The following is a result of me checking the right way to flush my engine of contaminated coolant in my 2014 prius, but it applies equally to modern Toyotas. my coolant was contaminated due to a blown head gasket !
The lowdown: fill it with distilled water, use it for a day in light traffic (Don’t let the water sit, you have to fill it and use it for a day, if the weather is hot, you should not stress it as water has less cooling capacity), then, flush as much as you can from those 6.5 liters of distilled watter, and once you have removed 5 or more liters, fill it up with SLLC (Not a drop of LLC is allowed)
The coolant from Toyota for modern cars (2004+) is super expensive ($21 for every 2L), my 2014 Prius for example has 10 liters of coolant in both engine and inverter loops, that would set me back around $100,
The coolant suitable for such new cars is called the SLLC (Super long life coolant), it comes premixed 50/50 (With distilled water)
Can i mix SLLC with the older LLC ?
You certainly can not ! they are chemically incompatible, You are not free to mix and match.
SLLC is compatible with both inverter and aluminum engine cooling systems, LLC is not, they have different chemical formulations and should not mix in any way. here is what is given by Toyota in the MSDS documents, obviously done by Toyota in a way to keep it ambiguous and keep others from copying the formulation
| Long Life (LLC) | Super Long Life (SLLC) |
| Ethylene Glycol 107-21-1. 87% – 95% | Ethylene Glycol 107-21-1. 45% – 50% |
| Diethylene Glycol 111-46-6. Less than 5% | |
| Hydrated inorganic acid, organic acid salts. Less than 5% | Hydrated inorganic acid, organic acid salts. Less than 5% |
| Water. Less than 5% | Water. Less than 45% – 50% |
| Bittering agent (Trace amounts) | |
| NOTES: | NOTES: This is P-OAT chemistry. OAT = Organic Acid Technology “P-OAT” or “Phosphated OAT” |
So what alternative coolants can be used ?
The coolant compatible with your aluminum engine is a P-OAT, which in Toyota terms is called the super long life, if you find the brands “AISIN or Zerex”, that is the OEM for the SLLC, as for the LLC the OEM is probably castle, As they have a product that comes in an identical container, but that is not definitive proof.
Things you DON’T need to know
LLC *(The one you should not use on modern cars) is not premixed, you add 50% distilled water, but this is for older vehicles.