OVERHEAT AT RACE AT THUNDERHILL - WATER PUMP ?
10-03-2016, 12:48 AM
#106
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Thread Starter
by the way Greg... just measured the impeller to housing gap....... the gap was .040" for the gebe pump..... the laso from the old bad bearing lasso pump 8 years old was .010"..... wonder what the spec is and if the impeller was migrating..... seems the gebe now is .030" more toward the block than the lasso pump i pulled off. . uggggg. hate to think of the damage it could have caused!
thanks for the info along the way.......
thanks for the info along the way.......
10-03-2016, 05:29 AM
#107
Rennlist Member
Mark,
I trust you have learned something from this episode. As a few of us have intimated to you in your thread, running the motor when you hear "strange noises" is not a good idea. That you could pick the noises up and isolate the source is commendable but to then ignore them is somewhat dumb *** would you not agree- and I say that [hopefully] as a friend not a detractor.
All this supports the notion that the pump failed, you thus stopped pumping coolant around the system [the overheating] and more than likely [?] some coolant was lost via the pump seal. As to the sequence of events that may remain a mystery. That you see the rust colour staining on the impeller shaft is quite a give away- that [I suspect] did not happen only on race day but..? As per your own words if you did not check the coolant level before the race then maybe it was on its way already.
Clearly the noise you did hear was the impeller rubbing on the high spots of the volute. Similarly the clearance between the pump body and the impeller is also a clue. When the impeller leaves the shaft the temperature shoots up rapidly [well it did on both occasions it has happened to me- once with a factory pump, the last one on a Devek rebuilt pump that lasted many years by the way] and both wth plastic impellers. Having seen this happen I would never run a metal impeller unless I had absolutely no choice. My current pump is a new Laso with plastic impeller and also have a factory spec spare that came from the TBF'd original GTS motor [unknown provenance though ]that I may use one day given I can now do the timing belt job myself [but not for a long time-hopefully].
For sure it seems you just dodged a dangerous bullet by the skin of your teeth. Now the interesting question is why/how the impeller came loose and seemingly [?] reseated itself on the shaft. When my impellers came off they stayed off falling out as the pump casing was removed. The clearnce from the impeller to the casing volute has to be very tight or the pump efficiency takes a huge dump.
Rgds
Fred
I trust you have learned something from this episode. As a few of us have intimated to you in your thread, running the motor when you hear "strange noises" is not a good idea. That you could pick the noises up and isolate the source is commendable but to then ignore them is somewhat dumb *** would you not agree- and I say that [hopefully] as a friend not a detractor.
All this supports the notion that the pump failed, you thus stopped pumping coolant around the system [the overheating] and more than likely [?] some coolant was lost via the pump seal. As to the sequence of events that may remain a mystery. That you see the rust colour staining on the impeller shaft is quite a give away- that [I suspect] did not happen only on race day but..? As per your own words if you did not check the coolant level before the race then maybe it was on its way already.
Clearly the noise you did hear was the impeller rubbing on the high spots of the volute. Similarly the clearance between the pump body and the impeller is also a clue. When the impeller leaves the shaft the temperature shoots up rapidly [well it did on both occasions it has happened to me- once with a factory pump, the last one on a Devek rebuilt pump that lasted many years by the way] and both wth plastic impellers. Having seen this happen I would never run a metal impeller unless I had absolutely no choice. My current pump is a new Laso with plastic impeller and also have a factory spec spare that came from the TBF'd original GTS motor [unknown provenance though ]that I may use one day given I can now do the timing belt job myself [but not for a long time-hopefully].
For sure it seems you just dodged a dangerous bullet by the skin of your teeth. Now the interesting question is why/how the impeller came loose and seemingly [?] reseated itself on the shaft. When my impellers came off they stayed off falling out as the pump casing was removed. The clearnce from the impeller to the casing volute has to be very tight or the pump efficiency takes a huge dump.
Rgds
Fred
10-03-2016, 05:54 AM
#108
Under the Lift
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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.
