More cooling fans and temp issue at speed
05-02-2018, 06:00 AM
#31
Rennlist Member
Good call- similar thing happened to me about 17 years ago with my late S4. Probably caused by hitting the chin spoiler on a speed bump - nowadays I have Carl's bash plate fitted- well worth the $$$'s for the protections it gives- had my money's worth many times already.
05-02-2018, 08:10 AM
#33
Three Wheelin'
Thread Starter
if the other cars are much later than the 928, this is irrelevant
regarding that front part, the PET calls an air guide, is there a better way to attach to the
front spoiler/bumper? it appears to just fit into grooves? certainly not going to drill any holes
or fit self tapping screws, but perhaps some silicone adhesive?? or some sort of clips?
05-02-2018, 10:48 AM
#34
Rennlist Member
Well done - excellent perseverance on your part. Just proves the proverb "A problem shared is a problem halved". I thought it may be helpful to you and others playing along at home to share some thoughts I have gleaned about the system over close to 20 years of 928 ownership in an extreme climate.
The cooling system controller looks at several scenarios and decides what action has the highest priority. As the coolant temperature rises the controller increases the voltage to spin the fans faster to do whatever it can to control the situation in the radiator. When the coolant temperature reaches 95C the fans get full voltage. If the coolant temperature drops to 77C the fans switch off. The most critical element of the system control wise is the thermostat. When the engine is cold the water pump circulates coolant within the block and this duly picks up heat within a couple of minutes or so- just watch and time the engine temperature indicator on the dash. When the temperature of the internally circulating coolant reaches exactly 83C the piston starts to move and by the time the temperature reaches 98C the piston has fully extended and should be in contact with the inner seal face. If this face is not in perfect condition the system will not stop internal circulation and some of the flow will not reach the radiator thus a careful check of its condition is prudent when one changes the coolant. I typically change my coolant every three years to maintain the anti corrosion potency, I have also added another bottle of water water to extend the life a further year. I take the point of view that a water pump should last 10 years or 100k km but I change the timing belt every 5 years. For coolant I use a 30% glycol mix with a bottle of Redline Water Wetter and for fans I use the Spal 12 inch twin fan setup that has been in service for the last 11 years.
Regarding the effectiveness of the fans for sure at idle and in slow traffic they do a good job and I reckon by about the time one reaches 40 mph they are probably irrelevant. My system can keep me cool all day long at 80 mph in 40C heat and at some point north of that the a/c performance starts to drop off. Most of what I see these days keeps the engine temp gauge needle at around 98C [just before the last white line] and I have seen similar values indicated in ST2 that is reading the output from the Temp2 signals so presumably the coolant is about 15C degrees less- somewhere in the region of 85C. At 98C engine temperature my motor seems to perform very well. when the engine is cold the motor feels "tight" and I load the motor lightly until the engine temperature gauge reaches mid way between the two white lines and then I reckon it is good to play with.
If one follows the coolant temperature fan operating curves the voltage applied modulates over coolant temperatures in the range 85C to 95C suggesting Porsche expect engine operating temperatures loosely in the range of 95C to 110C. If as I stated the last white line is 100C, there is still a bit more scope before it enters the "red zone" so a value of 110C for maximum safe operating temperature makes sense. Again, following the coolant temperature curve, the diagram ends at a coolant temperature of 105C so my assumption is that the high temperature alarm will show at around this value or approximately 120C for engine temperature. What I do not know is where the "high temperature" alarm is generated, the sender used to trigger it or the value it goes off at- any offers?
When I first had to deal with the cooling system and trying to optimise it. I figured that cooling flaps were something of a mystery- what are they intended to achieve that the thermostat and the cooling fans did not? At the time I was advised by a well respected gent that the flaps were intended to optimise high speed aerodynamics that facilitated a couple of mph on top end - true or false I have no clue. At the time [as stated earlier], my flaps were wired open and the motor disengaged. I was advised to remove the slats as they restricted airflow to the tune of 5% or so- had them removed and the S4 immediately ran about a needle's width cooler. Same when I first ran Redline water wetter.
Bottom line- I figured that the 928 cooling system was in fact pretty good in the stock trim even out here and with a few enhancements including my custom all alloy radiator no real issue whatsoever. It seemed to me that the cooling slats might have value in a cold climate but not in a hot climate.
