Disappearing Coolant

[DrivingZiggy]

My first post, so be gentle!

I've been losing coolant and asked about it on the OOIDA forum. One of the guys directed me here. So I've been reading and watching videos for about 4 hours now. Since I can't see any leaks, I'm going to have to assume it's the EGR cooler that's leaking.

But from what I've been reading/viewing, looks like I should buy myself a coolant pressure test kit. Any opinions on The Mityvac MV4560 Radiator/Cooling System and Pressure Test Kit for $47.78 on Amazon?

Oh, the truck? 2010 Volvo 780, ISX 525/1850 pre-DEF. From what I learned from one of Rawze's vids, it's the 871. 322,000 miles, never had anything done to it except replacing tghe air compressor twice and the a/c compressor twice, also. Non-engine compartment replaced the air drier. And now I'm seeing that soot could have caused at least some of these problems.

So, any ideas about where the coolant is going?

Also, what the heck is this "@m*m^2" that I'm seeing all over the forum?