Climbing with 450 hp and Allison 6 speed

[MTrif]

We recently purchased an 2016 Allegro Bus 37 AP with the Cummings 450 HP and Allison 6 speed Automatic Transmission. We tow a Jeep Wrangler behind. Took it for its first trip up some steep grades and had the temp light come on. On the first grade the Cajon Summit out of Los Angeles area I manually downshifted as I climbed and tried to hold RPMs at 1500. On the second big grade on the 395 north of Bishop let the auto transmission do its thing. Still got the temp gauge and both times coolant and transmission temps were fine.

So any recommendations on best way to climb long steep grades would be appreciated.

[MSHappyCampers]

If the coolant and tranny temps were fine then what high temp reading are you getting?

[YC1]

You can use higher rpms of course which will keep the fan up to a higher speed if a fixed blade system.

A clean radiator and good thermostat is a must. I would be interested in the actual engine temps and tranny temps. 210 is a good goal for my rv with the 400 ISL. I can push it up a bit but no reason to rush and overwork the engine.

[345 desoto]

Faulty gauge/sender?...

[rrtribble]

When you say the coolant and trans temps were okay, can you share what they were reading? Are you using the 'guess-a-gauge' or the temp in your dash listing?

Could be sensor.

Richard

[Kuzzy]

At 1500 RPM on a long grade it’s probably the exhaust gas temperature.
Keep your revs closer to 2000 with less throttle input and see if that helps.

[Crasher]

I suspect you may have a defective sensor. I keep my 450 ISL at 1800-2,000 rpm when on a long mountain incline. The peak torque is near 1400, but peak hp is about 1900 where it is also the best cooling for engine and transmission. My temp will range between 185 up to 210 when the fan switches to high speed bringing the temp back down.

[96 Wideglide]

Originally Posted by Kuzzy

At 1500 RPM on a long grade it’s probably the exhaust gas temperature.
Keep your revs closer to 2000 with less throttle input and see if that helps.

This.

It will also spin your water pump faster.

[CountryB]

Originally Posted by Kuzzy

At 1500 RPM on a long grade it’s probably the exhaust gas temperature.
Keep your revs closer to 2000 with less throttle input and see if that helps.

Do any Coaches come with an EGT gauge?

[Milford 47]

Originally Posted by Crasher

I suspect you may have a defective sensor. I keep my 450 ISL at 1800-2,000 rpm when on a long mountain incline. The peak torque is near 1400, but peak hp is about 1900 where it is also the best cooling for engine and transmission. My temp will range between 185 up to 210 when the fan switches to high speed bringing the temp back down.

My temperatures mirror your's climbing grades or passes towing and at similar rpms

[wolfe10]

Originally Posted by Kuzzy

Keep your revs closer to 2000 with less throttle input and see if that helps.

Good answer. Use the down arrow to lock in a lower gear so you are at the higher end of your engine' RPM range (water pump and fan turning faster) and back out of the throttle.


If moving the throttle from where you are to WOT (Wide Open Throttle) makes no/little difference, you need to select a lower gear.


Physics suggests your speed on a long grade will be faster than loaded 18 wheelers and slower than empty ones.

[MTrif]

Thanks to everyone for your help...this forum is a great resource. Ok so to update some of the questions
1. The radiator got around 200 flat driving usually around 175....it is a Guage so guessing a little.
2. The transmission temps on the scrolling screen normal 185 got up to 214.

I found out the light is in fact for high exhaust light...now that I retread the manual. So it seems if I get the RPM hight near 2000 might help on that. According to the manual the High Exhaust warning is to let the driver know to keep it away from flammable items and people. Says not a mechanical issue.


So higher RPM and next climb and will see what happens. Will be a while as the drive home from Mammoth back home is all down hill. Will be interesting to see MPG going home. 7.1 mpg coming up.

Thanks again to all for the great input!

[Mr_D]

On my ISX the hot exhaust light only comes on when doing a regen. But it's older and no DEF.

[Old Scout]

PS--coaches/engines vary but 175 degrees seems kind of cool for normal engine ops....vs 190-195--that lower temp would likely result in a bit less MPG.....might check gauges or fan controller -- sounds like engine fan is running too fast/too much??????