I fear a blown head gasket

What reasoning do you have that you suspect a head gasket?

 

I know nothing of paccar engines but I'd say unless you had prior symptoms of pushing water out the over flow I wouldn't be concerned

 

Well if your radiators leaking, you know you at least need a new one. I’d be worried too, since it’s only 5 yrs old. Unless you’re stranded far from home, and have no choice. I’d price radiators at the Dealer, and the aftermarket. Same with Labor. Don’t need to be a Peterbilt Mechanic to put a radiator in. Once it’s fixed, a simple pressure test, (which should be done anyways after installing a new radiator in a perfect world), will show any excessive coolant pressure build up. Go from there. Radiators from the Dealerships are almost twice as expensive than an aftermarket from what I’ve seen. They’re not any better. Just dropping it off, and letting them have at it can be costly. Especially when they start stacking jobs. Add miscellaneous shop fees, environmental fees, clean up fees, Red oval fees. Might be a good time to check the CAC, since it’s coming off anyways. If it’s leaking, the money you save can pay for a new one. Labors free.

 

I seriously doubt you've got a headgasket problem. A lot of the rads these days are cheap aluminum and plastic pieces of trash. Where's it leaking from?

 

I had one blow but not a Paccar. Loaded uphill with my foot in a hurry. Started raining on a clear day ( water droplets on windshield ). Just cheep junk radiator I thank but changed the t stat also. No problems afterwards. Hope that works out for you as well.

 

Pull the dipstick. If it's milky you have lost a head gasket. EDIT: Or you have a crack in the block. Had a 6.9 Ford Diesel do that.