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Slow down coolant so it have time to cool off in radiator?


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Hi,

 

If you run without a thermostat it's common to add a washer or somekind of restrictor in place of the thermostat.

 

I often hear that the reason for this is to slow down the coolant so it has time to absorb heat in the radiator. Is that true?

It will spend less time in the radiator but it will also spend less time in the engine.

 

I would think the reason for adding a washer is for something else, like making sure the water pump works or something.

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1 minute ago, MoparBoyy said:

yes.  so what i did was take the thermostat and remove the center piece but leave the outer plate, so its basically the thermostat is just open all the time.

 

So why did you add the washer?

 

To reduce flow and "increase time in radiator" or to give some backpressure to the water pump?

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iceracer wrote: The old Ford flathead V8 would overheat when driven hard,ie:dirt track racing. Problem was cavitation at the pump because of a high pressure drop through a poor coolant system design combined with marginal pump efficiency. After installing restrictors to raise the pressure delta across the pumps, thereby increasing the suction pressure and delaying cavitation, problem solved.
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3 minutes ago, turbogrill said:

 

So why did you add the washer?

 

To reduce flow and "increase time in radiator" or to give some backpressure to the water pump?

It's a rough way of doing what the thermostat does automatically: regulate the water flow to get a particular engine temp. 

 

"Increase time in the rad" is another one of those car myths that won't die...

Edited by mender
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4 minutes ago, turbogrill said:

 

So why did you add the washer?

 

To reduce flow and "increase time in radiator" or to give some backpressure to the water pump?

 

add the washer?  i basically just removed all the moving parts of a thermostat so its basically open all the time.  removing the thermostat entirely will increase flow.

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5 minutes ago, mender said:

It's a rough way of doing what the thermostat does automatically: regulate the water flow to get a particular engine temp. 

CAT does it on large diesels probably partially to allow them to use the same scac or JW pump on differing cylinder number and power range engine's for commonality of the pumps.  We then publish specific curves for the combination , ie: 3516 1800 RPM pump X , 3512 1800 rpm pump X, etc.

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Found a good explanation:

 

"Restricting flow is done not to help the water go through the radiator slowly but to help build presure on the back side of the thermostat (the engine). You want to build presure on the back side of the thermostat/washer to stop steam pockets from forming."

 

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1 hour ago, mender said:

If your cooling system overheats with the stock thermostat in place, you have problems than the thermostat, it only sets the minimum operating temperature.

Down where it never freezes, the thermostat is considered a liability rather then necessary component, we lost a engine to a failed stat, never again, not even sure how it got in one of my engines, must have been a late night where there was no time to defeat the warmup recirculation ports.

We would rather restrict airflow or deal with crappy GPH till the day warms.

57 minutes ago, turbogrill said:

build presure on the back side of the thermostat (the engine). You want to build presure on the back side of the thermostat/washer to stop steam pockets from forming."

This is the actual answer.

 

Not graceful but worked fine for 28 races, note the smashed t stat.

 

49990037932_b78ca3a60d_b.jpg

Edited by Team Infiniti
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Every engine is different  but  way back in the eighties i ran super late models with a sbc and every body back then ran water pump pulleys to slow down the pump, which was fine until i ran a destroked 400 but then i struggled to get the car under 240 on hot nights.I called griffin radiator about a baffled radiator but he told me to try what the cup guys were doing first which was to run 1 to 1 pulley and run restrictor washers in themostat housing.that alone lowered temps temps 15 degrees due to less cavitation in the cylinder heads.I personally would never run a thermostat because it one less thing to fail.

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9 hours ago, turbogrill said:

Hi,

 

If you run without a thermostat it's common to add a washer or somekind of restrictor in place of the thermostat.

 

I often hear that the reason for this is to slow down the coolant so it has time to absorb heat in the radiator. Is that true?

It will spend less time in the radiator but it will also spend less time in the engine.

 

I would think the reason for adding a washer is for something else, like making sure the water pump works or something.

old drag racing trick is to drill holes in the t-stat.. or you can un-core it. This slows the amount of water that passes thru it. 

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The heat transfer equation is a function of the area that the fluid touches and the differential temperature of the two fluids. Therefore, if you slow down the coolant this delta temperature decreases resulting in less efficient cooling. You always want the highest/fastest delta T theoretically in the radiator. Now with cavitation and warm up time, there are reasons to restrict flow sometimes. 

Edited by cowboys647
Pressure =\= Temperature
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14 hours ago, cowboys647 said:

The heat transfer equation is a function of the area that the fluid touches and the differential temperature of the two fluids. Therefore, if you slow down the coolant this delta temperature decreases resulting in less efficient cooling. You always want the highest/fastest delta T theoretically in the radiator. Now with cavitation and warm up time, there are reasons to restrict flow sometimes. 

Delta t does not have a time component to it.  It is literally just the difference in temperature.

 

Fast or slow moving has the same delta t for the fluids.

 

Differences in pressure is what gets fluids to move.  With no delta p you get no or minimal flow.

 

In other words, the restrictor is for a pressure differential,  not temp.

 

 

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46 minutes ago, wvumtnbkr said:

Delta t does not have a time component to it.  It is literally just the difference in temperature.

 

Fast or slow moving has the same delta t for the fluids.

 

Differences in pressure is what gets fluids to move.  With no delta p you get no or minimal flow.

 

In other words, the restrictor is for a pressure differential,  not temp.

 

 

 

But an automotive water pump is just a centrifugal pump, right?  And don't those always flow highest with no pressure on the pressure side?  I've only messed with them for irrigation applications which are open systems, so maybe they behave differently in a closed system.

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7 minutes ago, mender said:

There's one more thing to consider: heat. The idea is to shed engine heat to the ambient air.

 

Duh, think so?  Thats pretty much the only thing in this discussion. 
 

9 minutes ago, mender said:

Obviously the highest heat transfer will happen with the highest delta T and the highest flow rate


You should have stopped here. 

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On 7/11/2020 at 10:32 PM, karman1970 said:

 

But an automotive water pump is just a centrifugal pump, right?  And don't those always flow highest with no pressure on the pressure side?  I've only messed with them for irrigation applications which are open systems, so maybe they behave differently in a closed system.

I think the problem is often on the suction side, where the pressure can drop too low to keep the coolant liquid.

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There is some misinformation in this thread.  The job of a thermostat is to divert water to the radiator to exhaust heat from the coolant and control the engine temperature at an optimum range. For the most part, the flow is fairly constant in what doesn’t go thru the radiator recirculates through the head and block to transfer heat into the coolant. Why people remove a thermostat can vary but a lot of times it is an attempt to deal with a cooling issue mistakenly. A system running under 1 bar of pressure (typical cap relief rating) should operate well below a vapor pressure to avoid cavitation at the eye of the pump. In the energy system design world this would be known as net positive suction head required. The hotter the fluid the closer this gets to the vapor pressure. In other words if your cooling system isn’t working correctly and is getting too hot, you need to deal with your cooling system issue not remove a thermostat. In some cases the thermostat can be the restriction but that is probably rare since the manufacturer probably designed it with enough margin to flow enough to exhaust heat properly given enough heat exchanger (radiator) is available.  Air flow and radiator surface area are two ways to deal with that. 

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