I have the 2003T, but it's basically the same motor
, with another cylinder and a turbo.
First thing is that sometimes the impeller looks fine, but under load actually fails to turn. So good that you replaced it!
Take the exhaust elbow off yourself and clean it - its not too hard to do and will save you some $. If you stick a screwdriver through it when chipping off the soot and rust, it was knackered anyway - you should not be able to damage it like that anyway! Make sure the water injection port is clear, these block fairly commonly.
So, it has a heat exchanger?? Many of these are just raw water
cooled, so no heat exchanger present. Raw water
cooled ones sometimes have the block filled with sand and mud.
Presuming it is fresh water cooled, and has a heat exchanger, it will also have an oil
cooler, in behind the heat exchanger. The oil
cooler has smaller tubes than the primary heat exchanger, and these can be totally blocked with growth. It is good proactive to remove both the oil cooler and heat exchanger, and mechanically clean them every year or two. I use a .22 rifle cleaning
brush for mine. No need to pay someone, although if it is really bad, it might be easiest to take it to a radiator shop or engine rebuild
place and have it acid bathed. Once it's clean again, keep it clean!!
Also, in the copper tube that goes from the thermostat housing to the exhaust outlet, there is a small plastic fitting. Yes, in side the tube. It should have a pinhole through it - if it does not, the engine will overheat. The pinhole is prone to blocking...
It takes me about 3 hours to remove, clean, and reassemble the oil cooler and heat exchanger, and an hour to put them back on..