10-03-2016, 12:49 PM
#109
Rennlist Member
Never seen it happen with a good cap on properly. The only time boiling forces coolant out the vent is when the pressure is not maintained and the engine is stopped. The stored heat in the motor confronted with coolant not circulating and no pressure can cause a boilover geyser. So, if you think you lost coolant that way, it was from a bad cap when you stopped the motor.
If the pump stops spinning, even momentarily, under full load then all that heat gets absorbed by the now-stationary coolant in the block and heads. The temperature spikes and the water vaporizes which raises the pressure way up-- pushing everything towards the only outlet, the pressure cap. Even if the engine is shut down instantly there is still a lot of latent heat in the block.
I saw this first-hand a few years ago, riding shotgun for Dan H in his 6.5L car while we did some Sharktuning. We were WOT nearing redline in some gear when the WP impeller decided to stop turning. The effect was instantaneous: The dash lit up like a Christmas tree with temperature warnings, which distracted from the fact that the windshield was covered by steam as a gallon or so of coolant was ejected from the reservoir. Dan shut the engine down instantly and it was all over in a couple of seconds. No hoses burst, nothing was harmed, just had to wait while the rescue squad (Sue) brought some water...
The reason the impeller stopped in that case is unrelated-- it was an early Ed pump with a coupling between pulley and impeller which was designed to disconnect the impeller if the load got too high, i.e. failing pump. In this case it disconnected under normal-but-extreme load, which Ed quickly corrected. The lesson is that there is a significant amount of torque required to spin the impeller at high RPMs.
If Mark's impeller spun on the shaft-- which it certainly looks like it did-- then the same would happen on the track: Vaporize large quantities of water, barf it out the reservoir, and overheat. That might also explain Mark's flaccid hoses: as soon as the block cooled down below 212F the water vapor would condense back to liquid and the pressure would drop. This could happen quickly if the impeller only slipped at high RPM, which also looks likely.
10-03-2016, 01:05 PM
#110
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Bill, Here is what i think happened. (and by the way, there was no coolant loss in the pits at all with engine on or off)
HERE is where the collant went
Here is why there was air in the sysstem
Here is why all the air doesnt have to be in the overflow.
Here is why the pump was not a factor in the overheat. (this one im not positive about)
The engine was started before race time with air in the system giving partial circulation.. enough to run normally and trigger on the t-stat as well as regulate temp with fans based on the bottom of the radiator temp sensor switch.
the engine's circulation was compromised by air in the system and started to over heat.. the over heating caused the fluid to boil... the boiling pushes up on the lower overflow hoses, from the top of the radiator vent hos as well as the back of the engine hose..... this pushed the water out the top of the pressure cap at 14psi.
now the engine is running 2 quarts low . steam has take the place of the water in the engine block. I notice the temp is high (upper white line) and shut down racing and just keeping speed of near 80-100mph for two laps. temps drop down too just above normal (just below white line).
what happened next: The steam condenses and its reduction of volume creates lower pressure in the system . a vacuum starts to form in the engine and what fills that vaccum? air in the overflow, from the top line near the cap, easily fills the void in the engine with air. the water level stabilzes at mid level as the air now has filled the engine voids left by condensing steam.
I come into the pits.. the lines are soft, the cap is secure and working. there is even more air in the system... water level looks fine, but hoses are soft.
after cooling the water level is down 2 quarts (maybe near 3)and i fill the system.. burping the lines to get all air out.
tests on the street show it running find. temp was able to be controlled by fans. turning off fans, i could get system temp to upper white line... hoses aer at high pressure.
Conclusion: the water pump was making bearing noises, but thats pretty normal for a pump that will start to leak soon..... Greg says that the rust on the shaft says it moved, and that seems very possible that it was slipping and maybe caused the overheat... ill never know that.. but i would think if it was stopped i wouldnt have been hearing the clicking noise of it touching the block and it wouldnt have been able to run the car hard on the street perfectly with temp control.
with good stethoscopes you can locate and hear a lot in the system. the bearing noise i heard at the track and at home went away with some drving but there were still tell tale signs that the bearings were going bad. and that maybe the pump impeller was touching the block.
edit: there are plenty of ways water can get pushed out the overflow. ive shown one way, plus dont forget that scot with a blown head gasket , was forcing air into the water jacket and ejecting all the water on the track and on the track only. when half empty, temp control was not possible so he came into the pits. (8 quarts gone). all out a perfectly good radiator, and cap.
