Yet another overheating problem
10-12-2015, 11:21 AM
#31
Chronic Tool Dropper
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So a couple members are experiemcing similar symptoms but looking at different possible causes.
NOTAGURU: The cooling system in the 928 depends on the thermostat to modulate flow through the radiator, similar to what one might expect in a "conventional" cooling system. In that "conventional" system, there's functionally a minimum flow bypass line around the thermostat, sometimes in the form of a short hose, sometimes in the form of a small passage. With the Reynolds block in the 928, the thermostat actually modulates that bypass flow, so that full coolant circulation is maintained through the block when coolant temps are lower. This prevents uneven heating of the block, looking specifically at avoiding hot-spotting at the tops of the cylinders and the heads. Removing the thermostat causes almost all the flowing coolant to take the path of least resistance to flow, recirculatiing through the block. To maintain flow through the radiator, you MUST come up with a method for blocking the bypass port that's directly to the rear of the thermostat housing area of the water bridge. Without that, the engine will warm up nicely and continue to warm up until it overheats, since there is virtually no coolant being directed to the radiator. While it's possible to block that recirculation port with something, Porsche supplied an automatic flow metering valve arrangement for that purpose, with the flow bias based on coolant temperature. I recomend that you use the Porsche method or risk damage to the engine from overheating. Unless anduntil you have a complete understanding of the thermostat's function managing coolant circulation in the 928, DO NOT DRIVE THE CAR WITH THE THERMOSTAT REMOVED.
GAZ: The 1989 car uses a combination ov variable-speed fans, variable-position flaps in the front grill, and the modulating thermostat to control coolant temperature. The fans and flaps work in concert to make sure that the temperature of the returning coolant is low enough for the thermostat to do the final trimming on flow needed to accurately control temperature in the block. It's a system far ahead of its time, considering we are seeing similar flap systems appear only lately on more common production cars. Porsche abandoned the flaps in later S4 cars though. Many owners who are experiencing heating at speed problems disable the flap controller (pull the fuse) while the car is engine-off and the flaps are relaxed in the open position. Some go to the extreme of removing the flaps completely.
The operation of the fans and flaps is completely documented in the workshop manuals, and I'm not going to try and describe here the temperature charts and function descriptions in the WSM. I do recommend that you read that section, and take advantage of the troubleshooting methods if you don't have correct functons. Since you are experiencing problems with heating at speed, fan operation is less likely to be a factor. However, flaps stuck in a not-full-open position could easily cause the symptom.
NOTAGURU: The cooling system in the 928 depends on the thermostat to modulate flow through the radiator, similar to what one might expect in a "conventional" cooling system. In that "conventional" system, there's functionally a minimum flow bypass line around the thermostat, sometimes in the form of a short hose, sometimes in the form of a small passage. With the Reynolds block in the 928, the thermostat actually modulates that bypass flow, so that full coolant circulation is maintained through the block when coolant temps are lower. This prevents uneven heating of the block, looking specifically at avoiding hot-spotting at the tops of the cylinders and the heads. Removing the thermostat causes almost all the flowing coolant to take the path of least resistance to flow, recirculatiing through the block. To maintain flow through the radiator, you MUST come up with a method for blocking the bypass port that's directly to the rear of the thermostat housing area of the water bridge. Without that, the engine will warm up nicely and continue to warm up until it overheats, since there is virtually no coolant being directed to the radiator. While it's possible to block that recirculation port with something, Porsche supplied an automatic flow metering valve arrangement for that purpose, with the flow bias based on coolant temperature. I recomend that you use the Porsche method or risk damage to the engine from overheating. Unless anduntil you have a complete understanding of the thermostat's function managing coolant circulation in the 928, DO NOT DRIVE THE CAR WITH THE THERMOSTAT REMOVED.
GAZ: The 1989 car uses a combination ov variable-speed fans, variable-position flaps in the front grill, and the modulating thermostat to control coolant temperature. The fans and flaps work in concert to make sure that the temperature of the returning coolant is low enough for the thermostat to do the final trimming on flow needed to accurately control temperature in the block. It's a system far ahead of its time, considering we are seeing similar flap systems appear only lately on more common production cars. Porsche abandoned the flaps in later S4 cars though. Many owners who are experiencing heating at speed problems disable the flap controller (pull the fuse) while the car is engine-off and the flaps are relaxed in the open position. Some go to the extreme of removing the flaps completely.
