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500 SE (1989), 304,000 km.
659 Posts
Discussion Starter · #1 · (Edited)

I did a search on this, but didn't come across the answer I needed. First off, I don't constantly fill my gasoline tank. That's because it's a weekly driver, or sometimes less, and I drive it about 30-40 miles a month. I'm just wondering first how much I should keep in the gas tank all the time. I must admit that since the price of gas has shot up (since last winter), I have had the gas pointer on yellow (i.e. reserve) for quite a bit of time, but never down to the very last morsel (of the 20 litres reserve), and of course, when ever I take her on a long ride, I always make sure the tank is at least 1/2 full.

1) Would you suggest that I keep her, constantly, at a minimum of 1/4 full, or half full, even though my W126 is not a regular driver. (What could happen if I keep her at, say, 5% gas amount when not being driven regularly? Or is just keeping her running weekly the key, and then making sure that the yellow "fill 'er up" indicator never shows, so that 10% gas amount in tank will suffice when she's not being driven?)

2) Would a fuel stabilizer be good for me to use? Are fuel stabilizers good for our V8s? (If so, would you recommend Red Line, or which brand?) -- I notice from posts that some of you have used stabilizers, but I want others' opinions too, plz.

3) If you do, indeed, recommend a stabilizer, should I use the entire bottle (or only partial bottle), and what amount of gas should be in the tank for the "mix".

4) Again, if you recommend a stabilizer, is use of a stabilizer best done every year for "not-so-much-driven" V8s?

I know that my import wasn't driven at all, really, between spring 2004 and summer 2005, before I bought her (sitting outside in dealer's garage lot), so I'm just wondering how I can maintain her. Since summer 2005, I've had all fluids and filters changed to new ones, so I'm not neglecting her in any sense of the word -- I just want to make sure that I also look after the carburetor and engine, too, to prevent any gum forming by using fuel stabilizer if needed, and want to learn proper gas filling recommendations. She starts up well, the idle's just right, and no probs in this regard.

Finally, when I do fill her to around 50% gas that, as I remove the gas cap, it's as if a rush of gas vapor pushes out of the reservoir (blowing sound, like vapors being released with some force). Is this a normal sign of a healthy Benz?

Advice sought, guys. Sorry for any dumb questions, since I'm not exactly a newbie here. :D


PS. I will post pic of my re-flush of the p/s reservoir some time this month. I've been soooo busy to-date, and just haven't got round to it. (In my previous posts about my p/s flush, I wanted to get a clearer light-yellow result in the reservoir, so I hope to achieve this by another 2 flushes.)

1966 200 Diesel; 1985 500 SEL (wrecked); 1991 420 SEL; 1979 280E (Home Market); 1993 190E 2.6
584 Posts
I think thats a lot to worry about. If your car got used, say twice a year, then I think you would have more to worry about. If you don't think a full tank is prudent for your driving habits then keep a half tank on hand. They like to be driven, don't lock it in a garage.

I was told by a chemist friend that fuel stabalizers simpily put a layer on top of your gas to prevent the evaporation. I dont know the truth to this but there it is.

Id say just keep a 1/4 tank of the good stuff in it unless you are going far.

1991 500SEC Euro, 1987 560SEC Federal
5,464 Posts
Hi RS,

That fuel cap operation is normal for a gas car. See andrew_falky's post titled: WHOOOSH. Good discussion there.

Fuel stabilizer I use my car much more than you. We just got back from a 1300 mile SEC road trip.... Just in a few days blasting down the road.

I use a fuel stabilizer solution in my cars when stored for the Winter months. I do have some 'old favorites' that have yet to be driven this year. The stabilizer claims to keep the fuel viable for two years, a fact I have observed. It is nice to have a car that lights off first crack, after sitting for nearly a year.
As to the amount one would use, mixing instructions are on the label.

In addition, I keep the tank full to minimize the effects of airborn moisture inside the tank.

If I used a car infrequently, I too, would be inclined to use a fuel stabilizer in solution with the fuel - and keep the tank pretty full as well.

Cheers, MBL
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