What rpm should a 240D hit under normal operation?

[tadrak]

I've got a '79 240D w/ a 4-spd manual and no tach. I'm curious as to high I should run the rpm before shifting? The speedometer has maximums on it (1st gear=22mph, 2nd gear=36mph, 3rd gear=60mph), but is it ok to hit these maximums on a regular basis, or should I "lug" it down more?

Also, what is the proper operation of the manual choke knob located on the dash to the left of the steering wheel and underneath the instrument cluster? I've been turning it all the way to the left when the motor is cold, then arbitrarily turning it to the right a half turn or so after it's warm. After turning it to the right, at idle, the rpm will drop and the oil pressure will come off the max quite a bit. Is that ok?

Finally, a previous post pertaining to oil consumption talked about flooring the accelerator and hitting the "kickdown" switch. What is a "kickdown" switch, where is it and what does it do?

Sorry for the laundry list, but this is stuff I've been wondering about for awhile.

[johnathan1]

Only cars with Auto transmissions have a Kickdown switch.

IIRC, oil pressure at warm idle is supposed to be around 1.3bar?

[ghoward@goldrus]

T'he knob to the left of the steering wheel is a fast idle knob, not a choke. Diesels don't have chokes or throttles. When the engine is cold, before starting, depress the accelerator, turn the knob full counter clockwise, then start. Depending on the temperature, I usually return the fast idle knob to its driving position (full clockwise) about 30 secs. after starting.

Normal oil pressure when cold is pegged at idle, when warm, between 0.5 to 2 bar at idle, pegged above idle.

I usually only hit the shift marks on my speedo occasionally, but do not believe there is harm in keeping it there, except that the diesel runs more efficiently with a wide open accelerator, so higher gears are preferable, load permitting.

You should buy and read the user's manual.

[lkchris]

the diesel runs more efficiently with a wide open accelerator, so higher gears are preferable, load permitting.


It sure does, and there's no throttle ever, so all "wide open accelerator" does is maximize fuel delivery, which is not the most efficient.

Diesel runs most efficiently at idle, actually, where air/fuel ratio can be as high as 150/1.

[Maxbumpo]

The OM616 engines (in 240D) have unfortunate habit of increasing oil consumption when under load and at higher RPM, so you may be increasing oil consumption/polluting environment.

I also would hesitate to run the engine that hard without ensuring that the timing chain stretch is under 3 degrees and the valves are adjusted.

Once or twice a drive, once the engine is fully warmed up, probably won't hurt anything, but I wouldn't make it a habit of doing that for every shift. Maximum torque is at 2400 RPM and max. horsepower is at 4800 RPM. Max. engine speed is slightly higher at 4950 or maybe 5000 RPM.

[tadrak]

If you don't have comprehensive repair records, how do you know when the timing chain needs to be replaced?
When you have the valves adjusted at a repair shop, do they reset the timing also?
Thanks.

[Maxbumpo]

The timing chain stretch can be measured when the valves are adjusted, takes an extra 5-10 minutes. Basically you line up a mark on the camshaft pully with a mark on the front cam tower, and then read the value on the crank damper with the pointer. If at 3-4 degrees, you've got time to schedule repair. At 5 degrees or more, do the job immediately before the chain breaks and the engine is destroyed (valves will collide with pistons causing many bad things to happen).

If the shop you are using does not know how to do this, find a new shop. Search this website using the search tool and you will find pictures and more detailed explanations.

[tadrak]

Well, took the Benz to the indy shop that I've been using for several years and sure enough, the valves were pretty bad; exhaust too tight and intake too loose. The BEST part, of course, was the fact that the timing chain syndicate was all messed up. I didn't understand all the jargon, but some rail relating to the tensioner was bent and the mechanic had no idea how that could happen. He said the timing chain could last another 50K miles, or it could explode tomorrow. So, valve adj., fuel filters, timing chain = $1,200. Lucky me. I just hope that the work is done properly and it will last another 230K.

[tadrak]

I forgot to mention that the lack of acceleration was the easy part. The linkage from the pedal to the motor was slipping, so it wasn't being opened up all the way.

[Maxbumpo]

Well, took the Benz to the indy shop that I've been using for several years and sure enough, the valves were pretty bad; exhaust too tight and intake too loose. The BEST part, of course, was the fact that the timing chain syndicate was all messed up. I didn't understand all the jargon, but some rail relating to the tensioner was bent and the mechanic had no idea how that could happen. He said the timing chain could last another 50K miles, or it could explode tomorrow. So, valve adj., fuel filters, timing chain = $1,200. Lucky me. I just hope that the work is done properly and it will last another 230K.


$1200 sounds extremely expensive!! Unless he's planning to completely take apart the front of the engine to replace all the timing chain rails as well, I really don't see how the price can work out to $1200.

Make sure to ask to see the old parts when he's done. Normally the chain rails last the life of the engine, and when the chain is replaced you simply remove the chain tensioner, remove valve cover, break a link in the old chain, attach the new, then manually turn the engine while feeding in the new and taking out the old, until you have access to both ends of the new chain. Disconnect the old, install new link, and double check the timing of camshaft to crankshaft to make sure you didn't jump a tooth, and you are done.