Mrmerlin

I would also surmise that the boiling point of the coolant mix your using is lower than regular coolant and water a street driven machine will use.

That said using a fresh coolant cap to hold pressure will reduce the tendency of any coolant to flash to boil .
Follow Gregs schooling

mark kibort

yes, this seems to be a mystery for anyone that dosent under stand the simple physics here. so, a little physios required. Let me explain: correct, The cap holds 1 bar pressure...........the pressure goes up to 7-10psi normally as it gets to boiling, the pressure will exceed the spring pressure of the cap of 14.7psi ,and release pressure in the form of fluid. and then as the system finds equilibrium there is now air in the system. (steam). replacing that volume. you are right up to that POINT! HOWEVER, as the system cools, it goes below boiling point and the pressure goes down proportionally. this is how it can be at operating temp of near 180 and have no pressure with air in the system.. Proof, the water level is near the cap level. (overfill now). the only way that the pressure will go up, is if the temp of the engine goes up again and starts to expand to create pressure.

make sense?

ONE MORE TIME.....now, the reason that the cap was able to be removed and the hoses soft, was because the system held pressure up to 14.7psi and then started to release about 1pint of fluid. pressure was then very high... hoses were firm and bloating! had i removed the cap then, it would have been a fountain! (very dangerous) i left it running with both fans screaming and some RPM so that the system would cool. it did. pressure dropped during condensation and contraction again, proportional to the temp drop. if you understood some physics , it would be simple to understand. im trying to help you understand the conditions characteristics, and the events leading to the overheat and then cooling of the system ths ONLY works when the sytem has expanded and ejected a certain amount of fluid. i hope i explained this in a way that you can understand.

you kind of get it with your last paragraph, where you talk about the system cooling in 5-10 mins after ejection.... and this is basically what i did, by letting the engine run to get the engine temp below normal operating temps ..... The system is now under 180F and the lines are flacid, so the cap can be removed with no danger.

mark kibort

it's a moot point.... with the fans i was able to get the coolant down to under 180F. the higher boiling point is essential when trying to prevent boil over during operation. it overheated and boiled as the light momentarily went on. ... the lines had very hard pressure. i kept the engine running at no load levels and turned on the second fan... it quickly droped the temps and reduced the system pressure. gas law 101. greg needs to study gas law. pretty simple stuff. there is NO problem here other than user operator issues of making that last run when the temp was sitting higher than the mid line and one fan was not turned on. it over heated. very simple... pressure was high in the system. steam from boiling was condensing. HUGE volume reduction . make sense?????

the cap is perfectly fine! tested!

jcorenman

Physics: steam <not equal to> air

Replace your cap, check the hose routing-- something is not right. And if you are going to run the engine under load while stationary, set up a big fan. The engine is designed to be water-cooled, steam does a lousy job.

mark kibort

Jim, i was referencing the steam that causes the water to be ejected. the air enters as the water pulls back its level after it has condensed. when the air enters the system as it cools, you can feel it as voids in the cooling hoses.... ( it can be felt at the hoses, and seen by the higher water level line.)
the cap is fine... there is no problem with hose routing.. this car has run for 20 years, in this configuration and has had NO issues unless ive lost a water pump or radiator and overheated due to a cooling issue. due to air in the system or extra hot ruining conditions. (100f or greater)

When i do the WOT, i have to take the same care as i do at the dyno yes.. fans, or i'm limited to 2 runs and then a big cooling rest. i did 3 runs..temps were climbing and i did a 4th because the video didnt capture the data off the timing light and harmonic balancer. TAKE NOTE> when it was hot, the lines were so hard they were going to burst. they are always like that. with only water, you cant have a sub-par set up cooling system because water boils at the ambient prssure plus system pressure.........no extra slack like you might have with anti freeze. again, liines hard as rock...........i cooled the engine down as you dont want to just shut down an engine starting to overheat... turned on the other fan (i have two) and waited it to cool down as not enough water was missing to stop cooling flow.............. in a few mins, the temps droped to well below normal and the pressure of the system dropped as well.......basic gas law. PV=nRT

dr bob

FYI --

Water fizziks is very well documented these days. From a saturated-steam table, and pure water:

212º F 0.0 PSIG
230.6º F 6.3 PSIG
240º F 10.3 PSIG
250.3º F 15.3 PSIG

Impurities in the water generally increase the boiling point, raising the temperature at which we see a particular pressure. In the stated case, impurities include Water Wetter and a splash of coolant. I'm not sure why the coolant was added, as 7% (one quart of coolant in the ~16 quart system) doesn't materially affect the temperatures and pressures for this discussion. Anyway, the pressure in the closed system is determined by the hottest spot in the system. At the point where the cap relieves at 1 bar, the corresponding hot-spot steam bubble temperature is just a little shy of 250ºF. As others share, steam in the system does a poor job of carrying heat away compared with liquid. The steam pockets almost invariably happen in the cylinder head, causing the aluminum head to expand much more than the aluminum block. The head gasket fails due to the differential expansion and the movement at the gasket surface. Detonation happens because of the percentage of hotter cylinder head that forms the combustion chamber, exacerbating the heating and localized hot-spot vapor issue. Note also that the state change between liquid and vapor includes serious changes in volume, such that the bubbles forming and collapsing are like micro grenades that erode surrounding metal over time.

