Downshifting on steep hills

[JDHarrin]

My wife and I drove 450 miles to North Carolina to inspect and buy our Aspect 28B a few weeks ago. After a full days inspection, we left for home, me driving the RV, her driving the car. We were enroute to Northern Virginia. I hoped to return the same route we went down because it was relatively flat until the last hour of travel. But Waze took us another way; up and down through the Shenandoah Mountains.

On the first really long, downhill slope, I seen a sign saying trucks should use a lower gear to control their speed. It seemed to make sense that I should do the same with the RV, so I downshifted the E450 into third gear, which as expected slowed my descent. A minute or so later, I seen all this black smoke behind me and at first, thought it was a car I couldn’t see in my mirrors. Then my wife called saying To pull over quickly; that the RV looked like it was on fire; There’s so much black smoke. I quickly shifted back to drive and rode the brakes the rest fo the way down the hill. The smoke cleared up and we drove the rest of the way with no problems.

I thought I’d raise the issue here to see whether I did something wrong or if there’s something I need to have looked at. Any input or suggestions?

[creativepart]

How about telling us the year of the coach, new or used? So we know it it’s under warranty. But in general that sounds like something I’d have looked at by a commercial ford truck dealer. That smoke could be a sign of engine or transmission problems.

Have you checked fluid levels? If not that would be a good starting place.

Also I suggest not letting any GPS “make” you go a route that is different from your planned route. Especially Waze.

[Goodspike]

How many miles on the engine would also be helpful. And how much oil the engine looses under normal conditions--a quart every X thousand miles.

Generally downshifting shouldn't be an issue unless maybe you're letting the RPMs get up near or above redline for the engine. But back in the day when engine tolerances and materials were not as good as today it was quite common for an engine to smoke AFTER going down a hill WHEN the driver applied power to the accelerator pedal. I don't recall seeing smoke when continuing down the hill without power being applied, but I suppose that would be possible if the engine were bad enough or the slope long enough.

I don't even have a theory as to why it would have been the transmission. But this is an instance where it would have been nice to have a bluetooth OBD-II scanner setup on your phone so you could have checked the transmission fluid temperature.

[JDHarrin]

Sorry, it’s a 2010 Winnebago Apect 28B with 32,700 miles on it. It never went above 3,200 RPMs downhill.