Thumping noise in cooling system

I have a 1992 Ford Ranger with the 3.0l V6. It has just under 100,000 miles on it. After the truck gets warmed up I will hear a thumping from under the hood. A quick check shows this is air bubbles traveling through the upper radiator hose from the block into the radiator. I also hear the thumping after I shut off the vehicle when I arrive home. This does not happen every trip, but seems to occur more in the winter time (Pacific NW winter, rarely into the mid-30’s).

All cooling system hoses, thermostat and radiator cap have been replaced and the system burped, yet the symptoms persist. Honestly, I suspect a blown head gasket but my dealer poohed-poohed the idea.

I would have it checked for a head gasket.

Why did you take it to the dealer? Most mechanics can handle a 1992 Ranger. Dealer mechanics are no better (or worse) than independent mechanics, but they almost always charge more. It would seem your dealer is not one of the better ones or you would not have had any need to ask the question here.

I agree with the head gasket possibility, but what concentration of antifreeze do you have in the car? If it is not strong enough, or the radiator cap is loose, the potention for boiling exists and if you are lucky a simple fix could correct this problem.