The Deputy

Yep, this is my first rule of repair (besides getting the best description of the problem, as possible, from the driver).

Example, our transportation supervisor had an issue with his own personal vehicle, a one ton 4X4 Ford. The front-end/steering wheel would wobble, when he first drove the vehicle after sitting over night or for more than a few hours...after that...it would be okay. While getting advice from another mechanic in the shop, he replaced the brake pads and rotors (not cheap on this beast), tires, wheel bearing (both sides), had two alignments at two different shops...without repairing the issue.

Being one not to butt into someone elses repair job unless asked...I just watched from afar. Well, finally the supervisor asked me what I thought. Slid under the truck and immediately noticed the u-joint for the axle shaft was completely shot, rusted up solid on two caps and other two caps loose. Told him to get that fixed, maybe because it was froze up...it is holding the wheel from going straight for awhile after sitting and once it warms up from driving it is less of an issue. Other mechanic, who had originally been helping...said..."oh I saw that...but that couldn't cause this type of issue".

Well, after replacing the u-joint (and two thousand dollars later/cost of tires, brakes, bearings, alignments, etc)...the problem was gone.

So, yep...fix the stuff that jumps out at you first...your life will be a whole lot easier.

Disclaimer...normally never click on one of these 7 page discussions/debates/agruements/drama-filled-sagas about a simple overheating issue, especially when I know the parties that will be involved...was just bored and wanted to see what OTR18wheeler had to say about the whole thing...lol...so, continue on at your own pace.

Brian.

mark kibort

Getting the magnifying glass out .. ill take another couple pics.

the fact remains. the pump was working and it overheated , had air in the system and when burped the problem went away.

I don't think the pump having bearing noise had an effect on the system efficiency.

mark kibort

yes, for street driving and the ability to heat cycle the engine you are correct. HOWEVER, on the race track there is localized boiling, it adds air to the system and If you want to go out again after it sits for an hour or so, good luck if you don't burp the system..... it might be ok and then it might not.

the point is, yes for the most part, the system is self bleeding if you can go through an entire heat and cool down cycle

the reality is , if you have air in the system and some folks run on the street with some air in the system ..... on the track, this can be an issue., you need to get the air out and burping does work well. I didn't do this all day with sessions back to back to back.... the air built up and was an issue during the race.

so, here is the truth.. the car has no problems....everything is working and functional. no leaks and a new pump (that has a slight bearing noise)
if you don't burp out the air before a race, on a 100F temp day, what happens, happened! its that simple.

it boiled... pushed water out, over heated, it cooled and the lines became soft due to the missing fluid and volume not being replaced when it cooled.

Ive run hotter days for longer periods of time over the past 9 years, and 80 hours of racing . its the first time I DIDNT check the air in the system before I went out. its an easy test..... when cool , or slightly warm with no pressure, you open the cap and squeeze the hoses at the same time. repeat.
that's all you need to do. (for anyone that tracks the 928)

its not as self bleeding as you think it is... good for street, but more care is needed for the track.

I had some pretty sensitive listening devices on the pump and determined that it wasn't catastrophic and continued to do some tests to narrow down the issue.

Brian.. that's a classic situation of car problem solving... ive had many of those.. I remember my bmw.. shaking... on the freeway randomly. the lower control arms had some play... all the experts said that was the cause.. so I replaced them.. still the vibration (violent vibration). turns out the calipers were clamping down and not releasing the rotors. changed the master, and the problem went away. through many steps of investigation, I found the issue. wasn't alignment, tires, balance, etc... it was something that had to be thought about and investigated to find. same methodology I'm doing here

Bill Ball

Stan: Thanks for pointing this out so emphatically. Lots of people I talk to do not believe the cooling system is self-burping and start squeezing hot hoses and practicing other voodoo rituals when all they need to do is run the motor a bit and recheck the reservoir level, and repeat until it the level stable just a bit above the center seam.

Mark, boiling water does not create air. It creates water vapor which recondenses once it cools. Regardless, any air that may be in the system will move to the reservoir. I don't know how you are "burping" the system, but you are just venting steam. You mention you were 2 quarts low on coolant. You don't seem to know where that coolant went, although if you practiced repeated "burping", opening up the system and venting steam without topping off the reservoir, that might have contributed,. Regardless, you were 2 quarts low and the pump may have been exposed and become ineffective. A properly pressurized system (15 PSI cap) with water wetter and water should not boil until about 250F. Sure, there can be boiling around the cylinders duer to higher local temps, but that should recondense as long as it doesn't vent.

