Piston Slap: Overheating at any speed? | Hagerty Media

[Hagerty]

Dan writes: I have a '64 Corvair with a six-cylinder engine. It runs okay after I rebuilt the carbs and seems to be mechanically fine. However, it overheats. I have locked the air discharge flaps at the lower rear of engine compartment open to allow air flow.
https://www.hagerty.com/media/advice/piston-slap/piston-slap-overheating-at-any-speed/

[Sajeev]

I received some excellent feedback from a Corvair expert via email too: 

  Often after overhaul, mechanics fail to re-install a metal air deflector under each Corvair cylinder head bank. This piece of metal is held into place by two small wire clips, and is hard to re-install. Clips are a pain, and clip onto the metal rods that hold on the cylinders. This deflector is required to direct air flow onto the heads. If these two pieces of metal are missing, heads will over-heat.

The pieces of metal can be seen through the open bottom air exit doors when you open them. Metal pieces (2, one on each side) are about 18 inches long and about 3 inches wide, and are "waffled" to fit under the cylinders. Corvair owners must use 30 weight conventional oil. Never synthetics or mult-weights. 30 weight motorcycle oil is good to use. 

I am an old Corvair expert. I have raced and owned over 30 Corvairs in my past. I had over 11 at once.

[Swamibob]

Hey Sajeev:
This one seems like the Golden answer. Air cooled machines need their tin to make the air go where the Engineers want it to go. It's of vital importance on any air cooled engine that has tin covers! I was going to mention only using straight 30 weight or possibly 20W50 racing oils in, older, air cooled engines. They are typically built with larger clearances to deal with the higher temperatures, but your guy beat me to it.

[Sajeev]

Yeah I really think both are the issue here, after hearing from the experts!  

[WoodBear]

you also might have a restricted oil line that also can make an overheating issue.

[Dkelfarm48]

Thanks everyone for your suggestions. It definitely overheats to the point of oil fumes in engine compartment. I will investigate further based on your thoughts. I do have 10w30 oil in it so will change out to 30w. Hope I return with good news.

[ValuedCommenter]

10w30 is the correct oil for a Corvair. It's what was specified by Chevrolet. You just need to make sure that you're using an oil with the correct amounts of zinc and phosphorous for the flat tappets. Many diesel engine oils that are formulated for older diesels have the correct amounts. Stick around in the Corvair hobby any amount of time and you'll find widely divergent opinions on the right oil, so much that the moment oil gets mentioned in a Facebook thread, the moderators have to shut it down. Here's everything you need to know about Corvairs and oil: https://www.widman.biz/Corvair/English/Links/Oil.html

As far as your overheating problem, follow Kyle's suggestions first. You've almost certainly got an impediment to airflow under your main shroud.