55mph saves lives, oil, and fuel - PeachParts Mercedes-Benz Forum

oilslick · #1 01-31-2003, 11:24 PM

My '82 240D has been a glutton since I purchased it the week of Christmas. It has not been good on fuel and has slurped oil like it was chugging booze. I have not been too impressed with it's economy.

I came to a conclusion this week. I had a really bright idea. I thought maybe I am pushing this ole gal too hard. I have been keeping her floored on the highway, 65 to 75 mph. Since having that revelation I have been driving at 55 to 60mph on my somewhat longer trips and I have seen the 240D decrease it's fuel and oil habit significantly!

I am still seeing a "little" blue smoke at idle so I assume that the valve seals need replacing. I am a little bit apprehensive about trying to do this job myself. I have adjusted the valves myself but when it comes to replacing valve seals I am fearful of loosing a valve down in the cylinder. Pointers would be very well received.

Have a good'un,

Kevin
Oilslick

Sigivald · #2 02-01-2003, 01:41 AM

Over at MBZ.org's Diesel list, this sort of thing is a constant topic, and a little advice stands out:

1) Word is that valve seals are *very rarely* bad on a Mercedes diesel.

2) Mobil 1 oil. Use it, it'll clean out the crud and loosen the rings if they're stuck in with carbon. (Also, you'll get easier starting and quieter operation. I can vouch for this, at least, personally in my 300D.)

3) Drive it like you stole it. Mercedes made that 617 engine to be driven hard. It will *thrive* at high RPM, and maximum load will keep it hot enough that carbon won't build up. Carbon buildup is bad for the engine and for power.

I've had my 300D since the end of September; with a few thousand miles of driving, most of it at high speeds (a lot at 85+ on I-5 for a few hours at a time), and the last 2000 on Mobil1 15w50, it already runs smoother than when I got it.

What _I_ would do in your case (YMMV), is fill it with mobil, give it a few cans of Diesel Purge, and drive it hard. If the rings ARE stuck, hard driving and synthetic oil should cause them to come un-stuck and stop burning so much oil. Babying it isn't likely to help - after all, these cars were designed for the Autobahn.

leathermang · #3 02-01-2003, 09:10 AM

OilSlick, This is sorta hard to have an intellegent discourse about without you giving us SOME facts...
Like how many miles per gallon you were using at 65 ...
And how many you used at 55....
I ask this because there is a chance you had unrealistic expectations out of your 616 engine and trans.... a turbo 617 is more efficient ( my wagon got 27 out on the road and my 240 is getting 24 )
The valve seals are made of rubber.... and will make a difference if worn out or damaged when installing... and it is relatively easy to change them... and they are cheap ($15 a set?)... so if you have an indication they are bad I recommend you change them...

Your descriiption of your foot on the floor at the speed you are driving may be an indication something is not set properly... your 240 should be able to do 80 or 85 out on the road according to TXBill.....

If everything is set right consider doing this : accelerate to slightly more speed than you plan on driving at and backing off the throttle to get to your driving speed... an engine tends , for some reason, to use more fuel if left at the pedal setting which got it to that speed .... ( this is from old hints about thrifty driving)

I still think any indication of poor fuel usage should warrant a check of the precombustion chambers and injectors... look at the manual... seven tiny holes your injectors ( if they are set properly for spray pattern) which spread out the fuel... any carbon build up there is going to effect power and fuel usage...

I agree with Sigivald on the rest of it... don't bother babying it...

and don't drive 55 if all the rest of the traffic is going 70... you will get run over.... or assaulted.....

Ok, I just reread your post... we also need to know what basic stuff you have done to the car since you got it at Christmas..Valves set, etc ?

#4 02-01-2003, 12:40 PM

please excuse my ignorance, but i'm still learning about this car which is fairly new to me. i have a 5 cylinder turbo diesel engine, is this the 617 engine everyone refers to?

leathermang · #5 02-01-2003, 12:54 PM

The car in the first post is a four cylinder 616.???
All 300 five cylinders are 617.???
A turbo five cylinder like you have should be 617.952 I think...
the turbo engine has a tiny amount less compression ratio,oil squirters for cooling the bottom of the pistons, and larger bearings...( and ?).....

#6 02-01-2003, 01:13 PM

thanks

rwthomas1 · #7 02-01-2003, 03:48 PM

A Turbo!!! LOL, I'm killing myself! I just couldn't resist.... RT

#8 02-01-2003, 06:20 PM

I'm happy with a constant 23mpg. I don't think I can find a car as big, safe and reliable that gets that kind of economy. I could probably get 30mpg out of it if I drove close the speed limit on the highway.

oilslick · #9 02-01-2003, 06:54 PM

First of all, thanks for the advice. I have been so excited since I found this forum.

