Reply to "Question about expansion tank cap"

Pre-L Panteras overheating? That story goes back to 1971 when the first gen radiators had coolant tank baffles that negated cooling from about half the core. Redesigned from a vertical baffle to horizontal baffle in '72; problem fixed. Remaining "overheat problem" comes from a water temp gauge that reads wrong AND has too small a gauge span. V-8 cars built in the late 20th century run 210-240F ALL THE TIME. The early Pantera gauge shows 0-220F: result was panic in unknowing drivers when the needle swung way-right. Fix for that mental issue was the '73 gauge that has a 0-250F span and maybe a more correct calibration with the U.S sender.

On aluminum rads: virtually everyone talks endlessly about heat transfer coefficients and theory without addressing the real issues. That is, water flow thru the assembly. Brass rads use maximum 3/4" wide x 1/8" tall x 0.040" wall transfer tubes inside. Aluminum rads use 1", 1.25" or sometimes even wider x 040" tall x 0.050" thick wall transfer tubes. Result is, the aluminum rad flows 2x to 3x more water at the same internal pressures. Any brass rad is a flow restrictor! Thinner or larger brass tubes cannot structurally support stock water pressures- and rad makers have tried endlessly.

Second, in some areas of the country the local water is SO corrosive, it will dissolve a piece of scrap aluminum in a tumbler overnight. The fix here is No-Rosion additive or something similar. Corvettes & Z-28s have had alum rads since 1980 and the specialty shops have a test they run using a GOOD VOM. Remove the cap and drop a lead into the coolant & ground the other lead, with the meter set on minimum amps. If the meter reads above 50 milliamps of electrochemical current, the chemical action inside your cooling system is very busy dissolving metal. My coolant system reads 18 milliamps with local water, 50% Prestone and no sacrificial anodes. I still change it yearly. My 13 yr old aluminum rad, 25 yr old aluminum heads and aluminum waterpump all show no corrosion inside. Note this current reading occurs with the key off and zero power to the car; the car battery can even be removed.