OVERHEAT AT RACE AT THUNDERHILL - WATER PUMP ?
09-26-2016, 12:25 PM
#1
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OVERHEAT AT RACE AT THUNDERHILL - WATER PUMP ?
Had a great weekend at Thunderhill this weekend, right up until the temp gauge started showing the top liine and , at one point, above. backed it down with the power and RPM as oil temps started to climb as well, over 260F.
So, i get in the pits and the fans are both running, but it cant get the temp down from the upper white liine. BUT, the main thing i saw was that there was No pressure in the water hoses..... cap was secure, but was able to open it up with no pressure... BUT, no leaks..
waited as the engine cooled off, and restarted and noticed the pump was making bearing noises. (rememgber , i justs replaced this pump at the beginning of the season with a GEBA)
so, im thinking pump failed, because it souldnt make bearing noise howl. but why no pressure in the system.. usually oveheat means water pressure rises , boils at a much higher temp and then overflows out the tube.. not the case
radiator is hot from top to bottom, so not stuck t-stat. if i clamp the hoses with my hands,it feels like there is flow... could it be the impeller is slipping intermittently..(the very worst condition to diagnose). but then, how does that make the pressure go away.
the most simple cause might be the overflow container cracked or the cap bad, but thats unlikely but will check.
any thoughts and help welcome!!!!
Mark
So, i get in the pits and the fans are both running, but it cant get the temp down from the upper white liine. BUT, the main thing i saw was that there was No pressure in the water hoses..... cap was secure, but was able to open it up with no pressure... BUT, no leaks..
waited as the engine cooled off, and restarted and noticed the pump was making bearing noises. (rememgber , i justs replaced this pump at the beginning of the season with a GEBA)
so, im thinking pump failed, because it souldnt make bearing noise howl. but why no pressure in the system.. usually oveheat means water pressure rises , boils at a much higher temp and then overflows out the tube.. not the case
radiator is hot from top to bottom, so not stuck t-stat. if i clamp the hoses with my hands,it feels like there is flow... could it be the impeller is slipping intermittently..(the very worst condition to diagnose). but then, how does that make the pressure go away.
the most simple cause might be the overflow container cracked or the cap bad, but thats unlikely but will check.
any thoughts and help welcome!!!!
Mark
09-26-2016, 12:44 PM
#2
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I believe it was like 102 degrees there Yesterday. And you have no real oil cooler just the heat exchanger in the radiator which in your case had 260 degree oil heating the coolant. The exchanger goes BOTH ways 
But bearing noises from the water pump are never a good thing. I would agree that you should have had pressure in the coolant system with things that hot. Any signs of oil /water intermix ?
But bearing noises from the water pump are never a good thing. I would agree that you should have had pressure in the coolant system with things that hot. Any signs of oil /water intermix ?
09-26-2016, 12:58 PM
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I believe it was like 102 degrees there Yesterday. And you have no real oil cooler just the heat exchanger in the radiator which in your case had 260 degree oil heating the coolant. The exchanger goes BOTH ways But bearing noises from the water pump are never a good thing. I would agree that you should have had pressure in the coolant system with things that hot. Any signs of oil /water intermix ?
But bearing noises from the water pump are never a good thing. I would agree that you should have had pressure in the coolant system with things that hot. Any signs of oil /water intermix ?what do you think could cause loss of pressure.. could the pump being bad do this? the bearing noise is just too coicidntal that i have a problem with overheat too. dont know if i want to run the car to test, incase that pump has given way and the impeller is grinding on the block. ive never had that happen but scot has . the noise is the characteristic howel at the water pump and then with a quick blip, it instantly goes away. then comes back. cant tell if it is the pump impeller spinning and then not spinning.
09-26-2016, 01:09 PM
#4
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09-26-2016, 01:18 PM
#5
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I can't think of anything that would cause lack of pressure at high temps, other than venting somewhere. And I would think that a vent, anywhere except the top of the reservoir, would be venting water and not vapor. So assuming the water level did not also drop, then that points to the pressure cap or the two small hoses that come off the top of the reservoir.
Which of course has nothing to do with the pump making noise. But that, plus the sudden overheating, is a pretty loud message to break out the wrenches. Something is wrong, and debating possible causes won't fix it.
Which of course has nothing to do with the pump making noise. But that, plus the sudden overheating, is a pretty loud message to break out the wrenches. Something is wrong, and debating possible causes won't fix it.
09-26-2016, 01:48 PM
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I can't think of anything that would cause lack of pressure at high temps, other than venting somewhere. And I would think that a vent, anywhere except the top of the reservoir, would be venting water and not vapor. So assuming the water level did not also drop, then that points to the pressure cap or the two small hoses that come off the top of the reservoir.
