Engine coolant and inter-battery coolant

i would follow the maintenance schedule with your owners manuals.

pay attention to time or miles, and severe duty

 

Not sure what you meant "inter-battery coolant"? It's an air-cooled battery.

 

Maybe spell-check for "inverter"?

 

^This.

Specifically, the US Warranty and Maintenance Booklet says:

Engine Coolant: 100K miles or 10 years, whichever comes first
Inverter Coolant: 150K miles or 15 years, whichever comes first
Both, thereafter: 50K miles or 5 years, whichever comes first

FWIW, Toyota Canada recommends to do both circuits at 160K kilometers (roughly 100K miles) or 10 years, and so on per the US.

So yeah, you jumped the gun for the (US) inverter coolant change, and I'd say you're slightly overdue (by miles) for both an engine and inverter coolant change now, at 156K miles.

 

The 100k/50k mile coolant schedule is only if you use Toyota pre-mixed coolant. If you use the red concentrated coolant the 50k drops to 30k miles.

 

Specifically: Toyota Super Long Life Coolant.

It's a bit frustrating that you can't get this concentrated, not pre-mixed with water: there are times when the cooling system needs a water flush (say to expel head gasket sealer products). When there's residual water in the system, the simplest way to subsequently get back to a 50/50 mix seems to be:

1. Determine system capacity (spec in Owner's Manual)
2. Add 50%* of that capacity, with full strength coolant
3. Complete filling with distilled water.

*FWIW: Toyota Canada supplies Toyota Super Long Life Coolant in a 55/45 coolant/water mix.

 

With 4th gen and keeping up the maintenance, you'll likely get there. Third gen has an Achilles Heel, the #@*% newly minted EGR system, and the failing head gaskets, the second likely a consequence of the first. But keeping on top of that they're ok. Anyway, 4th gen, they seem to have worked out the kinks.