GregBBRD

Now that....I understand.

"What part of this did you expect to be cheap.....The Porsche or the racing?".....Greg Brown circa 1985.

dr bob

Mark-- The only "air bubble in the system" was in the reservoir. Anyplace else, once the coolant circulates the air is pushed to the highest place in the system, the reservoir. Air captive in the water bridge can keep hot liquid from reaching and opening the thermostat. That will cause overheating in a matter of minutes after start-up. You didn't overheat minutes after start-up, so that wasn't a problem.


Maybe the thermostat didn't open -enough-, restricting the max amount of flow available through the system.


What's puzzling is how you managed to lose a couple quarts of coolant from a hot system with no pressure on it. And no leaks.

GregBBRD

Air bubbles can be trapped in the rear of the cylinder heads. The way the water pump sends water through the cylinders, the driver's side does a pretty good job of flushing itself.

The passenger side does a good job, also.....unless the hose to the heater is blocked off.

That is a disaster waiting to happen.

Venting the back of both heads back to the overflow tank ensures there is no possible trapped air bubble....a trick learned keeping the 427 Fords alive.

jcorenman

So what we have here is one obvious problem (noisy water pump), and a bunch of fuzzy problems (no pressure, overheated, water went missing, all for reasons unknown). Right?

When I was a kid engineer (half a century ago) my first boss (Captain Obvious) said "Kid, you've got an obvious problem here along with a bunch of mysteries. Why the heck are you spending all your time working on the mysteries? Fer chrissakes fix the obvious problem first, its the one thing you know how to do. Then see how many mysteries are left".

Pull the freaking water pump !!

GlenL

"Because the obvious problem isn't interesting."

mark kibort

bob, everything until this post has been interesting and correct
however, there is ABSOLUTELY ways to get voids (air pockets in the system) its why we birp the system when we change the water out. the reservior will be full, but there is a lot of air in the lines.... when the engine cooled off after the race,the reservior was about half full. i birped the system and it went down to about the very bottom of the reservoir. put about 2 quarts in and it was full. where did the 2 quarts go?? they were pushed during the over heat.

I also had a problem a long time ago with a sticking themostat ... (since fixed) would warm it up... it would start to climb in temp.. i would shut the engine down... the T-stat would then heat soak and open... starting the car again, and the engine temp dropped dramatically, and the radiator went from cool to hot!

when the radiator is hot... the t-stat is working . i guess its possible that the t-stat could partially open, but i think that is a stretch. it worked welll on the street last week functioning normally.... just the small amount of water pump bearing noise.

anyway, you can have the tstat open and air in the lines and system.. the tell tale situation is that the system is pressureized but the lines feel like balloons, no water in them.

so again, my theory is that the engine overheated with a closed no leak system.... boilled, and that pushed out 2 quarts of oil.... there is some smokinig in the rear view cam showing the passengerside of the car tossing out steam or smoke. (cant tell for sure) then, when i backed off and cruised at 100mph for 6 miles at low throttle and RPM, the sytem cooled... enough circulation to keep temp at top white line, (or maybe just air temp in the bubble area near the sensor) and came in to the pits with the system now at ambient pressure, no pressure in the hoses and radiator very warm top to bottom.

it is a puzzle... kind of reminds me of the school questions where the class was asked to solve these kinds of engineering puzzles. i think the key clue here is water was pushed out under pressure, one way valve, so when temps were lowered the system pressure was at near ambient due to the loss of water and the temperature reduction vs the time of boiling.

the reason for the overheat is the real mystery now , not the low pressure hoses or the missing water (if the above is true). was it just air in the system to start, or was the pump impeller jammed or slipping?

sometimes true, but how many times do you remove the obvious issue and there is something else wrong? in this case understanding what happened might point to an easier fix....the downside is that trying to solve this particular issue with a bad water pump or failing one, or one with just a bearing noise, might cause a greater issue (if that pump starts to run into block or jams and burns the belt and breaks it) that is the reason most here are just saying... "just change the flipping pump" its only a few hours and will at least start the mystery solving process with no down side. so you are right.. and its coming off today....(as long as the pump is in the mail from Mark A. )

hacker-pschorr

Don't worry. Mark is fully aware that if irreparable damage happens to that block, a replacement is as easy as:

• Buy a block from 928 International $??
• Have cylinders bored: $1,000 - $1,500
• Ship to US Chrome: $500
• Nikasil process: $1,800+
• Ship back to Cali: $500

This doesn't include removing all hardware from the block before shipping, extensive cleanup after it arrives home and reinstalling all hardware......and rebuilding the engine assuming nothing else was damaged.

Piece of cake!!!!!