Which of course has nothing to do with the pump making noise. But that, plus the sudden overheating, is a pretty loud message to break out the wrenches. Something is wrong, and debating possible causes won't fix it.
Which of course has nothing to do with the pump making noise. But that, plus the sudden overheating, is a pretty loud message to break out the wrenches. Something is wrong, and debating possible causes won't fix it.
good point about the reservior, so i guess i should presureize it to find a leak there. cant believe its the cap, but ive had the reservior crack before.
BUT, even if it did crack, why didnt it boil over when hot and force fluild out the overflow? boiling point would go down, water should boil and then force itself out the overfllow...
09-26-2016, 02:30 PM
#7
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Mark,
If you had no pressure in the coolant system then the coolant was not overheating or it would have boiled so something in your description of events does not quite add up.
At atmospheric pressure the coolant mix will boil somewhere in the region of 105 degrees C [about 220F]. Quite a few folks have seen that even with no pressure seal the coolant did not boil though on a race track one might expect the system to be somewhat pushed. That your temperature gauge went up is understandable especially if the coolant level dropped [due to a small leak] and the radiator ended up not fully flooded. A 928 running hard in hot weather will take the coolant to the last white line or slightly over and on a factory setup can go to towards the red zone. If like me you have a bigger radiator or a lean coolant mix [20%] with say Redline water wetter the needle should stay a bit lower.
As to the noisy pump maybe the bearing has gone and taken the seal with it [the leak path?]. It may not be leaking buckets full but a very slight leak will suppress build up of pressure. Suggest you knock up a hydro test at 15 psig and see if the cooling circuit holds pressure [I doubt it will]. If it is not holding pressure try to ascertain where it is leaking from. The leak path should be more obvious with pressure driving it.
By the way if there is no pressure the coolant temperature does not go up as the coolant boils at a fixed temperature. Once you get to that temperature the liquid boils. If the system is holding pressure the coolant temperature can increase without boiling taking place [that is what is supposed to happen]. experience suggests that even with no pressure, the temperature can rise close to the redline and boiling does not take place but it must be damm close to it by then.
Trust the above helpful.
If you had no pressure in the coolant system then the coolant was not overheating or it would have boiled so something in your description of events does not quite add up.
At atmospheric pressure the coolant mix will boil somewhere in the region of 105 degrees C [about 220F]. Quite a few folks have seen that even with no pressure seal the coolant did not boil though on a race track one might expect the system to be somewhat pushed. That your temperature gauge went up is understandable especially if the coolant level dropped [due to a small leak] and the radiator ended up not fully flooded. A 928 running hard in hot weather will take the coolant to the last white line or slightly over and on a factory setup can go to towards the red zone. If like me you have a bigger radiator or a lean coolant mix [20%] with say Redline water wetter the needle should stay a bit lower.
As to the noisy pump maybe the bearing has gone and taken the seal with it [the leak path?]. It may not be leaking buckets full but a very slight leak will suppress build up of pressure. Suggest you knock up a hydro test at 15 psig and see if the cooling circuit holds pressure [I doubt it will]. If it is not holding pressure try to ascertain where it is leaking from. The leak path should be more obvious with pressure driving it.
By the way if there is no pressure the coolant temperature does not go up as the coolant boils at a fixed temperature. Once you get to that temperature the liquid boils. If the system is holding pressure the coolant temperature can increase without boiling taking place [that is what is supposed to happen]. experience suggests that even with no pressure, the temperature can rise close to the redline and boiling does not take place but it must be damm close to it by then.
Trust the above helpful.
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09-26-2016, 02:44 PM
#9
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Thread Starter
Mark,
If you had no pressure in the coolant system then the coolant was not overheating or it would have boiled so something in your description of events does not quite add up.
At atmospheric pressure the coolant mix will boil somewhere in the region of 105 degrees C [about 220F]. Quite a few folks have seen that even with no pressure seal the coolant did not boil though on a race track one might expect the system to be somewhat pushed. That your temperature gauge went up is understandable especially if the coolant level dropped [due to a small leak] and the radiator ended up not fully flooded. A 928 running hard in hot weather will take the coolant to the last white line or slightly over and on a factory setup can go to towards the red zone. If like me you have a bigger radiator or a lean coolant mix [20%] with say Redline water wetter the needle should stay a bit lower.
As to the noisy pump maybe the bearing has gone and taken the seal with it [the leak path?]. It may not be leaking buckets full but a very slight leak will suppress build up of pressure. Suggest you knock up a hydro test at 15 psig and see if the cooling circuit holds pressure [I doubt it will]. If it is not holding pressure try to ascertain where it is leaking from. The leak path should be more obvious with pressure driving it.
