Hi all, I recently purchased a 1990 John Deere 750C series 2 dozer. It has worked well all winter. In the hot weather, though, it loses power after a couple of hours to the point where it won't push at all. Can you help me understand what could be the cause? Thank you.
If I remember correctly they did not make the C series in 1990 much less the series II
Engine power, or the track drives? The hydrostats are fussy, they like the right oil, obsessively clean, and comfortably cool... If they're working good cold you most likely have a cooler issue or a weak valve issue, but it could be just wear, excessive leakage causes heat which thins the oil which causes more leakage and it's a downward spiral from there. Might just need service and the proper drive oil in it.
I am sorry about the mistake, it is a 2000. I believe it is the track drives. If the cooler was the issue, would I not see the temperature gauges go up? There is no sign of oil leakage anywhere on the machine and we have been paying close attention to this. The gauges all stay within normal limits, the hydraulic oil was replaced about 6 months ago with JD hy-guard. I had recently changed the engine oil and filter. I now plan on changing the air, fuel and hydraulic filters. If this does not fix the problem, what do you suggest I do next? Thank you.
Get a manual, start checking pressures, charge pressure especially but also the stalled pressures. This age machine seems to be at least partially computer controlled so it could be a borderline sensor or wiring issue. Found a note elsewhere on the net that seems to indicate pump sensor issues were common on these. If they're not reading right the computer may be cutting the pumps back because it thinks they're maxed out.
lantraxco, Thank you for your help. I just noticed that the hyd and tran oil are supposed to be 10w30, but at least the hyd oil is hy-gard which I understand is 5w30 - this should not make a difference in hot temperatures though, should it? Would a sensor issue have an effect only in hot temperatures? Also, if it is a sensor than should it not be an all or none phenomenon? The weakness seems to occur gradually over a couple of hours or so.
Hy-Gard should be fine, check with the dealer though. Yeah, with multi-weights basically the second number, 30 in this case, means the oil has roughly the same viscosity at 212 degrees F as a straight 30 wt would. If you're not seeing any rise in oil temps as you say, I would look for an electronic issue maybe. Sensors can have all sorts of issues, erratic behavior, sudden but intermittent failure, or simply drifting out of spec as they heat up. I don't know anything about this particular system but some will "auto-calibrate" each sensor on power up, and over time the sensors may drift. Have you tried shutting it off for a couple minutes and then powering it back up again? Probably need a dealer tech with a computer to check for codes and sensor calibration.
I replaced both fuel filters which seemed filled with sediment. I am not sure if this could have been algae. The machine seems to be working normally again. I am not sure why the problem only arose in hot weather? Does anyone have a clue? Also, I feel like I should probably clean out my diesel tank. It does not have a large entry port. Does anyone have any suggestions on how to do this best? Thank you.
Algae usually shows up as black slime. Depending on parts of the country the color may change a bit. Cleaning the tank may not be required, small amounts of sediment is normal to a degree, dirt entry and rust buildup is a result of poor fuel management. Make sure the nozzle is clean before sticking it in the tank, keep the bulk tank near full if possible, and fill the machines tank before shutdown at the end of the day. When temps fall at night, and the tank is low on fuel, the warm fuel and cold steel tend to draw moisture into the tank, which in turn starts to sweat on the exposed walls and top of the tank. This moisture then runs down to the bottom of the tank and sits there causing algae and rust, which only finds it's way to the filters when stirred up enough. This is especially true of machines that are not used every day, all day. We have machines that have had very rusty tanks and still operate just fine once proper fuel handling is done. Maybe a few filters will be needed to cleanup the system.
I agree with Lantraxco, check hydrostatic charge pressure. If that is good, you can do a case drain test. You pump may be within spec but if your rotating groups are worn and leaking oil it will cause heat and lose of tractive effort once they get warmed up. I'd also do an oil sample just to see whats going on. If you haven't sampled before you don't have a base line but if your Fe (Iron) content is off the chart you some a direction to go.
It seems that the power issue was entirely fuel related but the light blue smoke continues and seems to have gotten worse some. I had a very good mechanic come out and he felt the oil was thin and suspected that fuel was getting into the oil causing it to thin and get past the cylinders and burn. He suggested replacing the booster pump which I did (and replaced the engine oil) but that did nothing - maybe made the smoke worse. He said the next step would be to replace the injection pump - but thats about 2K. I am not convinced that is the problem. The whole problem with the machine is that it works really great otherwise. Do you feel next step would be to take an oil sample? If so, can I pump some out the belly pan or do I have to get a sample by draining the oil from the bottom? Any other ideas would be appreciated.