At the pressures we are limited to in the system, the liquid and the steam vapor are both heavier than any air in the system. Air will be the first thing expelled as the system pressurizes, so the heated system will be liquid or saturated water vapor except at those hot spots in the heads, where there may be a slight amount of superheat. As the system cools and the total coolant volume decreases, air is drawn back into the top of the reservoir. There is no easy way to avoid this. A fresh supply of oxygen is added back, so corrosion can start again if/when that air comes in contact with aluminum parts. Good news: The reservoir is not in the circulation path, so there's nothing to cause that air to become entrained in the liquid flow. The system isn't quite as well isolated as a sealed expansion bladder, but it is pretty well thought out. Most modern cooling systems now include "expansion reservoirs" with a liquid seal for just this reason. They tend to be on the atmosphere side of the pressure cap, but offer similar benefits.

OK, coffee break is over. Back on your heads!

mark kibort

Bob, i think we all are aware of the raising of the boiling point of the coolant based on temp and inpurities. given mine is distilled water and a little bit of "other things", we can just say its around 250F might be alittle higher, but that point is moot..... by the way, you mention the "antifreeze" added.. why would you think i added it for cooling??? . its added for a little bit of water pump lubrication.... (im not supposed to run any, so i just run a little to be safer)

you laid out the senareo. the temp goes up, the coolant expands, probalby in the 4-5% range at a warm operating temp going from 20C to 100C, and with the temps rising to boiliing points as i saw under 15psi pressure (yes the cap is perfectly fine... in fact, i had a HUGE explosion a couple of seasons ago when the lower radiator hose exploded. that couldnt happen unless the cap was working ! not to mention the cap being tested at the shop with the proper cap tester!) the boiling water moves around and creates space until all the air in the reservoir is pushed out and water starts to flow out the overflow, to try and equalize pressure. the system is at 15psi at this point.

as the system cools, the water in the system contracts in volume and any condensation occurring causing collapse of any voids.... this reduction of temp causing the reduction in pressure, causes the overflow to start to take on air to replace the volume of the overflow that was previously filled with water. any voids in the upper water bridge, or upper radiator, would take on air directly from the from those bleedlines

the bottomline, after an overheat and subsequent cooling running or not, there will be voids left in the upper radiator hose. this can be done while the car is running or not as long as the temp is reduced. to below boiling point. at this point the system is not at any pressure over ambient pressure and still could be just below normal operating temp. the point is, the system is not closed, its open based on pressure levels. too much prssure and it vents.... as pressure goes down and volume of water is lowered, air is drawn in via the pressure cap freely so no relative vacuum can occur. (no collapse rubber hoses) . this is exactly what i observed and re-verified with an minor overheat in my garage doing WOT tests.. in a nutshell.. as temp goes up, pressure goes up. as temps go down, pressures go down, to a lower point than normal operating conditions because of the air that is replacing the prior, ejected water.. simple, right?

dr bob

Mark, the boiling point depends on the pressure, or vice-versa. If you saw the cap puking vapor or liquid, and the cap is working at the correct pressure, you had at least 250º someplace in the system. If the coolant was expanding that much, there are steam pockets that may be at much higher temps locally (superheated steam bubbles).

As soon as the cap starts venting, air is the first thing that exits.

Your stated "taking in air from those bleedlines" ignores gravity. As the heat input is reduced and the coolant volume drops, any air drawn in will sit at the highest point in the system, the top of the reservoir. The vapor (steam) bubbles collapse with the loss of heat input, replaced by local liquid and the condensed coolant. It's a connected system, not a network of isolated cells.


You really need to sit through a couple of my steam math and fizziks classes for power plant operators. This would make a lot more sense to you.

Speedtoys

My daughter met kids like this at UTI when she started there.

