Hello i need help with a dc 75 dozer 2005 works well for 2 hrs then hydraulic fluid gets hot machine dosent steer worth a damn right side goes first dealer installed two drive motors at a cost of 13 k did nothing , i changed the thermostat on the hydraulics did nothing , changed fluid to special oil that wont break down when hot did nothing, i'm at my wits end going to have to get rid of it if i can't figure it out , just finished installing a secondary oil cooler looking for suggestions while i have it apart thanks
This is a comparable model to the case 650K, which I am familiar with. There is multiple issues that can cause overheating. Need some information first. 1. Which way is the fan blowing? (sucking air from the front is best) Also tach the fan speed. 2. What did the dealer test? What failed in the drive motors? Did the dealer check the cross over reliefs? 3. What is the temp drop across the oil cooler? (When at operating temp, check inlet temp and outlet temp of oil cooler) 4. How hot is the hydraulic oil getting? What I have seen is the cross over reliefs fail. This will cause the system to overheat. The quickest way to test this is to just swap the forward reliefs with the reverse reliefs. (you usually don't need much pressure in reverse, so unless the relief comes out in pieces, this will work) When you remove the reliefs, a failed relief is often blue, and heat marked.
I was really hoping you would respond mr hoff I've read some of your post and you seem quite knowledgeable on these machines 1 fan is blowing forward ( cab machine don't know if fan is reversible i will check ) 2 I don't know what they checked I checked various pressures which were in spec except charge pump pressure was 400 cold instead of 350 hot 3 machine starts malfunctioning at about165 I'm losing approx 15 degrees across cooler. I will look in manual tomorrow morning and switch cross over relief valves and post again thanks very much for your response
garyhoff i assume you are refering to pressure relief valves located on top and bottom of pumps ,top being forward and bottom being reverse
If swapping the reliefs doesn't help.... Oil temp is 165 or coolant temp is 165? Might try disconnecting the temp sensor wire at the hyd tank, see if that affects it at all. Thinking it may be a control issue rather than a mechanical issue maybe?
lantraxco once oil temp gets to 165 approx. is when machine loses power and yes tried disconnecting wire no difference
Odd, I wouldn't consider 165 to be extreme, piston motors for example are usually rated for 200F+ Anybody check flushing flow, or loop temperatures? If the hot oil shuttles aren't dumping sufficient oil out through the motor cases to the cooler the hydrostat loops will be hot as hell and performance will degrade rapidly even though the tank temp won't be all that hot. Just a thought.
tank temp is hot as hell, we pulled the pressure relief valves and on the outside they look ok, we pulled them apart and they were blue all four so i don,t know if switching them is going to help does anybody know if replacing the seal kit [cost $200 ] will repair them or do i have to buy new valves [cost $800 ea] thanks for the help
frem, The later reliefs were manufactured slightly differently, so they have some blue on them. The area of concern is around the seat of the relief, it may be grooved or heat marked. You may not visibly see damage to the relief, as sometimes the spring gets weak, and its cracking pressure is much lower then full opening pressure. Since the way Case/new Holland sets up the pumps (they don't destroke the pumps) the forward reliefs are prone to this issue. (Tends to be forwards, due to the normal direction of travel) I generally don't recommend re-sealing the reliefs. I would still swap the reliefs, before ordering new ones. You also have to remember that the drive train controller will de-rate your pumps when you are overheating. So a bad temp sender will trick your drive train controller. Most hydrostatic hydraulic components are rated for 180F. I would consider 165F getting too hot, especially since its still winter time in Ontario. A good operating temp is 120F to 145F. The thermostat valve opens fully at 145F. I would also like to know how hard you are working your machine. Do you find yourself stalling the tracks often? Has this been an ongoing issue? Are you operating the machine at full throttle normally? It needs to be at full throttle for proper cooling. I would hope that you and your dealer checked the obvious things first, (oil cooler plugged, fan belt, ect.) Is the overheat alarm actually coming on? Not sure if your machine had this update, but they changed the oil cooler hoses from size 16 to size 20, to help reduce restriction of flow to the cooler. The other update, was to add a 25ohm resistor inline with the hydraulic temp sender, so it would show a accurate reading on the cluster. When the machine is hot, check the temp of the travel pumps. As Lantraxco said, maybe just the closed loop is not flushing properly. HeavyEquipmentForums
garyhoff the blue on the valves seems to be more from manufacturing than failing given its not at the seat area so we switch valves and going to try that once the rain stops[ its a mudfest right now] if that don't work i will change hose going to cooler it is a 16, can i pull the thermostat out i really don't think i need it we don't use it much in winter also machine hyd overheat no matter how hard you work machine i'm usually in 5th forward and 6th in reverse i've tried all gears final grading ,scraping it don,t matter it gets hot thank you for the response
frem, The best gear to work in is 6th or less. (you will have the most torque in this range) As long as you are running the machine at full throttle (as much as possible), and usually using 6th or less, you are operating it correctly. Hopefully swapping the reliefs will help.