The operation of the fans and flaps is completely documented in the workshop manuals, and I'm not going to try and describe here the temperature charts and function descriptions in the WSM. I do recommend that you read that section, and take advantage of the troubleshooting methods if you don't have correct functons. Since you are experiencing problems with heating at speed, fan operation is less likely to be a factor. However, flaps stuck in a not-full-open position could easily cause the symptom.
10-12-2015, 11:33 AM
#32
Rennlist Member
Thanks for the thermostat explanation, Dr. Bob.
The OP car is an 83. No flaps, just an auxiliary front pusher fan. There is also some question whether the crank driven fan is working properly. A quarter turn when hot sounds like a failing viscous clutch, which the OP chose to refill. This may or may not work. There is no mention of whether the auxiliary fan is working, so her may have very little air movement. Just an idea.
Dave
The OP car is an 83. No flaps, just an auxiliary front pusher fan. There is also some question whether the crank driven fan is working properly. A quarter turn when hot sounds like a failing viscous clutch, which the OP chose to refill. This may or may not work. There is no mention of whether the auxiliary fan is working, so her may have very little air movement. Just an idea.
Dave
10-12-2015, 12:04 PM
#33
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Dr Bob - THANKS for the clarity. Trust Stuttgart to find ways to complexify a simple system that has worked well for almost a hundred years. But perhaps Porsche's method works better in this not-so-simple engine...
This week my new2me supercar will go on the DIY rack. The plan is to drain and replace oil, coolant, brake fluid, PS fluid (that'll take a while), auto transmission. I'll also inspect all bushings, look for leaks (garage floor says there aren't any), etc.
The car has 68k miles now, and despite the lack of documentation it shows evidence of proper maintenance. Its life has been spent in San Diego, where the only weather excitement is on the news.
At the risk of triggering an avalanche, I plan to use dino 30W oil and a Fram filter for a few miles, then refill with (5-50 or 20-50) synthetic with a proper Mann or Mahle filter.
The cooling... I think it's improved since adding fluid to the viscous coupling, and Water Wetter to the coolant. If the problem persists, I'll pull the radiator (which looks new, and there is no detritus at the bottom). And if that doesn't do it, I suppose the pump is next.
This week my new2me supercar will go on the DIY rack. The plan is to drain and replace oil, coolant, brake fluid, PS fluid (that'll take a while), auto transmission. I'll also inspect all bushings, look for leaks (garage floor says there aren't any), etc.
The car has 68k miles now, and despite the lack of documentation it shows evidence of proper maintenance. Its life has been spent in San Diego, where the only weather excitement is on the news.
At the risk of triggering an avalanche, I plan to use dino 30W oil and a Fram filter for a few miles, then refill with (5-50 or 20-50) synthetic with a proper Mann or Mahle filter.
The cooling... I think it's improved since adding fluid to the viscous coupling, and Water Wetter to the coolant. If the problem persists, I'll pull the radiator (which looks new, and there is no detritus at the bottom). And if that doesn't do it, I suppose the pump is next.
10-12-2015, 12:57 PM
#34
Rennlist Member
notaguru, even though we have very different cooling systems, I will keep this thread up to date with what I test and find and learn on my car. Hopefully we have a common problem and can help each other...
10-12-2015, 01:27 PM
#35
Team Owner
Gaz FWIW I was working on a 87 that was experiencing the heat build up issue and I went through everything, new thermostat, new water pump new radiator, everything to do with the cooling system was replaced, and it worked great most of the time.
The only time it wouldnt work well was when the driver went up the mountain to his home.
The next step was going to be pull the heads,
and swap in new HGs and inspect the heads for cracks.
The end to this story was the owner found a good running GT engine from a wrecked car and had me swap that into the car, this fixed the problem .
The only time it wouldnt work well was when the driver went up the mountain to his home.
The next step was going to be pull the heads,
and swap in new HGs and inspect the heads for cracks.
The end to this story was the owner found a good running GT engine from a wrecked car and had me swap that into the car, this fixed the problem .
10-12-2015, 01:30 PM
#36
Rennlist Member
Dr Bob - THANKS for the clarity. Trust Stuttgart to find ways to complexify a simple system that has worked well for almost a hundred years. But perhaps Porsche's method works better in this not-so-simple engine...
This week my new2me supercar will go on the DIY rack. The plan is to drain and replace oil, coolant, brake fluid, PS fluid (that'll take a while), auto transmission. I'll also inspect all bushings, look for leaks (garage floor says there aren't any), etc.
The car has 68k miles now, and despite the lack of documentation it shows evidence of proper maintenance. Its life has been spent in San Diego, where the only weather excitement is on the news.
At the risk of triggering an avalanche, I plan to use dino 30W oil and a Fram filter for a few miles, then refill with (5-50 or 20-50) synthetic with a proper Mann or Mahle filter.
