So a guy comes down off the mountain after the busiest week of tours so far to shower, poop someplace where the water swirls around and use a little borrowed wifi only to be greeted with my least favorite part of SteelSoldiers, the wolf pack. Let’s make this quick, it is my birthday and I am supposed to go climb a mountain with my son.
ELC Coolant: It is true that there are some ELC’s that contain the nitrates and acids but as long as your coolant meets the Cummins spec CES14603 then you are going to be fine and it is what the company recommends. My last stuff was a Fleetguard product and I have topped up with a Chevron stuff. You are looking for the red coolant with that CES14603 or better number. However you can use essentially ANY coolant you want as long as you are dip testing for PH every 6 moths or so. All coolants will get acidic with time. Here is the great part, you don’t have to trust me at all, just call Cummings and ask them. Cummins Care at 1-800-CUMMINS™ (
1-800-286-6467) in North America. This is like the IBIS towbar and running motor oil in the Allison all over again. Just call the manufacturer on questions like this, don’t trust strangers on the internet. Have your motor’s serial number handy. However it is important that you have the proper cavitation additive.
Read up on cavitation here:
https://www.cumminsfiltration.com/s...oduct_lit/asia_pacific_brochures/3300963A.pdf
It is our assertion however that while these motors have a serious cavitation issue that is not what has been killing our motors. Cummins can confirm that the ELC DID NOT HARM OUR LINERS OR O-RINGS (remember you can use any ELC as long as it doesn’t go acidic on you but I would just run what the motor manufacture specs) We think the NHC 250 is a motor at the edge of it’s operating parameters and a few tweaks either direction can cause failure. I firmly believe that most if not all of the NHC failure attributed to o-ring failure in situations where the liner has not been perforated is the result of extended periods of high EGT
Cylinder liner picture 1 (not our liners or picture)
So as you can see in this picture, the large red arrow represents the area of the piston liner that is bathed 360 in coolant. This is very efficient in terms of wicking heat away. The lower small red arrow represents the o-ring sealing area at the bottom of the liner. That area gets it’s cooling from direct contact with the block. Also because the lower edge of the liner sticks down below it can radiate heat. As the combustion cycle operates the majority of the heating happens in the upper part where the water jacket can whisk it away. The exception is the top of the piston itself. The piston is aluminum, is a fantastic conductor of heat and is cooled in part by the exhaust and intake strokes, especially as atomized fuel floods in. However on power stroke it is hot and it is my opinion (based on research, consultation, conjecture and study) that what is happening inside the NHC is the piston transfers some of that heat thought the rings and oil coating the skirts to the lower section of the liner. All pistons naturally cock to one side or another just a little on their stroke, dragging some. I found in our torched motors that that corresponded to the area where the liner o-rings suffered the most serious damage. We think the pistons start to expand from the heat and start dragging more and more on the walls of the liner, building even more heat. Always in every motor, o-ring damage corresponded to the natural orientation of drag. Now when I asked around for EGT numbers on the NHC I got only a few responses. One responded with numbers that were as crazy hot as mine, one responded with how he had put a turbo on his NHC to bring the EGTs down to acceptable levels. Privately I was very sure that adding the turbo to an NHC would kill it but I took the time to listen to what he was saying, look over his material, benefit from the research he did and confirmed it with my own separately. I have come around but that is another issue.
Picture: Squirter
Now in most big motors this extra heat transferred to the piston by combustion is dissipated via oil squirters that pop the underside of the piston with a shot of oil. That pulls the heat out of the piston into the oil which is then cooled and sent back around. One of the things the heavy truck shops I brought my melted pistons and torched liners to kept saying was they thought I had a plugged squirter on that hole. They were confused to hear that the block didn’t have any and kept asking if I was sure. It is my opinion that the contract for these motors omitted that part simply as a cost savings item.
So how come the motors were fine in the older trucks? That I think is due in part to the manual transmission. I have never driven a M809 series so I don’t know how big the gear gap is or if it is comparable to the Allison. It makes sense to me however that they would be turning higher RPM. It is speculation on my part.
In these videos you can watch me push my truck over the pass to Ennis for the 4th of July parade. The Pyromiter is the bottom left on the sift column and you can watch me struggle to keep the RPMs high enough to bring the temps down below 1100 and despite my best efforts got nearly 1200 once or twice. To head off the preventative screaming about my temp and oil gauges. Yea they twitch and bounce around, I have confirmed them with a manual check and if I wiggle the wires they will settle down.
Video 1
https://www.youtube.com/watch?v=5scPqShP8yQ
Video 2
https://www.youtube.com/watch?v=dFCy0SeZlYc
Note how fast the EGT temps rise. I know the motor temps are hard to read but what I did was tap on the camera twice each time the fan clutched in. Motor never got over 185 even with EGTs near 1200. If I had let them I could have seen 1400 easy on this hill and that is way, way too high. I think if some of you put a pyrometer on your trucks you will see that you have been driving them at scary temps.
