Hello, I come with bad news:
After replacing timing belt, water pump and thermostat in my 2000 Intrepid 3.2, now coolant is mixed with oil, a mechanic told me that he thinks that radiator surely was in bad status, and with new new water pump with more presion, it must be broken and mixing oil with coolant. He thinks radiator in these cars refrigerates both oil and coolant.
What do you think about this? Can I fix this replacing radiator? Is it important to use an original Mopar radiator or can I use aftermaket? Would you recommend any particular radiator model?
The 3.2 and 3.5 did have an oil cooler built into the radiator. I forget what year they removed that oil cooling system, but pretty sure that 2000 still had it. Look for two hoses (probably 13 to 15mm in outside diameter) running to the radiator on the passenger side (very similar to the transmission cooling connections on the driver's side of the radiator). If you have those hoses, then it has the oil cooling in the radiator. A leak internal to the radiator between the oil and the water (antifreeze) must have developed. I do not think that a new water pump would have caused the problem - it would not have added much pressure difference between the water (antifreeze) and the oil.
The best replacement radiator would be the OEM one from a dealer, but they would cost more than aftermarket (I don't know how much more, especially on the EU market). Aftermarket radiators for these cars had lots of problems with quality and durability a few years ago, but I think some brands have fixed the problems over the years. I replaced the radiators in both of my Concordes - one was bad right out of the box, and the other one failed after exactly one year. They were of the Readi-Rad brand (not sure they are still around). Both were replaced under the guarantee, and I didn't have any problems since then with the replacements - that was probably around 7 or 8 years ago. Still using one of them with no problems (the other car got scrapped).
Recommendations on many aftermarket brands on parts like this are almost meaningless because in a particular brand, one month you might get a radiator made by one company, and 6 months later, you would get one made by a different company, but both would be under the same brand name when sold to you. It all depends on which manufacturer they got the best price from that month, with quality being of little or no consideration for many common brands.
Antifreeze is very damaging to the bearing inserts on the lower part of the engine (crankshaft bearings and lower connecting rod bearings). You could try just replacing the radiator, but there is a risk that the engine will fail very soon due to bearing damage. The safest way would be to check the bearings for condition and replace if there is any question. Whatever you do, you need to flush the engine out thoroughly to get rid of all antifreeze in the oil. You should do several oil changes within about 150 km of each other to get any antifreeze out. There may be special flush chemicals to help with that, but I don't know much about that.
You might find two versions of the radiator for our cars in OEM or aftermarket brand - one with the oil cooler, the other without. There are no other options. Some brands might only offer the one with the cooler because it can be used for both applications, and when both are offered, the one with cooler is cheaper anyway.
EDIT: Didn't see In-trepid's post - was still composing my post when he posted.