Bob...read my reasoning about why the boiling created more air in the engine . I think that is a fairly good scientific reason for what happened.
Jim, yes, i agree.. however, do you really think the pump stopped spinining. obviously i heard bearing noise and felt flow through the hoses . PLUS, i also have experience with the Porsche pump losing the plastic impeler.. it would just go to red heat levels!! i would shut down. wait for 20 mins start it and it would climp to near read for me to shut it down. i was driving back from laguna seca and got to about seaside before calling a tow truck. i could cycle the engine every 4 miles and turn it off just before overheat... the pump was spinning intermittently and then finally was not spinning at all.
so, i was able to run several laps in this hot , semi overheated condition running 3000rpm and low throttle . the pump had to be spinning
Fred... i take the comments from you as a "friend" thanks! Now, was it "dumbass" to run the engine... probably! i do that.... my comment to greg was that my issues are denial.. ill admit that. BUT, i think the tests i conducted were pretty indicative that there was no rubbing on the block and the bearing noise was not as noisy as the pump that failed after last seasons last race (that left a puddle after the race, on the trailer and on the garage floor).
I dont thin we lost fluid out the bearing. it's sound. pressure tests all pasted at higher pressure than running pressures.. however, it might have migrated forward .030" which i dont know if that is catastrophic for efficiency.. illl see when i get the Lasso today from Mark A and measure the gap.
whatever happened with the over heat, i think we know what caused the hoses to be soft in a closed syetem at high temp. Gas Law !
HERE is where the collant went
Here is why there was air in the sysstem
Here is why all the air doesnt have to be in the overflow.
Here is why the pump was not a factor in the overheat. (this one im not positive about)
The engine was started before race time with air in the system giving partial circulation.. enough to run normally and trigger on the t-stat as well as regulate temp with fans based on the bottom of the radiator temp sensor switch.
the engine's circulation was compromised by air in the system and started to over heat.. the over heating caused the fluid to boil... the boiling pushes up on the lower overflow hoses, from the top of the radiator vent hos as well as the back of the engine hose..... this pushed the water out the top of the pressure cap at 14psi.
now the engine is running 2 quarts low . steam has take the place of the water in the engine block. I notice the temp is high (upper white line) and shut down racing and just keeping speed of near 80-100mph for two laps. temps drop down too just above normal (just below white line).
what happened next: The steam condenses and its reduction of volume creates lower pressure in the system . a vacuum starts to form in the engine and what fills that vaccum? air in the overflow, from the top line near the cap, easily fills the void in the engine with air. the water level stabilzes at mid level as the air now has filled the engine voids left by condensing steam.
I come into the pits.. the lines are soft, the cap is secure and working. there is even more air in the system... water level looks fine, but hoses are soft.
after cooling the water level is down 2 quarts (maybe near 3)and i fill the system.. burping the lines to get all air out.
tests on the street show it running find. temp was able to be controlled by fans. turning off fans, i could get system temp to upper white line... hoses aer at high pressure.
Conclusion: the water pump was making bearing noises, but thats pretty normal for a pump that will start to leak soon..... Greg says that the rust on the shaft says it moved, and that seems very possible that it was slipping and maybe caused the overheat... ill never know that.. but i would think if it was stopped i wouldnt have been hearing the clicking noise of it touching the block and it wouldnt have been able to run the car hard on the street perfectly with temp control.
with good stethoscopes you can locate and hear a lot in the system. the bearing noise i heard at the track and at home went away with some drving but there were still tell tale signs that the bearings were going bad. and that maybe the pump impeller was touching the block.
edit: there are plenty of ways water can get pushed out the overflow. ive shown one way, plus dont forget that scot with a blown head gasket , was forcing air into the water jacket and ejecting all the water on the track and on the track only. when half empty, temp control was not possible so he came into the pits. (8 quarts gone). all out a perfectly good radiator, and cap.
