SeanR

Yep, which is why, if in fact Mark had air in the engine before heading out on the track, his res was empty. Otherwise it was full. He lost coolant due to over heating and that boiled off through his res cap unless there is another escape route. Most would call that a leak. It doesn't matter what Porsche's engineers did or the whys of it, Mark can come up with a million reasons as to why it's not true.

GregBBRD

Yes.

mark kibort

again not true..... it is SO common to have air in the lines after a hot race. ive been doing this for what, 20 years now Sean? before the race or session i can go to the engine compartment and feel air in the lines , especially after a hot session before hand and the engine is cool. if i burp the system, the air is pushed out of the upper area of the engine and hoses.

again, when i started, the reservoir was at the half way seam of the container.

Its funny, you and others might not believe anything i say here.. but its the truth and many have seen it first hand. im not making this up.. this is what happens at the track. you are right though, i did boil over and lost 2-3 quarts of coolant. in the pits, the reservoir was half fullll ... after burpiing when it cooled , it was near empty. 2 -3 quarts added and it was fulll again.

there were no leaks. ive pressure tested the system and cap and all are functioning well.

try to wrap your head around this................. if you fill the system up with water, you will have a LOT of air in the lines and block. the reservoir will be full.. this will never change if you just let it sit there. a year later, it will still have air in the hoses.. theoretically and some have seen, if you drive the car, it naturally willl self bleed.... i believe this too ..... But, if you go out racing or tracking the car, there is not enough time for self bleed.. the engine gets hotter, their are voids in the engine, it can overheat because of inefficient circulation. come in the pits, the water level will be higher and there will be air in the lines for the reasons i mentioned earlier..... especially if you get a slight boil over. (pushing water out the overflow). the void is filled with air from the reservoir through the upper tube, which directly connects to the top of the engine, as the steam condenses back to water.

EDIT: Sean , also remember when the reservoir is half full or less, which it was when i went out racing.. water level WAS checked, so you are wrong on that assumption too... it was NOT emtpy when i started............. the race car is going through 1.5 g loading turns, and 1g loading breaking, and the combination of both can change where the high spots are in the water system . this is why ive found that its important to start a race with the fluid level at 3/4 min.

GregBBRD

Yes.

GregBBRD

Yes.

And no.

GregBBRD

You are sort of correct.

Once the system s bled and there is no air in the system, there will be no air introduced into the system....unless enough water is lost to empty the reservior....at some point during the running.

On a fresh fill, there can be air trapped at the back of the cylinder heads. This is simple to get rid of. Run the engine until the thermostat opens (lower hose gets hot), with the cap off. Rev the engine up to move the coolant and air. Wait until the two overflow hoses to the reservior no longer have bubbles flowing into the reservior, and install the cap. Allow the engine to cool....and top off the reservior.

Done.

mark kibort

while the engine is running for some time, it does a fair job of this.... ive driven a newly coolant changed engine for a few miles and still found air in the system.. just did the 6 liter of gregs.. .same thing. you drive it,, you let it cool and pop the reservoir cap and then sqeeze the hoses.. the air is released. proof???? the water level goes down proportionately to the air released. add more water.............all is good
the porsche design is good, but not perfect.

Jim, just because its the high point, doesnt mean that all the air will automatically be forced out!!!!! why is this so hard to understand? all the lines have horizontal areas where ALL the air cant find its way to the reservoir
look at the system. YOU FORGOT ONE MAJOR FACTOR here.
#1 the rear of the engine has a hose , top of the heads that leads to the bottom of the reservoir. good... thats one... anything in the head that can be forced out, will be . however, still places for air to get trapped.
#2 the other line leading to the bottom of the reservoir goes to the top of the radiator, which is just below the engine front hose connections. .

this is why when you squeeze the hoses, the air is pressed into the upper lines and vents out, and the water level rises from the bottom... you release the pressure and the water fills the voids.

read what i posted to Jim..... for the most part it works,but it takes a few heat cycles on a street car to get the air out. eventually , it does. ive been doing this a long time.... i can remember a few times where i didnt do the burping after a fluid change or after a race or session and this problem i described occurred.. it wont likely be an issue on the street, but it is on the track. it never has the time to "self bleed" and more air can be added in the system when running at WOT for extended periods of time when you start with air in the system...

there is a little experiment you can do... get to a high temp... pop the cap to the first stage (not removed) ....... let it boil over and eject a gallon of water... tighten the cap. the reservior will be near full, yet there is steam in the lines.
wait until it cools. level might be at 1/4 mark.... but feel the hoses.... they will be fulll of air. warm the car up again and it will self bleed but not fully. or you can squeeze the hoses and bleed the system perfectly.

hacker-pschorr

Mark,

Is your favorite past-time licking 9-volt batteries?

