Engine Temperature

[D.Hearne]

But any pressure built is relieved by the bypass hose if and when the thermostat is closed. If you still think there's pressure there just from the pump, start your engine when cold, rev it up for a minute, then remove the radiator cap. Bet you won't hear any pressure built when you crack the cap.

 

[Fast63]

But any pressure built is relieved by the bypass hose if and when the thermostat is closed. If you still think there's pressure there just from the pump, start your engine when cold, rev it up for a minute, then remove the radiator cap. Bet you won't hear any pressure built when you crack the cap.

Wtf? Why would you hear any pressure at the radiator cap? The pressure is between the pump and the thermostat.... In the block.... w...t....f...

 

[D.Hearne]

You were the one who claimed pressure built by the pump, added to the pressure in the system So, if that were true, some of that pressure would escape thru the radiator when you cracked the cap open.

 

[NewStangOwnr]

Pressure makes things cooler as we all learned in Cooling 101.
Warning hot liquid inside!

 

[rbohm]

Pressure makes things cooler as we all learned in Cooling 101.
Warning hot liquid inside!

not true. pressure increases heat, but it also increases the boiling point of a liquid.

 

[Fast63]

You were the one who claimed pressure built by the pump, added to the pressure in the system So, if that were true, some of that pressure would escape thru the radiator when you cracked the cap open.

Absolutely wrong. There is not enough flow out of the thermostat to build a bunch of pressure from the thermostat, through the radiator, and back to the pump. That's why the pressure is built in the block.

As far as checking the pressure built by the pump only, you can't really measure that at the radiator cap. If you take the thermostat out, there is no restriction for which to build pressure. If you leave it in, there is no way of determining what pressure is made by the pump and what is made by the temp increase. Once the thermostat opens, the temp is already hot and building pressure.

It's easy to tell if there is pressure in the block. Put a pressure gauge behind the thermostat and see what's there. According to what you're saying, if you put a pressure gauge behind the thermostat and started an engine cold, so the thermostat is closed, there would be no pressure in the intake. Would you like to try it and see what the results are? It would clear this all up.

 

[NewStangOwnr]

not true. pressure increases heat, but it also increases the boiling point of a liquid.

I meant in that increasing the boiling point will help keep things cooler. I wasnt very clear there haha

 

[D.Hearne]

I stated that the pressure in the system comes from the pressure built from the expanding coolant. This is what you came back with:

It comes from both..

Now, if the coolant is at ambient temperature, there's no pressure from it. So, where's the added pressure from the water pump going to added to? What little pressure may reside in the block, is relieved by the bypass hose, back to the pump. And the heater circuit, when the control valve in that system is open. The water pump in these engines really only flows the coolant, it doesn't pump it to any point that could be called pressure. As I said before, it's not a positive displacement pump, it circulates the water more than pumping it. When it looses it's prime, any flow it was producing stops as the impeller cannot build pressure due to the loose tolerances between it and the pump body. So what pressure, if any, will escape back around this and the bypass & heater hoses.

 

[blown65]

Absolutely wrong. There is not enough flow out of the thermostat to build a bunch of pressure from the thermostat, through the radiator, and back to the pump. That's why the pressure is built in the block.

As far as checking the pressure built by the pump only, you can't really measure that at the radiator cap. If you take the thermostat out, there is no restriction for which to build pressure. If you leave it in, there is no way of determining what pressure is made by the pump and what is made by the temp increase. Once the thermostat opens, the temp is already hot and building pressure.

It's easy to tell if there is pressure in the block. Put a pressure gauge behind the thermostat and see what's there. According to what you're saying, if you put a pressure gauge behind the thermostat and started an engine cold, so the thermostat is closed, there would be no pressure in the intake. Would you like to try it and see what the results are? It would clear this all up.

My electric water pump moves 55gpm, just like you stated, it will develop pressure inside the block and behind the thermostat. Even with that little hose as the bypass, there is no way its going to flow 55gpm. As for these pumps not being pressure building pumps, I work on pumps for a living, open faced pumps build pressure. Now is it a significant amount, doubt it. But you figure the system pressure is at 10-20psi cause of fluid expansion. Then you have to add the backpressure of the stat and bypass hose into it. Obviously the better the water pump you have, the more pressure it can make. Some are cheapy open faced pumps, but some of them are pretty good units with closed vane impellers. Im sure those can do some fairly good pressure thru the block.

 

[D.Hearne]

The pressure (if any) will depend on the pump impeller, in many stock pumps there are three sized impellers, small(low volume-high rpm) medium(std volume) and large(high volume, these are listed as Police/taxi pumps and/or extra cooling. The small and medium obviously won't build any pressure to speak of, there's too much clearance between the impeller and pump body. The bypass hoses are typically 5/8" diameter, although I've never tried it, it's not hard to imagine feeding 55 gpm thru a hose this size. Maybe I'll try it on the 55 gal drum I behind the shop when I get time.

 

[blown65]

The pressure (if any) will depend on the pump impeller, in many stock pumps there are three sized impellers, small(low volume-high rpm) medium(std volume) and large(high volume, these are listed as Police/taxi pumps and/or extra cooling. The small and medium obviously won't build any pressure to speak of, there's too much clearance between the impeller and pump body. The bypass hoses are typically 5/8" diameter, although I've never tried it, it's not hard to imagine feeding 55 gpm thru a hose this size. Maybe I'll try it on the 55 gal drum I behind the shop when I get time.

Sure, and make sure while your at it run it at no pressure trying to get 55gpm thru that 5/8" hose. Aint going to happen. Don't forget that the part the hose hooks to is rather small in ID, dont just figure the hose into your equation. All pumps build some sort of pressure.

Explain this then, Edelbrock.com - Water Pumps - Introduction

Edelbrock themselves state

"PRECISION CAST POWDERED METAL IMPELLER

6-vane powdered metal impeller is larger than other high-performance impellers to produce greater pressure and volume."

Just maybe that added pressure is to keep flow thru the engine block/heads/intake that slow the volume? It takes pressure to overcome friction loss, of which every bend, reduction in size, tee in the system will take away.


And yes, it will depend on the impeller just like I stated the first time. However all of them are going to build pressure, some more than others.

 

[D.Hearne]

That may be true, but my point was the pressure in the block doesn't add to the pressure in the system. Contrary to what Fast63 was implying. If it did, then some of that pressure would be built up just after starting the engine, and before the coolant warmed up to cause expansion. The pressure at the cap after the coolant warms and expands is purely from the coolant expanding. It's this pressure that determines the boiling point of the coolant. The mere presence of coolant in the block is what will prevent a meltdown of the block and heads while the engine is running. But once that flashes to steam, all that goes out the window as far as preventing a meltdown.