit. My concern is that if they are very tight (and the tank is still in the car) you run the risk of rounding the fuel hose and not getting it out so in a worse position that leaving well alone. But it also occurred to me that if the strainer screws in with the same direction thread as the fuel hose, how do you know who inch will screw out first? Obviously you would expect to hold the strainer with a spanner but in the car there seems no way to do that. Any tips? I assume they are the same direction threads? And any view about the likelihood both will easily come out without taking the tank out? The car has been in constant use and is not that rusty underneath which should help. Many thanks, John

[@MikesMercsandothercars]

Thanks for your comment. Often, the best way to get the fuel pipe out is to cut it and then use a deep socket with a big extension. Trying to get that loose with just a spanner is nigh impossible. Often the strainer comes out with the pipe. If you are changing the pipe, definitely change the strainer - it’s not that expensive. Once again use a socket rather than a spanner to tighten. Remember that the hose for early DJetronic is different than for later SL’s Where are you based? Mike

[@jonnybigpotato4263]

@@MikesMercsandothercarsThanks Mike. I’m in Chorley, Lancashire. What you say makes sense - i guess once you cut the hose you are all in! Whereas now there is no leak but the rubber hoses which are visible are clearly cracking so my assumption is that the main hose (which is braided so rubber not visible of course) must be at least as bad. I have done all the fuel pipes under the bonnet and had the injectors refurbed and refitted them with new seals so this is the last bit. Also awaiting with interest whether you get the US fuel pump from the US and to see if it works - mine works but needs at least a clean and a lick of paint. Best, John

[@MikesMercsandothercars]

Hi - sadly the fuel pump from America never arrived. I think I'll get someone in USA to buy one and physically bring it back. Let me know how you get on with the rear fuel pipes. Scary when you go beyond the point on no return! Mike@@jonnybigpotato4263

[@MikesMercsandothercars]

By the way, if you do want to overhaul your fuel pump, I am selling a refurb kit on ebay for £4.99. It includes the O rings and stainless steel screws. I only have 1 left so let me know and I'll set it aside for you. Mike

[@jonnybigpotato4263]

@@MikesMercsandothercarsah i see it is an auction. If you are able to re-list it with a buy it now price I’ll buy that from you thank you