The cooling... I think it's improved since adding fluid to the viscous coupling, and Water Wetter to the coolant. If the problem persists, I'll pull the radiator (which looks new, and there is no detritus at the bottom). And if that doesn't do it, I suppose the pump is next.
This week my new2me supercar will go on the DIY rack. The plan is to drain and replace oil, coolant, brake fluid, PS fluid (that'll take a while), auto transmission. I'll also inspect all bushings, look for leaks (garage floor says there aren't any), etc.
The car has 68k miles now, and despite the lack of documentation it shows evidence of proper maintenance. Its life has been spent in San Diego, where the only weather excitement is on the news.
At the risk of triggering an avalanche, I plan to use dino 30W oil and a Fram filter for a few miles, then refill with (5-50 or 20-50) synthetic with a proper Mann or Mahle filter.
The cooling... I think it's improved since adding fluid to the viscous coupling, and Water Wetter to the coolant. If the problem persists, I'll pull the radiator (which looks new, and there is no detritus at the bottom). And if that doesn't do it, I suppose the pump is next.
Dave
10-12-2015, 02:04 PM
#37
Rennlist Member
Plus..its a -better- design, in no way more complicated at all. Regulating flow to meet a temperature goal done better.
The thermostat still costs the same..no additional parts.
And still following the same rule..if it has a thermostat, you give it a thermostat. Simplez.
10-12-2015, 02:07 PM
#38
Rennlist Member
Your camshaft lobes _really_ wont like that.
Use the recommended grade of oil and make sure it has a high zinc content for the old style flat tappets.
Pitting and shearing metal off the lobes is what happens with the wrong grade and low (no) zinc oils.
10-12-2015, 02:49 PM
#39
Rennlist Member
Gaz FWIW I was working on a 87 that was experiencing the heat build up issue and I went through everything, new thermostat, new water pump new radiator, everything to do with the cooling system was replaced, and it worked great most of the time.
The only time it wouldnt work well was when the driver went up the mountain to his home.
The next step was going to be pull the heads,
and swap in new HGs and inspect the heads for cracks.
The end to this story was the owner found a good running GT engine from a wrecked car and had me swap that into the car, this fixed the problem .
The only time it wouldnt work well was when the driver went up the mountain to his home.
The next step was going to be pull the heads,
and swap in new HGs and inspect the heads for cracks.
The end to this story was the owner found a good running GT engine from a wrecked car and had me swap that into the car, this fixed the problem .
Now I'm just ITCHING to get it back so I can wring it out and the check fan & flap operation. Still waiting on the ABS relay though. And now the CS has to go in for new shows and tech inspectioon tomorrow, so there will be some heavy duty car juggling going on in my neck of the woods...
Is my theory that "if it has deposits in the radiator then it probably has deposits in the cooling channels" sound? Both are aluminum and therefore would attract the same kinds of deposits.
10-12-2015, 03:30 PM
#40
Chronic Tool Dropper
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Dr Bob - THANKS for the clarity. Trust Stuttgart to find ways to complexify a simple system that has worked well for almost a hundred years. But perhaps Porsche's method works better in this not-so-simple engine...
This week my new2me supercar will go on the DIY rack. The plan is to drain and replace oil, coolant, brake fluid, PS fluid (that'll take a while), auto transmission. I'll also inspect all bushings, look for leaks (garage floor says there aren't any), etc.
The car has 68k miles now, and despite the lack of documentation it shows evidence of proper maintenance. Its life has been spent in San Diego, where the only weather excitement is on the news.
At the risk of triggering an avalanche, I plan to use dino 30W oil and a Fram filter for a few miles, then refill with (5-50 or 20-50) synthetic with a proper Mann or Mahle filter.
The cooling... I think it's improved since adding fluid to the viscous coupling, and Water Wetter to the coolant. If the problem persists, I'll pull the radiator (which looks new, and there is no detritus at the bottom). And if that doesn't do it, I suppose the pump is next.
This week my new2me supercar will go on the DIY rack. The plan is to drain and replace oil, coolant, brake fluid, PS fluid (that'll take a while), auto transmission. I'll also inspect all bushings, look for leaks (garage floor says there aren't any), etc.
The car has 68k miles now, and despite the lack of documentation it shows evidence of proper maintenance. Its life has been spent in San Diego, where the only weather excitement is on the news.
At the risk of triggering an avalanche, I plan to use dino 30W oil and a Fram filter for a few miles, then refill with (5-50 or 20-50) synthetic with a proper Mann or Mahle filter.
