Cooling system problem

[jmg8550]

I have a difficult question concerning my cooling system. Recently I rebuilt my 4.0l pushrod engine and have had this problem since. I rebuild my engine to stock specs and replaced the heads(cracked). Ever since the rebuild my engine coolant system seems to be building pressure spikes. It only does this after driving short distances at highway speed and engine fully warmed up. When coming to a stop or idle, the coolant pops and bangs(audible), and if I grab onto the upper radiator hose it is also felt. I have replaced the t-stat twice. replaced the intake manifold gaskets, used a snap-on brand air lift tool numerous times. and tested the head gaskets and heads for combustion leakage into the cooling system, the results were negative. I have absolutely no coolant leaks and no air in the system. A new radiator cap has been installed as well as a brand new water pump. I am beating my head against the wall trying to figure out the problem. All gaskets have been fel-pro premium gaskets. The block was only honed as it didn't need bored. Any suggestions? This problem is a little hard to explain so feel free to ask more questions. I am an experienced auto tech and have a fairly good understanding of technical diagnostics. Thanks to all help in advance.

 

[shadetree]

I would have the radiator cleaned. If the heads were cracked, it was because of a previouos overheating problem. The 4.0's usually don't crack from any other problem.

When I rebuild an engine, I never guarantee it if the cooling system is not refurbished along with it.

Other things I would look at: bottom hose collapsing when engine is revved.

Correct radiator cap. Is the cooling system percolating, gurgling, spitting out the overflow when the engine is shut off?

Make sure the engine is burped to get out all the air.shady

 

[jmg8550]

Like I said, all air is removed from the system via vacuum. The percolation only happens at idle. The engine never heats up past 210 degrees(according to the datastream from a snap-on scanner). I have a 16# cap as per my altitude(4800ft). And the cooling system never got oil in it from the heads cracking. All the coolant went into the oil. The coolant is extremely clean, a 50/50 mix and has been drained numerous times from me trying different solutions, it's clean. By the way all parts are from NAPA. I only buy and use the high end parts.

 

[shadetree]

The radiator tubes can be clogged up and the coolant still be clean.

Hold the radiator cap up in it's normal position. Observe the center valve on the cap. It should pulled snug against the cap. If it is hanging down, it is the wrong cap.

If the cooling problem is only at idle, you may have an airflow problem. Check the fan clutch, restrictions, shrouds, etc. shady