I have a 99 3.0 with 184k miles.
The other day I starting the truck (cold start after a weekend of sitting) and drove about 2 miles and heard the coolant res lid pop open because of pressure in the cooling system. I also noticed the temp gauge on the dash was all over the place, the needle was flying up and down. This was the first time it had happened so I put more coolant into the rad and kept driving and made it home. When I got home I used a tester kit to see if there was exhaust present in the rad and it said there was, however it took a loooong time for the color of the test to turn yellow and I suspect some exhaust from outside the rad contaminated the test. Anyways, there is a leak at the bottom of the rad and now it cant hold coolant so that needs replacing but more importantly that means I cant run another test on it. I suspect either cracked heads or head gasket leak but it could be something as simple as the thermostat being closed shut. I am going to replace the thermostat when I fix the radiator. Also recent repairs include new brakes, brake bleed, new AC compressor and new transmission as of 5k miles ago. The power steering pump is bad and the serpentine belt is fraying on one side, I have the new pump and belt and plan on replacing it when I do the radiator.

Here are my questions:

If I replace the rad and there is a leak in the head gasket will it break my rad again before I can fix it or should I even run the test again?
If it is an exhaust leak into the coolant through the head gasket do you recommend trying to use a head gasket leak fix like Blue Devil before paying to get the repair done?
Do you think that the power steering pump or the serpentine belt had anything to do with this?

Side note:
I have asked Scotty Kilmer during one of his live Q&A sessions on YouTube what he would do and he said that he would use the Blue Devil first just as a last ditched effort before the big expense but I wanted to see what others thought about this.

 

Don't waste your time with head gasket sealer. If your going to invest in a radiator and such, you may as well prepare to spend money on a possible bigger fix. You can test for exhaust in the cooling system again, but I wouldn't waste antifreeze doing so. Just fill the system with water. If it checks out ok, drain and refill with coolant. If you do the work yourself, replacing heads and/or gaskets is way cheaper. Having someone else do it is the biggest part of the expense. A machine shop can rework the heads for much less than buying new/refurbished ones. If you do have to get a new head or 2, I've had good experiences with Rockauto.com. Oh.. and when you do a new radiator, always get a new cap. I change mine once a year, no matter what. Sounds like if you get this done, you're going to have a near new truck. Probably last you another 250k miles. lol

 

Update:
I decided to flush the system and replace the radiator. I replaced the upper and lower hoses as well as the thermostat. Once I got the cooling system sealed up and the air was bled out I never had another problem. It looks like the leak in the bottom of the old radiator was causing those symptoms.