The cooling... I think it's improved since adding fluid to the viscous coupling, and Water Wetter to the coolant. If the problem persists, I'll pull the radiator (which looks new, and there is no detritus at the bottom). And if that doesn't do it, I suppose the pump is next.
Once on the DIY 'rack' and you start changing fluids, a reminder that the block includes two galley drains that MUST be opened to get everything out below the water pump center. The drains are actually bolts that thread into bosses in the block adjacent to the motor mounts, with aluminum sealing washers. The factory torque spec is way overtight for the duty, so owners are recommended to add a little TFE thread sealing paste to the bolts and the washers, then tighten to 16lbs/ft. Since the original bolt torque was excessive, you'll want to use a 6-point socket and a long-handled ratchet or bar to break them loose initially. Acess is less than ideal I'm afraid, but things are much easier when the car is up high enough to see what you are doing.
Coolant choice is just south of motor oil choice in the debate schedule. The Zerex G-05 coolant spec'd for the cars is generally available at CarQuest stores in California, from Roger at 928srus, and from online sources such as Amazon. Be sure to flush all the old green coolant out before adding new. The aluminum is sensitive to reaction components and mineral deposits, so use distilled water only as the make-up fluid with the coolant. The Water Wetter is Good Idea in my experience. If the car will never see anything cold, one gallon of the coolant will be 25% concentrate, plus the Water Wetter, and a little over three gallons of distilled water. Guru Greg Brown recommends a blue Porsche-branded coolant, and his recommendations generall carry more weight than mine.
Your proposal to do an initial oil fill with "5-50 or 20-50" I'll assume is a typo. The minimum especially in your always-warm climate would be 15w-50 synthetic or a 20w-50 conventional or synthetic oil even for your 'maintenance flush'. The 'what brand' discussion will be left to others. I use M-1 15W-50 in 5-qt bottles from Wal-Mart with no issues in a street-only car that did regular-driver duty in the Los Angeles/OC area for 15+ years under my stewardship.
With all the coolant out, consider pulling or at least inspecting the radiator bottom tubes with a mirror or inspection camera. Removing allows you a better look, and the opportunity to clean out the accumulated debris that finds its way into the fins and the cavity behind the AC condenser. Debris there is right up there on the list of possible causes of your symptoms, so removal should be considered while everything is so handy/convenient.
Power steering service includes replacing the filter/reservoir. These are ZF reservoirs somewhat common on Euro cars of the period, so are not expensive. Unless you are doing an active flush, you'll need sealing washers for the banjo bolts at the rack where the hoses connect.
-----
Invest in at least the CD set of workshop manuals. They are available from 928srus in a set that includes technical publications, etc. Worth the money from the first mistake that they help you avoid. Your 928 isn't the same as 'common' imports, with just enough particular requirements to make the manual set a very worthwhile investment. And if you don't have a set of good torque wrenches already, invest now against future savings. With all the relaively particular aluminum bits on the car, these are much more reliable than "that's not goin' anywhere!" or the 'tighten until you just start to feel the bolt stretch' tight.
Invest in Rennlist membership too. I daresay the value you receive will cover the cost many times over in teh first year alone. We've already saved you an engine cost by keeping a thermostat in the crossover. Membership allows you to add a sig line that includes the year/model in every post so you don't have to remember to type it every time. It also bypass a lot of the pop-up and inserted ads that RL needs to share with you to cover your costs when you don't pay.
Oh, and welcome to the group! Post pics when you get a chance, we all live vicariously trough the writings and sharings of others here. Madness is easier to endure when you are in a ward with others at least as mad as you.
10-12-2015, 08:03 PM
#41
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More information...
I found more history on the car. A treasure trove of documents was cleverly concealed in an unlikely place*. If the original owner's logbook can be believed, the car WAS regularly driven and properly serviced from birth on 4APR83 until it moved from Reno, NV to S California in 1990. Between then and now it was less regularly driven and serviced. In the weeks preceding my purchase, it got a 20W50 Castrol oil change plus some other work. I'm happier. It still runs hot, but ambient temps are dropping so it's staying in range. I can defer the diagnostics, and focus upon other things. Hopefully.
SPECIFIC QUESTIONS from Gaz
notaguru - questions....
1) do you also build heat with the AC off but running high revs (ir, 4k and over during "sporting" driving)? YES
2) will the engine temp climbstop or reverse itself if you leave the AC on but turn the system to blow heat too? DOES NOT CHANGE. WITH A/C OFF AND HEATER ON, TEMP IS NO PROBLEM.
Thanks!
