What is the difference between a cat 6B and the old cat 6 8u/9u is there any difference? I don't have much information on ether. How do you tell the difference/ ID plate.

I see in my question I forgot to put the D in front of the 6 I have noticed that there are books for the cat D6B and separate books for the D6 8u and 9u's Most have a number on the back of the unit. I have been leed to believe that the D6 that im going to look at starts with a 44 number and the book has something with a H on it if I remember the 44 number was referring to the wide gage and something like 37h was the narrow. I have very little information, but don't want to miss identify the unit. From what I have heard is that this until has Glow plugs and electric start. The other thing I am looking at is it should be under 20000 lbs if it's the older D6B.

Well, what vehicle is it in and I can give you more. Generally speaking, Cat's 6 series isn't their best. They were just adding in the required emissions stuff (I'm assuming this is a diesel, that's the only Cat 6 I have experience with). Their older and newer engines have good reputations and performance.