EGR Cooler

[lynns hubby]

For the last couple of months the heater in our 2006 XC70 D5 has not been as hot as it used to be. I had the same issue last winter and searching on here lead me to the resistor thingy in the AC panel. A quick check with a torch and it was covered in fluff. I removed this with a cocktail stick being particularly carful as advised on here. All was fine and the heat was back. Then as mentioned before, a couple of months ago it started to cool off again. I checked the resistor but it was clean this time. I got a call from my wife a couple of weeks ago to ask me to rescue her as the car was belching out thick white smoke from the exhaust. It was obviously not oil from the colour of it and there was no smell of diesel. I therefore concluded it to be steam and thought instantly of a HG There were no engine warning lights on the dash and the car was showing no signs of being short of power or misfiring. I drove the car home and the smoking stopped. It was driving fine. However just as I pulled into the drive the coolant warning message appeared with the red triangle. I topped the system up with 1/2 a ltr to get the level back and the message disappeared. I drove the car round for 20 miles and nothing more happened. The daughter borrowed it that evening and rang me to say that the warning had reappeared on the dash. She topped it up with water and drove home with no issues. After reading numerous times on here that a HG failure is rare on these engines the only other culprit I could think of was the EGR Cooler and a search on google gave just the symptoms that I had. No external leaks but loss of coolant.
I went for this and changed the cooler for one from a breakers (god knows what Volvo would have cost for a new cooler). Ran the car with no issues. The wife and daughter took it to Crufts for the day (around 320 miles return) they phoned when the got there and said it ran fine but there was NO heat from the heater. The following day I checked the heater hoses and sure enough the inlet hose was hot but the outlet hose was cold. Removed the hoses and back flushed with a garden hose. The amount of crap that came out was obvious that it had blocked the matrix. When I looked at what had came out, it was black soot. I checked the header tank and that was black too so I flushed the whole system. Refilled, with tap water, drove the car round and drained again. I had to do this 5 or 6 times before I eventually got clean water out. However, although warm, the heater is nowhere near what it should be. Checked the heater hoses again and BOTH are hot to the point where you can only touch them momentarily. So is it now time to change the resistor thingy in the AC panel? At no time throughout this has the car overheated or even risen above the normal (Needle in middle) temperature