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  #1  
Old 03-28-2002, 03:49 AM
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Redline limiter (300E m103)

Ok, so I admit I've been having too much fun lately with locking my car in first and just letting it scream up and then kick 2nd gear, but it just brought a concern to myself. I noticed on my '86 300E that if you don't have the gas punched pretty much all the way down, it will just hang in first and then hit redline limiter, drop a few hundred rpms, then back up again. Now this has happened to me twice (I learned to keep the pedal down now if im doing the 1st gear launch), but I'm just wondering how bad this is for my car. My assumption is that since it stops it pretty close to redline, it probably isn't hurting it much, maybe speeding up engine wear though. Oh, and while I'm at it, I might as well bring up a few other thoughts that come to mind. As far as the 1st to 2nd gear change goes, does this only happen when the pedal is down far enough to push the little switch on the floor? And my last thought is about redlines in general... what sets the redline? I mean, how do they determine the redline of an engine, and what exactly are the effects of going over it? Does it just overheat? does it cause quick engine wear? when you add mods on to your car, does this redline change or is this only when doing major work like cams or crankshafts? Sorry for all the questions, I'm just a curious guy
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  #2  
Old 03-28-2002, 05:25 AM
David C Klasse's Avatar
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Firstly, the redline is determined by the highest engine speed deemed safe for the motor. If it is exceeded (though we have rev limiters), the engine cannot handle the high rate of speed... it was only designed to be revved so high before parts starting breaking/blowing/etc. I am no expert though, but this is a pretty good idea.

If your car is in good mechanical order, and you have good fresh oil and GOOD TRANS FLUID (IMPORTANT) then I wouldn't worry much. I have driven the SH** out of my engine for the past 60k miles and it still drives like a dream with good maintenance. Just make sure you have good fluids... and there is a line to draw... I wouldn't do it TOO much... but your engine is a damn good motor that was designed by Mercedes engineers... the cars in Germany are driven like that ALL the time.

If you floor the gas, but no kickdown, it will change into 2nd gear below redline, about 5500 RPM. If you keep it in kickdown, floored, it will shift into 2nd at redline. If you have the shifter in 2, and floor it (no kickdown) it will shift about 100/200 RPMS shy of redline. (If in 2 and kickdown engaged, then it'll shift at redline)

Hope this helps!
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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)
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  #3  
Old 03-28-2002, 09:10 AM
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On the 1986 to 89 300E's the RPM cutout is controlled by the fuel pump relay. The 1990-92 cars use the MAS relay & that also is the fuel pump relay. SO these cars shut the fuel off at max engine speed.
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Old 03-28-2002, 07:16 PM
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Good to know, thanks guys! I noticed these engines can take a lot of beating... on most other cars ive driven, or what my friends drive, you'll smell something after pushing the thing hard. With my car, i can pull some drag races at the max of my car's ability and then cruise on home normally without abnormal smells, engine temps, pings, etc. Now, the only thing left that I find weird is that 1st gear start thing still... my car won't shift unless the pedal is down enough to hit the kickdown lever on the floor (otherwise it hits rev limiter and sits there in first), I tried it again today to double check. Not a big deal to me, just found it odd because I thought it would shift at redline or before no matter what. Maybe something needs to be adjusted or something, but it doesn't concern me much. One more stupid question though... which is what's usually the first thing to break after passing redline? I'd assume something in the valves or cams, but not sure. And if you put higher performance parts in, this would up your redline wouldn't it?
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Old 03-28-2002, 07:21 PM
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Quote:
[i]One more stupid question though... which is what's usually the first thing to break after passing redline? [/B]
Your wallet
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  #6  
Old 03-28-2002, 07:30 PM
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Your car is designed to start in 2nd gear, unless KICKDown is activated, or the shifter is put into 2 at a stop. If you do a search under "first gear start" you'll find TOO much info on the topic... so there is no lack of info on this subject.

Your car was designed to safely operate just under the redline, at the maximum point before your engine falls apart.

MANY MANY things could happen... you'd really SCREW up the camshaft, you'd overheat the engine, warp the head, bend some pistons... a lot of MAJOR ***** would be endured on the engine! Don't worry about it.. because, good thing, YOU aren't able to do it. (Just don't put it into 2nd when cruising above 68 mph!!)
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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)
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  #7  
Old 03-29-2002, 12:37 AM
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if you exceed the max engine speed, you will have valve float and if it is an interference engine (i dunno about the M103 and M104), your valves will make a high-speed, spectacular, and expensive acquaintance with your pistons.

usually, there is a margin of safety between the redline and the real max engine speed (which is higher than redline). This is because, although the computer controls the engine speed via the fuel supply, it cannot prevent an over-rev if you downshift into a lower gear that will make it exceed the redline (those are the marks on the speedo corresponding to the gear#).

beyond that, the forces of the reciprocating masses (pistons, con rods) will cause failure somewhere.
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Old 03-29-2002, 02:13 AM
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oh, hey i just thought of something else (sorry). when cruising along at 50 or so, if i shifted it down into the '2' position, would the transmission automatically know to hit 2nd instead of 1st because of the speed im going or would it kick into first instead?
the 68mph barrier is for 2nd gear right?
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  #9  
Old 03-29-2002, 02:34 AM
David C Klasse's Avatar
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Location: Mission Hills in the City of San Diego
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Quote:
Originally posted by KNanthrup

the 68mph barrier is for 2nd gear right?
Correct, altough it might be slightly different for your model. Your Owner's Manual should tell you exactly what yours is.

Yes, the car knows that 2nd gear is the gear of choice when driving.
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2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)
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