Thermostat

[Guest Pegasus76]

I heard that if you removed the thermostat it can keep your car running cooler than if with a thermostat in. Is that true? Or is someone's car just a little messed up

[johnc]

Your temp guage might read cooler but the cylinder heads and engine itself will actually be hotter. Heat transfer takes time. The thermostat acts as a restriction that slows the coolant flow down enough to properly transfer heat from the block and heads into the coolant and transfer that heat from the coolant into the radiator and air.

[Guest Pegasus76]

Ahhhhh I see! Thanks for clarifying that for me

[Tim240z]

John.....for once, I disagree with your comments:

From my reading:

Different coolants require different minimum flow rates, but contrary to popular belief, you cannot make the coolant flow too fast. This rumor was started because people removed the thermostat to gain flow, because they had an over heating problem, and it aggravated the problem. The real reason they ran into problems is that removing the thermostat also removes the restriction that builds pressure in the engine, so they gained flow, but reduced the boiling point of the coolant in the block. Running a higher flow thermostat and a higher volume pump to maintain pressure, will give no such problems. If you think about it, making the coolant flow twice as fast will also make it flow though the engine twice as often, so there will be more even temperature across the engine.

 

From GrapeApe Racing: http://www.grapeaperacing.com/GrapeApeRacing/tech/coolingmods.cfm

[JMortensen]

I thought system pressure was determined by the radiator cap and flow pressure by the water pump, so the system pressure wasn't affected by the flow pressure. Also, seems like there would be plenty of other restrictions in the system, ie radiator, coolant passages in the head, etc.

 

As always, I could be wrong...

 

Jon

[SpeedRacer]

I guess I have to disagree with Grape Ape Racing. First of all, you can not pressurize water because it's hydraulic and can't be compressed. You can pressurize the air that's in the system and that's done with the radiator cap. As we all know, caps come with different pressure settings depending on what the system was designed to handle. Pressure raises the boiling point just like in a pressure cooker. Every pound of pressure increases the boiling point about 3 degrees F. The pressure comes from heat expansion and NOT from restriction in the engine. So, Grape Ape Racing thinks you can just rev up a cold engine and get 15 PSI – NO WAY!

 

Coolant can flow too fast and not absorb the heat which is why most street engines that are converted to racing run a restrictor in place of the thermostat. Try this, turn on the burner on your stove. Run your hand (don't burn yourself!) over the burner slowly and then rapidly. The slower you move your hand the hotter it gets.

 

The coolant in a car has to move slow enough through the system so it can absorb the heat in the engine and also, so it can dissipate the heat to the radiator which in turn dissipates the heat to the air.

 

Also, BTW, pressure is pressure and will always exert itself equally on every surface in the system.

[VRJoe]

The pressure in the system is created by the expansion the coolant as it's heated, not by the air. There is waterless coolant called NPG+ that I'm thinking of trying. It's by Evans (http://www.evanscooling.com). One of the listed bennefits is low pressure. Looks interesting.

 

If air is trapped in the system, it also expands and displaces coolant leading to hot spots and higher temps. It can even expand to the point of creating a bubble that can block coolant flow. That's why it's important to get all the air out. That's the purpose of the expansion tank, to allow the coolant to expand and contract without drawing in any air.

 

- Joe

[johnc]

I'm sticking with my original post. I'm also really confused by this statement on GrapeApe's web site regarding System Pressure:

 

The pressure in the block is higher than the radiator pressure, this is because the pump is building pressure due to the thermostat being a restriction. This pressure raises the boiling point of the coolant and reduces the chance of steam pockets, so never run with out a thermostat (or some form of restriction). The radiator cap will usually hold 15-18 psi, if the radiator holds the system at 15 psi, the boiling point of plain water will be raised to 250° F. The water pump can then make an additional 40-45 psi in the engine and bring that boiling point close to 300° F. So as you can see, pressure is important.

 

If their statement that system pressure is a result of the water pump backing up against a restriction (the thermostat) how come we don't instantly have 15psi in the system right after the car is started cold? How come system pressure isn't higher then 15psi until the thermostat opens?