In a lot of the threads that chew over engine cooling issues 'high flow' thermostats get a fair amount of recommendation. When I asked for one at my local parts outlet I got a blank stare in return followed by "I've never heard of such a thing."

Are these real or do they fall into the 'metric crescent wrench/screw driver/pliers/hammer' category of automotive levity?

If they are real, what makes them different from a regular thermostat (besides the obvious verbiage difference)?



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Jim Olson 

"The Toys"...!!!  Save the Wave!

Where I've been in a Corvette...!!!

I personally dont think there is much to them... quality seems better..

but tell someone that the normal thermostat is 5$ and the high peformance one is 25$ and quite a few people will spend the 25$

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=146676&prmenbr=361

http://www.stewartcomponents.com/html/tech_support/techtip3.asp

in fact stewart says that myself and quite a few others here at c3vr have been operating under a misconception

A common misconception is that if coolant flows too quickly through the system, that it will not have time to cool properly. However the cooling system is a closed loop, so if you are keeping the coolant in the radiator longer to allow it to cool, you are also allowing it to stay in the engine longer, which increases coolant temperatures. Coolant in the engine will actually boil away from critical heat areas within the cooling system if not forced through the cooling system at a sufficiently high velocity. This situation is a common cause of so-called "hot spots", which can lead to failures.


in fact stewart says you must use a high flow water pump on stage two pump.. the main diff seems to be that you have bypass holes... which i guess is why i got away with using standard thermostats.. i always drill two 1/8" bypass holes.. (stewart uses 3 x 3/16" holes)

|UPDATED|6/16/2004 11:59:54 AM (AZT)|/UPDATED|

I'm not sure about the high flow either, but I just bought a t stat for mine and the counter guy asked if I wanted the "Fail Safe". This thing is supposed remain open if it ever fails. Never heard about that! Bought it any way, figured it must be pretty smart to know when it's broke and just opens

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It is a thermostat that has three quarter inch holes drilled around the side to allow water flow before the thermostat opens. When you have a hi flow pump it is recommened.
http://www.stewartcomponents.com/html/products/thermostats.asp


Roy

High Flow is supposed to have a bigger hole and flow more water.

Fail Safe will fail in the open position.

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1973 Coupe    


(click to see a bigger version)

The article states use a t-stat instead of a restrictor. The t-stat IS a restrictor

The high flow theory is not just theory. If you flow the coolant too slowly it will pick up too much heat and boil, overheating. Very true. High flow does help. But it can take longer for the engine to warm up. Minor detail. For a daily driver that needs heat in the winter, or needs to warm up so the computer can function fuel control at best mileage and lowest emission, the high flow t-stat is a bad thing due to longer warm up time. If you don't care about emissions or total fuel mileage on short trips, it won't matter. New cars with OBDII computer systems are less forgiving. These are 1996 and newer.

But ask any pro racer about NO thermostat. Too much flow WILL cause overheating in some engines under some conditions. That's why all stock cars use a restrictor instead of a t-stat or wide open hole. It is not a myth. Dirt track racers also use the restrictor. But keep in mind these cars operate at VERY high RPM almost all of the time. That means much more flow. For a car driven at idle to 3000 most of the time, you likely won't have enough flow to have the overheat occour. It takes a LOT of flow. More flow than normal driving or a bit of street racing will create. In this case the high flow water pump can help by flowing more, and cooling more.

The other factor is air flow through the radiator. 50 MPH air will transfer a given amount of heat. 100 MPH air will transfer more. The faster you go, the more likely it is to affect your car. The flip side is the engine will also produce more heat at higher load demands.

The next factor is the radiator itself. Remember the radiator is a restiction. If it can't flow enough volume, the overheat won't occour with nothing in place of the t-stat. Restriction is restriction no matter where it is in the system.

So there is a trade off, and most cars won't overheat without a t-stat. But due to engine design and operating conditions, some will. I have repaired overheating cars by installing a missing t-stat. Real world cars, real problem, real fix. It is not a myth. Common? No. Likely? No. Possible? Yes.

There are many different designs. The person who wrote the article may have never tested the right combination of machine and operating conditions to see it happen.
I have seen it.

|UPDATED|6/16/2004 2:01:13 PM (AZT)|/UPDATED|

Thanks everyone! You're the best...!!!

Guess I should get in the habit of driving the extra few miles further to a performance shop rather than the nearest parts outlet when I need something for 'The Toy'.
____________________________________

Jim O.
Save the Wave...!!!

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Jim Olson 

"The Toys"...!!!  Save the Wave!

Where I've been in a Corvette...!!!

kstyer said: There are many different designs. The person who wrote the article may have never tested the right combination of machine and operating conditions to see it happen. I have seen it.

Ken you were one of the few people who was right in the previous threads...

some of us shadetree guys should either listen or read
more..

It did make me feel better about drilling holes in my thermostats as Ive always done though.

Drilling the holes yourself makes your own high flow stat. You can save a few bucks. Always a good thing.

Oddly enough, many mfg put a hole in as stock equipment. Not large enough for high flow, but to break surface tension. The cars actually build up a steam pocket behind the t-stat before it opens, and the gas space instead of liquid delays the heating of the t-stat, delaying opening. The result is the car almost overheats, then drops to normal temp when it finally opens, and operates okay until next time.
The small hole allows the steam pocket to leak through, preventing the problem. The hole must be in the highest position to bleed the air.
These holes often have a tiny piece of metal through them that will bounce around. This breaks the surface tension allowing the air to pass through the water blocked hole.

|UPDATED|6/17/2004 8:27:17 AM (AZT)|/UPDATED|

kstyer said: But ask any pro racer about NO thermostat. Too much flow WILL cause overheating in some engines under some conditions. That's why all stock cars use a restrictor instead of a t-stat or wide open hole.

one of the things ive done roadside for overheating is to cut the guts out of a thermostat... voila.. instant restrictor.

my GF (Mechanic) and Father (Hot Rodder) always told me NEVER take the whole thermostat out... just gut it.