Piston Slap: The reconditioned Corvair’s distinct lack of cooling

Dan writes:

I have a ’64 Corvair with a six-cylinder engine. It runs OK after I rebuilt the carbs and seems to be mechanically fine. However, it overheats. I have locked open the air discharge flaps at the lower rear of the engine compartment to allow air flow. Engine cooling fan seems to run properly, as the belt is tight. It will overheat whether it sits idling for a few minutes or is driven a couple of miles. Your suggestions?

Sajeev answers:

I was on the verge of blurting out, “OMG, U HAVE A CLOGGED RADIATOR!!!”

Even though I just typed it, I do, in fact, know Corvairs are air-cooled, but my sentiment has some merit. You clearly do not have a clogged radiator, but something is restricting airflow. I am no Corvair expert, but luckily Hagerty’s own Kyle Smith is quite the guru. So here’s his input into your cooling system quandary.

Kyle Smith writes:

Hey Dan, Corvairs are simple cars at the end of the day, but folks often overthink the cooling systems. The key is no different than a liquid-cooled engine: air flow. On the Corvair flat-six the airflow has a relatively simple path: the fan pulls air from above the engine and pushes it down through the cooling fins on the cylinders and cylinder heads before the air exits below the engine through the door you have already found.

I suspect there is a blockage or buildup of debris in or on top of the cooling fins. Start by removing the shroud—commonly referred to as the “turkey roaster”—and thoroughly clean everything. While you are there, removing the casting flash from the cylinders and heads makes a noticeable difference in keeping temps in check. Use a small hacksaw blade to reach in-between the fins and break or saw away debrits and flash. Reinstall all the shrouding, and make sure any and all holes are sealed up. The engine shrouding to body seal is a common failure and can be a pain to replace, but it serves an important function.

Overheating can sometimes be traced to fuel/air mixture issues, but we will assume yours are correct since you freshly rebuilt them. Last thing to check is the ignition timing. Improper timing can build heat rather quickly even though the engine could run relatively smooth. Reference the 1964 supplement shop manual for proper timing for your engine. The code stamped on the block near the oil filter adapter will designate the engine you have and how the timing should be set. Please let us know if this helps; if not, give us a call. Maybe we can figure it out together.

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