As I am basically a chicken, I decided after this summer's rash of "radiator failed and I lost my coolant" messages to buy a new Nissen unit from RPR and install it in my 1990 745. The 745 was built in July, 1989, so the original Blackstone aluminum/plastic radiator was exactly ten years old, in the age range where I began to worry that I would lose it catastrophically some hot summer day. It showed no evidence of leakage or corrosion, but then reports show that the plastic side tanks fail first, and usually through a large crack. I used Volvo blue-green for the first six years, switching to Havoline Dexcool orange in 1996. Coolant has been changed every two years.

The installation of the Nissen was a piece of cake. The new unit is at least twice as heavy as the old one, the result of brass and not aluminum construction. While removing the top hose from the old radiator, I pulled off the inlet hose plastic fitting, so some plastic embrittlement was evident. I also found that the fins on the old unit were absolutely filled with dirt, bugs and assorted crud. When I banged on it, lots of dirt fell out.

After finishing the job, I decided to do a little destructive testing on the old unit. I used a ball peen hammer and whacked the plastic side tanks to see where they would fail. They were actually quite robust for 3mm thick plastic, but I found that the weakest area was around the inlet area on the top, which makes sense because the hottest water enters at that point and any temperature-related plastic fatigue would tend to start there. That cracked far more easily than the outlet area, which tends to stay cooler in operation.

I then peeled back the tabs holding the side tanks and removed the tanks. Amazing! There was absolutely no evidence of any internal corrosion whatsoever. Each tube was in pristine shape, the header ends appeared brand new, and the transmission cooler was in superb condition. The rubber gaskets sealing the joint between the tanks and the radiator shell were elastic and clean. The only thing I noticed was a little bluish-green silicate precipitate film on the surface of the side tank near the outlet fitting (the coldest area of the radiator) related to the pre-1996 Volvo coolant that I used. Otherwise everything was clean.

The only weak point in the radiator was the embrittled plastic on the upper side tank near the inlet hose. Otherwise, these are very high quality units (and I speak from experience with mid-80's GM radiators, which corrode and fail every five years.)

My recommendations to everyone are:

-Make sure you change the coolant regularly;

-Dexcool seems to work very, very well in an all-aluminum radiator;

-Pull the fan shroud back (two bolts, easy!) and use compressed air or a car wash high-pressure soaping wand to blow out the dirt from the fins.

-Think about changing the radiator after ten years when side tank plastic embrittlement will become a problem. Due to the nature of the aluminum tabs holding the tanks in place, it does not appear possible to replace the tanks alone, since in doing so you will crack the tabs.

I hope the Nissen unit will have the same robust metallurgy and last just as long.