vzdude

As long as it is Diesel Water Wetter. Big differences. I would post a link, but I don't think they are a sponsor. Just Google it. So .....we agree I guess?

CamperAndy

It is a two part issue, without some dwell time in both the block and the radiator neither would transfer heat correctly. So it would be impossible to BALANCE the heat transfer. Thus we have thermostats that control the dwell time (flow) between the block and the radiator to maintain correct water jacket temps.

Now when you restrict flow that velocity converts to pressure so we are back to the question of what the block pressure is doing during hard acceleration with an engine that is not 100% up to temperature.

So who is going to be first to install a water jacket pressure gage??

XLR8R

Already got it covered...

Raspy

The faster the water moves through the cooling system the more heat, or BTUs it will remove. If you had the valve in the system, that I mentioned in my earlier post, you could just crack it open to bring the block up to temp. Then instantly open it all the way for max flow when you applied max power. No delay at all. Max flow removes max heat. Remember, we are not trying to heat the cooling water, we are trying to remove the cylinder and head heat. BIG difference. Maximum heat transfer occurs at maximum flow and maximum temp differential. Get the maximum amount of the coldest water you can for best cooling. High flow rates also help keep water moving in what might otherwise be a dead spot like small passages in the head. Around a rough cast surface, like the outer cylinder wall, there is a boundary layer that does not move much. The more turbulence the better, and the more flow the more turbulence. Basic heat exchanger theory.

I'm convinced that the pressure is getting so high because there is no way to rapidly get rid of the heat produced and the poor little relief tube at the radiator cannot keep up with the resulting extreme pressure rise. The block is being turned into a boiler. A full flow tstat bypass to the radiator or removing the tstat and replacing it with a valve is probably the best solution. If extreme presssure still is a problem then a larger vent system or an expansion tank is needed. But lower pressure means a lower boiling point.

Start the race with the block warm and the radiator cold. Allow max flow from the radiator to the engine during the run. If the pressure spikes add an expansion tank.


Wetspirit

vzdude

I think I have to politely disagree with the maximum flow/ maximum heat transfer thinking. I have seen this too many times to count - remove thermostat/restrictor, and engine will overheat causing damage. All the while , the temp guage never goes up past 160 degrees. Just my experiences. My comment on the whole pressure in the block thing... I'm still trying to theorize it in my head. Still cannot believe there would be 60 lbs. of PSI in the block! That would be enough to push the thermostat open. Remember, pressure is constant within a system. If there was 60 lbs in the block, it would be in the radiator as well. Wheres the separation between the radiator and the block. Thermostat, and water pump. That much pressure would bypass the vanes in the water pump and backpressure the radiator IMO. Thus pushing the thermostat open. Just how I picture it working in my head. I try not to listen to the voices, but they have some good ideas sometimes! ( stole that from someone on here! )

CamperAndy

It actually is not that hard to get your brain around if you look at it as the two separate pressure chambers that are created with the pump and the thermostat being the beginning and end points of the two chambers. There are a few basic elements that.

Pump - A pump moves liquids from lower pressure to higher pressure, and overcomes this difference in pressure by adding energy to the system.

Thermostat - is a device for regulating the temperature of a system so that the system's temperature is maintained near a desired set point temperature. The thermostat does this by controlling the flow of heat energy into or out of the system.

Radiator pressure cap - Is used to raise total system pressure to raise the boiling point of water, limit pressure in the radiator and provide a means to recover coolant lost during thermal expansion in the closed system.

The pumps flow and the radiator thermal exchange rate are such that the radiator will exchange more heat then it receives under most conditions thus the thermostat will always be modulating somewhere between fully closed and fully open.

1 - Cold system - all points within the system will be at ambient pressure, thermostat closed and zero flow.
2 - The engine is started - the pump rotates and generates a differently between the pump inlet (radiator) and pump outlet (block). The flow does not return to the radiator as the thermostat is closed. The pressure in the block raises due to high head no flow condition. The pressure in the radiator drops initially due to the pumps suction of fluid from the radiator.
Note: There are a couple of issue at work here to prevent much increase in pressure anywhere in the system. First there is a 1/2" block recirc line from the intake side of the block back to the pump suction and second there is a bleed port in the thermostat. The 1/2" recirc line prevents stagnation in the block but is too small to limit pressure build up, the bleed hole in the thermostat is used to purge air from the block side of the thermostat.
3 - Acceleration of the cold engine - Adds force to the pump which generates more differential between the radiator and the block. This pressure builds up in the block since the thermostat is closed and restricts the flow of coolant. At this point you will have two distinct pressure zones within the cooling system. The high side in the block and the low side in the radiator.
4 - As the coolant warms - the thermostat will begin to move but just enough to maintain system temperature. This will also maintain the pressure differential between the block and the radiator, as the pump is always trying to pull pressure down in the radiator and pack it into the block. The overall system pressure will rise due to thermal expansion in the system. The radiator pressure will rise to the lift pressure of the radiator cap (15 to 16 psi). The block pressure will rise based on the force applied to the pump and the restriction in the flow controlled by the thermostat.
5 - Hard acceleration - This is where things can go bad. Significant increase in force to the pump due to increase in RPM but no increase in flow as the thermostat has not reacted to the increase heat, thus the block pressure increases significantly. How significantly depends on what the temperatures were prior to the hard accel. As the thermostat reacts to the heat it will open and the head will drop and the flow flow will increase. This whole time the radiator cap is adding or taking away small amounts of volume to maintain radiator pressure at 15-16 psi.