There still has to be a reason why I am having greater issues with this that other Allison trucks and I think that comes down to elevation and the shear number of miles I drive them. This year we will have close to 400 miles in low-range alone on the truck. In the mountains the already underpowered NHC is kicked down another 15 to 20%. I also don’t think they were that fine. While it is often said you can’t trust the odometers in these trucks I don’t feel the military is in the habit of swapping them for no reason and the odometer isn’t a high failure item. I have looked at a number of trucks while buying mine and they were all relatively low numbers, the highest I saw was 50,000 and the lowest was 6,000. You could tell by that truck, wear on the peddles, shifter, mats, hinges, linkage, spring hangers and what not that the truck had next to no mileage. That is why I bought it and it is the 925 we run today… but that truck had already been through a motor swap. I know the military will sometimes just take them out and put them in for practice or what not but still even that truck had a transplant. I think this has been an issue on the 939 trucks which is why they swapped to the 8.3. The motor has the same HP and would require all new supply chains. I know there is the right way, wrong way and the military way but it remains odd to me that they would bother to swap for a motor that is a little lighter, gets a few more MPGs but outputs the same HP. Don’t know, haven’t looked into that motor.
A few other points from the pack:
Test injector pump. It is a common rail system so you could run it just fine off of an electric fuel pump and a regulator. Other than checking to make sure they had not been turned up we have not messed with them or put a manual gauge on. Plan to but it is clear that isn’t the issue. Why do we know it isn’t an issue? Few clues, first no smoke from the stacks on any of the three different trucks, pickup was about as lousy as normal, they had the proper buttons, they were three completely different pumps with the same exact issues and one of them came directly from the motorpool to me with no opportunity for change. Sure it is possible I managed to three trucks with tweaked pumps but if they did it then they did it a strange way inside because as I said, they have the correct shims.
What about gulf war? Not sure the question. If it is about the ambient air temperature then the ambient air temperature has little or no effect on EGT. That isn’t how it works, you might want to study up on the subject then. If it was about did the trucks survive there under loaded war time conditions well I have only found and spoken to one motorpool guy (hardly a cross-section) and he said that anytime something went wrong they just dropped a motor in it and never messed with the why of it. That is all I know.
You are driving it wrong!!!!!! Well sure maybe, but I have been driving trucks of all types for a long time and have had none of these issues with other trucks. It is an automatic so the truck will downshift or upshift as programmed. Is the motor at such a fine ragged edge that the parameters of the tranny can cause killer EGT numbers? I think yes and the lack of quirters has taken any safety net away from the motor. But we are a commercial operation so I have over 600 hours of camera footage of me driving. If you are so entrenched at this point to still believe that we haven’t done so very, very much of our homework then feel free to watch for yourself. These 8 videos are most of an entire tour shot from the bed camera (the only one to record audio) have an honest look and tell me if I am beating on this truck hard enough to kill motors in any normal sense. Turn the sound down, camera is near speakers.
One:
https://www.youtube.com/watch?v=s1oPp4F0SqY
Two:
https://www.youtube.com/watch?v=JhhoTXxTmCY
Three:
https://www.youtube.com/watch?v=hnhD0omB_bY
Four:
https://www.youtube.com/watch?v=jB0JIkn0trQ
Five:
https://www.youtube.com/watch?v=qlwu6Q-KlNI
Six:
https://www.youtube.com/watch?v=3M_QhCxXFsI
Seven:
https://www.youtube.com/watch?v=YnTLLa7LkgE
Eight:
https://www.youtube.com/watch?v=0_ub6Ece0Rk
To summarize, I drive these things commercially and put way, way more miles on the trucks than the average guy. We spend a lot of time and effort on researching issues related to our trucks and sharing that information to help others. At our elevation and mileage a year with me is probably five or more years of what I would call ‘average’ use for these trucks in private hands. I think that most of the mystery fuel issues are going to come down to EGT, I think most of the liner failures are going to be EGT. My firm belief is following my recommendations 1-5 will gain you serious life out of the motor. Once a few people put a pyro on I am sure it will become crystal clear whether or not we have drawn the correct conclusions.
Here is one of the fascinating bits I did have at my disposal, Donaldson’s EGT and CFM charts for this and other motors:
http://www.asia.donaldson.com/en/exhaust/support/datalibrary/1053747.pdf
That is all the time you get from me on my birthday to deal with this, not even going to proof read it. If you can put forth your documentation so I can read it then I can maybe understand more about your position because it isn’t what I find when I am researching. I can put more of my documentation up once we are back home because they are not on this old laptop. Thanks for all the private messages both on and off SS. It has always been this way and probably always will. Off to climb a mountain with the boy.
Ken