Please don't throw rocks at me but I have to be honest in saying that my odometer does not work correctly so my fuel mileage is only speculative. I did a check on it and I am getting around 24-26mpg at speeds of 60 to 65mph. I took a trip that I knew the mileage for and returned with an almost empty tank. The light was on for some time. Here's how I figured the mpg. Before I left on the trip she was empty so I put $9.00 worth in the tank, which was only 6.2 gallons ($1.45/gal), and upon my return I did the math and came up with a very satisfactory result- 26mpg! I am satisfied with that.

My real concern was the oil consumption. I am confident that everything is adjusted fine. The car has the power. She takes off like a champ and she will cruise on the highway great. However, she does lose about 10mph on an average interstate hill. Keep in mind when I say average I am talking about a South Carolina interstate hill, upstate South Carolina(Go Tigers!) Anyway, on that same trip, which was 165 miles rt, she used about 1/2 quart of oil, yikes!

Today I had my wife drive the 240D and I followed her for about 20 miles. She drove 55 to 60 mph and I noticed that the car smoked very little at cruising speed. I do mean very little! On take-off it was a puff, automatic shift to second, small cloud, shift to third, small cloud, shift into fourth, only a whisp of smoke. At idle the smoke was somewhat blue, valve seals I figure, but while driving the smoke was not black-black but charcoal gray.

I have been almost two hundred miles (knowing the territory I can deduce that) and the oil level has not dropped. I have driven these miles at speeds of 55 to 65mph. I have not rocketed off at any traffic lights or stop signs. I have not "punched" her (the 240D or my wife) in traffic. I have been very moderate in my driving. The fuel gauge has moved what I consider to be an acceptable amount.

OK guys, tell me where I go from here. BTW, why does an odometer only work when the car is cold? Mine only registers for the first ten miles on a cold morning and then retires until the next morning or until the speedo gets really cold.

Thanks,
Oilslick

What is the difference between a matchbox car and a MB?
Flip the matchbox car over and it will say "made in Tiawan"
Flip the MB over and it will say " made in hell"

kerry · #10 02-01-2003, 07:46 PM

There is a pot metal gear press fitted onto a shaft that clicks off the miles. When things warm up, that gear is slipping on the shaft. Do a search on 'odometer' and you will find threads that describe the fix. No expense to the fix, just about an hour or so of work.

MikeTangas · #11 02-01-2003, 07:47 PM

Do a search on speedo/odometer problems. You'll find plenty of info. Basically you have two choices: try to repair it at home or farm it out to a pro. I farmed mine out for repair and have been getting accurate mileage readings since. First tank through the 4.5 I saw a whopping 5 MPG, fixing the odometer brought me up to 10 and a little work/tweaking has it steady at 13.5 in town and almost 16 on the highway.

leathermang · #12 02-01-2003, 07:47 PM

I am using two quarts per 100 miles... and I am not kidding... ask TxBill....
Put the seals on it.. not that hard,,, but follow directions in the shop manual... your time and $20 could really fix you up... if not you learned a lot about your engine and you know it is not the seals.....check your chain elongation while you are " there"....

oilslick · #13 02-01-2003, 07:50 PM

What is an easy and reliable way to check chain stretch?
Keep in mind I want it easy!!!

leathermang · #14 02-01-2003, 07:57 PM

It will be particularly easy because you will be messing with the valve which you have to take all the play out of the adjuster nuts on top.. then use a dial indicator and turn the engine until the valve is moved a certain distance ( about 2mm I think ) and then you just look at the number of degrees off your line on the crank is when read on the tdc degree marks..
You need to find JimSmith's description or use the factory shop manual... it really is easy and you will do it everytime you adjust the valve from now on just for the fun of it ...

psfred · #15 02-01-2003, 08:14 PM

Excessive oil consumption and blue smoke at idle could be valve seals, but is more likely to be worn valve guides. Do you get a puff of blue smoke on startup? If so, its valve guides and/or seals -- the oil leaks down the valve stems.

Other possibilities are a leaking vac pump (only if there is a hose from the vac pump to the intake. If there isn't one, the vac pump vents into the crankcase), a leaking oil separator in the air filter housing, or a plugged oil collector drain (or a leaking drain 0-ring).

There is a cyclonic oil separator in the air filter housing where the blowby is spun around to remove the oil before it goes down the intake. If the seals between this separator and the rest of the air filter housing are bad, or the drain line is plugged, all the oil will go down the intake instead. Quite a bit of oil will burn completely without making blue smoke, unlike a gasoline engine.

I would also check for leaks, too.

Peter