I drained the cooling system today and pulled the thermostat housing so I could check which one was in there.  There wasn't.  I half suspected that because it only made sense- took a while to warm up, once it was hot it stayed hot with the larger pulley, the smaller pulley must move the water around enough that it doesn't get hot to begin with.  

A 180* is going in there after open up the carburetor plenum.  

WITH RESTRICTED BYPASS AND FASTER TURNING WATTER PUMP,MY GUESS IS cavitation of the pump is happening,which means water is airiated and not flowing threw the block and up to the heads.as Henry design.
my 292 with4vHOLLEY ALUMINUN RAD 180 THERM AFTER 15MIN ON THE ROAD 160 ,WITH MECKANICAL TEMP GAUGE,TAKEN AT THE THERM END OF INTAKE(DRILLED AND TAPEG FOR CAPILERY TUB STAND WARNER TEMP GAUGE. I LIVE IN THE FRASER VALLEY CANADA SO IT IS10 DGRS. OH THE HEATER WORKS  FINE. HAVE 2 ELCT FANS THAT START AT 180(1)SECOND FAN STARTS AT 190.

Thanks all.  This is all in a Model A coupe with an electric Stewart gauge reading the head temp and a Mooneyes under hood style gauge in the thermostat housing.  I've also always had good luck with 180* thermostats and have never had this problem.  I will pick one up and a brass pipe plug and see what I can make happen.  

Thanks again.  

My plug was 3/8” brass pipe. 1/8” hole. Sounds to me the smaller pulley is working at idle to cool your engine as it helped me. You may not need it but you also need to know the thermostat is opening. I always test in a pan of water on the stove with a cooking thermometer. I personally use a Mopar high flow thermostat but I want ours to cool in 90* plus weather with the AC on. I don’t mind 180 to 195 at all but don’t like 200+. Good luck. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

I used a brass pipe plug and drilled the hole. Won’t rust, softer than stainless.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Since it stays cool, the thermostat is opening.  It would not stay cool if the thermostat remained closed.

The temperature difference is about right so that means that the gauges are at least indicating similarly to one another but that does not mean they are accurate.

A restrictor should have an outer diameter which is equal to the inner diameter of the hose.  Without checking, I think that is 5/8"


Lawrenceville, GA

Start with the thermostat. The infrared guns are not necessarily accurate. Your temperature gauge is not necessarily accurate. Ted (Eaton) has drilled and tapped the thermostat housing for temp sender, being that the location provides a more accurate reading. You could do that and connect it to a quality aftermarket gauge, while retaining your OEM gauge as well.  

That Mustang pulley really cooled the '59 Fairlane 292 off but now I'm concerned that it's too cool.  Temp gauge plumbed into back of head says 155-ish, small one in the Thermostat housing says 165 while driving and idling after a 40 minute highway ride.  I'm wondering if the bypass isn't allowing the water to get warm enough to open the thermostat.  Also wondering if there is a thermostat in there.  

My plan is to pick up a 180 degree thermostat and put that in whenever I get around to it- winter time if I can wait that long.  Trying to enjoy this while I can.  

When you guys restrict that bypass to 3/16"- what do you use to make that restrictor?  Just a stainless rod?  What diameter?

I'm just worried my oil isn't getting warm enough to evaporate the moisture.  I have a temperature gun on the way so I can check it- not sure how to really do that, though or even what temperature is for oil in a non-PCV engine.  

Thanks.