Rover Overheat – by Spencer Smirl
I have had to diagnose and repair a variety of different faults and failures on a variety of Cat machines. This would be expected of anyone with nearly ten years history with Finning, Caterpillar’s largest equipment retailer. Even though I have had a broad range of experience, a powertrain system overheat was completely new to me. Being in Antarctica, the coldest continent on the planet, an overheat is something I hadn’t anticipated.
When I say overheat you might think bells and whistles going off in the cab and smoke rising from the machine. That would be very bad but would be a true overheat. Because me and Richmond have been operating our machines every day for the past 10 weeks we have learned their habits quite well. It might sound strange, but this much time spent with the same machine day in and day out gives you amazing insight into specific characteristics of operation. The sounds, the vibrations, the way they move, even their smells. Every machine is unique. Even though Seeker and Rover are only two serial numbers apart (meaning they were almost neighbours on the assembly line), they are no exception. Rover runs hotter in all systems, moves slower and tends to burn more fuel. Whereas Seeker makes a lot more noise and shakes a lot more. These are subtle differences, but even the other members of the ice team are starting to get a feel for each Cats personality.
We had just finished climbing the first set of substantial inclines. The first and last of these three slopes forced us to relay our loads last time. As anticipated, we were able to climb all three this time without spinning out. When we made our depot run we were each towing approximately 65 tonnes, this time we had two less fuel scoots, no Belgium sledge and we weren’t packing 80 extra drums of fuel. This accounts for an almost 40 tonne weight shed. When we had summited the third climb Richmond called me on the radio and asked me what increase in temperature my torque convertor and transmission oil experienced during the climb. His curiosity was the result of a small rise in his operating temp, from 88C to 96C. It isn’t a very big rise and 96C is definitely not hot enough to cause any alarm in a powertrain system, but it was noticing this change in normal operation that was key.
First Richmond changed his operating inputs to see if he could influence a drop in temperature. He dropped down from 2nd gear into first to reduce the slip in the torque convertor and opened all his compartment panels. His temperature continued to climb and soon it was nearing 120C. The level one temperature warning alarm will sound in the cab at 121C in the transmission. As we are in an environment where I can’t afford to repair the massive amount of collateral damage that can be caused by a full overheat, I wanted to avoid allowing Rover to get hot enough to sound the alarm.
We halted travel of both trains and I ran back to assist with the visual inspection. First we confirmed the absence of any fluid leaks and checked the oil level in the transmission. It was a little overfull but this could be the result of fluid expansion caused by the near overheat; I wanted to let it cool before I drained a bunch of oil out unnecessarily in a panic. We dropped the Belly guards and continued our inspection. Using an infrared thermometer we checked over various components in the system looking for hot spots. Failing pumps, malfunctioning valves and sticky brakes can all contribute to a rise in system temperature. There wasn’t any “out of the ordinary” thermal concern to any of the components checked. Although, there is a bypass valve in the oil cooler lines for the powertrain oil which raised a little suspicion. I have had engine thermostatic regulators do strange things in the past in cold temperatures and when I checked the lines going out from this bypass valve to the cooler they were quite cool to the touch. As this valve stays closed until the temp rises above 84C and Rover had already cooled to below 75C. I didn’t want to condemn this valve just yet.
We rechecked the oil and found it was still a little overfull, so we took out about 15 litres. We closed up all the guards and Rover was back on the trail. Rob took over driving Seeker so I would be able to come inside and study. I also used this time to assemble our transmission test kit which consists of nine gauges and all the test lines to connect them.
Rover was carrying on and holding temperature much better, however, the trail was flat, almost downhill slightly, and Seeker’s temperatures were definitely a lot lower than Rover’s. After two hours of running, the temperatures had risen back up to a concerning level and I made the call to stop and park up. As it was only 16:30 and we still had plenty of daylight, Richmond and I went straight to work on repairing Rover.
Although I still suspected the temperature regulator valve (cooler bypass), I thought this disruption to travel was a good excuse to complete the testing and adjusting of all the powertrain pressures on both machines. The testing and adjusting of these pressures would also reveal any differences between the two bulldozers and would indicate a fault within the torque convertor if we had one. If our problems weren’t caused by the temp regulator valve, I was sure it was going to be a torque convertor failure of some sort. This absolutely terrified me as all my torque convertor parts were over 100kms away at our fuel depot. I had to leave the majority of my parts there as I didn’t have the space to bring them all with us back to Crown Bay. I had to decide what I thought would be the most likely failures within the next 660km of travel and leave the rest, and honestly, a torque convertor fault in under 500hrs was pretty low on that list.
The next morning Richmond and I were up quite early to start warming up Rover’s systems. To complete all the testing and adjustment of any pressures you need to have the oil at operating temp to make your adjustments accurate. After checking all the pressures on Rover we did the same to Seeker. To my relief they were bang on spec. All pressures on both machines were an identical match. I continued with the pressure calibrations in ET (Electronic Technician, Cat’s product communication software).The forward clutches and the 2nd speed clutches needed a bit of adjustment on both machines due to this being the gear that the majority of our towing was done in, but all other pressures were good.
As we hadn’t located a definite cause to our fault at this time, I decided to pull apart the temperature regulating valve in the power train oil cooler circuit, and inspect it for any signs of binding or sticking. It was quite difficult to get the spool out and when I did I found the oil in the valve was quite sticky to the touch, even at 55 degrees. I knew Rover had only had one oil change from new and the oil in there now had a little over 400hrs on it. I thought there was a very slight chance that there was some break in additives left over in the system from the previous oil change and had somehow caused this regulator to stick closed, bypassing the oil cooler.
We decided to change the power train oil and filter in Rover. While the oil was drained we checked the magnetic suction screen for debris. Clean as a whistle. We cut the filter open for inspection as well, not a spec of contamination visible. We refilled Rover with oil, closed all the panels and re-assembled the cab. Tomorrow we would find out if we would have to dig deeper to repair this hot blooded kitty.
It is very difficult diagnosing a symptom such as an overheat with such little development in the problem. Here in Antarctica our trouble shooting will always need to been done this way. We have to be aware of a problem immediately upon its arrival and begin to repair it before it can cause any further damage. We do not have an endless supply of parts for trial and error diagnosis and we definitely do not have the luxury of mild conditions to work countless hours scratching our heads. Our trouble shooting needs to be quick and precise. When Rover made it the entirety of the following day without cooking the new oil and even seemed noticeably less sluggish and ran cooler in general, I knew we had accomplished just that.
Comments are closed
There are 5 comments