Snark Shark

I don't see how additional air got in the system unless you had a leak. Localized boiling would just create steam, of course. That would push coolant out the expansion tank relief vent. When it started cooling down, air would then get sucked in through the vacuum valve in the cap, but that air would just stay at the top of the expansion tank. I would keep checking for leaks and make sure the little metal vacuum valve at the very bottom of the cap moves freely.

Unless you think the air pockets were that large right from the start, which also sounds likely.

jcorenman

GregBBRD

In the picture you took, there appears to be a red deposit on the impeller radiating from the bearing shaft.

If that is rust, that would indicate that the impeller was/had spun.

I grew up working on road tractors....from the age of about 12. By the time I was 14, I could drive a 10 speed Roadranger or a 12 speed Spicer. By 16, I could back a 40 foot trailer into a dock, between two other trailers....quickly.... from almost any starting angle. One of the first things my dad taught me was to look for rust coming out from two iron based surfaces. Any kind of movement will release microscopic particles of metal, which rust almost instantly.....and this is a foolproof way to find loose hardware/pieces.

But I digress......

Porsche changed the design of the water pump in 1989, to a water pump with a plastic impeller. Having worked exclusively on Porsches for over 45 years, the one thing I've found is that Porsche doesn't go looking for ways to spend money, for the fun of it.....there's always a reason for any changes.

I've always thought that the metal impeller mass was probably too high to keep it reliably pressed onto the shaft once the 928 engines became more powerful and accelerated quicker....like on the GT engines (coincidently also introduced in 1989.)

If the engine can change rpms more quickly, the water pump impeller must also keep up with this rpm change.....

Thus the change to a lighter plastic impeller.

The fact that you are running a metal impeller on an engine that accelerates quicker that any stock engine should be food for thought. While Mark Anderson may "goodwill" warranty a stock Geba pump with a metal impeller on a race engine, I'm guessing that the Geba engineers would laugh at you, if they were consulted.

I know, from your past threads that you believe you live in a unique 928 world, where nothing typical ever happens to what you work on/what you own. I realize, for some strange reason, it is important for you to think you have totally unique experiences....this thread is the perfect example.

A smarter approach might be to look at the typical things first....and if you can't find anything, start looking for the obscure.....instead of the other way around.

mark kibort

Bill, you are forgetting one small (but important point) of the situation. remember, I said in the pits, the reservior was at the same level as when I started (or near the same level. ) I know steam is not air. it creates a void though, which pushes out the fluid through the overflow. during this void, the system is low on fluid and the pump doesn't pump efficiently... so you get more overheating, and more boiling with more fluid pushed out the overflow. when I came into the pits ,the level is now maybe slightly higher than I started, pointing to air in the system. the vacuum in the system can draw air from the top hoses..........and then when the system cools, there is now air in the lines.
Remember.... the system has no leaks
it had air in the sytem upon starting the race.
the level was lower than I usually start with and I didn't birp out the system as I usually do

you are forgetting that the hoses attached to the over flow tank, CAN carry air too in reverse when the system is under a vacuum as it cooled. steam pushes out coolant, creates less volume of water, and when the steam condense and the hoses contract, air is brought in from the overflow. the cap is one way.. under vacuum, it works even better as that seal is force to seal even more

Jim... if you have a theory, lets hear it..... there is always a reason for things... I think ive chased the obvious and simple now... because of that, maybe this is a little more complicated than it seems.
1. system lost 2 quarts
2 over heated
3. lines were soft in the pits immediately after race while temp still at upper white line

tests show:
1. slight water pump bearing sound
2. pressure tests were positive with cap and engine cooling system checks with rental tool. no leaks.

what do YOU think is happening... what is so obvious that I am missing here?


