Motorhome Overheated on Mt. Pass

[docj]

Originally Posted by Bob (WA0MQE)

I guess my question is how do you guys do it? I've heard some say they just let the EXHAUST BRAKE handle it entirely but if this is true mine doesn't seem to keep it slowed down enough to not use the brakes to assist it. This worries me that I might be overusing the brakes which can cause them to get too hot.

I think part of the confusion here is that many of the folks posting have exhaust brakes and a smaller number have true compression (Jake) brakes. I have a 2-stage Jacobs compression brake (Jacobs does make exhaust brakes, also) and I can descend the steepest hills with virtually no use of my "wheel" brakes.

Recently I came down Lookout Pass on I-90 going into ID from MT and followed an 18-wheeler at 45 mph with the Jake on full and the transmission locked into 3rd gear (on Allison's with compression brakes it's common for 4th to be the gear that is forced by the Jake; anything lower I have to use the "arrow" keys.) I don't think I touched my brake pedal more than once or twice in the entire descent.

A key to using a compression brake is to understand that it provides maximum braking action at very close to the engine's redline. I can safely run up to 65 mph in 4th, but to maintain maximum braking at 45, in this case, it was necessary to force the transmission to 3rd to keep the revs up.

[Five2o]

Originally Posted by RickO

That sounds great but how does it work? Your signature or profile doesn't list what type of rig you have. Is it a DP with Allison 3000? If so did you have the engine brake reprogrammed to latch mode?

Thanks,

Rick

Err sorry Rick

I have a 42AD Ellipse and it has a 2 stage Jake and 3000 Allison. Nothing programmed from stock.

Cruise control going downhill with the Jake is cake. It kicks in exactly at 5 mph over the cruise speed that is set...slows rig to cruise speed then allows a 5 mph speed gain before grabbing again.

Fine adjustment during decent is easy by pressing the set button to lower speed by 1 mph or the resume button to let the coach speed up a bit.

[Dutch Star Don]

Madrona.......It sounds like you did everything right. I would check the sensor on your fan. I also had an indicator that Monaco installed that as we drove the coach home from purchase in Fresno, California, an alarm came on as we got about 3 miles from the base of the Grapevine in Southern California. We pulled over and called Monaco. They told us the alarm was added on by Monaco and disregard it. They said If I had a real issue, the Cummins would derate and start slowing down. We disconnected the alarm and we never had another issue.

I also added a Silverleaf computer program to my coach (I posted how I did it on a budget a year or so ago....check post). It was the BEST investment I EVER made for the coach. I can watch all of the functions as I climb grades and make adjustments from the data. Its also FUN to watch!

About two years ago I changed out my coolant to the "Final Charge" Organic Acid Technology (OAT) coolant. No more DCRs or SCRs to worry about. My coach actually runs 5-10 degrees cooler with the OAT coolant. That is an experience that most find when changing the coolant.

Finally...BOB.....There has been a hodge podge of info on the post about how the transmission and exhaust brake work....some even from people that don't have the system.

The Cummins 400 ISL came with a either an exhaust brake or a two speed engine brake. The engine brake came on some of the higher end models. I don't have an engine brake, but my understanding is that its a lot more powerful than the exhaust brake and gives you more adjustability.

The exhaust brake has a lot of limitations. On my ISL, the transmission indicator indicates "2" when the exhaust brake is engaged. It doesn't mean the trans shifted to second gear. It means that is the lowest geat it will acheive before the exhaust brake disengages. The newer models have a double window and indicate "2" and the gear it is in. Some are programmed to indicate "4" as the desired gear. Mine disengages at about 15 mph in second gear. Someone said theirs works with the crusie control on. That is a fairly new feature and didn't work with a lot of the older models. Once you turned the exhaust brake switch on, cruise control turned off. There is an aftermarket switch that remedies this and doesn't engage the exhaust brake until you tap the brake pedal and releases it when you touch the throttle.

On mine, at speeds above 63-65 mph the exhaust brake does not engage. The shifter will go to "2", but I don't really get any exhaust braking. When I dropped below 63 mph, the exhaust brake begins to do it's thing and the trans shifts to 5th gear. If the grade is 6% or less, my exhaust brake will keep the coach from speeding up. Anything steeper than that my coach will gain speed.

