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  #31  
Old 02-21-2012, 12:25 AM
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The pressure is dependent on the volume of liquid (27 quarts), the liquid expansion coefficient, and the vapor space that is "acted upon" by the liquid expansion. The partial vapor pressures of coolant at 190-200*F is small.

Exhaust gasses get hot pretty quick. The degas bottle pressure stays low for quite a while. It seems unlikely that the coolant is flash boiling in the EGR cooler for lengthy periods on each start-up cycle (until the degas bottle reaches 6-8 psig). Could be wrong on that, but it doesn't seem likely that the system would be designed that way.
 
  #32  
Old 02-21-2012, 06:13 AM
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the coolant should never flash boil.there should always be enough coolant flow to prevent that from happening. unless I missed a step the egr flow should be almost nothing until the engine is warm, or working hard. low flow = not much heat for the cooler to dissipate.
 
  #33  
Old 02-21-2012, 06:51 AM
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You are right - I plain forgot about that. That was a calibration update that Ford did fairly early on (minimize EGR flow until engine warms up). Thanks for that reminder nitrogen!
 
  #34  
Old 02-21-2012, 02:35 PM
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Originally Posted by nitrogen View Post
lower pressure does mean lower boiling point. that lower boiling point definitely would increase the likelihood of coolant boiling in the EGR cooler. the metal beside the resulting gas pocket can then get much hotter than the coolant(like exhaust temp hot) that causes egr coolers to burst and cause issues. also higher than coolant temp temps in the cooler increase the likelihood of coolant forming solid particulates that then plug oil coolers. any of you guys ever had an oil cooler get plugged. yup I thought there might be one or two of you. can i say for sure nope I can't but I for sure am going to go check my cap and have it tested. pressure as any boiler engineer can tell you is directly related to temperature. simple enough to find out what the correct pressure should be at 195. now if we all test our caps and they are good, he is full of BS, however if many of them fail, we have to start asking if it is part of the chain of failure.
While there could be EGR cooling problems you also have to consider where the heat is coming from. The cylinder liners are also seeing that heat. The lower boiling point, due to a failed pressure cap, is going to increase the possibility of liner cavitation.
 
  #35  
Old 02-21-2012, 02:58 PM
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possible but not probable. the coolant still has its additives(until they all become solid particulate anyways) which inhibits cavitation corrosion.when the oil filter plugs the coolant flow through the egr cooler stagnates but the coolant in the block is still behaving normally. if memory hasn't failed me totally the front cover is aluminum which would actually be more susceptible. I think there have been a few cases of them corroding heavily enough that the owner replaced them. not enough cases to really tie up my knickers though
 
  #36  
Old 02-22-2012, 10:30 PM
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Originally Posted by nitrogen View Post
the coolant should never flash boil.there should always be enough coolant flow to prevent that from happening. unless I missed a step the egr flow should be almost nothing until the engine is warm, or working hard. low flow = not much heat for the cooler to dissipate.
I got curious today ............

I hooked up the degas bottle pressure sensor and watched that pressure reading and the EGR valve position from a cold start.

The EGR valve started opening around 160 - 165 *F coolant temp. At this point the degas bottle pressure was 4 psig.

After driving and getting the coolant and oil up to stable/normal temps (190*F coolant and 196*F oil), the degas bottle pressure was 8-9 psig.

These back pressures only add around 10 to 20 degrees F of margin in the coolant boiling point. Not a lot, but clearly it is enough!
 
  #37  
Old 02-22-2012, 11:18 PM
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Originally Posted by bismic View Post
What Bill isn't saying is that a degas bottle cap is different than a radiator cap.

With a radiator cap, the liquid expansion pressurizes the radiator cap to the design pressure of the cap and then it relieves. The coolant system is maintained under pressure due to the back pressure of the radiator cap.

With a degas bottle cap, the pressure is generated ONLY by liquid exansion due to the temperature rise - acting upon the amount of vapor space left in the degas bottle. The increasing liquid volume reduces the vapor space and a pressure rise results as the vapor is compressed.

