is it bad to redline it? - Page 3 - PeachParts Mercedes-Benz Forum

wolf_walker · #31 01-11-2004, 02:38 AM

Quote:

Originally posted by Brad123D
tjohn,

Your SD is an automatic transmission...what do you do , manual shift it to get your "Italian tune-up" ?

Every properly functioning auto trans I've ever dealt with will shift at or near redline at WOT, and being that most of these diesels are limited by RPM to about 100mph, full throttle runs are not out of the question for many. These two, either seperate or in conjunction are a suffeceint "italian tuneup".

#32 01-11-2004, 02:03 PM

Quote:

posted by 82-300td
So we should drive around town in S until we need to go faster than 4Krpm?

Yes! Keeps you in the hp range. Much more responsive. No noticeable decrease in fuel economy. Engine is spinning faster with less load. I feel it keeps the engine cleaner. It may also decrease transmission wear. Fewer shifts and less load.

#33 01-11-2004, 02:06 PM

One other thing, more rpm=more oil pressure.

wolf_walker · #34 01-11-2004, 02:11 PM

Somewhere online there is an excellent paper on diesel performance from an outfit that builds motors for Semi's, serious performance motors. I'm sure some of you have read it. One thing it mentiones about driving style is to basicaly not get anywhere NEAR lugging them, don't make that wonderful low end torque do all the work and load things down so badly if you don't have to. Sure you could climb a grade in 4th at 2500rpm for instance, but it'd be kinder on the motor to pull it in 3rd at 3200rpm. It was an excellent read if anyone has a link to it on hand..

Brad123D · #35 01-13-2004, 02:40 AM

Back to where I came in on this thread-

High RPM = shorter engine life

A partial quote from cars.com-

"...engine wear is largely determined by piston speeds..."

It IS that simple.

tjohn · #36 01-13-2004, 08:02 AM

And again, all I am saying is that your engine will operate better if it is consistently run at 75-80% of full throttle than if it is constantly driven at low revs. I am not saying that there isn't some increased wear at higher rpms, but I am saying that this is preferable to the negative effects of low speed, multiple short drives, in which the engine doesn't get good and hot. Operating the engine near its performance limits helps it get hot and clean out those nasty carbon deposits that car rob performance lead to increased blowby. Ultimately, of course, its your car and your choice.

JimSmith · #37 01-13-2004, 10:42 AM

This is an interesting thread. I think the problem has another dimension, namely, what causes the wear in these engines. There is a factual basis for the higher rpm=higher wear statement, but it assumes all the wear mechanisms are equal across the rpm range, except piston velocity, and that is somehow non-linear within the operating range.

In our Diesels that is not actually the case. In reality there are thresholds of operating characteristics that, when exceeded, result in increased wear rates. Piston velocity is only one of these operating characteristics and Mercedes-Benz hardwired that limit into the injection pump. If you stay below the threshold, while the wear rate might be slightly higher at redline than at another rpm, it will not control the rate of wear in the engine by itself.

For example, good oil (and the oil today is far better than the oil that existed when these engines were designed) and frequent changes, or not, can change the wear rate more than the rpm range you use. In most cases serious engine wear in these machines can be traced to poor maintenance, with nfrequent oil changes being a major culprit. So, theoretically there should be a threshold beyond which point the oil becomes a significant or controlling contributor to wear and below which oil condition makes no controlling or quantifiable contribution. The board mantra from Larry Bible, "change it hot and change it often" is intended to make sure we stay below the threshold.

The coolant system, induction system and exhaust system, as well as the valve train all contribute to the actual conditions and thresholds for each particular vehicle. Any one of these systems malfunctioning can unbalance the rest and result in operating conditions that increase wear rates.

One of the major oil performance degrading aspects of Diesel engine operation is the generation of soot. More soot in the oil, more wear as the oil ages faster and begins to perform poorly, and drag soot, not a lubricant, into places where it does not do any good. Soot is not produced at equal rates across the rpm and load range, so again there is probably a threshold of rpm and load that extends across the rpm and load range, where soot production is much more significant. There are probably other thresholds that suggest at certain rpm ranges more soot stays inside the engine or more goes out the exhaust.

Soot that stays makes it way to the oil by going past the rings or does other unhelpful things like clog the prechamber passages to the area on top of the piston. On its way to a resting place in the engine, soot can deposit for a long or a short while. If it ends up in the groove with the ring and is allowed to accumulate there it can interfere with the function of the rings, allowing more blow-by and more rapid contamination of the oil, leading to increased wear rates.

I have always been a believer in moderation, and for many years I have driven my Diesels avoiding the red line area unless some road condition specifically warranted it. While I owned them they always smoked a little at idle, when accelerating, etc. or a lot.

Well, my daughter used our 1982 240D while attending college (Rensselaer Polytechnic Institute) for four years in Troy, New York. This city is located on the slope of the Hudson River valley (probably the banks in bygone times), and has some very steep hills. My daughter found it "necessary" to drive up these hills in 2nd gear with the throttle wide open, nearly all the time. At first I thought it would just kill the car and she would be out a vehicle. My policy was to give each child a single car that was built within six months of their birthday, preferrably a car we drove as a family vehicle, that they learned about by doing the maintenance for good bit of time before college.

