I recently read the entertaining thread started by hottee18m regarding driving hard. I've been driving the 280SEL (huge car with a smaller engine) for over a year now, which has resulted in my developing a heavy right foot. Now that I own a 300SD, the 280SEL is parked and waiting to be sold.

It is such a great feeling to stomp on the pedal of the 300SD, let the turbo kick in, and fly up a 7% grade mountain pass at 70 mph in overdrive, while all the huge engined SUVs poke up the hill at 60 mph. I just love the torque that the diesel provides. Here is the problem: my 300SD has some blowby. The blowby is not excessive, i. e. my engine starts on the first or second crank and I have only added about 2/3 of a quart of oil since the last oil change (2400 miles ago), but nevertheless, the blowby exists.

I would like to postpone the act of rebuilding my engine for as long as possible, so obviously it would be best to drive the car gently. However, I find it hard to not enjoy my cars capabilities on occasion. What I would like to know is how fast the effects of harder driving will worsen my blowby. Should I never accelerate hard (unless I must for the purpose of remaining safe), or is it okay to drive with a little more pressure on the accelerator?

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Ben

The MBs:
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K

Ben,

The oil consumption rate you describe is about a quart in 3,600 miles. This is not oil consumption. I would expect that this is about the oil consumption rate of these engines when new.

Excessive oil consumption worth concern is when it drops below about 1,000 or 1,200 miles per quart. Even then, these engines will run many, many miles if kept full of oil and changed regularly.\

Keep climbing the hills, check the oil, keep it from dropping below the add mark and enjoy yourself and your car.

Have agreat day,

To day I drive a spark ignition engine.
I have driven the compression ignition engfine in the past.
There are two distinct different methods for driving these two different machines.
Simply putted: A spark ignition engine(gasloine) is driven with the throttle position from the top down. The very soft pedal to reduce the combustion chamber pressure and give longer engine life and decreased fuel consumption.

The compression ignition engine(Diesel) is driven with the pedal from the bottom up. Full throttle to obtain power and forward motion. As the speed builds you relax the pedal toward the top and the cruise position.

Your driving technique is holding with a diesel engine.

Your crankcase blowby is a different matter. You should have a cylinder leak rate performed, this may help isolate your problem; if you really have one.

Larry told you right in oil consumption rate, you don't really have one.

Happy Trails Beep Beep from Houston

Donald

I would usually never disagree with the two esteemed MB experts that have replied to you on this forum, but I might have one small disagreement with Mr. Swinford's statement.

In heavy diesel trucks and buses, you add a little throttle pressure at a time and allow the combustion to catch up with the injector timing. The reason for this is that you can easily "overfuel" the engine at low speed by stomping down too hard on the throttle. I believe that this is true of all diesel engines. Try it and see. Push down a little way on the throttle, hold steady, and wait. The engine should continue to accelerate until the engine has "caught up" with the injector spray. "Overfueling" results in excessive black smoke (and soot) which is produced by an excess of unburned diesel being expelled by the combustion chamber with the exhaust gasses. When you see a diesel engine producing an excessive amount of black smoke, it is due to the operator "overfueling" by pushing down too hard on the throttle while the vehicle is at lower speed and as such, under heavier load than at road speed. There is nothing wrong with punching it at road speed if you choose to.

Don't worry about the "blowby" produced by your engine at this point. From what you say, it's minimal. Follow Mr. Bible's advice about oil changes: "Change it hot, and change it often." and you can't go wrong.

I am glad to hear that Colorado is still there, I lived in Denver as a child, and grew up in Pueblo and attended College there.

__________________

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."

Wow Ben... I guess we're kind of alike! I love flooring my 300D up a hill and watching traffic dissapear behind me. I'm not sure if I'm leaving them behind distance-wise or maybe I can't see them because of that lovely diesel smoke. Either way, it's a great feeling... LOVE the sound of the 5 cylinder engine! Anyway, after some hard driving there is some blowby. Pretty normal I've been told.

These engines are known for blowby compared to most diesels. Have you ever pulled the oil filler cap of a VW diesel. Wow, it will blow your hat off and thats a new engine. The MB's are somewhat the same. Don't worry. If you can blow by other vehicles up a 7% grade at 70mph you have a good engine. Blowby is a sign of a worn engine with low compression. Low compression=low power and lots of smoke.

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Mark
82 300SD 110k
91 Caprice SS
92 Jetta TD
97 Cadillac Concours(300hp)
84 Celebrity 4.3L diesel

Mr Longston,
Does not the diesel have a loop rail system? Is not the system pressurized to a high degree and is there not a return line to the fuel tank??? Does this not mean, in fact, that stomp or no stomp, any fuel which is not metered into the cylinder chamber, is not not used.

thus, doesn't this lend credence to the "bottom up" theory above mentioned?

