'67 L71 Temperature Control

[Duke W.]

Re: '67 L71 Temperature Control

Before spending hundreds of dollars on radiators and water pumps, do the easy things first like converting to full time vacuum advance if OE is ported, checking fan clutch function and rebuilding or replacing if required, and checking the radiator as I recommended in post #3; and if you can find an old fashioned radiator shop, a "rod out" is much cheaper than a new core.

Also understand that the engine is not "overheating" until the temp gets above 230F, and running over 180 on a non-exhaust emission controlled engine (195 on and emission controlled engine), which is the minimum temperature maintained by a properly functioning thermostat is normal in hot weather low speed stop and go driving.

What you call "crappy modern fuels" have nothing to do with engine operating temperature; and in fact, with a properly set up spark advance map, the higher the compression ratio the cooler the EGT, which means less heat transferred to the coolant as the exhaust gas passes through the head port. That's because higher compression ratio means higher expansion ratio and the combustion byproducts cool as they expand. This is also why a higher compression means higher thermal efficiency.

Duke

[Skip N.]

Re: '67 L71 Temperature Control

Hey Duke - good to hear from you,

I have owned my 1967 L68 since 1974

- tried several iterations of ALL your recommendations++, TRYING to COOL the car over approximately 40K miles I put during ownership

- my L68 would ALWAYS run needle width below 210 on the gauge at all highway speeds ; even in over 90 degree weather

I can only relate my Real Life experience with this Vette

- NOM motor with factory cam and heads would run at 70MPH+ on freeway at a needle width below 210 degrees
(all orig radiator 'rodded out' correct fan/clutch and full factory shroud and your recommendations)

- HOWEVER, EVERY time I got in a SLOW Cruise at 90 Degrees outside (like Woodward Cruise); the motor would QUICKLY boil over

- IF I could get to a highway before I lost much water , it would cool back down to just above 210 degree mark for the drive home

As you and I have discussed, I had to rebuild my 427 in 2022 PLUS

- Dewitt Alum Radiator

- then REMOVE Frt bumpers

- add Stewart High Flow Cast Iron Water Pump ; with machined impeller

NOW I run at 2 needle widths below 210 mark on 90 degree days!

- SO....I am very happy that my overheat condition is now FIXED

[Duke W.]

Re: '67 L71 Temperature Control

Before you bought the new radiator did to inspect your radiator for deposit buildup, or remove it and take it to a good radiator shop for inspection, rod out, or new core as required.

Radiators don't last forever and the antifreezes from the sixties and seventies had silicates, which were good for preventing corrosion, but over the longer term precipitated out clogging the tubes, which can significantly reduce heat transfer.

I'm always for doing all the reasonable diagnostics first and then look are repairing/rebuild original parts to as new spec as a first choice.

Duke

[David M.]