Sounds like a complex project. You don’t know how often previous owners did things like fluid changes, or changed filters. And, if yours is hidden like mine, and a royal pain to get out and clean, they may have never done it.
I’d find the inlet filter and check it out first. It would account for the problem, and is one of the easiest things to remedy. First rule of trouble shooting is to look at teh easiest to do, and least expensive things to solve first.
When my Dad was in his decline, Mom’s Volvo started overheating, at least that is what the gauge said, and she ran out of gas a few times. I told Dad that there was a voltage regulator box behind the fuse panel. And, that if it went bad, it sent 12-volts to teh gauges, instead of 9-volts, and the gauges would read high. they went out frequently enough, and had been used by Volvo for a couple of decades at the time. I was near their place for a Doctors appointment so I swing by to say hi.
Dad had the radiator out of the car, and had dropped it off to be rodded out and rebuilt. I called Mom later in the week to see how things were going, and she said that Dad had the car back together, and it was still overheating. I told her that maybe it has an air block or something, and I’d come out that weekend and see if I could figure it out.
I went to the Volvo Dealer and bought the voltage regulator for under $20. I went out to their place on Sunday, arriving when they were at church, and put in the new relay. Then put a nice pork roast in the oven, and watched football until they got home.
After Lunch we went out and checked on Moms car. I burped the radiator hoses, and we took it for a test drive, and it didn’t overheat. I didn’t want to embarrass Dad, and tell him he wasted a couple hundred bucks. So, i never mentioned teh new regulator.
Lesson learned from Dad, Which he forgot as his age advanced, was to do teh simple stuff first. If you pull out the pre filter for the hydraulic system and it is in great shape, you have eliminated that problem. On T233, you have to drain teh hydraulic fluid, because the filter and pump inlet are at the low point, and all the fluid is coming out if you pull the filter. But you can catch the fluid if it is relatively new, and reuse it.