By the way if there is no pressure the coolant temperature does not go up as the coolant boils at a fixed temperature. Once you get to that temperature the liquid boils. If the system is holding pressure the coolant temperature can increase without boiling taking place [that is what is supposed to happen]. experience suggests that even with no pressure, the temperature can rise close to the redline and boiling does not take place but it must be damm close to it by then.
Trust the above helpful.
If you had no pressure in the coolant system then the coolant was not overheating or it would have boiled so something in your description of events does not quite add up.
At atmospheric pressure the coolant mix will boil somewhere in the region of 105 degrees C [about 220F]. Quite a few folks have seen that even with no pressure seal the coolant did not boil though on a race track one might expect the system to be somewhat pushed. That your temperature gauge went up is understandable especially if the coolant level dropped [due to a small leak] and the radiator ended up not fully flooded. A 928 running hard in hot weather will take the coolant to the last white line or slightly over and on a factory setup can go to towards the red zone. If like me you have a bigger radiator or a lean coolant mix [20%] with say Redline water wetter the needle should stay a bit lower.
As to the noisy pump maybe the bearing has gone and taken the seal with it [the leak path?]. It may not be leaking buckets full but a very slight leak will suppress build up of pressure. Suggest you knock up a hydro test at 15 psig and see if the cooling circuit holds pressure [I doubt it will]. If it is not holding pressure try to ascertain where it is leaking from. The leak path should be more obvious with pressure driving it.
By the way if there is no pressure the coolant temperature does not go up as the coolant boils at a fixed temperature. Once you get to that temperature the liquid boils. If the system is holding pressure the coolant temperature can increase without boiling taking place [that is what is supposed to happen]. experience suggests that even with no pressure, the temperature can rise close to the redline and boiling does not take place but it must be damm close to it by then.
Trust the above helpful.
the hoses were soft, and removing the cap at any thing close to mid line, usually results in boil over in normal conditions. so maybe the water wasnt that hot , but the sensor was because it was void of water?
(not circulating).... like air in the lines.
i hand bled the system as it cooled and filled the hoses by doing so. .level not too low , so its got to be a slow leak somehwere that i didnt notice... the cap or a crack reservior or maybe a small leak at the pump... especially since its making noise. intermittantly... i can rev the engine and it goes away, rev it again and it comes back. that water pump howl.
so, im over heating, but there is no pressure .. maybe it was just shy of boiling over, which is a good sign, but also , the temps might have been higher, but not registering at the sensor due to the air bubbles in that area due to some localized boiling or air in the system.
09-26-2016, 03:30 PM
#10
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Mark,
If the system cannot build pressure then as the coolant approaches or reaches boiling point the liquid will start to film boil on the outside of the cylinder wall. When this happens the fluid entering the pump will invariably cavitate, a concept that I will not try to decribe here but its outward symptom is a "pinging" sound . This is basically caused by very small particles of liquid being accelerated to sonic velcoity as the liquid breaks down and is replaced by the vapour phase. The force the particles travel with rapidly destroys metal surfaces and in the case of a pump it is usually the impeller that gets destroyed. As the engine speeds up the pump needs more nett positive suction head to prevent cavitation and in a marginal system as you rev the motor and flow increases cavitation can and will take place at some point if the liquid is at or near to boiling point. Whether or not this is what you were hearing I do not know. On big pumps that I used to deal with [5MW] it is very pronounced but I have not experienced such on a 928 water pump. If you do a pressure test on the system and does not hold pressure then the above might explain what was going on.
Regards
Fred
If the system cannot build pressure then as the coolant approaches or reaches boiling point the liquid will start to film boil on the outside of the cylinder wall. When this happens the fluid entering the pump will invariably cavitate, a concept that I will not try to decribe here but its outward symptom is a "pinging" sound . This is basically caused by very small particles of liquid being accelerated to sonic velcoity as the liquid breaks down and is replaced by the vapour phase. The force the particles travel with rapidly destroys metal surfaces and in the case of a pump it is usually the impeller that gets destroyed. As the engine speeds up the pump needs more nett positive suction head to prevent cavitation and in a marginal system as you rev the motor and flow increases cavitation can and will take place at some point if the liquid is at or near to boiling point. Whether or not this is what you were hearing I do not know. On big pumps that I used to deal with [5MW] it is very pronounced but I have not experienced such on a 928 water pump. If you do a pressure test on the system and does not hold pressure then the above might explain what was going on.
