Coolant Flow Path Mystery
09-21-2003 | 01:48 PM
#17
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From: Nashua, NH
I predict that locking the rear bypass will not solve the problem. It didn't in my case. I'm currently focusing on my oil cooler, but I THINK Old&New's oil cooler is in his radiator and mine is separate.
We both have oil thermostats.
We both have oil thermostats.
09-22-2003 | 10:50 AM
#18
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From: Southern New England
Dennis,
(New) rear hose is not collapsed; I think this might only occur if the radiator is plugged.
I'm going to check the fan voltage, and procede with the "remove & plug" test. If it doesn't run cool, then it isn't a thermostat issue. I'll then spray the radiator continuously with cold water. If it doesn't run cool, it is most likely a waterpump issue.
(New) rear hose is not collapsed; I think this might only occur if the radiator is plugged.
I'm going to check the fan voltage, and procede with the "remove & plug" test. If it doesn't run cool, then it isn't a thermostat issue. I'll then spray the radiator continuously with cold water. If it doesn't run cool, it is most likely a waterpump issue.
09-22-2003 | 11:39 AM
#19
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From: Nashua, NH
Spraying the radiator with cold water will tell you whether spraying the radiator with cold water will make the car run cooler.
It will NOT tell you whether you've got a radiator or a water pump problem.
It will NOT tell you whether you've got a radiator or a water pump problem.
09-22-2003 | 12:49 PM
#20
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From: Southern New England
Ernest,
Thanks for your help. Let me rephrase.
If the car will not run cool in this condition:
-> thermostat removed, bypass port plugged
-> like-new radiator chilled with 55 F tap water
-> O2 sensor hunting at 0.5v
-> timing belt is tensioned properly
...then there is probably not enough circulation, and I will suspect the water pump may have an issue.
What flaw do you find in this logic?
Thanks for your help. Let me rephrase.
If the car will not run cool in this condition:
-> thermostat removed, bypass port plugged
-> like-new radiator chilled with 55 F tap water
-> O2 sensor hunting at 0.5v
-> timing belt is tensioned properly
...then there is probably not enough circulation, and I will suspect the water pump may have an issue.
What flaw do you find in this logic?
09-22-2003 | 09:22 PM
#21
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From: Wine Country, CA
Turbochargers also have this "radial inflow" characteristic on their turbine section....gasses flow from the circumference, past the impellor "buckets" and then into the center toward the exhaust.
The intake or pumping side has the air entering the center and being pumped to the outside the same as a belt driven supercharger. All conventional radial pumps push from the center towards the outside.
09-22-2003 | 10:00 PM
#22
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From: Southern New England
Good news. Anyone with a cooling problem should take note. Actually, everyone should take note. 
I found ~7V at the fans at ~190F (where they should have ramped up to ~9V). There is a significant difference in the amount of air being moved between these two voltages.
Cleaning the ground point which is located nearest the ballast resistors corrected the problem.
I found ~7V at the fans at ~190F (where they should have ramped up to ~9V). There is a significant difference in the amount of air being moved between these two voltages.
Cleaning the ground point which is located nearest the ballast resistors corrected the problem.
09-22-2003 | 10:09 PM
#23
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From: Nashua, NH
It's interesting to note that highway speeds do not appear to provide enough air flow for adequate cooling without the fans. I would have assumed that your problem would have been worse in city traffic if the fans were the problem. In my case, jumping both fans to 12 volts didn't help.
09-22-2003 | 10:19 PM
#24
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From: Southern New England
Ernest,
The ambient temperature changed a few times over the course of my observations, and may have mislead me a bit. Also, I tie-wrapped the flaps wide open at some point which also affected things.
All-in-all, this was a significant finding which I have not seen mentioned anywhere before & should be checked by anyone who has the problem.
The ambient temperature changed a few times over the course of my observations, and may have mislead me a bit. Also, I tie-wrapped the flaps wide open at some point which also affected things.
