Just to recap on the transmisson cooler failure that Tim experienced, this is where we were with input from Dave Wheatley at Rocore..... skip the next four paragraphs if you have a good memory and are still up to speed on this...
These coolers have two primary failure modes that can occur. Corrosion is one possibility. I indicated that most of us use ELC coolant and Transynd and he said that we are using the latest state of the art chemistry with very low corrosion rates, so lets consider that one a non issue. If you are using the non ELC coolant check your PH and keep it optimized with additives.
The second failure mode is thermal fatigue causing a crack. On start up the engine coolant and transmission coolant rise at different rates and as the thermostat opens and closes there is some thermal shock that is involved. The tubes must expand and contract from ambient to maybe the 220 degree range of fluids and that stresses the tube bundle. If you have a retarder, and luckily we do not, that adds an increase component of stress due to higher temperature excursions. So we have the temperature excursions of normal travel and those due to desert travel and mountain pass climbing, again all individual driving habits and travel patterns. Prediction of useful life is hard but he was clearly concerned about a tube crack due to thermal fatigue in the shell at some point. The life of the unit depends on your use and probably the best guidance we could get would be data from failures in multiple coaches (Tim has one data point). If anyone knows mileage and age of several more we may be able to use that info to come up with some logical mileage and age value to guide us. This all assumes that we do not have an early fail due to a defect in the cooler build and I would guess that we are all pretty much beyond that at this stage.
There is a better cooler design that has evolved to eliminate the thermal fatigue fail that he would recommend. There is a floating bundle design and he thought that if that design was used, he was comfortable that in our application it would last the life of the coach given that corrosion was not an issue and that the floating bundle design does not suffer the thermal fatigue failure mode. The bundle expands and contracts without restriction.
The issue is that there is not an exact bolt in conversion. He will provide us recommendations along with drawings and insight into the differences that would have to be allowed for in a conversion. They are not that major but fittings and mounting may have to have some alteration. He indicated that the thermal performance would be equal to or better for this cooler over the 1249T design. He would get to this when he returns after the 1st of the year and I will pass the info along. Maybe Gerald or anyone else into the mechanics of these things could offer up an opinion as to what would be needed to physically change over and not worry about this issue again. We will take our time and see if some logical path evolves...
New News...
First regarding the database of mileage vs failure, we basically have about 15 coaches ranging in mileage from 32k to 223k miles. Tim has had the single failure with the exception of several coaches that I did not include in our database, which had the transmission cooler built into the main radiator assembly. That design was prone to failure at a higher rate and fewer miles than the 1249T.
Usually in this kind of situation when you are life testing for wearout, you would thermal cycle assemblies beyond the normal use to accelerate the failure until you reached what is known as the T50 point which is where half the units in the sample test have failed. Then you would model the useful life to assure that either the unit lasts beyond the normal use lifetime or define when you would replace a unit before it would fail. We do not have that kind of data and with the information in our database having just one fail at 140k miles, what we can predict and conclude is limited. It would be in each of our best interests to make a personal decision regarding how conservative you would want to be regarding this issue. I think being conservative would mean changing your cooler unit out before the first known fail would have occured, maybe considering cooler change in the 120K mile range. There are just three coaches in our database beyond the 140K miles where Tim had his fail, one at 145k, one at 151k, and Lamar at 223K miles. Obviously units can last longer than Tim's did, they will not all fail at the same time but the way things work with fatigue and cracking is the more times you heat and cool the cooler the closer you are to when it will fail. In time we may see a cooler fail earlier than Tim's did, but until we see that, the 120K miles seems like a reasonable approach as to when you would consider your options. If the failure was not such an expensive and difficult situation to deal with we would not be taking such a hard look at this. So that is my own personal perspective on this cooler issue for now...
Dave Wheatley at Rocore has been dealing with some health issues so things have gone slower than expected. I did get the drawings of the current cooler design for the 1249T which I have attached. Dave was to also research alternatives that use the floating bundle design which is allowed to expand and contract without the metal stress issue and therefor is not prone to this failure mode. The issue we would have had to deal with a change in configuration in a tight space.
Dave and I dicussed Rocore making a floating bundle drop in replacement for the 1249T and I am pleased to report that they had drawings for that unit and he got permission to have that unit become an active design. I do not have price and availability information yet but I will pass that info along when I get it. If you consider changing out your cooler this would be the more reliable design.
Hope this all helps along the way in preventing someone else from having to go through what Tim did. Sorry this got so long...
Later Ed