Not a guru
*glove compartment.
GLOVE COMPARTMENT! Whoda thunkit?
I found more history on the car. A treasure trove of documents was cleverly concealed in an unlikely place*. If the original owner's logbook can be believed, the car WAS regularly driven and properly serviced from birth on 4APR83 until it moved from Reno, NV to S California in 1990. Between then and now it was less regularly driven and serviced. In the weeks preceding my purchase, it got a 20W50 Castrol oil change plus some other work. I'm happier. It still runs hot, but ambient temps are dropping so it's staying in range. I can defer the diagnostics, and focus upon other things. Hopefully.
SPECIFIC QUESTIONS from Gaz
notaguru - questions....
1) do you also build heat with the AC off but running high revs (ir, 4k and over during "sporting" driving)? YES
2) will the engine temp climbstop or reverse itself if you leave the AC on but turn the system to blow heat too? DOES NOT CHANGE. WITH A/C OFF AND HEATER ON, TEMP IS NO PROBLEM.
Thanks!
Not a guru
*glove compartment.
GLOVE COMPARTMENT! Whoda thunkit?
10-14-2015, 06:37 PM
#42
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An IR gun sees a 50degF difference between the TOP of the radiator and the BOTTOM. Though the cooling system was flushed 30k miles ago, it appears that it's accumulated scaling, etc.
This weekend I'll pull the radiator. A local shop claims to be expert in disassembling, cleaning, and etc. Hopefully that will fix my overheating problem.
Others with this issue might do the same check.
Meanwhile, ideas are welcome.
This weekend I'll pull the radiator. A local shop claims to be expert in disassembling, cleaning, and etc. Hopefully that will fix my overheating problem.
Others with this issue might do the same check.
Meanwhile, ideas are welcome.
10-14-2015, 07:26 PM
#43
Rennlist Member
Well... I just got my car back from my wrench today, so I immediately turned on the A/C, drove it until the engine temp came up, downshifted TWO gears and ripped up a certain usually-deserted (very) local road with some very nice sweeper until the temp needle got to the upper mark, then drive hime in low gear & high revs, stopped in the driveway and popped the hood to see....
...only my auxilliary fan (on the passenger side) turning!
Ladies and gentlemen, we have a diagnosis!!! In my excitement and exhiliration I neglected to test anything else about the problem, whether the main fan turns on when the aux is off, or anything useful like that. I will check whether it runs without the A/C on when the engine is at normal temps, and if not, will check whether it runs at all with 12V applied to it directly, then proceed from there based on the empirical observation and rational consideration. But in the meantime...
:thu mbsup:
...only my auxilliary fan (on the passenger side) turning!
Ladies and gentlemen, we have a diagnosis!!! In my excitement and exhiliration I neglected to test anything else about the problem, whether the main fan turns on when the aux is off, or anything useful like that. I will check whether it runs without the A/C on when the engine is at normal temps, and if not, will check whether it runs at all with 12V applied to it directly, then proceed from there based on the empirical observation and rational consideration. But in the meantime...
:thu mbsup:
10-14-2015, 08:22 PM
#44
Chronic Tool Dropper
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Your statement that the system was flushed 30k ago yet is accumulating scaling sparks the next question: How many miles and how long since the coolant was last changed? The comment about scaling in particular has my curiosity. Coolant has perhaps a 2-year useful life in the aluminum 928 block, even the magic coolants that carry a "5-year protection" banner on the label. A pH test (swimming pool tester is OK if you have one) and a visual test will guide you, but my eperience is that more than two years on any coolant charge starts you down a path of corrosion that's irreversible. The scaling is typically mineral and metal precipitate from ions scavenged from the water mix and the metal exposed in the cooling system. Neither is good.
Gaz has landed on some issues with his cooling fans that might be his problem. I know you've recharged the thermo fan clutch. Have you confirmed that the aux electric fan is working? It should come on with the AC, and also when coolant temp in the radiator return-side tank gets too warm.
Your report that the car cools noticeably when the AC is shut off and the heat is turned on may be a clue. Refine the test, this time just turning the AC off but leaving the heat off. You should hear the electric fan come on when AC is turned on and engine running, based on a temp switch in the condenser piping by the receiver-drier. The other trigger is the temp switch at the bottom front driver's side of the radiator, under and behind the front of the AC condenser.
Remote diagnosis of this stuff is, um, fun. I casually chased the same symptom in my S4 for a couple years, problem only above 90-95ºF and only at extended times at speeds above about 80 MPH. Just not enough opportunities for those conditions to concur where we lived in the L.A. basin. Hot yes for sure.