Any hydraulic guys on here? I have a 1998 315B, 12500 hours. Did a hydraulic service on it in the last 25 hours including new oil (46) and all filters. When the oil temp gets up to operating level and i swing and stick in fast it will squeal or shreak. Everything seems to function fine other than it makes that noise, not every time but often enough. Notice it when im loading or hoe chucking and its fast moves. Any ideas? Thanks!
Did the problem start after you did the service..? Your OP is not clear on that. By the sounds of it the pump is cavitating. Check all the lines from the hydraulic tank to the pump for any places air could leak in. Also if the hydraulic tank is a sealed one and is designed to pressurize a tad when the oil is hot you may have a problem with either the tank cap or the pressure relief valve on the tank not sealing fully.
Maybe it is an auxiliary relief valve opening? Was the oil the same viscosity?
The rad-style cap you found is designed to pressurize the tank to X psi (not sure what X is but somewhere around 10). This pressure assists with the flow into the hydraulic pump when the implement system demand is high. I'd suggest that you replace the cap with a genuine Cat one despite the fact it might look as though any kind of automotive rad cap might fit. While you're doing that make sure that the neck in the tank where the cap fits is in good condition and undamaged. Also, regarding your oil. 46 oil is a bit on the heavy side for your climate in Canada, the spec is an SAE10W which equates to an ISO 32. I'm not saying you have to change the oil right now but I do suggest that next time you change the oil go for a 10W/32 oil. The oil being a tad heavy will not help flow into the implement pump.
Youve certainly got me questioning that cap now. I will have to look into that. Didnt think there was too much of a differnece between the 46 and 32. I did go with the 46 reason being im 99% summer work and run a mulcher head. Good info thank you!
To give you an idea we only used to switch from ISO 32 to ISO 68 in hydraulic systems when the ambient temperature was pretty much permanently above the low 30's Celsius