bemills 05 SYG #2999
Mixing the types of antifreeze is not a good idea. As Dave said, you would be best served by finding out what type was in the rig before you added any. That may be difficult to do now because adding orange to green ( or vice versa ) makes brown.
To answer your most pressing question, the mixture of the two types will probably not immediately create issues internally with the motor. However, gaskets may be effected quite quickly, which can create other problems.
The antifreeze is not really special, just a specific type recommended for these engines (heavy duty for diesels). If your rig came with green, stick with green. If orange, stick with orange. Now, please understand that I'm using these colors because they "represent" the two types, however, you can get both types in both colors, so don't go by color alone.
If you have combined the two types, I would recommend that you have the system professionally flushed ( I have never spoken to anyone who was able to adequately flush a system with any kind of DIY method). After doing the flush, you can use either type. But, as stated above, I suggest you stick with the type that the engine came with. The two types of antifreeze contain different additives that function in different ways to prevent corrosion. Cat, MB, and Cummins probably have different ideas about how to tackle the corrosion issue, hence the different types.
There are extended life products that give you up to 5 years before you have to change. Some require regular testing and use of Supplemental Coolant Additives (SCA) to get to that 5 year life. Others don't.
If you have a shop do the flush and change for you, MAKE SURE that they use distilled water. Many will tell you it doesn't matter. If they say that, go to a different shop. Both the antifreeze manufactures and the engine manufacturers tell you to use distilled water. FYI, both types of antifreeze are available in either premixed ( 50/50 solution) or concentrate. The price is about the same. But if you consider that a gallon of distilled water is about a dollar, and a gallon of diluted antifreeze is $20-$30, it doesn't take a rocket scientist to figure out that you can save several dollars by buying the concentrate and distilled water.
05 SYG 72999