More power on almost empty tank---Why? - PeachParts Mercedes-Benz Forum

mholbrook · #1 11-05-2003, 11:15 AM

I usually fill the tank on all my cars just before they get to 1/4 tank. The last fill on my 300TD however, I ended up running a few errands and the tank went down to almost the point of Empty. The low fuel light did not come on but it was much lower than normal.

Funny thing is that I noticed a dramatic increase in power and the motor just reved so totally smooth. I think my car runs pretty good but the difference was so dramatic that it has me wondering if I have some blockage somewhere or what???

Any comments appreciated.

R Leo · #2 11-05-2003, 12:00 PM

Hey, my '83 TD does that too. I'd just figured it was psychological.

Joe Blowe · #3 11-05-2003, 12:21 PM

Maybe it's all the additives that are floating on top of the fuel, and you're finally able to use them as the tank gets near empty.

Toblin · #4 11-05-2003, 12:27 PM

Only a guess mind you. You may be getting a small amount of water with the fuel when you're sucking from the bottom of the tank. It's an old trick used on navy carrier fighter planes during WWII. During takeoff water was injected into the cylinders from a small tank. The water turned to high pressure steam in the cylinder resulting in added boost. The water was injected only during takeoff.

Obviously this caused the engines to ware out much sooner but since engines were “deep sixed” after a few hundred hours it was no big deal. Again, only a guess.

mholbrook · #5 11-05-2003, 12:28 PM

Nice theory, but I drive pretty hard so I think things stay stirred up in there pretty good.

The feeling is that the motor is very "free reving" and "responsive", more like a gas motor than a diesel which might be better described as "plodding" (at the risk of starting a flame war).

Don't get me wrong, I love my 300TD but if it ran like it does on empty all the time, I'd be in turbo-heaven!

jbaj007 · #6 11-05-2003, 01:20 PM

It could be the weight differential of the car when your 400 gallon auxilliary tank is near empty.

240Demon · #7 11-05-2003, 08:01 PM

Actually, there is an explanation for this...

Your fuel most likely has Algae in it and when the tank gets down to a lower level, the algae settles to the bottom of the tank and is no longer floating in the fuel, therefore not clogging the lines. Check your tank screen and change your fuel filters.

R Leo · #8 11-05-2003, 08:20 PM

Quote:

Originally posted by 240Demon
Actually, there is an explanation for this...

Your fuel most likely has Algae in it and when the tank gets down to a lower level, the algae settles to the bottom of the tank and is no longer floating in the fuel, therefore not clogging the lines. Check your tank screen and change your fuel filters.

T'aint it! Marlene's tank is clean as a whistle...anyway, once a filter is clogged, it's done...nothing is gonna 'magically' unclog it as the tank gets closer to empty.

Next guess?

redbaronph123 · #9 11-05-2003, 08:40 PM

hmm.. i have the same experience with you guys... i wonder why?

*uhm... how do i check the screens in a 79 TD?

R Leo · #10 11-06-2003, 12:06 AM

Quote:

Originally posted by redbaronph123

*uhm... how do i check the screens in a 79 TD?

Same way you do on an '83 I'd guess. Check this thread for more details:
Fuel Tank Plug

redbaronph123 · #11 11-07-2003, 12:35 AM

thanks for the reply.. will check it out soon as my tank gets near empty.. it is quite full as of the moment...

Grdenko · #12 11-07-2003, 02:40 AM

my car is like that too, i always thought it was just the weight, but the additive theory sounds alright, i dont know.

the water theory doesnt work though, because diesel is lighter than water, so the water would always be at the bottom, plus having water in your fuel is bad for your engine.

i think its probably the weight though. a gallon of diesel weighs what? like 7 or 8 pounds? that times a 20 gallon tank would be an extra 160 pounds. not a whole lot, but my car is also noticeably slower whenever i have a passenger.

luckys420 · #13 11-09-2003, 05:12 PM

thats strange, my car is the opposite. it will start to run really rough and lack power after it gets low on fuel. any suggestions?
william

BoostnBenz · #14 11-09-2003, 08:16 PM

I also notice more power and smoother idling on a low tank. I was also thinking it was the additives floating to the top because I don't think adding or removing weight will change how it'd idle.

Perhaps I could write Redline a little email asking them this.

Sounds like you may have water in your fuel luckys420. Do you use any additives? I use Redline DFC, it displaces equal amounts of water. When it gets below 30*F I use an antigel and a water remover (displaces 3X the amount added) as well. If you try any of these water removers it'd probably rid of this problem.