The drilling of an additional hole in the thermostats is something that was passed on to me back in day one when I started out in the general automotive repair business.  It was done this way due to documentation showing fewer thermostat failures with the thermostats modified versus not.  The size of the holes being installed were not significant in regards to gaining any additional coolant circulation.  Besides these addedl holes allowing the thermostat to open smoother or in a less pronounced cyclic manner, it also assists in bleeding the air out of the system prior to starting the engine with fresh coolant.  The higher end thermostats you now buy will have some sort of small hole in them already to allow air and/or coolant to bypass the poppet.

Lorena, Texas (South of Waco)

Dave:

My water pump drive is also zero cost.  I used a heater motor from a '68 Ford I had laying around.

John - "The Hoosier Hurricane"

Steve, IMHO, drilling more holes isn't the answer.  Your poppet thermostat already offered zero coolant restriction before any holes were drilled.  Interestingly, nowhere is this 5% mentioned in Stewart's web site.  Open means open.  Zero restriction = free flow.

I mentioned before, I think an electric fan is your answer IF your radiator is efficient enough to cool your system.  If it isn't, look for a good radiator.  The combination of radiator & fan (heat transfer) are of monumental importance for desert cooling.  I believe bypassing your thermostat doesn't do much to cool because it simply prevents your stat from doing its job.  At times you need heat, other times you need to carry heat away.

There are a couple points I do not agree with Stewart on.  One is, aluminum transfers heat better than copper.  Oh no it doesn't.  Silver is the best (put a silver spoon in hot coffee), then copper, then aluminum.  Farberware's most premium pans have a copper bottoms.  Their 'standard' set has aluminum.  I have both sets.  NO comparison, copper uses less heat to cook because it transfers much easier.  Your thermostat is made of brass (copper and zinc) and it is submerged in water.  It doesn't need holes to transfer heat to that cone.
- Dave

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Dave......Easy decision my man....my pump is stock too - so I wanted - (1) more capacity to pass water (couldn't get more volume without a pulley change or buying an expensive souped up pump) and (2) regulation of most of the flow at the same opening temperature as the original.

Whomever answered the phone at Stewart the day I called, estimated the three holes raised the flow capacity of the thermostat by 5%. Might have been the counter clerk....dunno. Doesn't matter if its a stocker like mine or a race car - I'll take the 5%.

Since I read the June article in "Streetrod" mag I've been toying with the idea of (1) putting restrictor washer in the bypass hose and (2) finding a way to add additional flow capacity by drilling or notching the poppet. 

 
 Steve Metzger       Tucson, Arizona

John, all the parts on the 350 I saw came out of a JUNK YARD!  The guy spent NO money on a kit.  I've seen electric waterpump kits, stand-alone and otherwise.  This one blew me away because it was simple and available to everyone for half-nothing.

I was simply amazed.  It got the juices going, and I thought about two-speed fans and MOS-FET designs I could do with a simple thermistor input for variable speed control.

Dave Dare

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

I totally respect Stewart for making NASCAR waterpumps, but I don't have a NASCAR water pump, mine is stock.  In fact, Stewart says their water pumps WON'T WORK on stock thermostats:

"...and Stewart Stage 2, 3, and 4 water pumps simply will NOT operate with a regular thermostat because these pumps have no internal bypasses."
 

"Stewart further modifies its thermostat by machining three 3/16" bypass holes directly in the poppet valve, which allows some coolant to bypass the thermostat even when closed. This modification does result in the engine taking slightly longer to reach operating temperature in cold weather, but it allows the thermostat to function properly when using a high flow water pump at high engine RPM." Do you have a high flow water pump?  Then you need the holes at high engine speeds. Mine is stock, and yes, I pulled an original 160* stat out of the housing.  Did you also notice what Stewart said?: "Q9. What would be the correct pressure cap rating to use?" "A9. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept." "Q10. Which cooling fan do you recommend (electric or mechanical)?" "A10. Electric fans now outperform mechanical fans in nearly every application." "Thermostats #304-306 fit the following special applications: Ford: 1954-1964 309L (239); 1954-1965 4.2L (256); 1954-1964 4.5L (272); 1965-1967 5.8L (352) Dodge: 1951-1966 all 8 cyl.; 1967-1969 4.5L (273 cid); 1970 4.2L (255 cid); 1967-1978 5.2L (318 cid); 1968-1974 5.6L (340 cid); 1971-1978 5.9L (360 cid); 1967-1971 6.3L (383 cid); 1972-1978 6.6L (400 cid); 1967-1971 7.0L (426 cid); 1967-1977 7.2L (440 cid) Non Modified 2 1/2" dia. $14.95"

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Dave:

A large percentage of drag racers have been running electric motor driven water pumps for some 25 years.  Many buy a kit with the motor, timing pulleys, and a timing belt.  I drive mine with a small V belt.  It and the blow through cooling fan are on a thermostat, so they cool the engine down after a run, then shut off.

