My outfit (312) runs 100°-105°F over ambient - with this temp taken at the thermostat housing. So summer day at 105° ambient - the housing is 210° - and winter (Arizona) the temp goes down to the thermostat setting (160°F) and hangs there. These temps are taken from a long static idle (burn down) test. I'd like to get the range narrowed down so the idle tune is a bit more constant - so I gathered up this set of parts...

A high flow, 180°F, Mr. Gasket thermostat (big block Chrysler size) with three added 3/16 bypass holes drilled in the nose.

Single groove pulley from a '69 302 motor, aluminum spacer to accomodate the deeper nose, and a brass plug to shut off the bypass hose - so all of the water flow has to go through the thermostat / radiator.

The spacer is 1.0" thick with a long enough nose to engage the (six blade) fan bore directly - fan mount is right on the pulley face. The smaller diameter pulley should net about 20% overdrive (relative to the original pulley). The closed off bypass may not be good for Michigan warm-ups - but my engineer's brain keeps telling me it ain't a good idea to have a 5/8 hose bypassing the radiator on a 105° day. 

I'm sure others have others must have tried this before - does it work? This is for a driver car - belts loose at the track.

 
 Steve Metzger       Tucson, Arizona

You got more guts than me, trying a Chrysler thermostat and a windsy pulley on a 312!

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People should not be afraid of their government, a government should be afraid of the people.

--Alan Moore

that spacer that you used, where di you get it?????

I have a machinist across the alley from my office that builds aluminum telescope parts and fancy heat sinks for Raytheon. Gave him a drawing and bought lunch .....offered to pay for the work. Anyway, the piece showed up with a N.C. invoice - which means I'll be trading something for it later on.

I think one of the commercial 1 inch thick fan spacers will work (like from Speedway or?) - as long as the nose pilot sticks out of the C9 pulley far enough to hang the fan. I just put it on the inside instead of the front. 

PM me an email address and I can send you a PDF file of the spacer (or whatever works).

 
 Steve Metzger       Tucson, Arizona

Hello Steve! Just curious.Why are you using a 180 stat when a 160(same type) is available from Mr.Gasket.

  

I've got the 160°F Mr. Gasket high flow part in there now - Ford spec in my book was 157°. But with the original '56 spark advance scheme, three blade fan, etc. - the 'Bird wouldn't cool worth a tinker's d@#$%n. So it seldom went near the low setting and a good bit higher in summer. When I got the ignition sorted out and working to suit me, six blade fan - I ended up with that huge summer - winter swing (like 210°-160° = 50°). Does crummy things to the idle mixture.

I'm thinking (and hoping) that the upper number drops due to more water flow and then the 180° low end coming up will make the idle mixture requirement a bit more stable. A guy pointed out to me that the 5/8 "short circuit" bypass hose was letting a considerable amount of water escape the trip to the radiator. 

 
 Steve Metzger       Tucson, Arizona

Just wondering, what vehicle is this in, and what year?

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People should not be afraid of their government, a government should be afraid of the people.

--Alan Moore

Little green machine above. Or below

 
 Steve Metzger       Tucson, Arizona

Another purpose for the bypass hose besides allowing the heater to work prior to the thermostat opening is to relieve the potential for an air lock in the top of the timing cover.  Rather than eliminating the bypass completely, I’d suggest putting a restrictor in the hose to allow any air that’s in the upper part of the water pump and timing cover to be bled back to the intake and then back out to the radiator.  A 3/16" hole in the plug you have should be more than adequate in relieving any air that's trapped.

I’ll add that modifying the bypass is a good idea providing the thermostat is modified to always let some flow past it when it is closed.  This permits the thermostat to open in a more regulated manner.  You’ve already mentioned that you have modified your thermostat with some extra bypass holes so that part is already done.  I’ve blocked the bypass in the past on other engines with success where the cooling was marginal but always made sure that there was still a way to get residual flow past or around the thermostat when it is closed.  On the Y and due to the design of the timing cover, a small amount of bypass is needed though.

Lorena, Texas (South of Waco)

"I see.....said the blind man" - the air bleed-back feature, when the engine is stopped vents air bubbles up to the intake manifold. Drilling the brass plug for an air bleed won't be a big deal for sure.

For those that haven't seen the thermostat modification -here's the place where the three holes get drilled in the "Robertshaw' style of t-stat to replace the bypass.

 
 Steve Metzger       Tucson, Arizona