really ugly fluid

Last night while I was swapping out the original radiator our of my '95 XJ I noticed that the fluid was really "ugly". Brown in color. As I started checking around I noticed that the reserve bottle was dirtly (very dirty) so I hosed it out pretty good. My initial thought was dirt--though it has not been that long since the whole system was flushed. Since then, I have been wondering if it could have been engine oil or transmission fluid. Are either of those even possible? If so, what should I check? and how do I figure out where the nasty stuff is coming from. I don't want to ruin the brand new radiator that I just installed. Any help would be welcomed.

if you have an auto tranny it could be trans fluid as the radiator is used as a tranny cooler. could have an internal crack causing the 2 to mix. i would do a coolant flush and see if it reappears

Thanks for the help. If tranny fluid is getting into the coolant (which should now be fixed with the new radiator) is it possible for coolant to get into the tranny fluid? If so, do I need to drain and fill the tranny, just in case?

Not sure what it would look like (milky?) but you could always pull the drain plug on the pan and see what your tranny fluid looks like, that way you're only letting out 2-3 quarts if its still "good". If it looks like crap, then you might wanna flush that too!

The regular green anti-freeze, its anti-corrosion additives only last 2 years. Once those additives are used up, metal parts in the cooling system can start to corrode. Rust is brownish and can look muddy in solution with water.

As well, the silicates used to protect the aluminum in "Green" anti-freeze, is a derivative of sand. I'm NOT sure, but I think the silicate additives can degrade into a sand like residue.

Either way, you need new coolant every 2 years, regardless of mileage.

I'm currently degunking my cooling system, running distilled water with Prestone Flush (the citric acid that you run for 6 hours), it seems to work and really cleans out the gunk, even the coated on gunk you can't ever reach.

It won't do miracles, although my old radiator looks much cleaner, and the scale has started to break up a bit, there is still a lot of scaling in the radiator. I'm replacing the radiator, I'd rather use the flush on the old radiator, once I'm done I'll swap in the new radiator.

Unfortunately, many of the manufacturers have switched to a new "Universal Anti-Freeze" that works in all models with all colors of anti-freeze. From what I've gleaned from a little research, this new "Universal Anti-Freeze" is just GM Dex-Cool dyed another color. In fact, in the fine print, it says you have to completely drain and flush your cooling system before using it. So be careful when picking out anti-freeze, anything claiming to be "Universal" or Long/Extended Life is likely some sort of derivative Dex-Cool or G-05 (OAT and HOAT technology). Your cooling system was NOT designed for those fluids, its just the opinion of the manufacturers that if you flush your system well, their fluid will work well.

Look at the ingredients of the anti-freeze bottle, old "Green" anti-freeze uses Silicates and Phosphates for corrosion protection. If you don't see some form of those in the ingredients, then likely its some new derivative of Dex-cool or G-05.

Dex-Cool and G-05 have NO corrosion protection additives, instead they use additives that promote the metals to form their own natural layer of corrosion as protection, and preserve that natural layer. Thus their additives last much longer. I "THINK" the ingredient 2-hexane, something like that, in Dex-Cool is what caused all the nightmares you heard of about Dex-Cool (OAT), G-05 (HOAT) doesn't have that ingredient and even use a little bit of the silicates/phosphates for protection.

I've seen several opinions, that if your going to switch, that G-05 is better to go with than Dex-Cool for cars designed for the old "Green" anti-freeze, it should work better and be more compatible.

Personally, I'm using the original recommended fluid, It appears the NAPA generic and ACE hardware Generics Anti-Freeze has Silicates and Phosphates in them. Zerex makes an original "Green" formula, but I can't find it for sale anywhere in my area.