Can you put car coolant in motorcycles?

Absolutely not, automotive coolant contains silicates which can prematurely deteriorate water pump seals. There some automotive coolants that do not use silicates: Honda brand type 2 coolant is available at most Honda car dealerships and is silicate free. Also use distilled water - you will thank me later. Motorcycles have small water passages (almost capillary-like compared to automobile engines); tap water will leave deposits and cause scaling. Some chemicals such as chlorine and fluoride can react with coolant and thicken its viscosity. I also recommend a coolant system flush if you have the time, especially if you like to "honk on" on your bike when the weather is hot. My last piece of advise, stay away from GM Dexcool brand coolant, it has a very suspicious reputation for prematurely destroying seal. James