All-in-all, this was a significant finding which I have not seen mentioned anywhere before & should be checked by anyone who has the problem.
10-04-2004 | 03:11 AM
#26
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From: Boulder Creek, CA
Originally Posted by WallyP
How about if I look at an official 928 publication instead? (Porsche 928 Service Information, 4582.21)
It says:
"The coolant is forced by the pump (4) into the cylinder block thruogh ports (16), flows around the cylinders and into the cylinder heads through channels (17). After passing through the cylinder head the coolant goes to the thermostat housing (7), in which the thermostat (6) is located.
On a cold engine the thermostat closes the return from the radiator and opens the bypass passage to the pump (4). The coolant recirculates inside the engine.
Once the coolant has reached a temperature of 83 deg C, the thermostat begins to open the radiator return passage (19) to the pump. The bypass passage to the pump is closed more and ore. The coolant now passes through the radiator.
If the heater is turned on, coolant goes from the right cylinder head to the heater core and from there back into the filler line (22) or expansion tank (13). The filler line goes directly from the expansion tank to the thermostat housing."
The diagram clearly shows the coolant entering the radiator through the upper hose, and returning to the thermostat housing through the lower hose. This top-to-bottom flow is the standard flow through the radiator for virtually all cars with vertical tubes.
It isn't possible to make a centrifigual flow pump flow backwards by changine the impeller design or putting one on backwards. Flow is always in the center of the impeller, out at the outer edges.
Your problem may be due to a sticky thermostat. Instead of opening slowly and smoothly, it might be that it hangs shut until the expanding wax in the bulb forces the valve open with a snap.
Wally Plumley
928 Specialists
www.928gt.com
It says:
"The coolant is forced by the pump (4) into the cylinder block thruogh ports (16), flows around the cylinders and into the cylinder heads through channels (17). After passing through the cylinder head the coolant goes to the thermostat housing (7), in which the thermostat (6) is located.
On a cold engine the thermostat closes the return from the radiator and opens the bypass passage to the pump (4). The coolant recirculates inside the engine.
Once the coolant has reached a temperature of 83 deg C, the thermostat begins to open the radiator return passage (19) to the pump. The bypass passage to the pump is closed more and ore. The coolant now passes through the radiator.
If the heater is turned on, coolant goes from the right cylinder head to the heater core and from there back into the filler line (22) or expansion tank (13). The filler line goes directly from the expansion tank to the thermostat housing."
The diagram clearly shows the coolant entering the radiator through the upper hose, and returning to the thermostat housing through the lower hose. This top-to-bottom flow is the standard flow through the radiator for virtually all cars with vertical tubes.
It isn't possible to make a centrifigual flow pump flow backwards by changine the impeller design or putting one on backwards. Flow is always in the center of the impeller, out at the outer edges.
Your problem may be due to a sticky thermostat. Instead of opening slowly and smoothly, it might be that it hangs shut until the expanding wax in the bulb forces the valve open with a snap.
Wally Plumley
928 Specialists
www.928gt.com
Wally, can you post a pic of the diagram you are referring to here?
Thx
10-04-2004 | 04:07 AM
#27
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From: Midland, Texas
And don't forget fun seekers.
At least on the early models, specifically, my Weissach.
If there is a thermostat problem... where flow is restricted to the block, the temp. sensor that
wakes-up the cooling fan doesn't get the word because the over heated water which is now detonating in the block can't pass thru to the sensor.
Hopefully, as in my case, a hose will simply blow off -clamp and all-. Dave, Brett's friend made a jumper from my over equipped parts bag and we jumped from the Batt. jump point to power the fan which was OK. As a temporary repair I just drilled holes thru the thermostat to promote flow.
Although the thermostat came apart in 3 pieces the housing held it all together. Jay provided the DexCool and Temp. sensor location info, while Brett gathered the Creek water which we strained thru a T shirt to mix with the Dex.