Well, she took the car over at about 250,000 miles and it now has 312,00 plus on it. It used to smoke and be a pain in the rear to get started when the temperatures were under 30*F. It starts without any assistance in near zero temps now (5*F the other day) and doesn't smoke at all. It used to leak oil from the rear seal, and it still does now. So the red lining did not cure that ill. She still drives it and still runs it to the dots on the speedometer regularly. It runs on Delvac 1 and has the normal maintenance of other items, mostly done by my daughter.

It is also rusting, so it won't last forever. Which brings me to the last threshold. What finally kills one of these machines, if properly maintained and driven regularly, is going to be the cost of fighting off Mother Nature's relentless will to return these awesome examples of man-made order to disorder. When the rust makes ours a risk to drive, we will give it up. But like my first one, the 1975 240D, it will likely get towed off with a fully functional engine(with a rear seal leak that could get the EPA's attention by then).

Jen-Tay, go ahead an run Lil' Pete as hard as you like, as long as you make sure the oil is good, the valves are adjusted, and the filters are clean. Jim

leathermang · #38 01-13-2004, 11:16 AM

Great answer JimSmith....
There are a couple of other factors I have not seen mentioned lately...

1. The design of the cams ... to get more rpms out of a gas engine it is usual and necessary to increase the ' valve overlap' caused by the cam design.... This is pretty well not available for diesels due to the circumstances... So they are pretty much ' self limiting' .... IF THEY ARE UNDER LOAD.... they start reaching a point in the torque curve where they just don't rev any more... ( also helped by proper governor setting of course )

2. As to wear... being in a lower gear with respect to a particular speed of the piston travel means that the piston is doing LESS work per distance of movement... so things really get complicated..

3. When I acquired my 1980 240 manual there was the impression that it had a rebuilt engine..... and that it was using a quart every 300 miles or so.... so I was encouraged to try ' reseating ' the rings by running it up and down the rpm curve and under a load in the decreasing rpms.... since these were things which I had read over the years were suggested to seat new rings in the first few minutes after firing up... I decided to try it .. even though I had real doubts given the number of miles on the engine since the possible overhaul... ( note : the oil consumption SURVIVED the rebuild ... a Very strange situation )
Anyway, I have some hills on the road I live on and I took it out and revved that sucker for what seemed like an eternity... since this is not how I operate any machine.... It was really SCREAMING... and runs just fine today.... I really did not have a way to check the oil consumption because I don't use that car much.... but later did find that keeping the oil at the half ' max' mark really helped....

#39 01-13-2004, 11:50 AM

Jen,
Drive it like you STOLE IT!!!

spo out.

wolf_walker · #40 01-13-2004, 12:28 PM

Excellent post there Jim.

For the record, the 300D hardly smoked at all either. If I romp on it at night with headlights behind me, I can see some, but that's it.

dieselbeagel · #41 01-13-2004, 12:48 PM

With care and vehicle sympathy, u will own ur vehicle for a long time. This will be accompanied with less wear and tear, and hence less $$$ dished out to keep ur car in decent working condition.

Redlining it, driving it to see if u can hit 100 mph in X secs, trying to take corners on two wheels...etc, will cause more wear and tear than not. If u feel the need to do the above, a 20 year old diesel is the wrong car to do it in. ( BTW so is a Pinto )

Ask anyone that has kept a car well for a long time and they will tell u that not abusing ur car is one of the best things u can do for ur car and ur wallet. ( I would rather buy a car from an old lady than someone who is a speedster/street racer. )

I have been told that diesels r meant to drive at 70 mph, 24/7( 24 hours a day - 7 days a week). Drive with care, keep it at about 70 mph (+- 5 ) on the highways and goodluck.

The average age of diesels on this website seems to be about 20 years. A car in that age group needs care to survive. If u keep ramming it, something has to give. I believe that translates to more repairs and replacements.

Fredmburgess · #42 01-15-2004, 09:24 PM

Ah heck, just change the oil frequently, drive it gently until its warmed up, and then stand on it!

Mine's got more than 400,000 miles on it and I run it for hours at a time over 80 mph - every week - on used cooking oil fer cryin out loud. When I pull off the interstate it settles right back into a nice idle like I've only been around the block. Drive smoothly, don't bang through the gears or make an automatic do so, but don't worry about high RPM - wind it up!

....not that I've got an opinion or anything...

Gilly · #43 01-15-2004, 10:24 PM

Yeah, put it right to the floor and hold it there, Diesels just LOVE that crap

.

Gilly

rwthomas1 · #44 01-15-2004, 10:27 PM

Wow, this post got a little off track..... She just wanted to know if it was okay to shift at the little dots on the speedo! YES! Thats what they are there for! The dots indicate the max speed in each gear. If the user deems it neccessary to shift at these points to obtain satisfactory performance it perfectly okay to do so. Great post Jim, informative as usual. So Jen, the short answer is check the oil often, and mash the loud pedal as you see fit. RT

Gilly · #45 01-15-2004, 10:35 PM

I guess I am unaware of "dots" on the tach, which is what I assume she means-marking on the tach, so I am assuming the redline marks. Although I am also wondering, does a 240 HAVE a tach? I thought they had a speedo and a big ol' clock. I know there are those little mystery hash marks on the speedo. Or am I wrong about the dots?
I'd recommend against hard throttle application on an older engine like this. Once in a while, out on the highway to "exercise" it I can see, but full throttle just to "keep up" with traffic, or lets say to beat someone to the next traffic light? Bad idea. Poor lil Pete, he's only a lil 240!

Gilly