Bob...read my reasoning about why the boiling created more air in the engine . I think that is a fairly good scientific reason for what happened.
Never seen it happen with a good cap on properly. The only time boiling forces coolant out the vent is when the pressure is not maintained and the engine is stopped. The stored heat in the motor confronted with coolant not circulating and no pressure can cause a boilover geyser. So, if you think you lost coolant that way, it was from a bad cap when you stopped the motor.
There is another scenario which I think applies here. The heat flux from these engines under full load is huge, with a tremendous amount of heat being transferred from block and heads to the radiator. At idle it is almost nothing but when the engine is putting out 400 bhp then there is well over 500KW of heat being generated-- a couple million BTU/h. As long as the pump keeps spinning and there is airflow through the radiator then it all works. The boiling point of water at 15psi is around 240F, and by around 190F the t-stat is sending all of the coolant thru the radiator.
If the pump stops spinning, even momentarily, under full load then all that heat gets absorbed by the now-stationary coolant in the block and heads. The temperature spikes and the water vaporizes which raises the pressure way up-- pushing everything towards the only outlet, the pressure cap. Even if the engine is shut down instantly there is still a lot of latent heat in the block.
snip>>>>
If Mark's impeller spun on the shaft-- which it certainly looks like it did-- then the same would happen on the track: Vaporize large quantities of water, barf it out the reservoir, and overheat. That might also explain Mark's flaccid hoses: as soon as the block cooled down below 212F the water vapor would condense back to liquid and the pressure would drop. This could happen quickly if the impeller only slipped at high RPM, which also looks likely.
If the pump stops spinning, even momentarily, under full load then all that heat gets absorbed by the now-stationary coolant in the block and heads. The temperature spikes and the water vaporizes which raises the pressure way up-- pushing everything towards the only outlet, the pressure cap. Even if the engine is shut down instantly there is still a lot of latent heat in the block.
snip>>>>
If Mark's impeller spun on the shaft-- which it certainly looks like it did-- then the same would happen on the track: Vaporize large quantities of water, barf it out the reservoir, and overheat. That might also explain Mark's flaccid hoses: as soon as the block cooled down below 212F the water vapor would condense back to liquid and the pressure would drop. This could happen quickly if the impeller only slipped at high RPM, which also looks likely.
so, i was able to run several laps in this hot , semi overheated condition running 3000rpm and low throttle . the pump had to be spinning
Mark,
I trust you have learned something from this episode. As a few of us have intimated to you in your thread, running the motor when you hear "strange noises" is not a good idea. That you could pick the noises up and isolate the source is commendable but to then ignore them is somewhat dumb *** would you not agree- and I say that [hopefully] as a friend not a detractor.
All this supports the notion that the pump failed, you thus stopped pumping coolant around the system [the overheating] and more than likely [?] some coolant was lost via the pump seal. As to the sequence of events that may remain a mystery. That you see the rust colour staining on the impeller shaft is quite a give away- that [I suspect] did not happen only on race day but..? As per your own words if you did not check the coolant level before the race then maybe it was on its way already.
Clearly the noise you did hear was the impeller rubbing on the high spots of the volute. Similarly the clearance between the pump body and the impeller is also a clue. When the impeller leaves the shaft the temperature shoots up rapidly
For sure it seems you just dodged a dangerous bullet by the skin of your teeth. Now the interesting question is why/how the impeller came loose and seemingly [?] reseated itself on the shaft. When my impellers came off they stayed off falling out as the pump casing was removed. The clearnce from the impeller to the casing volute has to be very tight or the pump efficiency takes a huge dump.
Rgds
Fred
I trust you have learned something from this episode. As a few of us have intimated to you in your thread, running the motor when you hear "strange noises" is not a good idea. That you could pick the noises up and isolate the source is commendable but to then ignore them is somewhat dumb *** would you not agree- and I say that [hopefully] as a friend not a detractor.
