How high can it go? - PeachParts Mercedes-Benz Forum

Bens lover · #1 06-20-2006, 11:43 AM

Good morning gentleman.
Would driving at higher altitude affect the performance of a turbo diesel?
Last week i drove about 400 miles north of where i live and for some odd reason I had a funny feeling the performance wasnt as good very poor at times...A few days after returning from the trip as I was getting closer to sea level,the performance was getting better and better,more power and a better pick up under load.What would be the cause of this?Does altitude have anything to do with it?
Regards
Dan

ConnClark · #2 06-20-2006, 12:11 PM

Altitude does have an effect on the performance of a diesel. Your turbo regulates boost based on the difference between manifold pressure and atmospheric pressure. If atmospheric pressure is lower due to altitude, absolute manifold pressure will also be lower. The ALDA will compensate for this by reducing fuel. This is the most straight forward explanation.

There are other reasons too. Your turbo is most likely being pushed into an area of the compressor map that isn't as efficient so it takes more power to make boost. Then there is the plain fact you just aren't packing as much air into the cylinders to extract the energy released by the burning fuel ( Look here for an explaination of this concept http://tinyurl.com/jc7wb ) .

#3 06-20-2006, 06:08 PM

You want to talk about powerloss? Take a trip up Pikes Peak or Mt Evans. A at 14,000ft powerloss is hard NOT to notice.

Jeremy5848 · #4 06-20-2006, 07:16 PM

I just returned from a 1500 mile round trip from northern California to Salt Lake City. I didn't notice any problems over Donner Pass in the Sierra (7000+ feet) but then, I didn't stop or slow down any more than necessary. Actually, I was pleasantly happy to note that my 85 CA model pulled all of the grades without downshifting, providing I kept the speed up to where the engine would turn 3000 RPM (about 70 MPH/115 KPH). Below about 2500 RPM on a steep grade, the engine would gradually slow until the tranny downshifted into third.

It was also nice that the cooling system worked as advertised -- it was rather warm in Nevada but the coolant temp never passed 100C, even uphill with the A/C on full, and cooled back down to 90C or less on the downgrade. I don't think the auxiliary fan ever kicked on, either (and yes, it does work).

Driving around town in Salt Lake (4500 feet/1370 meters), I definitely noticed a lack of power until the turbo spooled up. Idle was also rough -- it has returned to normal now that the car is "home." I don't know how much compensation ALDA can handle but perhaps it would be best to have the thing adjusted if one made a permanent move to another altitude, as opposed to a short visit.

My gradually deteriorating inner CV boots were another matter. I had a wonderful Father's Day afternoon in the parking lot of Kragen Auto Parts of Winnemucca, Nevada. Just me and my patient wife, some CV grease, and a roll of duct tape. Kept the speed down to 60 MPH and got home at 2AM. Rebuilt axles are on order from CVJ in Denver.

[Edit] Just calculated that staying at 60 MPH gave me 26 mpg for the 360 miles from Winnemucca to Santa Rosa. At 70 MPH the mileage is about 24. Hmmmmm......