Greg, I get that you are thinking this through and the obvious facts are the ones to deal with first. the bearing noise for one .. I get it.. but remember, its not that I live in a "special" 928 world, but I do live in one that pushes the car harder more often than most. as far as quick reving, and forces on the impeller due to more hp.. that's really a function of blip revs, not so much under WOT under load. remember, HP is a fuction of force AND time..... so an acceleration that takes 5 seconds in 3rd gear 60-100, if it takes 7 seconds... 6 vs 7 is less than a rounding error for forces on the pump. and with quick revs, this is also dependent on system inertia and the change( faster rev) is still relatively small on the water pump.. the force that SHOULD be looked at is the high RPM that the pump impeller is subjected too, UNDER load! not the quick rev forces.. in fact, just a guess, I would say the load on the impeller is greater at 6000constant velocity vs reving from 4500 to 6000 in 1 second. but I digress..................

Greg, you have to realize, ive experienced things on the track that ive never been able to simulate at home on the street, even beating up the car up mountain roads or the hyway. I would think you would be interested in my findings at the track and ways ive fixed the issues.
this is a key one. the list has helped me find most of the solutions along the way, by the way.... you included ...and thanks for that.

the situation is pretty simple how it happened.... I'm trying to theoroize, but the reality is the pump is good (possible impeller slip.. ill post the pic)
I forgot to burp the system.. ive done this maybe 1 time in 20 years and this time it got me. how the system ended up with 2 quarts missing, and soft hoses is left to be discussed... ive tested the cap, and the engine cooling system for leaks.... no problem the block and lines were rock solid at 18psi for over an hour and the gauge didn't move at all. same with the cap at near 13psi.
plugs look good
compression tests out perfect at what it has shown for 8 years. about 190psi average per cylinder
sure, under racing conditions, a head gasket can show its ugly face and never have water enter the cylinder...... after all 1000psi of the combustion vs 15psi vs the cooling system is a huge difference (like Scots car when he had the head gasket) all that does is push all the water out the overflow until the engine is dry. . you would never know until you do the gas-in-the-water-test kit. we did that with his.

anyway, you seem to discount ive raced this platform with excellent cooling.. infact, I always smile on these hot days, because my car would run soooo cool........ this past weekend, it didn't. I think I know why.. nothing has changed vs the hot weekend at willows, laguna or sears point.

mark kibort

looks like the impller might have migrated or was too close to start. evidence under high magnification of flat spots exactly the same radius as the nicks in the block

you can see the rust.

Imo000

It's a shame how dirty that engine is.

mark kibort

very clean on the inside though!

GregBBRD

Yup. It spun.

Mystery solved.

BTW....you got really lucky it didn't ruin the block. Install another of the same design and try again....

GregBBRD

Stan:

If the hose to the heater gets blocked off, getting the air out of the rear of the passenger head gets more complex.

Now if he hooked up a hose from the stock heater hose fitting on the back of the head and ran it over to the stock position on the "y" pipe (essentially just bypassing the heater core), it would self bleed.

I have zero personal knowledge about what he has done....

mark kibort

thats exactly what ive done... the most logical thing i would think. instead of going to heater core and back to y pipe, just go right to y pipe with custom hose. so, i didnt block it off, and when i fill the system with water and drive on the street without bleeding the hoses always feel like they have air in them. burping them seems to fix that problem and the hoses always feel full of water with no air.
you think it could have been spinning on the shaft? maybe we should start marking the shaft and the impeller with a notch.
certainly think the high spots got knocked down by the block.. that was one of the things i could hear when hot.... a little tick tick sound like a rotor turning process at the start... tick tick tick.. taking down the high spots before you do the real actual material removal.
it feels solid, but the gap looks larger than the Lasso i pulled off. i think its .020" vs .030". ill measure again.

GregBBRD

The rust right there tells you it spun.

It moved slightly back on the bearing shaft towards the block, but not enough to trash the block.

You are very lucky. I had an impeller spin and move on a brand new stroker engine during the first 30 minutes of running....completely trashing the area.

I made my block repair tool and the inserts to repair the block, because of this one failure.....so I didn't have to start over.

Plastic impeller, plastic impeller, plastic impeller. In my entire 928 experience, I've seen one factory 928 pump with a plastic impeller that came loose. One. I've seen dozens of Laso pumps with metal imellers come loose. Zero Lasos with plastic impellers come loose, to date. (I only run factory pumps wtih plastic impellers on my high output engines.)

Even if the plastic impeller spins on the cast in bronze bushing that presses onto the bearing, it doesn't ruin the block.

.....If you've got a $20 head, wear a $20 helmet.....

.....If you've got a $300 928 engine, run a $300 water pump......

Lo mismo.