56 Bird, 312, auto.  While I didn't have a overheating problem, I have made some of the recommended things to keep it that way.  I installed a wide mouth thermostat (NAPA #6) and put the plug in the bypass hose (with an 1/8 hole in it).  The car runs at the usual mark on the temp gauge when fully warmed up, but I have noticed what I think is unusual.  When first starting and the car warms up, the temp gauge goes all the way to hot.  After 30 - 60 seconds the temperature comes down to its usual reading (thermostat opening).  After that, even if I let the car sit for a number of hours the same day it usually  works normal, regardless if the weather is warm or a little on the cool side. 

I saw that another early Tbird owner on another site mentioned he had the same thing.  The thermostat is new (I changed it when I first noticed this) and I checked the new one out with a thermometer in a pan of hot water before installing. 

Question is - any one else noticed this situation after installing the plug in the by pass hose?  Is it a TBird thing only?

This winter I planned to install the new spacer for TBirds and will probably remove the plug to test if the plug is the answer.





54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

My 56 Victoria does exactly the same thing. Always that's slight panic after a couple of miles whether it will open and cool down, but it has never fails. Does it only when cold never on a second start up after sitting a few hours. I've thought it might be the thermostat hitting the heater valve screwed in right above it but probably not the problem. I am doubtful that the plug is doing it as some water is being bypassed and in many ways like the engine getting a little warmer right at the begining to help the oil warm up. I've lived with it for over 3 years.

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

The people at Stewart waterpumps - be sure and check for their web site - sell a modified Robertshaw style t-stat. The modification is three x 3/16 holes drilled through the stat so that it "leaks". This is for use with a fully blocked bypass (race engine)........ When the engine starts pumping water, the intention is that flow begins toward the t-stat and directly over the wax filled "pill" and gets it open and regulating. 

I drilled my blocking plug (3/8 brass pipe plug) for the T-bird with another hole that I suppose provides a bit more initial flow - and mostly on the advice of Ted who says that the plug hole allows air out of the waterpump  when the system becomes "static" (engine stopped). 

 
 Steve Metzger       Tucson, Arizona

It could be, if the thermostat is not drilled as Steve describes, that cavitation, and some other dynamic events are occurring to cause a spike in the temperature just before the thermostat is able to open fully.





Lawrenceville, GA

This is what the Stewart Components modified thermostat looks like...... pretty easy to make the modification. It simply makes water on the top end of the engine migrate toward the "exit". 




 
 Steve Metzger       Tucson, Arizona

just waight you cooling engineers will see the results of no bypass. the holes in the stat is alowing water to circulate in the engine(by pass)replacement. temp rises as poor flow of water is heating as it enters the head.the cavitatin will creat hotspots and eventionly crack heads and other serious failures.also with temp sending unit at left rear of head not accurate especially withpoor flow.put on some miles and and use the engine on some good pulls you will see some  issues.tho most users dont put enough miles for thes to develop. i do not  know  of any engine  gas or diesel that does not have a bypass of some description to eliminate cavitation

I think the 3 x 3/16 holes in the T-stat have always been part of blocking off the bypass - some may not have read the whole discussion in past threads. Water has to migrate toward the t-stat to facilitate proper opening as the heads heat the top end of the engine. Try holding water in a bottle that has three such holes in it and you'll get an idea of the flow volume - though within our engines, an impeller is also pumping toward the opening.

If flow is stalled by complete blockage - the temp spike would be an obvious indication of no water movement.  

 
 Steve Metzger       Tucson, Arizona

'Scuse my ignorance here, but does the bypass water flow toward the thermostat/intake manifold, or toward the water pump?

Gene - Water exits the block through the neck on the front of the intake manifold. The neck contains the t-stat - and below it a bypass port that fits into a 5/8 hose. That short hose directs water back into the suction side of the water pump. When the engine starts up cold, the t-stat is closed and all of the pump output is directed to exit through the bypass port - most likely causes an impeller inefficiency (designed in CAVITATION?) due to the restriction. Heated water leaving the heads into the intake (moving to the bypass port) gradually warms the t-stat and causes it to open.

Once the thermostat opens and begins to regulate - it maintains temperature control by speeding or slowing water that is exiting the block - headed into the radiator. A portion of the water is always bypassing the radiator (even if you are up near boiling) - and is being recycled into the block with no loss of temperature. This volume of water is what the modification is intended to redirect into the radiator.

When the modified t-stat is in place and water is restricted at the bypass port - water leaving the heads at start-up exits through the drilled thermostat. Modified as shown above - the heated water goes directly over the operational "pill" of the t-stat, and it begins regulate temperature by controlling the exit. No hot water (or very little) is sent directly back into the block.  More - or larger holes may be possible if a different t-stat is used - but it could be set-up to have nearly the same restriction as the factory port.

 
 Steve Metzger       Tucson, Arizona

Thanks Greenbird, I couldn't make up my mind if the 5/8" hose port on the water pump was pressure or suction. I see warnings against blocking the bypass. I have a 3/16" hole in a plug blocking the bypass and three holes drilled into the outer ring of the thermostat. Do you think I'm on solid ground? 
Thanks again for the detailed explanation
Gene