Stranded in Flagstaff

Fred,

I have always limited my transmission temp to 230 even though I know the transmission brain is programmed to shut down the retarder if the temps reach its limit. My reasons were solely to be conservative to protect the transmission fluid whose life is compromised by higher temps.

Having said that I have learned techniques to allow driving in mountainous areas while minimiziing temperature gain, and they were used and proven in the Flagstaff area on a trip to Pahrump NV.

First, using two notches of retarder on my coach provides me with a downhill run on a 5% grade with a less than 230 degree temp and no increase in my set speed. When the grade is steeper I slow to below my 4th gear max speed of 55 and engage the retarder and fourth gear. I used that on 7% grades out of Flagstaff and the hills near Henderson NV. I never had to use the brakes and if the speed started to approach 55 I went to the third position on the retarder control. Again the temps were held to just below 230. On the steeper grades, in fourth I moved the retarder selector between the second and third positions to regulate my speed to just below the fourth gear limit of 55 (2100 RPM).

We are driving heavy vehicles and downhill runs have to be done under control at lower speeds. I was initiallly concerned about truckers being pissed because I had dropped below the speed limit until I realized they were doing the same thing. That is a western thing however, because on long steep grades in the east I notice truckers at or above the speed limit fairly common. I have stopped caring what they think of my speeds.

Using the retarder is a balancing act. If you leave it on all the time just heavy braking is going to cause your temps to spike. You have to be vigilant, avoiding heavy braking by anticipating and slowing. When you have an emergency, that is when you disregard the fluid temp spike and concentrate on braking, but by being ahead of the bus at all times you can avoid that need.

Or you can just drive the bus at car speeds, ignore the fact you have a 46,000 pound weapon, and push your fluid temps in which case your transmission fluid will wear out quickly. If you look carefully at the Allison maintenance schedule for fluid changes you will note that retarder equipped transmissions require fluid changes twice as often as those not so equipped. The reason is the heat.

BTW, the heat does not get to the transmission. The temps you see are measured at the retarder output just prior to the coolant to transmittion intercooler located on the drivers side low next to the engine.

That sounds like some great advice John. I'll try the 4th/55 combo on the next leg of our trip. Evidently, the 6th/65 combo isn't going to work :-)

I do appreciate the gravity (no pun intended) of operating a 46,000 pound monster and it's on the forefront of my mind at all times. My wife and I agreed that getting used to operating this vehicle is a bit like a new airplane of a type you've never flown before. Although you're an accomplished pilot, everything is "different". What was that sound? Is is supposed to do that? Some things are at first unsettling which later become routine and confident.

We're sitting at the shop in Vegas now, waiting to see what fortune will come our way. Our overall luck in Vegas has been mixed, but I'm hoping to break even on this round.

-fred

Fred,

At higher speeds you have more energy to absorb by the transmission fluid, so even if the transmission drops into 5th you still have the greater energy the higher speed possesses creating heat. By slowing in anticipation of a downhill grade or for traffic you are in effect avoiding that excess heat by getting rid of the speed more gradually. Leave the retarder off and see how even a small downhill grade can cause the coach to accelerate. I was a jake brake advocate, and still feel a jake has some very valuable features, but after learning to live with the retarder I find it to be more than capable and with practice easy to manage temps.

I am a fast driver in my cars, but in the bus and other large vehicles I have no choice but to drive slower because even with everything working right I still cannot stop as fast as the car ahead, I cannot make sharp turns, and generally speaking I just do not have the capability to alter speed or course anywhere near as easy as a smaller vehicle. The 62.5 mph I drive is for a reason.

Amen Jon. I'm all in on this thread. Tell us the verdict at the Allison shop Fred. GOOD LUCK!

Fred, Just a thought. Long ago, on Prevost-stuff, there was an owner of a early '90's Marathon H3-40 who was staying in Las Vegas, and he used to run a small mister under his coach keeping the pavement damp. This seemed to aid his cruise airs from hitting the HI PS in the 100 degree Vegas heat.

Our very own Jim S has misters on his Marathon Cruise Airs. He has a pressure switch on the high side and when the Cruise Air pressures reach a specific value the misters spray onto his condenser coils, dropping the pressure. A very simple and elegant set up.

I believe Steve Bennet has modified the fans in his Marathon to push more air across the condenser coils.

The point is that the key to good Cruise Air operation when on the highway is to make certain the cooling efficiency of the condenser is not compromised and if needed get more cooling across the coils. But before anyone starts to re-engineer their coaches the first step should be to pay attention to what Jack Finch has done, and that is to optimize the performance. Cruise Airs are very sensitive to the correct freon charge and if set up with the right charge their performance will be very good. If I remember on my old coach (haven't had to touch the Cruise Airs on my current one) as little as an ounce one way or another makes a big difference.

