What would happen if you didn't put the hto additive in the 10w30 that's I'm the hydraulic system. Would the oil foam up and cause the hydraulics to not function properly?
Depends - what machine are you talking about? My understanding is that HTO additive is needed by the drive motors if they are a gerotor style. Some older machines with radial piston style don't need the HTO additive.
It's is a 1996 case 1845c
Before serial number JAF0067438, the early 1845c's used axial piston drive motors & planetary gears. They do not need HTO additive. After serial number JAF0067438, Case 1845c's used gerotor drive motors. Those machines require HTO additive. The serial break is somewhere around 92/93 I believe. Guessing then your machine needs HTO. The only difference in the hydro system between the pre and post machines is the drive motors, so it reasons that the HTO is there to protect the drive motors. Not running HTO will probably shorten the life of the drive motors in later machines. I've got an 1989 1845c myself. It's run great for the last 20 years. I've never used HTO. Just straight 10w-30 motor oil.