sounds like a headgasket to me if you are 1 to 1.5 inches over the full mark and the oil is a milky brown.the mid 99-01 heads was a weaker head casting that was prone to cracking.they mostly cracked beween the 3rd and 4th exaust port but can crack other places as well.if that is the case dont pick up another head in those years.instead pick up a head from a 96-98 4.0 they are stronger and the exaust ports line up better for better flow.
drain your oil and replace it as well as the filter.pour in 6 quarts of oil and let her rip.if it goes over full and turns milky again i gurentee it is a head gasket leak or a cracked head.

You are overlooking the easy way to check for a head gasket leak,go to a good shop and have them use their leak checker.It is a special fluid in a tube that turns color when it detects combustion gas with engine running,5 min affair and very accurate.

Also,NEVER run 100% coolent,it will not protect as well,proven fact,if you get rust in your system,you already are way past when you should have changed your coolent.

Howdy 1949 Pure antifreeze will not boil till a temp of 400* is reached...which is good, right? However it gets "slushy" at around 0*F. For some reason adding water to the antifreeze causes it to NOT freeze till -40*F or so.
So for you guys up north you MUST add this water to the antifreeze to keep your block from freezing.
However us guys down here don't have to add the water and if we run PURE antifreeze we never get ANY rust. Another plus is the lubricating effect the pure stuff does on the coolant pump.
I have heard that the ARABS on the desert run pure as a matter of course. 400* boiling point is a good thing.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

Maybe so,BUT,have you tryed that to see if it is right?I'm old enough that I don't believe it until I see it <img src="/forums/images/graemlins/smile.gif" alt="" />

Since about 1964 or therebouts.. The only rides I have had with ANY water in the coolant were the ones that came from the factory thataway. After doing ANY work on them where the coolant came out I always put pure stuff back in them.
Of course if I lived waaaay up North I couldn't do that but down here it does fine...
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

I checked into it and it boils at about 290,however I found the right stuff to run without water,check this out <img src="/forums/images/graemlins/smile.gif" alt="" />
https://www.evanscooling.com/html/auto1.htm

Sounds just like pure ethylene glycol (pure antifreeze) don't it. Although it says nothing about freezing I'd betcha it gets slushy at around zero F.
Why not just use pure ethylene glycol it MUST be the same product.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />