1996 M35A3 Cat 3116 Turbo Diesel.
I thought my antifreeze/coolant was clean as it always appeared clear and green(think it was ethylene glycol) in the surge tank.
Off roading last week and put my A3 through some vigorous hill climbing and descending. Brought it into my shop for a chassis lube.
Checking the fluid levels I opened the surge tank cap to find a stinky black mess. I guess the rigorous driving stirred up some hidden sludge from within the cooling system as I have inspected the reservoir numerous times over the last year of ownership.
Drained the black antifreeze into 5 gallon buckets thru the petcock. Removed lower hose and began to flush into buckets for proper disposal. Removed thermostat housing and thermostat and flushed the block. Removed hose to heater core and flushed. Removed the surge tank and flushed it and noticed the small return port from the top small hose from the radiator coming into the tank was blocked. I cleared it using a small drill bit.
New thermostat and gasket(NAPA) and refilled with +/- 30 qts of Peak Fleet Charge SCA precharged antifreeze. Drove to operating temps and opened surge cap to find my new antifreeze was still a bit dirty. Decided it's time for a coolant filter. Bought NAPA #24019 filter base and #24079 coolant filter. As I began to drain the coolant to do the install I noticed the lower radiator hose was cracked but not leaking. NAPA was no help so I'm off to Philadelphia to Eastern Surplus for a new lower hose and 2 upper elbows. I drained the new but particle filled coolant into clean 5 gallon buckets and reused it after the filter was installed. My thought was to use the new,sort of dirty, $100 coolant to use as a medium to flush the system and utilize the new filter and replace coolant, again. at a later date.
Got it all together over the weekend and took a 100 mile drive today to check on the house at the shore. The new thermostat kept engine temps at 180. The coolant was clean and clear and it appears the filter is doing its' job. I'll replace and cut the filter open at 500 miles to see what it looks like.
I plumbed the filter from an available unused 1/2" port in the T-stat housing to the filter inlet. The outlet port from the filter was teed into the return line from the cab heater. If the filter were to fail or block it will not interfere with coolant flow to the engine.