John - "The Hoosier Hurricane"

Well, I don't live in Michigan and can't comment on the cold problems there - but in southern AZ we have weeks on end of 106°+. The Ford service manual for my bird says use a 157° opening thermostat - and I use a 160° Robertshaw style - with the three holes. Stewart Components claims that at the least it adds about 5% flow - and they are "the" NASCAR waterpump builders. I don't believe they run a waterpump bypass hose (just one more place to blow on a race car) and the vent holes probably prevent a pressure lock on poppets that open toward the engine cavity. The only other change to mine is the use of a six blade fan. Eddie Paskey has just about convinced me to buy a smaller fan / pump pulley from Concours - but so far the price has me holding out......

The cooling system of the bird is pretty inefficient due to the one inch "spacer" Ford put behind the water pump that leaves the impeller spinning in "no-mans land". Small radiator face too. Very dumb. Anyway - equipped as I described, the bird runs almost exactly 100°-110° over ambient. The temp rating of the thermostat simply controls the opening minimum. At no roadspeed idle -when the ambient temp drops below 60° F temp, the engine water outlet stays at about 160°/170° and regulates. It will tolerate ported manifod vacuum to the distributor in winter - but not in summer.

This 110° rise situation can get pretty uncomfortable in summer at stopped idle. I've run a considerable number of "burndown" tests. Only the pressure cap and antifreeze boiling point are on your side. So far - knock-on-wood - the tanks have stayed connected with a 13 psi cap. My local rebuilder removed the radiator tanks, rodded it out and claims to have put the "super-seal" on the solder job - and he has an excellent reputation for keeping desert radiators intact. Fingers crossed here. 

 
 Steve Metzger       Tucson, Arizona

  Some folks don't believe a thermostat REGULATES engine temp.  In Michigan, we know it does.  (Driving a cold car is miserable when it's below freezing.)  Drilling "bypass holes" in the thermostat doesn't make sense, either.  When a thermostat gets to its predestinated temp it slowly opens, below that temp it closes.  Thermostats operate flawlessly every time, for many years.

I've heard, there's a reason why stat openings are restricted to ~one inch.  Really?  Then why are all the rad hoses so large?  When your cooling system is maxed-out, and the radiator can't transfer any more heat, a high-flow thermostat makes perfect sense as a last-ditch effort.  It offers more flow at the same pump pressure, which puts as much heat at the radiator as possible.  If hot water isn't cooled by the rad, then the rad has a heat transfer problem, not your thermostat.

Last week I was in Mississippi for my first time.  I saw two things I couldn't believe:

*  A motorcycle had a CHEVY 350 cu in V8 engine.  (The giant radiator caught my attention.)  The drive chain was HUGE (probably an 80).  I asked the guy if insurance was killing him.  He said, "Not really.  When they asked what size my engine was, I told them it was 'a 350'.  They must have thought I meant CC's!"  The tank spread was so wide it would give me rickets.

*  A stock water pump on another Chevy 350, driven by an electric fan motor mounted above the water pump.  (That blew me away.)  It had a small v-belt between the pump and motor.  I'm sure the motor was thermostatically controlled.  After thinking about that for a while, I wonder why anyone needs a thermostat.   The motor was from a stock Dodge electric radiator fan.

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

The "Robertshaw" type thermostats look like this one - the entire lower cylinder shown seperates from the base a little over 1/2" (poppet is 1-1/2' diameter). Its a very big opening when its wide open compared with the everyday sort of part. At minimum probably 35% more flow.

As shown here this one is modified by drilling three 3/16 ports around the nose - which adds flow and creates water movement over the "pill" that operates the poppet. This modification is the suggestion of Stewart Components - and they can supply the modified part if someone wants to order one. Otherwise i just drill my own holes in a Mr Gasket "high flow thermostat"  - just be sure you order the one for the big block Chrysler to get the right size for a Y.   

 
 Steve Metzger       Tucson, Arizona