New Rad Vs. MPG
 

I read some post on the net about someone losing around 4mpg after replacing an old worn away rad, is there much truth to this? will running temps drop to the point of lost mileage?

4 mpg
 

The car would have to get on the order of 66.7mpg to generate that kind of mpg differential from the cooling system alone.

I doubt it'd be much of an issue, especially if you're regulating cooling with a grill block.

yea I run a few grill blocks so in theory I could just reduce flow if I find a change