I also put two electric radiator fan in the mid center intake hole of my Mid Cruise air. Just a dash switch to a relay and on they go. I have yet to have the chance to see if they do any good. My mid A/C is my problem child, major dismantling to get to and intake and exhaust close together under the bus. I these fans help but not enough I will add misters. I believe Jim Shoen found out that the mister will not hurt the AC fan or coils.
Greg

Quote:

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Originally Posted by flloyd

Our spirits are still high and we're growing accustomed to our new living quarters aboard the bus. It's very nice, overall. We're in the Oasis Las Vegas RV Park and it's got everything we need. Oh, and the rear CruiseAir konked out with HI PS again, two times. These things are simply not reliable when the temp is over 100.

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Fred,

I have found that my cruiseairs work quite effectively while parked in temps as high as 107 degrees (the limit we have been in so far). With roof air or cruiseair, I think giving them all the help possible in super hot weather makes a big difference. Opening the awnings helps shade the sides of the coach, lowering the internal shades helps even further, and not allowing the coach to get heat soaked to start with is key. I also have the sunscreens which attach to the windshiield and door and drivers windows. Those help as does closing the internal windshield shades on really hot days. That drivers area is quite a greenhouse and can generate a lot of heat.

Seems like all the testamonies and discussions on this site about the hi temp shut down of cruiseairs has occured while running with the coach in motion over super hot pavement. In the shade of a stationary bus, not sure I have heard of anyone having the problem. I have to believe you have some problem with the unit itself.

Aside from putting down shades and snapping on outside screens, Liberty suggests raising up coach when parked on hot pavement to increases air circulation under coach for the cruise airs.

It's called the Montana solution. Tonight I'm in Dillon Montana and the outside temps are an unbelievable 58 degrees F. Robin and I couldn't be happier just to be here.

We took the bus over to W.W. Williams in Vegas and spent a good part of the day there. It was about 110 outside and it wasn't long before we lost the fore and aft cruise-airs. Anyway, we hooked up the bus to the Allison technician's laptop and took it for a test drive. Nothing unusual. The only error code it had stored was a previous over-temp incident. No active error codes. The test drive of about 20 miles in the scorching heat was uneventful. The transmission shifted normally and I even threw in a few hard retarder decelerations to see if we could get an error - nothing. We returned to the shop and the tech smelled the fluid. He said it was fine. He had no recommended service as none was indicated.

I wanted to do _something_ so I had them do a fluid and filter change with Transyn. It was expensive ($682) but I felt that it would be my best chance at peace of mind. After a few hours we hit the road and headed north along I-15. The performance with Transyn seemed a bit better and a little cooler. It's normal that when you spend several hundred dollars on a hunch that it "feels" better and yes, indeed, it did.

We spent the night at a nice, quiet off-highway rest stop in Utah and aside from the generator giving us problems, it was a nice stay. This morning, we hit the road and continued northbound and landed in Dillion, MT, at a campground from the Big Rigs book. It's very nice and much cooler than we expected. We're loving it already. The trip had a fair amount of ups and downs, and even a few stretches of interstate in Utah where the posted speed limit was 80. I kept it at 65, however, except for some very long and gently sloped downhills where I let it creep up to around 75. The Silverleaf readout was indicating a ridiculously high MPG and the road was straight and clear for as far as the eye could see, and so it was comfortable going.

During the latter part of the trip, through Idaho and into Montana, we were usually at 65 or below and had some fairly steep downhills. I think I've mastered retarder handling now and was able to keep safe speeds and low temperatures throughout the route. All is well.

Getting back to the generator, a Kohler 20KW, did give us a bit of a concern last night. It was a dry camping night and we needed the AC units. It wasn't terribly hot, perhaps in the high 70's, and so we started with all four cruise airs on. One of the first things I notice is that when the generator starts very badly. By that I mean that it shakes quite a bit and sounds like it's banging around inside its compartment. It seems to start on one cylinder, then two and after a few seconds, on all four. It seems very apprehensive and I'm certain that it should start with less effort.

Once the generator is running, however, it purrs along at the customary 1800 RPM. Purrs, that is, until the load changes. Every few minutes, when one of the cruiseair compressors kick in, the generator RPM drops significantly, and we have a major brownout. I observed a voltage low of 108 on the panel and it took the generator 4 or 5 seconds to recover. I then shut down two of the units and still the same behavior. I'm thinking that this generator isn't getting enough fuel when it needs it, and/or the governor isn't keeping up with the load properly. Whatever it is, it's a problem that I have to troubleshoot and fix. The combination of sluggish starting and poor load regulation leads me to consider fuel starvation, perhaps a restriction in the filter, clogged injectors, an injection pump problem, or a governor problem. I plan on sliding the unit out tomorrow and observing its behavior as it starts and hopefully through a brown-out episode. Maybe I'll be able to see something and get some more information.

I know from Mango Mike's blog that this unit once had a fuel pump failure and he did a nice writeup on how to substitute and automotive electric pump in its place. This was temporary and eventually the factory pump was replaced. I'm not sure if any of this is related, but it's a data point to consider.

So, as things go, I suppose this thread, now moved from "Houston we have a Problem" into the Engines, Transmissions, axles and wheels area, is once again drifting off-topic. But, what the heck, we're sorting out transmission issues, cruiseair issues, and now generator issues. I won't even mention the streaks of oil I saw today coming out of the port side drive axle hub. They seem minor by comparison.

To all, your thoughts are eagerly anticipated...