In cars, the radiator is always electrically isolated from the frame. This is to prevent galvanic action between the thin aluminum (or copper) core and the iron parts in the block.

On a car, if you toss the rubber washers that isolate the radiator, it is going to spring a leak in a year or two. Aluminum (and copper) parts inside the block and plumbing corrode also, but they are thick enough that corrosion leaks are less of an issue.

Indeed, folks are not nearly as diligent in changing their auto coolant every year like one would be in an airplane, so the rust inhibitor in a car is more likely to go flat or be absent. Still, why push your luck?

    Bill Dube'

John Downing wrote:

Looking through  my pictures of the evaporators.  Are these best mounted on rubber isolators or mounted solid, it appears that they have been mounted both ways.  What is the consensus on this.  Monday I will have the bottom half of the cowling along far enough so I can position the coolers and fabricate the cooler mounts.  Thank you  JohnD