She was mercifully free of their presence by course #4..the school at some point simply stops taking your parents money.

mark kibort

yes bob, we saw the fluid exit the lines with the water level at the cap. the cap is working at the correct pressure. the only thing im questioning is how the air pockets form after the overheat and the condensation occurs after the system is cooled. . yes, as soon as the vent starts to vent, air is the first thing that comes out... thats obvious, and yes, thats due to gravity as well. after all the air is vented, water starts to be ejected and i think we agree here.

what i stated about the bleed lines, is if there was a lower pressure in the water bridge, why wouldn't air move from the vent line opening in the reservoir, to the water bridge? thats just a guess on how air could enter the system to form the air pockets. how does the bleed lines ignore gravity? you say "any temp drop and the volume goes down" yes, and we know that that volume reduction is only about 2-4%. and we are are talking about differential pressure Pressure differential can work against gravity as long as the force is greater. im assuming that during the formation of steam and voids in the cooling system that is being moved around, maybe a void is created. yes, i agree in theory, any void created would be closed by the condensing of the steam . but, im asking YOU what causes the voids in the system near the hoses after an over heat?

as far as air moving "again gravity". .. what if the water volume decreases on top of the water pump area ? it could create a differential pressure that could draw air in from the vent line leading to the air in the overflow container.. could it not??

The observation is that after the overheat, there is air in the lines after it cools and is running at or below operating temp. ... i saw this. i burped the system for all air, and everything is back to normal. diven the car 30 miles of hard WOT tests and still without air. what is your cause for the air during overheat?

i would love to sit in on your classes. its been SO long since ive studied much of this. its more complicated as many things in automotive , due to the multiple variable and inconsistent factors. when you speak of the "cells" im thinking of areas that are pockets in the hoses that are level, so that air cant move one way or another unless forced.



I've taken plenty of physics and thermodynamics. I pulled out the books last night and my head started to hurt. its been a LONG time when i try and review things i havent looked at in 35 years. Things i use for work, HP/torque Newtonian, etc.........clear as day............Gas Law, not so much. so, you are one to judge here? I'm explaining an observation. I'm guessing at some of the causes. (like where the air comes from) the basics are that with temp reduction comes pressure reduction. how the air ends up in the hoses is still not fully understood. but when GB or Jim or anyone says the cap is bad, they are NOT thinking the conditions through. the cap is fine. the system holds pressure, enough to bust hoses!!! (and its been tested) AND, i watched the fluid come out of the bottle under high pressure with lines bulging! so no need to be insulting when trying to explain a phenom that can assist others before they go out racing, or when they see what i have observed.

mark kibort

Greg, (Bob, Jim, Jeff, Stan) Let me answer your questions: first of all, I have seen the flow out of the water pump, coming out of a hose and its in the same realm of velocity as a garden hose. as the water pump pumps water to the engine, it immediately flows into a higher volume area where the velocity slows. then, it is forced up channels up into the heads, and back out the two small openings. I dont know the "feet per second" you ask for and i would guess you dont either. as bob suggested , as the time of overheat, there are areas that have some flow stagnation and super-heating of the steam that has been formed. This addresses your questions of #1-3.

Now, i should have been more clear. what i have proposed is more of a Hypothesis vs a theory. Based on my observations and general understanding of fluid flow and gas law, i have observed and predicted behavior of the system. The theory for why it happens with details, is not complete. And yes if there exceptions to the theory, the theory is void.... however, if the facts dont fit the theory, change the facts.. (Einstein).

what i have observed is that if you overhaeat your engine, to the point where the warning light just comes on and you are operating near race conditions, the system will expel fluid. if you remove the load and increase/ or continue cooling, the system will cool and thus contract. as it contracts, it brings in air through the overflow inlet vent in the radiator cap to resist a vacuum condition in the system. this air does NOT enter the engine until the pressure is at ambient or less. (no pressure in the cooling lines)

It is YOU that actually provided a theory that has been proven wrong, which nullifies it. your theory said that the system overheated due to a cap that didnt provide rated pressure release, otherwise removing the cap wold have resulted in a" Fountain". My hypothesis , clearly shows an explanation of the observation and a general reason of why what you said, DIDNT happen. My theory of the details of why its happening has questionable points as Bob and you pointed out. How the air gets in the system, after the overheat , is the main point of the theory that needs better reasons than i provided. (air being pushed in through the bleed lines, local boiling, etc.....) However, Bob did mention many of those concepts in his quick analysis as being potential causes that could impede flow and create voids.

There is no problem with the cap. there are no wrongly connected cooling hoses, This is just basic physics being shown by my observations. the system overheats, expels water, then when cooled, removes pressure with water level that has risen, stays higher than starting levels, and voids can be felt in the main hoses .

There is a good chance that much of the issue is not an issue for street cars as i have proven, i can drive indefinitely with a little air in the system and it does get better with each heat cycle. but for racers that have had a boil over or have just refilled the cooling system , burping is a good way to start and remove these voids... AND , at the track, assures better cooling , that might not be noticed during street driving.

