Mixing Coolants

[DRC]

Is it safe/unlikely to damage the bike to mix different brand coolants?  Both are ethylene glycol, both are silica and phosphate-free, and both are ostensibly safe for aluminum engines.  We're not talking filling the radiator half with one brand and half with another, we're talking topping off the reservoir.  Current brand is OEM HD4X Hybrid OAT coolant that is unavailable for purchase anywhere in the States near as I can find.  Potential top-off brand is simple Prestone pre-mixed. 

[Howie]

As long as they are both ethylene glycol and silica/phosphate free you are good.  You will be loosing the extended life of your OAT ant freeze though if the Prestone isn't OAT.  Oh, aesthetically, color matters.  You don't want to end up with brown.  

I should add hybrid OAT ethylene glycol can be mixed with conventional anti freeze, OAT that is not hybrid can't.  Also, hybrid AOT and AOT do not mix.  Do not mix ethylene glycol with Propylene glycol.

[DRC]

Thanks for the reply.  Although I'd probably be safe, I think I'll just wait until I flush the whole thing and replace the coolant with Engine Ice.