6k hour J08E engine. Bubbles (large) in radiator neck when started. If you put the radiator cap on, it'll push coolant out the expansion tank I put new cups in the head. No change. I put a new EGR cooler on. No change. No coolant in the oil or any consumption No fault codes, nor exhaust smoke. The boss man has me pulling the fan belt, as he claims the water pump can induce air into the system. He says the dealer did a J05E here for the same thing Is a Hino water pump capable of introducing aur into the cooling system?
Alright, belt is off. Scratch that idea. Constant bubbling at idle or WOT. I guess the head has to come off.
Had the exact same issue with the j08 in a hino truck. Also replaced the cups with no change. Pulled the head. Cylinder head was warped. Rebuilt head and a fresh gasket fixed it.
And if you can get part numbers from the dealer, call the hino truck dealer for the engine parts. Usually half the price of the off-road hino dealers. That was my experience with Kobelco. 6k for an EGR valve and 3k from the truck dealer.
Sounds like a head gasket. there was a bulletin about the seals on the water pump being to weak and allowing cavitation in the pump.