All this supports the notion that the pump failed, you thus stopped pumping coolant around the system [the overheating] and more than likely [?] some coolant was lost via the pump seal. As to the sequence of events that may remain a mystery. That you see the rust colour staining on the impeller shaft is quite a give away- that [I suspect] did not happen only on race day but..? As per your own words if you did not check the coolant level before the race then maybe it was on its way already.
Clearly the noise you did hear was the impeller rubbing on the high spots of the volute. Similarly the clearance between the pump body and the impeller is also a clue. When the impeller leaves the shaft the temperature shoots up rapidly
For sure it seems you just dodged a dangerous bullet by the skin of your teeth. Now the interesting question is why/how the impeller came loose and seemingly [?] reseated itself on the shaft. When my impellers came off they stayed off falling out as the pump casing was removed. The clearnce from the impeller to the casing volute has to be very tight or the pump efficiency takes a huge dump.
Rgds
Fred
I dont thin we lost fluid out the bearing. it's sound. pressure tests all pasted at higher pressure than running pressures.. however, it might have migrated forward .030" which i dont know if that is catastrophic for efficiency.. illl see when i get the Lasso today from Mark A and measure the gap.
whatever happened with the over heat, i think we know what caused the hoses to be soft in a closed syetem at high temp. Gas Law !
Last edited by mark kibort; 10-03-2016 at 07:40 PM.
10-03-2016, 01:09 PM
#111
Mark, the only way you had air in the motor was if the expansion tank was empty when you took off to hit the track. Read Jims post and then re-read it.
10-03-2016, 01:10 PM
#112
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At this point put on a new pump, new belt, and go race the damn thing.
This thread shouldn't have lasted longer than four posts, maybe five.
This thread shouldn't have lasted longer than four posts, maybe five.
10-03-2016, 05:44 PM
#113
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Thread Starter
fact: i came into the pits.. hoses were soft and full of air. overflow was half full. after cool down and burping.... it was near empty.
why is this so hard to understand? the coolant was pushed out of the overflow when the steam condensed and pressure was reduced, the air moved freely from the top of the coolant tank to the top of the engine area.
this thread is a good one as it takes basic information and relates it to situations that are not so basic....... nothing wrong with discussing it, right?
after all, i can run around town with air in the system and probably with time, it self burps.. dont know. never get to that point. i fill the system and burp it to get the air out. on the track, it seems that if you have air in the system, you could risk overheat... something to check before track time. (not street time)
since there are so many failures of pumps... another one with a new manufacture is not a bad thing. showing pictures of the old pump.. folks saying that rust is proof that impeller slipped.. are are interesting topics. the impeller gap im most interested in.. ive never checked that, but the bad one on the car is barely hitting the block.... it measures at .040" where other pumps i have at home measure around .010" . that's significant.
10-03-2016, 09:00 PM
#114
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If anyone else had started this thread, it would have gone like this:
Post #1: My car overheated...yadda yadda yadda
Post #2: Sounds like a water pump issue
Post #3: I pulled the pump, sure enough, that was the problem. I'll install a new pump / timing belt and be on my way
Thread over
The only difference is your thread took until post #5 for someone to suggest pulling the engine apart.
Sorry Mark, chalk this up as tough love, if we didn't like you we wouldn't bother, but my God......learn to shut-up and listen.
On that note, please tell me you are using a new different timing belt.
10-03-2016, 10:19 PM
#115
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10-04-2016, 01:17 AM
#116
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Mark sounds like you need one of these.....931 106 156 00 Genuine Porsche coolant bleed screw !! about $5.59 depending on where you buy it. Then go see where you fit it and then figure out WHY Porsche used it !!
10-04-2016, 01:44 AM
#117
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10-04-2016, 02:08 AM
#119
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But isn't the reservoir the high point of the 928 coolant system? Isn't that why those silly engineers shoved it into that impossible back corner?
10-04-2016, 02:18 AM
#120
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Yes Jim exactly the point !! Just trying to help Kibort understand that Porsche already had solved the "problem" and used it on all 944 and 968s BECAUSE they needed it !! The 928 did not and still does not BECAUSE the tank is the highest point of the cooling system. It self bleeds the air out especially with the heater hose circuit intact...... Starting to think Kibort just enjoys squeezing his hoses.