This is kind of long, but after reading on this forum that mixing Green and Red Antifreeze can cause sludge, it explains something that happened a while ago.

I have a 1994 Z28, with 87,400 miles on it. I just drained my radiator to take off the heads (broken exh manifold bolts). It looks like there is Red Antifreeze and it seems like it's been in there a while because whenever I checked the coolant level, it looked redish brown.

I had the Opti replaced under warranty back in 1996. When I got the car back, it was overheating badly. They took it back and replaced the radiator. Said that it was gummed up. Since it was under warranty I didn't think anything about it. Well, my guess is they put the red coolant in a 1994 that had green coolant when they did the opti. I am also guessing that they flushed the system and put red coolant in when they put in the new radiator.

Now, my questions:

1) How can I tell for sure it's the red coolant that came out of my car?

2) I assume that I should flush the system really good before I put coolant back in, so the real question is: WHAT COOLANT SHOULD I PUT BACK IN: RED OR GREEN???

Thanks,
Glenn

 

Red..Dexcool

 

I know that this probably sounds obvious, but does the coolant that comes out of your car right now look red or green? That's the easiest way to tell whether or not you have red or green in there currently. I do not know of any other way to tell the difference between the two.
You will definately want to flush the system out completely. As far as what to put back in, you can use either solution once the system is completely flushed. The DexCool (red stuff) lasts a lot longer than your regular green coolant, so many people would recommend that you use that coolant. I had similar problems to what you had, and I put the green stuff back in mine. Regardless, either one will work just as well, however you will probably need to flush the green system out every year, whereas the Dexcool is supposed to last like 50,000 miles or something I believe.
I think that the 93 and 94's come with the green antifreeze, and it wasn't until 95 that they started using Dexcool from the factory.

 

I looked at the old coolant. It does have a green tint on the top 20% of the jub, but it's brown on the bottom 80%. I wonder if it's been mixed. I'll do a really good flush and put the Dex Cool in.

Thanks,
Glenn