Ah, now I see. I thought you meant you would look at temps to diagnose a blinded filter, which I thought was odd, because it would easily be the number one suspect. I see what you're saying now. That's an interesting concept. My preference would be to measure flow directly rather than extrapolate it from another style of reading, but I do like the alternate perspective. I guess that means I'd rather stick my head up a bull's ass to get a good steak rather than take a butcher's word for it.I get that and whilst I have only given this so much thought there is plausibly merit in looking at temp differential using accurate temp measurement. Perhaps a waste of time but I'd most likely play around with installing a Tee and digital temp gauge and sender and seeing if I could establish a noteable differential in temp when placing some or more restriction on flow. It could be just single digit degrees changes but if it is reproducible that is still valid.