1970 cat, cali emissions 351c. Has been running steady at 195-200 degrees all summer. Hot and humid trip last week in traffic for first time and she got hot, about 230-235 and then ran rough on highway, engine cutting out.
Got her home without red zoning temp. Highway, she is normal. Same hot and humid weather a day later and she got hot again in less than 5 miles with a bit of stop and go. So I have parts coming, thermostat (for the 351c), shroud, and pump.
Reservoir is steady but i did put about 40oz of water in radiator. Could this be it? Much cooler outside today, let her warm up, drove on highway and let idle for almost 10 minutes (simulating stop and go traffic) and she stayed at 195 while driving and climbed up to 200-205 at idle but would head back down with a few revs…seems ok.
My 70 351C CA emissions car acted the same way on hot days. When it got to 230, I’d get fuel vapor lock and it would ping like crazy. Went to three row 24” radiator, 7 blade thermostat fan with correct shroud, RobertShaw high flow thermostat for 351C, and FlowKooler high volume water pump. Still had problems until I pulled the engine and rodded out the block - it was full of rusty sludge. Problem solved, but it sure wasn’t an easy fix.
I’ve detailed my Cleveland cooling system in my build thread. Thankfully my block was clean and the system was under capacity in both water flow and air flow for my intended uses.
I did install an Aeroflow coolant strainer recently. It works well and cleaned up the stuff that ended up in the block when I scraped off the gasket from the old crusty water neck.
