Cat 320L 9KK hydro oil pinned hot today, checked temp in and out at oil cooler and it seemed as no flow, temp was close to same. A little while later temp dropped and I checked temp in and out at cooler and there was a 30 degree difference. It seems as though it was like a thermostat opened and let the oil flow. What causes that ? I know there are cooler bypass and slow return, what would hold up flow and then let it through ? Thank you
hi , there are two main return paths to hydraulic tank one through the slow return check valve and the other through the bypass check valves, when the oil is cold the return oil is directed through the bypass check valves and not through the cooler ,as the oil heats u[p it is directed through the slow return check valve and also the cooler. I would suspect you have a sticky slow return check valve.
And how would I repair the check valve
If it is the slow return check valve sticking closed. it may just need to be removed and cleaned. the other possibility is the bypass check valves are stuck open allowing oil to bypass cooler. it is easier to remove the bypass checks to inspect than the slow return check valve Mark