The fix lasted for 6 months or so till Dennis prodded me into a new thermostat.
Of interest:
The needle remained below the center line until the hose blew at which point temp. maxed out , low coolant appeared and the pod and master lit up like a christmas tree.
At least on the early models, specifically, my Weissach.
If there is a thermostat problem... where flow is restricted to the block, the temp. sensor that
wakes-up the cooling fan doesn't get the word because the over heated water which is now detonating in the block can't pass thru to the sensor.
Hopefully, as in my case, a hose will simply blow off -clamp and all-. Dave, Brett's friend made a jumper from my over equipped parts bag and we jumped from the Batt. jump point to power the fan which was OK. As a temporary repair I just drilled holes thru the thermostat to promote flow.
Although the thermostat came apart in 3 pieces the housing held it all together. Jay provided the DexCool and Temp. sensor location info, while Brett gathered the Creek water which we strained thru a T shirt to mix with the Dex.
The fix lasted for 6 months or so till Dennis prodded me into a new thermostat.
Of interest:
The needle remained below the center line until the hose blew at which point temp. maxed out , low coolant appeared and the pod and master lit up like a christmas tree.
10-04-2004 | 05:42 AM
#28
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From: Boulder Creek, CA
Er... Thanks John... I don't have any particular issue with my cooling system at this time, having just gone through it soup to nuts... see my last few "Shark Attack" sections on my site.
[Edit]I'm just digging to satisfy my curiosity, to clear up some fuzzy areas I have around the "different" t-stat setup on these cars.[/Edit]
This was just the best explanation of the coolant circuit that I turned up in my search, and I was asking for the accompanying diagram.
You make an interesting point about a failure of the thermostat that keeps hot water from getting to the radiator to activate the fan switch. Though I'm not sure what value there would be in having the fan running, if hot water is not being pumped through the radiator. Sure, having the fan running would cool things down somewhat under those circumstances... but not by a significant amount. Certainly not enough to keep the car running, IMHO
[Edit]I'm just digging to satisfy my curiosity, to clear up some fuzzy areas I have around the "different" t-stat setup on these cars.[/Edit]
This was just the best explanation of the coolant circuit that I turned up in my search, and I was asking for the accompanying diagram.
You make an interesting point about a failure of the thermostat that keeps hot water from getting to the radiator to activate the fan switch. Though I'm not sure what value there would be in having the fan running, if hot water is not being pumped through the radiator. Sure, having the fan running would cool things down somewhat under those circumstances... but not by a significant amount. Certainly not enough to keep the car running, IMHO
10-04-2004 | 11:22 PM
#29
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From: Midland, Texas
Dave,
Didn't bootleg the thread ... just throwing in another quirk of the coolant system, and if I wasn't clear there was NO indication of overheating in that particular situation till the hose blew off.
If you don't get a response on the water path mapping in a week or so E-me -check profile- and I'll xerox a copy of whatever is in the WSM I hope there are sensors in the diagram as well but haven't looked yet.
Later.
Didn't bootleg the thread ... just throwing in another quirk of the coolant system, and if I wasn't clear there was NO indication of overheating in that particular situation till the hose blew off.
If you don't get a response on the water path mapping in a week or so E-me -check profile- and I'll xerox a copy of whatever is in the WSM I hope there are sensors in the diagram as well but haven't looked yet.
Later.
10-05-2004 | 12:58 AM
#30
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From: Boulder Creek, CA
Thanks John, good to know that a couple of drilled holes can limp you home with a t-stat "stuck cold". It's always interesting to hear about the idiosyncracies of these cars, and the weird things they do to express their displeasure of us. 
Anyway, I found what I was looking for... I was just digging in the wrong place. Here are the diagrams; first the full page then the diagrams themselves blown up:
Anyway, I found what I was looking for... I was just digging in the wrong place. Here are the diagrams; first the full page then the diagrams themselves blown up:
