How To Drive With Overdrive

[satboyz]

I have just got a Class A Fleetwood motorhome this summer we are planning to go to British Columbia.

When going up a steep hill what is recommended-- never drive in overdrive or use it?

[wolfe10]

Ron,

What chassis, the Ford V10 6.8l is a high RPM engine compared with the GM V8 8.1l?

What transmission, Ford 4 speed, 5 speed, GM 4 speed, Allison 5 speed?

Brett

[satboyz]

It is the 8.1 Chev motor, Workhorse Chassis. Not sure about transmission, 2006 Fleetwood 36D Pace Arrow.

[vtbigdog]

I have the 8.1 with the Allison 5-speed transmission. I drive at 62 MPH with Cruise Control on the highway. I also have a ScanGauge. When I am climbing a steep hill I watch the Load on the ScanGauge (LOD). When I see the transmission is nearing the downshift zone I cancel the Cruise Control and press the accelerator only hard enough to prevent the downshift. I can go as low as 50 MPH in overdrive, so if I am nearing the top of the hill and am still above 50 MPH I will work the gas pedal to crest the hill in overdrive.

If the hill is severe and a downshift is inevitable, I will wait until the speed drops to 55 MPH and then momentarily stab the gas pedal to force a downshift and then perform the same procedure in 4th gear and try to crest the hill in that gear. If speed drops below 50 MPH I turn on the flashers.

I also monitor transmission temperature on the ScanGauge and can use that as a guide. I have never seen a transmission temperature over 178, which coincidentally was going downhill.

My weight about 20,000 lbs and I have only had to downshift once into 3rd gear...at around 40 MPG to get up and over Fancy Gap on I-81 N

You also did not mention going downhill...which is more of a concern than going uphill. When I know a steep downhill grade is coming up I will slow down to 55 MPH. I will then stab the gas pedal on crest of the slope to take the transmission out of overdrive to keep the initial speed down. I then gingerly use the brakes and only to apply short speed-killing bursts.

[wolfe10]

I have a minor difference of opinion from the excellent post by vtbigdog.

On descending a grade, gas or diesel, the objective is to find a gear (with diesel, transmission gear AND use of exhaust or engine brake) THAT WILL KEEP YOUR SPEED IN EQUILIBRIUM. By that I mean neither accelerating nor decelerating WITHOUT USING THE SERVICE BRAKES/BRAKE PEDAL.

Those truck "Run Away Lanes" on major grades are for heavy vehicles that used there service brakes to the point where they overheated and became ineffective.

So, use gears/engine brakes to keep your speed in check-- IRRESPECTIVE OF STRAIGHT/CURVES in the road. As a good reference, your equilibrium speed will be faster than loaded 18 wheelers and slower than empty ones-- straight physics (braking HP vs weight).

Example: We were descending a 12% grade in the Green Mountains (REALLY steep). I was in second gear with the exhaust brake on in our diesel. We were going down about 18 MPH. Dianne was concerned someone would rear end us. Around the next corner, we quickly overtake and passed a logging truck doing about 8 MPH-- his equilibrium speed. Even though the curves in the road said we could go 30-35 MPH, doing so would mean WAY over-using the service brakes.

Brett