Greetings,

Recently acquired a 1984 300D (164k miles) with an automatic transmission. Mileage in mixed driving is ~15mpg. Performance seems fine although I don't have a direct recent comparison to make.

I'm set to change the fuel filter and have read that the valve adjustment may improve the fuel consumption. But, I find it hard to imagine those two things will have a drastic effect. I would appreciate some recommendations for what to check in order of impact/importance.

Other thoughts include sticky brakes as the car does not roll when idling in drive--is this strange? At 62mph I am seeing ~2700 RPM.

Is there a thread or forum or resource for mods for improving fuel economy?

Thanks!
yem

Check your odometer against a GPS to see if it is slipping. This is a common problem as these cars age.

Agreed, my SD shows .7 mile when in reality I traveled 1 mile.

__________________
83 SD

84 CD

brakes will indeed drastically affect mileage.
as will valve adjustment, and fuel and air filters and alignment.
all together along with your odo being worn, would easily be 10mpg..

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

thanks. does an automatic transmission car typically roll when in drive at idle? is 2700rpm at 100kph (62mph) sound right?

on a flat surface. usually. up a hill, to an extent. at 60M/h I have about 2000RPM but I have the 603. Not sure on the 617's RPMS. Someone else can chime in on that

__________________
hum.....
1987 300TD 311,000M Stolen. Presumed destroyed

this is a screenshot from the factory shop manual. seems i've either got a different rear end or a bad tach or ???

Attached Thumbnails

 

Go to different places for fuel.... Keep track of a tank... A switch in fuel can make a big difference...

__________________
All it takes for evil to prevail is for good men to stand by and do nothing.

Too many people tip toe through life, never attempting or doing anything great, hoping to make it safely to death... Bob Proctor

'95 S320 LWB
'87 300SDL
'04 E500 wagon 4matic

You have a 3.07 differential in your car if you have a US spec 300D Turbo. IIRC 62 MPH is 3000 RPM.

__________________
-------------------------------
'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car

For the Brakes you can jack up one Wheel off of the ground at at time and spin the Wheel to see the amount of effort it takes to turn them.

Also have someone (with the Engine running) apply the Brakes and release them and rotate the Wheel and see if they the Brakes free up properly.

__________________
84 300D, 82 Volvo 244Gl Diesel

Look at the air filter, diesels run well with clogged air filters but get bad fuel economy.

Also, are you running any kind of additive? Not a bad idea to run some sort of cleaner though there.

__________________
68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

thanks. had already changed the air filter before the last tank. it is an STP filter (with a lot less folds than the mann). i have ordered a k&n from peachparts.

correct tire size?

__________________
Providing a home for these cars:
1951 Buick Special De Luxe
1977 Rolls-Royce Silver Wraith II
1970 Rolls-Royce Silver Shadow
1986 Mercedes-Benz 420 SEL
2005 Mercedes-Benz E 320 CDI
2012 GMC Sierra 1500 4X4
1927 Pierce-Arrow Series 80
1931 Pierce-Arrow Series 43
1926 Ford Model T coupe

thanks. where can i find the right specs if not from the shop manual?

that shop manual is not for the 84 model. it's for pre81...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!