Engine coolant low, need to fill with lower quality coolant?

You should use the correct SLLC. If you mix in a different coolant then you would eventually need to drain and replace the coolant. "Flushing" is not too helpful since ~ 1/3 of the old coolant will remain after the coolant is drained - so if you use water to flush, the antifreeze to water ratio will end up being lower than it should be.

If you want to fix the problem causing DTC P1121, the engine coolant valve will need to be replaced. However that is a less important issue than making sure the engine coolant level is correct. $275 is a pretty good price for a Toyota dealer's service dept.

 

Low coolant has been known to cause a sticking control valve, the problem clearing once the fluid is topped up.

John (Britprius)

 

One option would be to top off with distilled water. Later you can bring the concentration up with Toyota super long life coolant. Make sure to keep note of the amount of water so you can put at least the same amount of llc in. Keep in mind your level of boil/freeze protection will be lower until you do so.

I second John's reply on low coolant causing a P1121. I recommend you see if the check engine light sticks around with the cooling system fillled up. I also recommend you check if your engine water pump is leaking as this is most often the cause of low coolant.

Avi

 

Are we talking about the radiator itself, or the reservoir?