Regards
Fred
Last edited by FredR; 09-26-2016 at 04:47 PM. Reason: Brain fart in last sentence
09-26-2016, 03:49 PM
#11
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Thread Starter
Mark,
If the system cannot build pressure then as the coolant approaches or reaches boiling point the liquid will start to film boil on the outside of the cylinder wall. When this happens the fluid entering the pump will invariably cavitate, a concept that I will not try to decribe here but its outward symptom is a "pinging" sound . This is basically caused by very small particles of liquid being accelerated to sonic velcoity as the liquid breaks down and is replaced by the vapour phase. The force the particles travel with rapidly destroys metal surfaces and in the case of a pump it is usually the impeller that gets destroyed. As the engine speeds up the pump needs more nett positive suction head to prevent cavitation and in a marginal system as you rev the motor and flow increases cavitation can and will take place at some point if the liquid is at or near to boiling point. Whether or not this is what you were hearing I do not know. On big pumps that I used to deal with [5MW] it is very pronounced but I have not experienced such on a 928 water pump. If you do a pressure test on the system and it holds pressure then the above might explain what was going on.
Regards
Fred
If the system cannot build pressure then as the coolant approaches or reaches boiling point the liquid will start to film boil on the outside of the cylinder wall. When this happens the fluid entering the pump will invariably cavitate, a concept that I will not try to decribe here but its outward symptom is a "pinging" sound . This is basically caused by very small particles of liquid being accelerated to sonic velcoity as the liquid breaks down and is replaced by the vapour phase. The force the particles travel with rapidly destroys metal surfaces and in the case of a pump it is usually the impeller that gets destroyed. As the engine speeds up the pump needs more nett positive suction head to prevent cavitation and in a marginal system as you rev the motor and flow increases cavitation can and will take place at some point if the liquid is at or near to boiling point. Whether or not this is what you were hearing I do not know. On big pumps that I used to deal with [5MW] it is very pronounced but I have not experienced such on a 928 water pump. If you do a pressure test on the system and it holds pressure then the above might explain what was going on.
Regards
Fred
im betting, like you said, the boiling created some air pockets and that caused cavitation or just lack of positive pressure.
what i was hearing was actual bearing noise, but maybe it was just the pump running dry. usually , the noise that i was hearing, sounded like a dry pump impeeller spinning. usually that water in the system damps the noise a little too.
09-26-2016, 04:02 PM
#12
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Given that water expands some 1,700 times when it boils there should have been LOTS of pressure if there was any boiling . And you run water only ?? any lubricant for the bearings / seals ?
09-26-2016, 04:21 PM
#13
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in the pits, with the egine running.. the hoses felt like they were not filled with water. very easy to squish, and i felt some flow, but not much. this am i went out to the cold car, birped the systema saw that i lost about half gallon in the overflow.. still fillled to about half way. the plastic contaner looks good but there might be some small cracks i cant tell if cracks or the lines from the manufacturing molds. i need to rent one of those pressure testers and see for sure. if thats it, then i can stop cursing the water pump. that makes sense.... no pressure, water starts to boil locally. flow stops , or is reduced and by the time it gets to the radiator which is working, it cools and stops the boiling .
good theory??
09-26-2016, 04:24 PM
#14
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Mark, Instead of trying to fully diagnose every potential why not just focus on the obvious one, the bearing noise in the WP. If they are making noise the pump needs to be replaced regardless, no? I would start there.
What does a simple pressure test indicate? If there is parasitic fluid loss that will show up on the pressure gauge. If there is pressure loss, then trace it from there.
Harbor Freight has a radiator pressure testing kit for $79 usd http://www.harborfreight.com/catalog...ressure+tester
What does a simple pressure test indicate? If there is parasitic fluid loss that will show up on the pressure gauge. If there is pressure loss, then trace it from there.
Harbor Freight has a radiator pressure testing kit for $79 usd http://www.harborfreight.com/catalog...ressure+tester
Last edited by S4ordie; 09-26-2016 at 04:27 PM. Reason: RE pressure tester - our posts crossed in the ether.
09-26-2016, 04:36 PM
#15
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Mark, Instead of trying to fully diagnose every potential why not just focus on the obvious one, the bearing noise in the WP. If they are making noise the pump needs to be replaced regardless, no? I would start there.
What does a simple pressure test indicate? If there is parasitic fluid loss that will show up on the pressure gauge. If there is pressure loss, then trace it from there.
Harbor Freight has a radiator pressure testing kit for $79 usd http://www.harborfreight.com/catalog...ressure+tester
What does a simple pressure test indicate? If there is parasitic fluid loss that will show up on the pressure gauge. If there is pressure loss, then trace it from there.
Harbor Freight has a radiator pressure testing kit for $79 usd http://www.harborfreight.com/catalog...ressure+tester
does anyone know if you can hear pump impleller grinding on the block? that might only happen at high RPM as i recall, we counldnt hear that on Scots car, but he got some nice grooves in his block. we didnt fix them, as it ran cool afterwards with a new pump. (i would think the impeller is pulled forward when is spinning fast and pulling water.)