[feeling convoluted today}

You are right. Again I'm caught with my Assumtion face with mud ALL over it. I made an assumtion and my suggestions were all wrong. Thank you for aiding our Hard driver.

But most of all I'm pleased you recognise my postion, I be da Kwink.

Happy Trails Beep Beep from Houston.

Donald da noes it all

Thanks to both of you for your comments on "Bottom Up". I don't think Sc---- meant to be contradictory, just added a little more info than I did.

Happy Trails Beep Beep from Bottoms up Houston.

Donald, no mud on my second face.

DEEZEL, you are basically right, but your points really do not compensate for the fact that a vehicle at slower speeds is under LOAD, and/or cold, and as such is not able to burn all of the fuel being metered into the combustion chamber as efficiently as it should, or would under ideal circumstances. And yes, the turbocharger does help...

Remember that early Porky Pig cartoon when he was strapped to a chair and forced fed pies? Ever notice diesel cars that have soot all over the rear of the vehicle? The metered fuel is injected directly into the combustion chamber At the top of the compression stroke and just at about TDC. What's in there is either going to completely burn, or not. Depending upon all factors, including outside air temperature. There's no going back (Thomas Wolfe) to the fuel tank after that.

My contention is that a diesel engine that is cold, and/or under load (at slow speed) will not fully burn all of the fuel supplied it efficiently enough to result in a "clean burn" if it is being fueled faster than it can do so. Ever notice how your diesel smokes more under hard acceleration? Hmmmm...

Also the fact is, that no one (not even Mercedes) has really manufactured a completely compatible automatic transmission for diesel engines. The optimum performance achieved by Rudolph Diesel's invention (1892) is done so only by the proper use of a manual transmission that allows the engine to operate in it's optimun RPM range, or "Power Curve". That's one reason that I follow Bob Bondurant's guidance on manually selecting gears in an automatic transmission.

Try it my way, and see if your results aren't better, your emissions less, and your transmissions and engines don't last longer. I was taught to drive diesels that way, and I never taught anyone to drive differently. Frankly, I went out today, and tried several different ways of driving my Mercedes diesel just for S&G, and I can't imagine how y'all can do it "your way".

Finally, "blowby" really is the amount of combustion gases that pass by the piston rings, so it really can't be accurately measured. Only compression can. As Larry Bible has pointed out numerous times, if your diesel car starts up right away, you got compression.

Ben, I think y'all's got compression, by gawd!

__________________

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."

You got the facts right but on some of our less aerodynamic designed machines, the air is turbulant and at lower pressure than further behind the rear of the car. It isn't a vacuum, just lower pressure and the mist or whatever comes from beneath the machine is lifted up and into that lower pressure area. That's when the heavy stuff falls out and onto the coach work.
Boy you didn't know I knew so much did you?

Happy Trails Beep Beep from fallout Houston.
Donald

BILL!

I remember as a boy, putting a bunch of CrabApples down the exhaust stacks of trucks that parked next to where I lived, and how much I always enjoyed the sight and sound of those SOOTY apples flying out of their exhaust stacks when they gunned the engines right after starting them up!

I would be real surprised to find that you haven't seen trucks with DRY black soot caked all around the tips of their exhaust stacks...

Next time you do, watch how much BLACK smoke comes out of that rig as the driver leaves your line of sight...

And of course it smears, it's diesel oil! Diesel is much oilier than any other form of fuel, it was designed to be! Now, don't get me wrong, you are right, a diesel with bad valves, and/or a bad oil leak from the engine or even the transmission will produce an ideal environment to collect more soot, and will stick more than just regular poor driving style soot will. But that soot hasta come from somewhere! Soot is primarily composed of unburned diesel fuel combined with diesel exhaust by-products. Oil blowby, and poor valve adjustment is one thaing, but bad truck drivin' is another, 10-4? Now, don't y'all make me get out my training materials I have out in the garage!

And Bill, I ain't got no damn soot on the back of my car! Thank You Verrry Much!

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Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."

As much as it pains me to agree with & support a Californian, Longston is right about using a light foot and trying not to add more pedal than the engine needs. I was taught to drive tractor-trailers by a guy who only owned one ( I was the part-time helper & co-driver), and he wanted to make it last & not use any more fuel than he needed to. He went on at some length about just how to feed fuel gradually, and occasionally had me practice backing off to see if I had more pedal down than I needed. He also had a technique he insisted on of backing out of the pedal (no, it's not a throttle, and it's not a gas pedal -- he would insist) when climbing a hill --- as the engine slowed from the ascent, it needed less fuel, and he did his best to give it only what it could burn .... and insisted that I practice the technique, too. It works. You'll use less fuel, make less smoke, have less soot on the rear end, and, I would expect, have less carbon crapping up the inside of your engine.

Ed