I have a pressure gauge on my degas bottle and I typically run 6-8 psig, unless I am hammering on the accelerator.

Single most important thing????
NOT - LOL.
Mark,
Just curious why Ford designed the degas cap to relieve at 16 psig?

I also noticed in the video that some of the degas caps tested seem to hold < 5 psig which makes me wonder about the original 16 psig design requirement. I suspect it doesn't hurt to have a pressure cap that meet's Fords intended specification, but I'm starting to wonder if the cooling system needs some internal pressure to function properly and/or have long term durability of the cooling system (ie internal pressure would prevent air from coming out of solution in the fluid and air is basicly a thermal insulator).
 
  #38  
Old 02-22-2012, 11:35 PM
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Bill at PSH is probably right on that one - most likely because that is a standard design pressure for most cooling systems (like the Gold was meant to be a universal coolant).

Most relief devices (and that is waht the cap is) begin to weep at 90% of the setpoint. That means that you are likely to see some small amounts of coolant at 14 psig.

When towing hard in the hot temps, I can see how the coolant can get to 215 degrees F. This will get you pretty close to the 14 psig (the increased thermal expansion of the liquid).

All these things get considered in the design of the degas bottle (size, shape, etc.). Looks like some folks missed the calculations since Ford revised the maximum level mark in the degas bottle.

Also, there is no doubt that the pressure will keep the system further away from the boiling point. I would bet that 16 psig is a safe point for the ratings on the radiator, hose clamps, etc.

I would love to see the design data on the EGR cooler (heat transfer coefficients, skin temperatures, total required heat removal, etc). I think Nitrogen probably hit the nail on the head - some of the early problems were related to the EGR system operating at the wrong points.

Probably didn't even come close to answering your question .............
 
  #39  
Old 02-22-2012, 11:47 PM
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While I think in certain situations that your coolant can flash boil or be damn close to it. I don't think it accounts for pressures over 16 PS I. Low flowing coolant leaving the oil cooler around 230 degrees slowly moving through a egr cooler seeing temps of 1000 degrees or more. If it can melt solder at this point then hell yes it can flash boil. In that situation, how much pressure does it contribute /shrug. But I'm sure it does some.

On a side note I did buy one of those stant caps for science. Not sure how it could ever be related, but I was finally able to get over 22 psi boost. In fact it went to 25 psi I have never seen it go over 22 even wot towing. Maybe the cap magiclly fixed my Turbo.
 
  #40  
Old 02-23-2012, 08:23 PM
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Originally Posted by bismic View Post
Bill at PSH is probably right on that one - most likely because that is a standard design pressure for most cooling systems (like the Gold was meant to be a universal coolant).

Most relief devices (and that is waht the cap is) begin to weep at 90% of the setpoint. That means that you are likely to see some small amounts of coolant at 14 psig.

When towing hard in the hot temps, I can see how the coolant can get to 215 degrees F. This will get you pretty close to the 14 psig (the increased thermal expansion of the liquid).

All these things get considered in the design of the degas bottle (size, shape, etc.). Looks like some folks missed the calculations since Ford revised the maximum level mark in the degas bottle.

Also, there is no doubt that the pressure will keep the system further away from the boiling point. I would bet that 16 psig is a safe point for the ratings on the radiator, hose clamps, etc.

I would love to see the design data on the EGR cooler (heat transfer coefficients, skin temperatures, total required heat removal, etc). I think Nitrogen probably hit the nail on the head - some of the early problems were related to the EGR system operating at the wrong points.

Probably didn't even come close to answering your question .............
Mark,
Thanks for your response and I agree with what you said. I'm of the opinion (with no facts to back it up) that some amount of internal coolant pressure may have other benefits. For example I would like to see how much cavitation the water pump creates with and without internal coolant pressure and how does coolant with air (in solution or out of solution) plays a role in a EGR cooled system.

Either way my coolant cap is original so I'm thinking maybe I should just replace it just for the piece of mind factor, but then again I'm not convinced this a source of major problems.
 
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