The question is generally posed in retrospect, by which time it is too late.

 

Ahhh, but why is it too late?

 

So, with the exception of the possible dillution of additives, no harm will come from mixing the two. I've had people claim the mix would begin to 'gel' after time. I figured that was baloney.

 

Coolant safe for aluminum radiators needs to be silcate and phosphate free.

 

Honda goes so far as to state coolant containing silicates will damage their water pumps

 

I've never checked the dealer shelves for a brand specific coolant. It should be there if is a concern exists, no?
I know Honda had a specific coolant some years ago that caused some print in the mags. For a buck or two difference between the auto parts and the suzuki store, why gamble. It's only once every 5 years, if you do it at all, right?

 

Your question opens up a lot of other questions.

There antifreezes with more than one combination of corrosion inhibitors with orange/gold/yellow dye. There are more than one antifreeze compounds with green dye (ethylene glycol base or propylene glycol base).

The most common orange AF is probably GM's DexCool. The most common green AF is the ordinary green ethylene glycol stuff. When mixed they work OK, but you end up with the shortest anticorrosion protection, 2 years at best.

The corrosion inhibitors become depleted before the antifreeze capabilities of the ethylene glycol wear out (if ever). Follow the recommendation on the label for the length of service (usually 2 years or 5 years), or use a voltmeter to test the system. Put one probe into cool coolant in the radiator neck. Put the other probe on the battery negative post. If you read 0.3 volts DC or less, the inhibitors are probably still doing their job. If the voltage is higher, the inhibitors are depleted and your cooling system has become a galvanic battery cell destroying the more active metals.

The type of corrosion inhibitors in the antifreeze to use depends on the metals inside the cooling system. Plus, Europeans prefer AF without phosphates due to the high concentration of minerals in some of their tap water. The Japanese prefer no silicates in their AF due to the way they design their water pumps. There are phosphate, silicate, borate, combinations of those two or three, organic acid technology (OAT/DexCool), a different organic acid compound (OAT/not-DeathCool), and hybrid organic acid technology (HOAT) corrosion inhibitor packages.

So...what to do? I prefer to use any motorcycle specific antifreeze (but these usually have only 2 year protection), or any Japanese auto antifreeze, or Zerex Asian Engine Formula antifreeze. If you buy a concentrate to mix with water, use distilled water especially if your tap water contains much mineral. Our engines seem to be very tolerant of just about any antifreeze, and we haven't seen reports that relate to problems with any antifreeze, nor with neglected systems.

Here's a good article:
Learning Coolant Fundamentals

 

When it comes to antifreeze/coolant.... you cannot tell what the chemical-mixture is by simply looking at the color.

It has already been mentioned above that OAT (Organic Acid Technology) coolant mixed with other technologies can actually GEL and plug up the small passageways within your engine. VERY BAD!!

The only proper and correct answer to the original question is NO! do not mix even the same color of coolant if it is not the same brand.

If you have any questions about your cooling system.... DRAIN, FLUSH and refill. (Use only distilled water to to mix with coolant)

Personally, I like the PINK coolant Pentosin - Antifreeze

 

why

The only reason I can figure to mix different coolants would be in a road situation where the coolant is low and you have no access to the right stuff. In that case it might be best to add pure distilled water, rather than anti-freeze. Then, when you get home, drain the coolant and put in new, proper coolant. Yes, diluted coolant will freeze at a higher temp and boil at a lower temp, but unless you are crossing Death Valley in the summer or riding in the snow in winter, it probably won't matter. And the higher concentration of water (assuming it doesn't boil) will actually transfer heat more efficiently. I doubt any significant amount of corrosion will occur in a week or two (or perhaps even all summer) so a lower concentration of anti-corrosives, in the short term, is unlikely to present a problem. Yeah you might get away with mixing, but then again, you might not. Why take the chance, especially if in the middle of a trip?

 

I have assumed that the reason some newer anti-freeze formulations plainly state on the bottle that they are compatible with any color is that in the past they were not. Incompatibility of colors was also the received wisdom passed down from former generations.

All of which makes me think that mixing colors was formerly bad but now OK. But since it is extremely unlikely that there would be any reason to add coolant except during a total flush and fill it probably is irrelevant anyway.

 

formulas may be compatible, but resulting color disguises impurities

never in any vehicle I own

 

I asked at Honda-waki dealer today, the parts guy suggested they use the Honda mix in the bikes they service. It's motorcycle specific. Something about the water pumps spin much faster than in a car?

 

The only thing I can think of with faster-spinning waterpump is "cavitation".

The Pentosin antifreeze I use specifically says "protects against corrosion and cavitation"