I recently bought some Carretex Concentrated Coolant. The instructions assume you have flushed the radiator and tell you to put the entire bottle (350cc) into the cooling system and then fill with water.

However, there are no instructions as to how to mix up a bit if you just want to top up the coolant.

Any ideas?

Most sites indicate 50/50 mix of ethylene glycol and "distilled" water. Make sure you do not use tap water due to the mineral content.

http://bioengr.ag.utk.edu/Extension/ExtPro...les/engcool.htm

Also verify which coolant you currently have in your radiator. There are two types G11 and G12 (ethylene glycol and propylene glycol where EG is the most common and PG is a newer safer version). One is red and the other blue and you can not mix one with the other.

My guess when you say concentrate it means not premixed with water and still need the 50/50 mix ratio. If you are only topping off a small amount then just add the concentrate, don't need to premix.

Thanks for that. I have a new Toyota, but the book seems to indicate ethylene glycol. However, it is definitely very blue.

But, the book warns against "silicates, phosphates and / or borates" which the reference you gave says are common in commercial coolant products.

I remain a little confused. Care is due for service soon, so I guess we'll ask Toyota....