This is when most normal people kill the ignition, tow the car back to the pits, tow it home and start tearing into the engine to avoid further damage.

Sure, it may be nothing and if I were racing a Miata with a $500 junkyard motor I wouldn't care. Having a $40k+ professionally built race engine out front usually changes ones perspective on things.

mark kibort

ok....now you are starting to scare me... im pullling the pump now!!!!

GregBBRD

This is worded strangely.

My English background would interpret this as you driving this thing around with a water pump noise.....but I'm having a terrible time believing that.

If true, I'm guessing that 99.9% of the people "playing along" with you, here, would shake their heads in utter discust and completely ignore this thread (including me.)

"While it is difficult to help unknowing, it is completely impossible to help stupid.."

mark kibort

Greg, if we stoped driving our cars after every single strange clicking , slight bearing noise, our cars would always just be apart and at your shop.
If you have an english background and you know my experiencd with water pumps and the 928, im not an idot. i had a slight leak after last seasons last race and pulled the pump.... the bearing noise and leak was minor, nothing move or got damaged, just a water pump going bad. i know some lock up or "explode" but ive only see 4-5 failures and they are all minor stuff that cant hurt anything...after all, we are talking lock up or impelller migration and i havent ever seen that.

so, i hear the noise after the race, it's not leaking and i have overheated the engine. easy to think there might be a leak . stethascope allows for me to hear things moving but just a little noise than im used to. feeliing the hoses allows me to fee flow too.

usually a bearing starts making noise and then you change it out. water pump, wheel bearing, etc. i dont think its an emergency situation.

anyway...... based on the fear here i just go right to changing the pump, even though the noise is there, but not that bad...... i know when its real bad and can see a leak!

So, I wanted to discuss to see if the pump was even worth pulling, but the fear of the impeller moving . (which would have made a racket, i bet on the stethascope), forced my hand to just dig in and replace it.. it's out and on the table next to last years 8 year old lasso bad pump to compare.

next post pictures

mark kibort

so, here is the pump... still looks new... even the gasket came off on the pump... (nice treat)
the gap looks a little larger, but not earthshatering vs the old failed Lasso (dirty one) (3rd picture down is the greater gap Geba)
bearing noise with lasso , much higher
bearing noise with geba is slight, and a little bit of bearing movment...if it didnit make the little noise i heard, i would probably put it back in.

look at the block... there was a little nicking sound i heard too, and i wonder if the pump was hitting the block to make the two scratches.
the gap was about 2x the lasso pump, but still looked acceptable

I was able to change it out with out pulling the harmonic balancer, but its apain. wont do that again. flywheel lock and 200ft-lbs on the crank bolt and its probably easier that way.


summary... the pump may have a bad bearing but it's not the smoking gun we were hoping for. the smoking gun is starting a race with air in the sytem and not birping it out before the race (and topping off the reservior)
it over heated.
there was NO leaks
system pressure checks out good
temp guage read upper white line, and fans running, yet hoses were soft and 2 quarts missing
reason????? ive tried to explain my theory , but open to others!

Mrmerlin

Mark I will tell this to you only once, its the truth and you should never forget it.

The 928 coolant system is a self bleeding system.


To fill the system place the car on a flat surface.
With an empty system.

Remove the coolant cap and pour 4 gallons of coolant into the bottle,

two gallons of the full strength and two gallons of the distilled water.

For your race car this could mean 3 and 3/4 gallons of distilled water and the rest water wetter.

It will take a little bit of time for the coolant to fill the system.

Nothing needs to be done like rolling the the car on the rotisserie 3 times or jacking the front end up 40 inches or burping or any other such folly.

The system has two bleed ports,
one on the top of the radiator,
and one on the water bridge,
these are the hi spots on the coolant system.
thus leaving the car flat facilitates bleeding the system.

Once the coolant bottle will not take any more coolant past the half way mark ,
open the heater control to full hot, start the engine and run till the fans come on and their is heat coming from the defroster vents this will take about 4 mins of run time at idle.
once the fans come on put on the cap and drive the car for about 5 miles then shut it off,
and let the engine cool,
once cool ,
top up the system to a fill of just above the seam on the coolant tank.

FBIII

So you are aware that the water pump has a noisy bearing and you are also aware of the damage a failed bearing can cause. But you are not overly concerned and continue to run the car. I must have missed the paragraph in the owners manual that guarantees a certain mileage that can be driven, once a bearing noise starts, before a catastrophic failure occurs.

GregBBRD

A close up of the center of the impeller would be nice....

OTR18WHEELER

,
You never mentioned the tire size, or what type of oil ..
... During the overheat event.
I've had better inane subjects die out in less than 3 posts.