mark kibort

bingo!! Kind of... once you bleed the system, you are good as you say... its closed and no air can be introduced.... However, you forgot one situation and the reservoir doesnt have to be empty ...... if you boil over.. you remove water from the system ... the steam has replaced the volume... air can travel back from the upper reservoir lines and filll the void as the steam condenses. in other words, the air takes the place of the steam at the top of the engine, and the hoses.. it cant do it on its own, unless you remove the cap and run the engine for a while.. (cant do that , or you will get more boil over), so you are done..nothign you can do but wait for the car to cool so you can burp the system.

remember, we did this with brians Lemons car. we over heated removed the cap as water was low and started to add coolant and burp . we added so much water so quickly that (while birping) that we were able to cool the system , remove all air and replace the cap and go out racing. without removing the air, it would have overheated again.

the key thing is there are many place that air can get trapped, but if run long enough, the trapped air will be released through the upper reservoir lines which attach from the front top of the engine. if not, you risk over heat, and possibly more air if that happens. and that happens because the air that is in the system reservoir, replaces voids in the top of the motor via those two lines.

mark kibort

back on some comparisons of the bad pump and a brand new LaSSo, i thought this was interesting
the impeller to structure gap is .010" for the lasso and for the Gebe that came out , .045"
I measured the marks on the block and they are the same spacing as the impeller leading edges.. so, the impeller either moved or its a bad design OR the nicasil coating was too thick. the spacing of the leading edge to center is 22.8mm and so are the marks on the block.
looks like the lasso impeller is 3mm vs the geba being 5mm... dont know if that means anything or what would be better. maybe for high RPM, the thinner is better. (like airplanes)

James Bailey

Mark the system is designed to always have air ..... the reservoir full level is not designed to be full. Water coolant expands at about 4% as it is heated to near boiling and THAT is what makes the pressure in the system. Water coolant easily displace air as it is much heavier and the block always fills up from the bottom FIRST . The small hose on the top of the radiator lets the air out of the radiator. The small hose near the top of the thermostat housing ( where the 4 cylinder Porsches have the bleed screw ) vents air from the block. If you properly warmed up the car after adding coolant it should be just fine.
After all the pumps flows something like 40 gallons per minute which pretty much flushes air out of the system Or would fill a standard bath tub in one minute !!!

dr bob

Mark--

Any air re-ingested after a boil-then-cooldown cycle will be at the top of the reservoir. There's no way to get air into the other pockets in the system unless the reservoir is completely empty of liquid as the air comes in. It's part of the system design really, a good reason to have the reservoir up so high in the system so any air would sit on top of the liquid. Purge the air out once after you service the system, and it will saty purged until drained again or enough coolant is lost to drain the reservoir.

GregBBRD

I figured it went without saying that if the system boils, you will have to start over....even my pet dog understands that.

The 928 cooling system is very robust and if they boil over, something is very wrong.

mark kibort

you are forgetting what fills the displaced coolant areas and how air can fill those voids.

think about it. there is steam in the system. voids in the system. the water is pushed out the top . its under pressure.. say 18psi .... then the pressure drops due to cooling. if there is air voids near the top of the engine, near the water pump, and the pressure drops due to cooling. theoretically, water goes into the lower reservoir hose and travels to the radiator and air in the line goes out the upper radiator hose area to the reservoir. however this is not usually the case.. what happens is the air in the hoses is a lower pressure than what is at the reservoir... so the air travels freely to the upper engine area and the hence, the reservoir level doesnt change. this is EXACTLY what happened to my car. its why the reservoir was 1/2 full and there was air in the lines.... a lot of air... after cooliing.. the reservoir was still half fulll and air in the lines. burping it got the air out and the reservioer went down to near empty... same as when you first fill the radiator.. same thing.

Jim, you know i know that the reservior is designed to have air.. thats at the top of the reservoir. the upper fill line. what you are not thinking about is what happens when steam pushes water out the over flow and then upon cooling there is a vacuum that starts. if there is air in the upper return lines, air willl freely fill the engine and keep the level steady.. science 101 here.
Think again ........ system cools down... steam condenses into water, vacuum started.... the water can go into the radiator top and the air is pushed into the overflow taking its place OR, the air goes into the upper radiator area, because its easier with less resistance and time to respond to the flow. THATS what is happening.

Jim, its happened to me many times ... i can show you any time on any 928 that this is the case. as Greg says, the only way to get the air out of the top of the engine is to run it to operating temp with the cap off. otherwise, you can have air in the system and that might not ever be removed and your cooling sytem efficiency is compromised.

mark kibort

yes it is... no argument here.... you hit the nail on the head. once you get boil over, you start over
your advice....... pop cap and get to running temp
my advice. pop cap and burp

same thing

your pet Dog can get this but others might not..... if you have air in the lines, again, you need to as you say, "start over".
by the way, i do get air in the system only on very hot days after a session. i do burp the system and add some water to keep the level at the 3/4 mark.
never have issues when doing this at the track, even the 110F races we had at thunderhill a few years ago.

on the race track if you start with air in the system, you need to start over. if you dont and you are racing, you will boil over in a few laps on a 100F day

by the way Greg... why do you think the impeller moved. usually rust means its NOT moving. its on the shaft, very snug. cant imagine it moving. do you think the impeller moved forward or was it made that way to start?