OVERHEATING

Mr bastid

i thought you were having a pop about evans coolant as i say i can't find anything either way to say if its good or bad and as i can't get it everywhere i choose not to use it

but now i see its about flow.. and you nearly have me convinced

I agree with what you say regarding temperature difference i.e the delta between ambient and coolant or indeed fin-surface on radiator. the bigger the gradient the more effective the radiator is at doing its job its all just balance, and heat energy spreads out from a place where it is concentrated to a place where it is less so like a drop of dye in a bucket of clear water.
i agree higher ambient temperature reduces the gradeint and yes you are more likley to overheat on a hot day due to this. this is obvious to all

BUT you arguemnt abount the coolant staying in the block too long only makes some sense if
the system is way under specification
if the system has the wrong rated cap
if the system is running pure water i.e boils at a temperature too low for the system it is being used as a coolant in

it doesn't properly take into account that fact that the system is presurised,
and if the coolant stays in the block longer and gets hotter as you state then the block and heads lost more heat eneregy from their surface to the coolant and the delta between the tmeprature of the coolant and the ambient temperature in the radiator again gets wider which make the effiiciency of the radiator better.... Up to a point. so slow is not neceesarily bad until one part of the system is way out of specification with the rest.

unlike the water in the bucket with a drop of dye, which will all end up slightly dyed the air flowing through the radiator has an infinte supply.... and as long as the temperature gradient stayes more or less the same the radiator works perfectly well and in a range of ambient temperaures.

if what you say is the case why did mopar put time and effort into producing a set-up for their race cars that slowed the pump down.... Thermo clutch fan, so i won't say slowed the fan down, as that would only be obvious, at, and just off idle and race cars don't idle.....
When they created engines with heads, induction and cam that moved the power and torque up the rpm range. i.e out of the range that the pump was designed for (grocery getting and freeway at 65 mph)

this was so that the pump turned at its optimum speed for best cooling. the pump has a sweet spot in the rpm range. its contsrained by its size position and shape. it pumps coolant of the kinda density you get with glycol and water at 16LB pressure 195F, the best at some RPM that is probably in the 2000 -3000 rpm range .

it needed to run at a speed that didn't cause cavitation and didn't, one presumes, pump the water round too fast. They must have found that too much pumping, a too high RPM at the pump had detrimetal impact on cooling.... maybe it didn't move the water faster, granted i could have the wrong end of the stick maybe , a too fast pump, just causes chaos and no pumping, but either way they spent money and time on working out that too fast at he pump impellor made the cooling worse

so my only crime is to assume that too fast pump=== too fast flow of water
and i'll agree that THAT may not be the case

so i agree with you on eveything apart from the bit about time in engine and radiator..i think there is more to it than either of us understand, but chrylser did, and changed the gearing on the pump to slow it down in cars that did the most work and created the most heat at an RPM that was greater than normal.

Dave