Running a 300DT in high altitude elevations - PeachParts Mercedes-Benz Forum

Veloce300DT · #1 05-23-2004, 03:17 PM

I took a trip to Reno NV from SF CA. The route brings you over Donner pass, which I believe is about 7000 ft in elevation.

On the highway I couldnt tell the difference in performance compared to being at sea level. BUT when I took an exit to grab a drink at a gas station it all changed. Accelerating from a stop in high elevation areas became a completely different driving experience. The engine seemed to lack power, driving more like a non-turbo 300D. I checked oil level out of curiousity and it was fine. I was also running Red Line 85+ through the fuel system.

Back on the highway the car performed as normal once I had it up to speed.. plenty of passing power etc..

And once I returned to sea level on the return trip home, the car drove perfectly, with the normal ample acceleration power.

Does altitude really have such an effect on performance, or was there somthing possibly wrong with my car?

(the temp gauge was at normal level throughout the trip, fluctauting ever so slightly on grades)

#2 05-23-2004, 03:30 PM

Nate.

Yes, it is normal.

The air is thinner at that altitude,so it has
less oxygen in it.

Since every engine needs fuel,spark and
oxygen to run,so reducing the oxygen
will affect performance.

The reason why at highway speeds it
feels fine is because air is being rammed
into the air intake and into the engine.
Could also be because at cruising speed
the engine requires less fuel then at take
off and this evens the mixture out.

Louis.

Veloce300DT · #3 05-23-2004, 03:34 PM

Very interesting... thanks for the information.

Just out of curiousity...what do people do who drive cars similar to mine in high altitudes all the tiime? Do you adjust the throttle or is there some other means of getting more power?

dmorrison · #4 05-23-2004, 03:36 PM

At 7000' MSL the air is approximately 25% less in pressure. So you have less oxegen in the air for your fuel to produce power with.
You will also find the transmission shifting a little harder due to the lower air pressure.

Dave

Veloce300DT · #5 05-23-2004, 03:51 PM

yeah the transmission was shifting like it was gonna fall out!, compared to the smoothness im used to.

langpfeife · #6 05-23-2004, 04:14 PM

At higher altitudes the car will accelerate a bit slower until it builds some boost (which will also
take a bit longer), so no worries.

I've driven Donner a million times BTW, one of my favorite drives in a turbodiesel Benz. The long
corners are a blast, as is bombing up the summit at 90mph.

I used to use the summit as kind of
a loose gauge as to how well my diesels were running. The best I ever did in my old n/a 300D (now sold)
was just above 70, after it's overhaul, and on a crisp spring morning. (Which is about as good as you can
get in one of those.) The turbo does it about 10-15mph faster.

Veloce300DT · #7 05-23-2004, 04:34 PM

Yeah!

It was the second time ive driven that pass in the 300DT. Before that I had only driven it in my moms C280, which is very different...

I LOVE driving it in the 300DT... it takes the inclines with grace, the curves are AMAZING, and the high compression of the engine made the brakes unnecessary.. all while maintaing a steady 80-85MPH... even 90 at places. Construction on the decend down to Reno made 55MPH at that point mandatory otherwise.

In the C280, driving at the speeds I drive in the 300DT means using the brakes more and naturally more GAS.. YUCK!

Veloce300DT · #8 05-23-2004, 04:37 PM

Also-

On the way back to SF, heading east on 80, I encountered a snow storm oddly enough.. heavy rain, slushy road for about 4 minutes at the peak, and then slick rain for another 5 minutes....

Felt safe and secure in the 300DT, was really upset about the salt minerals from the wet road being sploshed all over the car though!!

I stopped at our cabin further down the mountian to wash and detail her as the sun was back out.

coachgeo · #9 05-23-2004, 05:15 PM

Rub it in.... Go ahead RUB IT IN you miserable Donner Summit travelors

I long so muchhh to take that trip again into CA from Reno. Then take off toward Placerville. Then 3 days down the Rubicon back to Tahoe. Yep, all in my 300Dt. Well 300powered Diesel Truck that is :p

wanna be Unimogen the Con
George

#10 05-23-2004, 05:30 PM

Your turbo is more than adequate to compensate for the less dense atmosphere at 7000-8000', BUT the engine must be turning sufficnetly fast for the turbo to be generating significant boost. Until engine rpm gets to 1600-2000 rpm, the power loss will be VERY evident.

Re-tuning the ALDA so that there is a little additional fuel enrichment a low engine speed will improve the low speed torque at the cost of just a little fuel economy.

Marshall

ohcaptainron · #11 05-23-2004, 07:17 PM

I live in Evergreen, CO. 7300msl. I have been driving turbo diesels up here for over twenty years. Blocking the EGR line, making sure you are producing about .9 bar boost and getting the ALDA correct make all the difference in the world in a 123. My 85 300TDT will pull I-70 just west of Denver (7%) grade 6000msl, at 80 mph. On the slight inclines at over 100 mph. Still gets 23.5mpg. The critical altitude ( the altitude the turbo is no longer capable of .9 bar is over 11000 ft. Now the turbo lag is quite long but once up to speed it runs great. Overall a very good mountain car.

Veloce300DT · #12 05-23-2004, 09:31 PM

Cachgeo-

After I Donner summit, I made my way down the hill, into Auburn, after washing the car from the snow. I then decided to visit a friend in Pollock Pines, so I took 49 over from I80 into downtown Placerville. Then up to Pollock pines.
I spent alot of time as a little kid in that area, from everywhere in between Sonora, Jackson, Placerville, Pollock pines, north&south shores of Tahoe, and Carson City. Its really Beautiful as Im sure you know.
I remember taking a trip to cloroado. In my opinion, everything inbetween reno and colorado was soo dry and boring (being summer). On the way back going up through Tahoe I couldnt believe how much greener everything was... it made my appreciation for the foothils, the Sierras, and CA in general much greater.

A while ago I was reading a post from a guy in Pollock pines who turned his w123 TD into a 4 wheel drive by using the chassis and suspension of an Explorer or Blazer I think.... very interesting.

Happy motoring!

#13 05-24-2004, 07:50 PM

On the weekend after memorial day, I'll be taking a joy ride up the Pikes Peak toll road (14,500ft?) and I will be sure to report how well it does up there.

Just going from Tulsa, OK (800ft) to Littleton,CO (5120ft) made a BIG hit in pre-boost and turbo lag performance.

#14 06-01-2004, 07:49 PM

The trip turned out to be much better than I hoped. Going up was a breeze above 5psi boost. When I had to let off the throttle, it was a completely different story. Plenty of black/grey smoke in the higher parts.

At the summit, just touching the pedal would make a cloud of black smoke! But the big mistake was shutting off the engine.

It took 3 trys to get started again. The first time, it would not say above 500rpm.

If you have a 240D, I would think twice about going up the road...