darker forest-green, or a slightly fluorescent mountain-dew color?
Mountain-dew is *generally* universal
green is *generally* an older IAT formulation that has been superseded many times over
Honestly you can run universal if that's what's in there. It's fine. It's OAT, just like dex-cool. Where things get funny is when you start mixing phosphated / organic / inorganic / silicated formulas, neither of which apply against dexcool+universal. I'll put it this way: A LOT of independent auto shops just stock universal coolant for all their needs and you don't hear of any issues with it. Remember how we all heard about coolant sludging and mixing chemistries? That's when we were transitioning from IAT (old green) to OAT (pretty much anything from 2000 on). Mixing those two typically presents as a gel / crystalline buildup. Sound familiar?
If, however, you want to put anything specific in there: I'd drain and fill it a couple times with distilled water. Pop the lower rad hose off as well as the heater core lines at the water pump. That'll get quite a bit out. FWIW, you don't need to run the heat as these vehicles have full flow through the heater cores at all times.
if you do the DiH2O cleanup: buy *concentrate* and keep track of how much you add relative to the system capacity. If you add premix to a system that's half full of only water, you're gonna be real sad real soon.
I would also advise against using tap water, even for the flushing step. Dissolved ions in the tap water can do some funky thinks depending on what additive pack your coolant has.
fwiw... I run gen II honda coolant in my rig. Newer PHOAT formulation. Still rocking the original radiator, reservoir, heater core fittings. Meh.