My coach won't hold a steep grade unless I drop below 44 mph and the coach shifts into 3rd gear. I get really aggressive exhaust braking below that speed. On a REALLY steep grade and towing, I have to stab the brakes every so often to keep it in 3rd gear.

We were once on a 10% grade towing my truck with brakes that only engaged when I applied the coach brakes. The TOAD brakes don't apply when the exhaust brake is on unless you have a surge or sensor that detects the grade.

On the above grade, my coach kept revving and upshifiting to protect the engine and I was having a really difficult time slowing the coach. The brakes were getting hot so I pulled over and allowed them to cool. I decided to start off (manually shifted into 1st) and see how long I could hold first before it upshifted. To my surprise, the trans will not upshift out of 1st if its selected from a dead stop. We were able to descend the grade at about 15 mph.

The ISL is not a good engine for the old rule that you descend the grade in the same gear that you climbed it. The ISL has a lot of power and can easily climb a grade much faster than it should descend a grade. On a smaller engine the old addage may be true, but not the ISL.

Sorry this was long!

[Automobilist]

Mr. Five2o is right on regarding using cruise control with the exhaust brake. Makes it MUCH smoother. Without cruise on, the exhaust brake comes on abruptly every time you lift your foot of the fuel control pedal. (diesels don't have throttles) With cruise engaged, the exhaust brake only comes on when it really needs to slow significantly. So in gentle hills, its not slamming on and off.

[nuckels11]

We had an 'interesting' experience this summer in our 1997 Holiday Rambler Endeavor LE. We started seeing a rise in the engine temp in Northern NM. We thought it might be the thermostat and had it checked out in Albuqurque. They flushed the radiator and washed it down and did routine fluid checks etc. and said the thermostat was ok - $700+! We continued on without further heating (in AZ and CA in July and 100+ degree temps) until we were doing a minimal climb coming into San Bernardino. It started getting hot again. We pulled over and let it cool and then raised the bed and proped it open to get more air while we shut off the bedroom to try to minimize the noise and drove into Fresno where we changed the thermostat ourselves (as we had requested of the service people in NM) and sailed on home up the coast and through the Siskyous and it was cool as a cucumber all the way. It had a rear radiator as does our 2005 so this will be an experience we will keep in mind in the future.

[allegro5]

Hi, When I see my Dynasty is running hotter than I feel it should, I wait for it to cool. Then I spray a degreeser like Simple Green, all over the radiator! Wait a few minutes and hose it down! Always helps alot! Allegro5

[Dunner]

Originally Posted by nuckels11

They flushed the radiator and washed it down and did routine fluid checks etc. and said the thermostat was ok - $700+!

There's a reason they call some of them Stealers!

[Sohapi]

Originally Posted by Madrona

Recently completed a pretty long trip. Part of it was heading west over Sherman Pass out of eastern Washington. It's a fairly steep pass with lots of twists and turns and not much chance to get a run at it. I don't think I ever got out of 3rd gear. Part way up there was a warning for high coolant temperature. The temp guage has certainly been higher than it was when the warning came on. The tranny guage was not much over normal when climbing passes. Ambient temperature was probably in the 80's, maybe a little more. I pulled over (luckily in a shady spot) and shut the engine down. I opened the rear engine cover and everthing looked normal. I left it open to hasten cooling and waited about 20 minutes. Restarted and proceeded up the pass. Just before the summit the warning came on again but I was so close I just proceeded. I don't think it was on for much more than a minute when we crested the summit and started coasting down. The light went out very quickly and the rest of the trip was pretty normal, even though we did have another couple passes ahead of us.

So the question is, does this seem normal? Does hill-climbing in relatively hot temps cause this kind of reaction in a heavy vehicle?

Cummins ISC 330

This is what happened to us too.

[ahicks]

If I might add one piece I figured out? If you ask Freightliner for a t-stat, they're going to hand you a 190 degree version - unless you ask for a 180.

Ours, with fresh (190 degree) t-stat (no other changes) started encountering trouble on the longer grades. It would pull short steep ones no trouble. Long ones were finding us stopping on the side to let the old girl get her breath (cool off). After finding out both temperature versions were available, I switched to the 180, and no trouble since. FWIW, -Al