rpm for 300cd 1984 - PeachParts Mercedes-Benz Forum

#1 01-03-2003, 06:30 PM

i just bought a 84 300cd with a 4speed automatic trans and i love the car. the rpm is around 4,000 when at 85 mph. is this normal, seems a little high...there is not red line on the tach. i read somewhere the max speed for this car is 105mph, which would put the rpm pretty high. thanks for the help.

engatwork · #2 01-03-2003, 06:39 PM

Sounds pretty normal. Push it on up to 105 the next time you are on a closed test track - I think you will see between 5 and 6k rpm.

#3 01-03-2003, 06:41 PM

5-6k RPM? Impossible.

engatwork · #4 01-03-2003, 06:57 PM

I'll swear I seem to remember having seen my 300D above 5k (or was that 4K). Heck TD when you get my age you will do good to remember stuff like this

.
4k at 85 does sound normal though.

Nate Stanley · #5 01-03-2003, 07:02 PM

There's no redline because a governor in the injection punp will kick in and shut off the fuel before the engine scatters. Useful RPM is about 4400 max, and even that's pushing it IMHO.

This is a real high revving engine as diesels go, one more reason I have such respect for the MB 5 cyl.

#6 01-04-2003, 03:30 PM

i checked it again and i got 3700 at 85 mph. thanks for the help, i just bought the car from family and didn't know about this forum until yesterday...what a great forum. i sure know where to go with future questions.

Gil · #7 01-17-2003, 12:05 PM

Hey, hats off to you if you can get it above 85 without the wind at your back. That's about all mine is capable of, normally. I never knew a 123 was supposed to be able to hit 105mph.

Mine just seems to quit around 80-85. If I have a really, really long stretch of road, it may think about getting near 90, but that's about it. Not exactly a rocket ship. It isn't like the car is straining at those speeds, it just seems to say "Ok, pal , that's it for me."

Could be a cylinder compression/engine wear thing after so many miles. Anyway, congrats on the car and enjoy the forum.

#8 01-17-2003, 12:11 PM

I would expect a turbo 123 car to be capable of running 100MPH all day long. You would have to stop along the way for fuel, however.

Have a great day,

JHZR2 · #9 01-17-2003, 12:55 PM

Mine was still going well at 95 mph, but because I wasnt so sure about taking a car with 190K+ miles too fast on an interstate section known for having a lot of cops, I didnt go faster (I was at 95 mph for probably 1-2 mi though).
I would conficdently say that my 300D could do 100 all day. 95 was as comfortable as 75, except a little extra noise. No odd shaking, etc.

JMH

The Warden · #10 01-17-2003, 06:12 PM

FWIW, I'm running at 3000 RPM even at 70. This car'll go up to 90 and beyond, as I found out one day when I let my girlfriend's sister drive it down the I-5

I didn't know she had such a lead foot...car didn't complain, although I had her pull over shortly thereafter and took over...

I don't know how fast the car's capable of going simply 'cause I haven't had the guts to try it yet...be nice ot find a closed track where I can let it unwind, though; I tend to stick to the speed limit and the car wants to go faster

I was under the impression that these engines hit the governor at 4500 RPM? Certainly higher than my Ford

The Warden · #11 01-17-2003, 06:30 PM

Yeah, it's 2.83 on the rear end. When I say "federal", I'm contrasting it to the California cars that had the trap oxidizer and whatnot added on. This was originally a Texas car; in fact, I flew out there to get it.

And sounds good on the fluid

How much is there? Extra bonus if there's enough to do it all at once

1stimer · #12 01-28-2003, 10:06 PM

I just thought I would chime in and say I am hitting right about 3000 rpm when cruising at 70 mph also. I have a California version---1984 300D...Aloha

rwthomas1 · #13 01-29-2003, 12:05 AM

When you swapped the diff what did you do to recalibrate the speedo??? I want to do this mod. Also, how does the acceleration compare before and after the swap? My 84 turns 3400rpm at 75mph FWIW. RT

1stimer · #14 01-29-2003, 12:15 PM

Speaking of Hilo a guy from Hilo was e-mailing wanting to sell me his 116 300SD. It looked nice, but I wanted the 123. You know you can get pretty far up on Mauna Kea without a four-wheel drive. Cannot get to the summit, but it'd be interesting going up that high. I sure do miss the big island.

Good luck on your trip...Aloha

The Warden · #15 01-29-2003, 05:58 PM

Quote:

Originally posted by dieseldiehard
and the '85 trans is worthless for a conversion like this.

Why is this? Is there an inherent problem with the '85 tranny or something?

Mine's working fine thus far (somewhat hard shift between 1st and 2nd, though)...but if there's an inherent problem, I'd like to know how to try to prevent it before it manifests itself...