Sudden thermal loading from the engine will contribute to the overall system pressure until the radiator cap can bleed off the increased volume.

You asked why pressure does not bleed back around the pump to the suction side. Well it does but only a little bit and it is immediately sucked back up and pushed into the block again. Discounting the thermal expansion the system pressure in the block is limited to the efficiency of the pump. At some point it will begin to turn faster then it can move the water and will cavitate and recirculate more at the vane tips. Add in the thermal expansion and the block pressure can really spike but you have to have pump generated pressure to start with.

vzdude

That makes good sense, and you spelled it out very well. Kind of what I was thinking, but I just thought that, that much pressure would be able to go around the pump more than that. Sounds like a bigger/ and or more recirc line would help this condition? With all the plugs in this engine, surely more recirc lines could be added I would think.

53 willys

take out the t-stat and Plumb an old cable style heater control valve in the top hose and you could regulate flow by hand in the cab

signature600

Nice!

Those electric, high dollar water pumps might be looking better all the time...as long as they are variable speed!

Chris

XLR8R

I need to point out a few things here:

The water pump is NOT a positive displacement type; therefore, it's GPH curve will decrease as static pressure rises.

The thermostat, being a mechanical device, exhibits a significant amount of hysteresis - it doesn't snap open or snap closed.

Higher flow rates increase the possibility of velocity-induced cavitation; acoustical (vibration induced) cavitation is a natural and unavoidable characteristic of a compression-ignition engine.

Water-based coolant - or any liquid, for that matter - requires sufficient time to absorb, or release heat energy; BTUs do not instantaneously jump from the engine block into the coolant, nor do they immediately transfer from the coolant to the radiator metal, which then sheds the BTUs to the grill air.
As posted earlier - basic heat exchanger theory.

The freeze plugs are NOT blowing due to high RPM-induced excessive system pressure generated by the water pump.

Keep up the thoughtful posts, guys!

53 willys

then what is causing them to blow????

trik396

Excessively high temps which cause boiling of coolant in localized areas... In my opinion... To me which means the only way to stop this is using a coolant that boils at a MUCH higher temp than 260degrees. Evans boils at 375... hopefully that'll do it...

Raspy

Quote: 2 - The engine is started - the pump rotates and generates a differently between the pump inlet (radiator) and pump outlet (block). The flow does not return to the radiator as the thermostat is closed. The pressure in the block raises due to high head no flow condition. The pressure in the radiator drops initially due to the pumps suction of fluid from the radiator.


Camper,

The pump suction side is the block. Water moves from the block through the pump to the radiator. The pump does not pressurize the block. The big pressure buildup is from the big heat build up.

Wetspirit

Raspy

53 is right. It's not the pump. It's the heat that builds pressure. The pressure can not go down unless the radiator can handle the load or the relief can handle the flow. Initialy the tstat is closed and there is a lot of energy to get rid of.

You guys just need to look at this situation like and old fashioned steam boiler. It's the same thing. Exactly the same. An energy source builds heat in the system and there must be cooling, or a relief valve, or the heat sourse must be stopped to get the pressure back down.

Wetspirit

Raspy

[QUOTE=XLR8R;1482398]I need to point out a few things here:


Water-based coolant - or any liquid, for that matter - requires sufficient time to absorb, or release heat energy; BTUs do not instantaneously jump from the engine block into the coolant, nor do they immediately transfer from the coolant to the radiator metal,




I agree with all you said except this statement. Energy does transfer upon contact and immediately. The cool water does not sit against a hot metal surface and just stay the same temp for a while and then at some point start to absorb the energy. Conduction is upon contact. But it does take a period of time for a given volume of water to change temperature, depending on the surface area, the turbulance and the temperature difference. Remember, it's not a temp rise we're looking for in the coolant, it's a total amount of BTUs. Meaning volume and temp combined. And the cooler the water is when it entered AND exited the block, the more energy it removed from the block. This is because the only way to get the exit temp down is to increase the flow. And increasing the flow causes more turbulance, which means more intimate contact with the hot surface and it means that all the hot parts came in contact with the coolest water. In other words, maximum exchange.

When someone says you have to slow the flow to get more heat out they are looking at the problem backwards and measuring the heat removed by measuring the exit temperature. We are not trying to heat the coolant we are trying to remove BTUs from the block. That means a big temp difference. More flow.

Engines heat up with less coolant flow. That's what the tstat does, restricts the flow. When an engine over heats because the cooling system cannot keep up, the result is that all the coolant is hot. To keep and engine cool you flow more and more coolant as the HP increases. Not less. And you don't put in some coolant and wait for it to get hot before letting more in to wait for it to get hot. So, with a racing Cummins, you need lots of flow immediately when you start making lots of power. No delays. Or you have an out of control boiler.

Wetspirit