worked on pumps for the last 30 yeare,, if one of the pumps flows less than the other,, the other will cavitate,, we never put pumps to pump in a circle but the larger flowing pump must pump into the smaller flowing pump,this will increase pressure, if both pumps flow the same it will work and your flow will increase,,,just remember if the water goes through the HE too fast it will not have time to cool. try it and let us know, jim

at 65 mph my iat's are 5 to 9 degrees above ambient temperature
at 75 mph 11 to 15
at 85 mph 20 to 25