A question for Bob, since he is the fluids expert, is what causes voids in the system after an overheat and condensation of the steam that is creating the voids? if not coming from the vent lines, where? my thoughts were if the levels locally lowered, (due to a bubble or void they would get air to neutralize pressure from the vent lines either on top of the radiator or on top of the water bridge) air could be forced in from the vent line. I dont know, it's something you might have idea for the cause.

Mk

dr bob

Stop digging. Pretty Please.

mark kibort

You're the "self proclaimed" expert, why is there air in the main water hoses, after an overheat? All i have done is explained my observation.

GregBBRD

Are we ever going to learn and quit letting Mark suck us into these discussions where he already is 100% certain that he knows everything there is to know about the subject? (Every thread he's ever started.)

If a tree falls in the forest......bla bla, bla bla.


If absolutely no one ever comments on one of Mark's threads, again, isn't the end result going to be exactly the same?

mark kibort

GREG, Please read this carefully as i did put some effort in it for you and to help you understand a few things

You forget your personal private message you sent me when you thanked me for the Intermediate plate descriptions (you said , "you finally got it and thanks" remember? Do you want me to post it for all to see? i still have it. (" Breaking ears of the little H's because of the releasing force of the clutch") (the adjustment technique and disruptions i produced) do you remember?, the pinning of the Hs and how that has still held up 8 years later with no adjustment and no issues. things like that

Greg. this is just like you. YOU cant read the message, so you get on a high horse and dig in because you DONT understand a lot of the basic physics of some of the topics.


1. you couldn't grasp the forces of not rev matching a 4-3rd gear downshift. i explained. reverse torque multiplication exposure to the engine.........
2. you saw the scuffed up bores CT automotive had for scots engine and called it junk... yet it lasted with no issues.
3.. you saw my transmission shift fork misalignment and said it couldnt have happened and yet i read adjusted their position and the transmission is better than its ever been (poping out of 2nd for years and locking out 3rd to 4th.
4. you said that stock clutches couldnt handle 420ftlbs of torque, (they would shred in a day a the track like Joe did) yet mine have lasted 10 years and 200 hours of racing.......
5.: you said that Mark was the best driver in the world, porsche champ, and then basically told him he was a hack and didnt know how to match rev downshift after his car blew up. recently.....
The list goes on...
6. But most recently, you said the lines were flaccid after my overheating, after you failed to read the conditions. because my cap was leaking....... the engine was over heated. pressure was high.... i cooled the engine while running, and pressure went down so much so that you could remove the cap. this is basic Gas law .

Now, lets talk about the good. and there is so much.
1. You are a bright engine bilder and car mechanic. you have contributed much to the list. I loved and respected AND appreciated all the help you gave me in designing the '85 5 liter engine. i still can hear your words, blasting the porsche engineers as "cement heads" for having the incorrect offsets for the 85 5 liter pistons. we fixed that on the 5 liter build up for scot and i thank you .
2. you helped me with that freek water leak into my oil through the radiator, sold me a cheap radiator with side tanks and took it to a radiator shop to swap them on mine.. still working today! you saved me!!!
3. you give a TON of support for every issue folks have on the list and as busy as you are, find time for them.. that is remarkable and appreciated.
4. you and ken helped me with timing the cams when i broke the teeth of the cam gears of the holbert car. helped by picking the right cam strategy to get the car running again.
5. and many many great conversatoins about our 928s
EDIT
6: I CANT FORGET THE BIGGEST contribution was the clutch pressure plate redesign when my clutch slipped with the new stroker motor, i used your design of the pressrue plate made from old vs new parts to get more leverage on the pressure plate fingers to hold. i changed it at the track on my back an dedicated that race to you and Mark Anderson..... without it, i would have been done. no knowledge or interest or budget for the racing clutch conversion

you know the things you KNOW and there are somethings you dont, and i dont know why you cant admit them............curious.

Anyway, i only posted this threat to assist anyone that has this issue at the track and can prevent this from happening on the track. my car is find. it holds pressure fine. the hypothesis is clear. the theories are not,
(theories are detailed and confirmed reasons, descriptions of why something happens, and Hypothesis is just observations of something happeing) though Dr Bob may have the answer to why the lines have voids after an overheat and while still soft and at under running temp .

Greg, all my posts have been to share the experience. sometimes i ask for help and i get almost more than i need here and other times im just reporting for what ive seen to help others. thats it! dont make it an argument . its just me giving back, enjoying the dialog or needing help. this thread is not a need of help. i know there is nothing wrong with the cooling system . I know what a leaking water reservoir , or bad caps willl do to system pressure and overheat tendency! i know what headgaskets blown look like...........this is not one of those threads.