Drastic drop in fuel economy, mild loss of power & blue smoke on startup - PeachParts Mercedes-Benz Forum

michaelwoodcock · #1 12-01-2012, 08:45 PM

Hey guys, My gas mileage in my 1984 300sd went from 25-27 mpg all the way down to 20, and today I got a record low of 19. I've kept detailed logs of gas mileage, and this drastic drop concerns me. I also have a decrease in power, and blue, almost gray smoke at startup. I've checked the coolant many, many times, and it's not going anywhere, so I've decided to rule head gaskets & such out. I do have a small amount of oil consumption, but it's decreased since I've gone synthetic. I have increased the boost by 3 psi over stock, and the ALDA was adjusted then I bought the car, to almost full CCW, no other mods done, just lots of maintenence like valves, oil changes, all filters, etc. etc.

any advice?

happy motoring,

Mike

vstech · #2 12-01-2012, 08:56 PM

are you sure your odometer is not slipping... it's very common.
also, check if your brakes are dragging.

michaelwoodcock · #3 12-01-2012, 09:21 PM

hmm, I suppose the odometer may be slipping, it was broken for almost 10 years before I replaced the gears, but I am fairly certain the brakes are not dragging, on coast down tests, the car can coast forever! I will check the odometer vs gps and see if it's slipping, but it does seem I fill up more frequently now too, I used to fill up once every two weeks, and now I usually have to fill up at one and a half weeks or so for the same amount of driving

kerry · #4 12-01-2012, 11:48 PM

Plugged air filter?

Skid Row Joe · #5 12-02-2012, 12:02 AM

MPG is not a slam dunk constant. The last tank fill on my MB I recorded 27 mpg. The previous 3 tanks were recorded @ 22 mpg. No real discernable difference in the usage factors of the car in each tank.

michaelwoodcock · #6 12-02-2012, 12:28 AM

air filter is new, but I discovered something, diesel leaking through that cigar hose that goes to the filter housing, all over the engine, I guess that's part of the problem! Will see if I have the right ID hose tommorow, is a cigar hose critical? or can I use any hose that will fit?

vstech · #7 12-02-2012, 12:30 AM

if the CH is leaking ANYTHING is better!
however, the CH shape keeps the motor quieter!
any 5/16" hose will suffice.

michaelwoodcock · #8 12-02-2012, 10:19 AM

VStech,

It's early in the morning, but what do you mean by "anything is better" ? does a leaking cigar hose mean bigger problems somewhere?

Thanks,
Mike

kerry · #9 12-02-2012, 10:37 AM

No he just means anything is better than a leak. On my 409d van someone had installed a regular 5/16th hose with a fuel filter in it. I figured that person had thought the filter might make up for the lack of 'cigarness'.

Zacharias · #10 12-02-2012, 11:31 AM

The theoretical reason behind the cigar hose's shape is that it is supposed to dampen the pulses of the fuel as it flows out in the return.

In practical terms... not sure it makes any difference. I drove my current car for a year before I even noticed someone has replaced it with standard hose. I did install a cigar one, just to be 'correct' but it isn't something to worry about.

However, on a previous list I frequented, some people swore they got rid of mild 'chugging' or 'grunting' at idle by replacing that hose.