Aside from the plastic/aluminum radiator in the Volvo, my other car - a 1985 Mazda RX-7 - has basically the same combinations of metals in its engine, aluminum and cast iron. They form the head and block, respectively, of the Volvo, and the rotor housings and side housings of the rotary engine in the RX-7. Only difference is a soldered brass radiator in the RX-7. BTW, that radiator is HUGE, nearly twice the size of the one in my 745T.

Now, Volvo cooling systems are pretty well known for staying nearly pristine for decades if maintained properly and fed Volvo coolant. The RX, however, is just like any other car. That is, the RX-7's radiator builds up solder bloom and various crud after a while, even if well maintained. Could running the phosphate-free, low silicate Volvo coolant help keep the RX-7's cooling system cleaner? Are the seals and water seals (very different in a rotary engine) a factor in which coolant an engine can use?

If the aluminum in the Volvo radiator is a factor in keeping cooling system clean, I would probably search around and see if a plastic/aluminum radiator can be found for the RX-7.