[Frango100]

You have any idea what could cause the radiator cracking? Where does it crack to start with, at the plastic tank, or the aluminum core? Does it really crack, or does it form a small hole?
Was the radiator cap changed as well? The radiator cap has a pressure relief valve and if that one doesn´t work (well), it could cause overpressure and a consecutive failure of the weakest part in the system.
The cooling fan issue is strange as well. You see it happen quite often that the fan relay fries, but thats most of the time due to a bad fan which draws too much current. You changed the fan already, so that should be ok. The temperature sensor and the PCM are now left over. But the fan running with the ignition in off, means another fried relay.
I would check all the ground wires, because a bad ground could cause the current flow through other less resisitve paths.

 

[Frango100]

There is a good change that the radiator cap is not releasing the pressure to the overflow tank. That will result in something to break, the weakest point in the system, which probably is the plastic radiator tank. It is always a good idea to change the radiator cap when changing the radiator, its cheap and then at least you know the pressure release valve should be ok. Most of the time the valve opens too early or stays open all the time, preventing pressure buildup and lowering the boiling point of the coolant. In your case it seems to be the opposite.
Did you use the original mopar fan, or some paralel part?
Thinking further about it, you say it would release pressure from the reservoir, you mean the overflow reservoir?
Could be that you have a failing head gasket, which is causing the high pressure and overflow. I would start with a leakdown test to be sure that the head gasket is not the problem.

 

[Frango100]

I can imagine that a faulty coolant temp sensor could cause the fan to run all the time and maybe fry the fan relay due overheating. Just wonder what that could have to do with the bursting radiator. Did you change the radiator cap as well?
Still funny also that the temperature indication was indicating normal.
But i hope that you have solved it now.

 

[Frango100]

The only part in the system which controls the pressure in the cooling system, is the radiator cap. It should release the coolant towards the overflow reservoir when a pressure of around 18 PSI is reached and should stay at that pressure. This higher pressure increases the boiling point of the coolant.
But the important thing is that it is working again:thumbsup:.

 

[Frango100]

again?
They are in the plastic tank? No crack and just holes? I can understand how a crack will form in the plastic tank due to overstressing, but a pinhole?
Did you check the hose from the radiator neck to the overflow reservoir if its unobstructed? Could you provide a picture of the pinholes? It would be interresting to see what the pressure in the cooling system is during normal operation.

 

[Frango100]

I have a Spectra Premium radiator since 1 1/2 year and no problems.
Did you see any stress marks on this last radiator which had the pinholes? It looks almost if its indeed suffering from externally imposed forces, but still impossible to understand how it could create holes this time.
Does the 4.0 radiator have the transmission cooler in the right hand tank, as with the 4.7, or does it sit in the left hand tank, where the cracks and pinholes appeared?

 

[Frango100]

Just trying to put all posibilities on paper, but also can't understand what the transmission cooler could have to do with the problem. Maybe the left tank is the weakest by design and for that reason is the first one to burst. But what could cause these pinholes? Is it maybe just a bad batch of radiators with some kind of material failure?
Sorry, but running out of ideas.

 

[Frango100]

Your fan is running in opposite direction, it should take air through the radiator, into the engine bay and then overboard.
Was any wire connection spliced, so that maybe two wires where cross connected? The fan will most probably have a hard time to blow air against the driving airstream and will draw more current then normal and fry the relay.

 

[Frango100]

There is only the fan relay, which gets its signal for the fan speed from the PCM. Did you get the right fan? You could evently swap the wires to the fan, but this case is strange.