A few years ago (2019) a member by the name beef farmer posted of issues they were having with there 621f wheel loader. They did much diagnostic work on the pumps and those related areas and determined that when the hydro oil came to a temp of between 150-160 degrees the loader lift and steering would not react to as it seemed to go into derate type of mode where as not allowing proper amounts of oil to be directed to the pump but rather bypassed back to the tank. If any of you case guys remember that post. There never was a follow up on as to what caused that. Recently my 621f started doing the same thing between 155-160 degrees i loose lift ability to almost nothing and steering to very weak with the hydro pump making alot of noise as it sounds of being starved for oil. I will ad 1 more detail as i have 2 of these machines. The machine that does not do this when worked very hard took almost 2 hours of use to get to 160 degrees hydro temp i check with a heat gun at the pump and at the coolers to find the temps within 10-15 degrees of each other. The machine that is acting up only takes maybe 1/2 hour at best to get to 155-160 degrees hydro temp but when it goes into its "oil starving mode" the pump will be at 160 degrees but the coolers will be between 105-115 degrees so obviously there is a flow control valve that is not responding to open up for oil flow to the coolers i feel. My local case dealer feels that valve warrants replacement which i agree but before i go and tear this out im wondering if anyone else has seen this before and found what it could be before i rip apart a valve that may not be bad but could possibly be a sending unit that controls that valve. (not sure if there is but it seems as a likely part in how this works) Thanks in advance for taking the time to read this and for any help you may be.
If I remember right, there is a cooler bypass valve. Inside is thermostat that directs fluid directly back to tank or when open to the cooler. Remove the valve, pull the thermostat, and test on a stovetop in oil. 140 degrees should be opening, 165 fully open
Thanks for the reply first off. I didnt realize that it could be taken apart and tested that way. I will give that a try here and post what i come up with for a result. Thank you.
good afternoon so this morning i went to our local case dealer and purchased a new valve as it was about $400 and a new case hydro filter. (wanted to make sure we didnt have something stupid going on with the aftermarket filter we tried) We installed the valve and filter and ran machine. No new changes. Got to about 150-155 hydro degrees and the same thing happened. You hear what sounds like a snap and you loose hydro pressure. for steering and lift arm use down to almost nothing. Im going to double check the thermostat inside valve yet to make sure it opens properly. This has myself and our shop including the local case construction shop stumped. If anything else comes to mind id like to hear it. Thanks.