Engine speed seems high
 

Hello my friends :D

So I drive an old 407D from 1978, with the OM616 engine. It has no tachometer and is pretty loud, so I was wondering how much the engine actually turns when cruising. Normal cruising speed would be 75-80 kmph for this vehicle. I tried to use an online calculator to determine how much RPMs its turning at 80 kmph, and it said 3700 which seems pretty high! Is my calculation correct??

The tires are 6.50 R16, rear ratio 5.857 and translation 1:1 in 4th gear.

I am worried that the engine would take damage from such high RPMs for a prolonged time :confused:

Sounds like a relatively reliable calculation.

These old buses are geared for moving stuff not geared for racing stuff!

The engine is only "in danger" if you have not looked after it. Service the engine and make sure it doesn't over heat and it will do what it is meant to do. More frequent oil changes is better than letting them slip.

You might, however, wish to buy yourself some ear defenders for longer trips...

Yes I realize it's geared to be able to haul 4.6 tonnes, mine will never reach that weight though. So 3700 rpm is no problem for this engine? I swear it sounds like it's going to explode any second, and I have the engine cover insulated pretty well. I only give him Mobil Delvac MX oil and the temperature gauge is always at about 85C, but there's no oil cooler in it.

I also have another question which is how much an engine's load will affect its longetivity? It's obviously much higher in the vans, and I see that the new generation Sprinter with the small OM646 engine doesn't last very long. Usually needs a new engine from 200- to 250000 km, while the Sprinter 318 with the bigger OM642 V6 engine is much more durable. I drive one myself which has done 607000 km, and is using almost no oil at all! I even drive this thing hard, overloaded by a ton almost every day!

Some engines are better than others. The bigger 5 cylinder OM617 is known by some as the million mile engine. In some ways this is a load of crap - in others not so. The OM61X engines are good engines but they suffer badly when not serviced properly - the OM616 essentially has the same technology as the OM617...

...if your OM616 has been looked after properly - compared with a modern engine it has seriously short engine oil change intervals - then it will be capable of high speed revving and will last "a long time".

If, however, you are driving something and you think it is going to explode then it seems to me to be a good idea to check the condition of your engine to make sure it isn't going to explode!

On the non turbo OM61X engines there are the following noise making problems:

1) Vacuum pump (if fitted) - these can fall apart and shed parts into the timing chain and the rest of the engine

2) Oil pump drive - vertical and horizontal connection between pump and timing chain

3) Timing chain itself - check oil pressurised tensioner plus condition of cogs and chain

4) Injectors - worn injectors make noise / help to make noise as well as smoke!

5) Poor fuel delivery timing and valve timing


Compared with modern engines the OM61X is a crude sounding tractor engine - but it is pretty strong and has earned the reputation of being a "good one".

The problem with the vans is that access to the engine isn't so good so maintenance often gets missed.

Thanks :)

With the engine cover off it's actually no problem to work on the engine.

I think the engine is in good condition as it starts pretty fast, but there is some blowby which had me worried. I made 2 videos, the first one shows a first startup in almost 2 weeks, and cold blowby. Second one shows blowby with the engine at operating temperature. Let me know what you think :)

https://www.youtube.com/watch?v=Uk8hP2t73GQ
https://www.youtube.com/watch?v=-bm6W5K38ME

The engine only has 54000 km, so I didn't expect the cap to dance like this :(

A couple of comments that may be helpful...

First, your mileage should be roughly doubled to provide meaningful comparison with other MBs. Because your rear end ratio is so high your engine will turn over roughly twice as many times for each mile travelled. This would translate to halving the maintenance interval too - maybe to 1500mi vs 3000mi for a "normal" vehicle.

Second, the forces within the engine vary as the square of the velocity, specifically F=mv2 ("2" is squared not x2)...double the speed, 4x the force. At the same cruise speed, therefore, you have 4x the forces acting on the crankshaft, pistons, connecting rods, bearings, and so forth, which would presumably create larger than normal wear.

If it were me, I'd limit my speed to keep rpm at or below 3000...

My 1984 300D runs ~3000 rpm at 60 mph. My 1985 CA 300D has the .4xx transmission w/ a taller gear so runs ~2800 rpm at 60 mph, but still too whiny. Everytime I enter the freeway, I keep waiting for the final shift, then realize it is already in 4th gear. No idea why they couldn't have done better w/ 4 gears. These were luxury cars! (insert drunk German engineer jokes). Early 60's Corvettes managed w/ 2 gears. I guess I could jack up the rear and install taller tires to lower rpm and drive the only 300D redneck rig. Actually not, since I recall a photo of a W123 body atop a monster truck.

Well I've seen worse.

If the recorded kms are correct the engine is suffering from lack of use. Change the oil more frequently and you might find that things improve. You should be changing the engine oil at least twice a year because the engine has to work so hard in that big truck

These trucks are geared to shift stuff. They are not geared for economy or speed. 3000 rpm in top gear in one of these is probably not much more than 40 mph!

Yes, I need to take it up to 75-80 kmph on the highway, with headwind it won't go past 70 kmph though, and let's not talk about uphill :D

The km should be correct, this van is an old ambulance from the civil defense. It's been stored in the mountains for a long time because they have been replaced by newer vans, and the previous owner had just let it sit outside for 4 years. So could lack of use cause extra blowby?

Maybe I should switch to synthetic oil and drive it hard for a while? I can get the Mobil Delvac 1 5W-40.

Best not to discuss "which oil type" here! This forum is famous for its "oil threads".

(PM sent)

If an engine has not been used much as has not reached a proper operating temperature then things can get bunged up like the piston rings.

Synthetic sounds good. I recall talk that it helps dissolve gunk. Synthetic diesel oil is even better since CJ oils have more detergents. Some talk of using ATF since it is oil with even more detergents (I think), but you are going "off manual". Decades ago, auto parts used to sell quart cans of "engine de-gunker", which was more like diesel fuel I think. You idled with it for 5 min, then drained the pan. Might have done more bad than good. One thing I would try is drain the pan, remove the valve cover and brush down the valve train w/ diesel, or even better bio-diesel or even corn oil. Continue until you fill the pan and let it sit for days to degunk the oil pickup screen, then drain, pour down some clean oil to sweep gunk out, then change oil every 500 miles until it looks like normal diesel - dark but not gunky.