High altitude driving issues

I agree and you could change the equation by changing the carb jets based on altitude.

nohurry wrote:
Skip, I always enjoy and respect your posts, but that 10% per 1000 ft can't be right can it? That would mean if a N/A engine was running at 7000 feet elevation, it would only have 30% of its power. I know there is some loss, but I have heard figures in the 3% per 1000ft range.

skipnchar wrote:
With a normally aspirated engine (no turbo or super charger) you will be loosing something like 10% of your horse power for each thousand feet you go above sea level. If you have a turbo diesel or turbo charged gasser, this power loss is almost non existent. Also keep in mind that water (also coolant) will boil at a MUCH lower temperature at high altitude so you MAY have lost some water from your radiator. Check to be certain you have a GOOD radiator cap on your engine to keep the coolant under correct operating pressure.

Skip, I always enjoy and respect your posts, but that 10% per 1000 ft can't be right can it? That would mean if a N/A engine was running at 7000 feet elevation, it would only have 30% of its power. I know there is some loss, but I have heard figures in the 3% per 1000ft range.

First suggestion is have you cleaned the radiator, then fuel filters and air cleaner. Turbo charged engines stat to de-rate above 10,000 feet. On steep climes it is better IMHO to downshift and keep the RPMs up ~3000 over peak torque RPM.

Are you downshifting manually to keep the RPMs up? Or are you just letting the automatic decide when to shift? Try climbing in 4th - not as fast, but will keep the RPMs up.

Barb

You didn't mention if the cummins had a turbo or not, but I'll assume it's a turbo. One possibility might be the fan not pulling enough air across the radiator. As air density decreases, the fan will pull less volume for any given RPM. It's been to long since I took my aircraft powerplant classes back in the 80's for me to remember the formulas, but it seems a fixed prop lost about the same amount of power as an engine, which you could get pretty close to calculating by figuring 3 percent per thousand feet.

All that said, I've never noticed what you're experiencing.

With your rear radiator/CAC, have you checked the from of the CAC for blockage?

Freightliner chassis with a 300hp cummins. It isn't steep hills its anytime above 6500' and of course more noticeable on a climb.

We are from Alabama, and are currently heading through Wyoming. So the altitudes here are much greater. The temperature is moving higher above 6500'. We will check the air filter as soon as we stop again, and the radiator cap.

Please let us know what engine/chassis you have.

And is it elevation related or only on steep uphill sections?

I'm not sure what you mean by "high altitudes. I regularly operate my rig on mountain passes exceeding 7000' and have never noticed any indication of high coolant temps or loss of power. Perhaps your air filter & radiator requires some attention.