Thread: 318 running hot

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Originally Posted by Don Shillady

This thread is a bit old but still in 2012. I am excited to finally get my motor running after years of delays. It is a rebuilt 350 SBC two-bolt main '76 Corvette block with 882 heads shaved to 9:1 compression ratio and 0.030 rebore. I have a 15" flexfan on a Zip water pump setup and it overheats in about 15 minutes of idle at 1100 rpm with all Prestone in the Speedway Cobra radiator in a '29 Ford shell with a bottom cooler section for the trans. I have drilled one 3/16" bypass hole in the 160 degree thermostat, should I drill more bypass holes as well as add a shroud or add a restrictor washer or will just a shroud cool it? I like the idea of a restrictor washer but maybe holes in the thermostat plate can do the same thing? I would like to avoid a shroud if possible because it is really tight inside the '29 shell and I plan to run a stock Model A hood.

Don Shillady
Retired Scientist/Teen Rodder

Don,
First of all, why are you tagging your question onto an old thread instead of starting a new one? You will get a lot more attention if you start a thread listing your specific problem and your name in the by-line because people will look at this one and think it's old news already closed.

Don't drill any more holes in your thermostat or you might as well drop it in the trash can and buy a new one. The hole you drilled serves one purpose, to allow air to vent from the system as you fill it with coolant to make the job easier and less of a hassle. Without the hole the thermostat will be closed, trapping air in the block, and the only way to get it out is to start the engine, get it up to temp where the thermostat opens, and "burp" the system. In my experience this was a messy and frustrating process as the air bubble would burp big, pushing coolant out the open cap, and making a big mess. No more holes.

The missing shroud is your problem. At idle the fan is going to pull air from the path of least resistance, and that is around the tips of the blades, behind your radiator. Sure, you get some flow through the radiator, but you're losing efficiency. If you're running an electric fan, your shroud can be as simple as a sheet of aluminum with the edges turned down, and a hole a bit smaller than your fan diameter. Mine is 1/2" thick, fits over the back edge of the radiator frame, and adds 1/8" to the overall thickness. If I pull in hot it will cool while idling to just above the thermostat set point within three to five minutes. If you're running a mechanical, Tech pointed out the fitment for them above.