I'll bet radiator. To many have been replaced for the same reason. Thats also why some run coolant filters as well, to keep this from happening.

Chet

 

I just upgraded my E99 to the radiator with the cooler built in. I used a new ford radiator for a 2001. I also bought the factory radiator lines and added the 6.0 cooler.

Part Numbers
2001 Radiator = 4C3Z8005EB
2004 6.0 Cooler = 5C3Z-7A095-CA

 

Update: the new radiator is here. I've been running the green coolant and this seems like a good time to upgrade it. What do you guys run?

 

I use Rotella Ultra ELC in mine

 

I run cheap old 50/50 green stuff I can pick up anywhere.

Over 1.4 million miles without a coolant related failure so why change now.

 

Sounds great as far as the upgrades in rad, lines and 6.0 cooler!
But I hate to be the one to tell you that the E99's only like the green coolant due to the fact that the E99 injector cup sealant is totally different that the late99. And ELC coolant can cause the injector cups to leak. Hopefully someone explain it better than I. I don't have time now to get into it. But before you switch read up on E99 coolant and injector cups.

 

Well, the green stuff has kept it going for 13 years so I guess I'll leave well enough alone. Thanks for the input.

 

OK, another question, am I supposed to have a lower radiator mount on the passenger side? Mine doesn't seem to have one and I can't see where there was one.

 

I am sorry I couldn't explain myself better earlier but I was busy. Now there are some guys that have used ELc in their E99 without any problems but I have yet to hear the long term affects. Here is a very good post on E99's and coolant. https://www.ford-trucks.com/forums/8...ifreeze-2.html And I think Stewart-H post #30 does a great job pointing out the facts of the matter. So this is one of those subjects you can make your own choice on which coolant to use. Although most guys with E99's that change injector cups and oil cooler orings then switch to ELC.
And I am NOT a big fan of the old school green and sca's because in my truck I have a hard time keeping the SCA's right. But with over 200k my Blackstone reports come back clean for coolant. So I myself will switch to ELC when I change injector cups and replace oil cooler orings.
Just my 2 cents

 

Very interesting read, thanks for the link. I learn something everytime I get on here.

 

I am glad to be able to pass along helpful info. And I too am always learning something about these trucks thanks to the FTE 7.3 brotherhood. These guys are the greatest group of people out there when it comes to helping others out.
Thanks guys !!
Just like in this tread I have learned a couple things I didn't know too. So please let us know how things turn out.