Flush the radiator every 5 years or so, change the coolant every 3 years [or less], pop in new coolant hoses, thermostat and rear seal every 5 years or so and one cannot go to far wrong. The expansion tank degrades with age- mine is well past its sell by date and still holding up structurally but I fully expect it to go twang one of these days. I rather like the all alloy tank Carl produces and that is on my radar for my annual maintenance and project efforts next cool season.
Look after your cooling system and it will look after you!.
The cooling system controller looks at several scenarios and decides what action has the highest priority. As the coolant temperature rises the controller increases the voltage to spin the fans faster to do whatever it can to control the situation in the radiator. When the coolant temperature reaches 95C the fans get full voltage. If the coolant temperature drops to 77C the fans switch off. The most critical element of the system control wise is the thermostat. When the engine is cold the water pump circulates coolant within the block and this duly picks up heat within a couple of minutes or so- just watch and time the engine temperature indicator on the dash. When the temperature of the internally circulating coolant reaches exactly 83C the piston starts to move and by the time the temperature reaches 98C the piston has fully extended and should be in contact with the inner seal face. If this face is not in perfect condition the system will not stop internal circulation and some of the flow will not reach the radiator thus a careful check of its condition is prudent when one changes the coolant. I typically change my coolant every three years to maintain the anti corrosion potency, I have also added another bottle of water water to extend the life a further year. I take the point of view that a water pump should last 10 years or 100k km but I change the timing belt every 5 years. For coolant I use a 30% glycol mix with a bottle of Redline Water Wetter and for fans I use the Spal 12 inch twin fan setup that has been in service for the last 11 years.
Regarding the effectiveness of the fans for sure at idle and in slow traffic they do a good job and I reckon by about the time one reaches 40 mph they are probably irrelevant. My system can keep me cool all day long at 80 mph in 40C heat and at some point north of that the a/c performance starts to drop off. Most of what I see these days keeps the engine temp gauge needle at around 98C [just before the last white line] and I have seen similar values indicated in ST2 that is reading the output from the Temp2 signals so presumably the coolant is about 15C degrees less- somewhere in the region of 85C. At 98C engine temperature my motor seems to perform very well. when the engine is cold the motor feels "tight" and I load the motor lightly until the engine temperature gauge reaches mid way between the two white lines and then I reckon it is good to play with.
If one follows the coolant temperature fan operating curves the voltage applied modulates over coolant temperatures in the range 85C to 95C suggesting Porsche expect engine operating temperatures loosely in the range of 95C to 110C. If as I stated the last white line is 100C, there is still a bit more scope before it enters the "red zone" so a value of 110C for maximum safe operating temperature makes sense. Again, following the coolant temperature curve, the diagram ends at a coolant temperature of 105C so my assumption is that the high temperature alarm will show at around this value or approximately 120C for engine temperature. What I do not know is where the "high temperature" alarm is generated, the sender used to trigger it or the value it goes off at- any offers?
When I first had to deal with the cooling system and trying to optimise it. I figured that cooling flaps were something of a mystery- what are they intended to achieve that the thermostat and the cooling fans did not? At the time I was advised by a well respected gent that the flaps were intended to optimise high speed aerodynamics that facilitated a couple of mph on top end - true or false I have no clue. At the time [as stated earlier], my flaps were wired open and the motor disengaged. I was advised to remove the slats as they restricted airflow to the tune of 5% or so- had them removed and the S4 immediately ran about a needle's width cooler. Same when I first ran Redline water wetter.
Bottom line- I figured that the 928 cooling system was in fact pretty good in the stock trim even out here and with a few enhancements including my custom all alloy radiator no real issue whatsoever. It seemed to me that the cooling slats might have value in a cold climate but not in a hot climate.
Flush the radiator every 5 years or so, change the coolant every 3 years [or less], pop in new coolant hoses, thermostat and rear seal every 5 years or so and one cannot go to far wrong. The expansion tank degrades with age- mine is well past its sell by date and still holding up structurally but I fully expect it to go twang one of these days. I rather like the all alloy tank Carl produces and that is on my radar for my annual maintenance and project efforts next cool season.
Look after your cooling system and it will look after you!.
05-02-2018, 02:36 PM
#35
All these cooling fan threads got me thinking and needing to dig in to mine as any time the A/C was turned on, the fans would kick in to high gear. One of the things I did back in 2011 was pulled the high pressure sensor off the drier assembly to make room for the intake snouts. This caused them to kick on high all the time. Currently have the sensor off the drier but plugged in and the fans come on low when A/C is kicked on. Will have to test on a warmer day to see if they do still cycle from low to high as they heat up.
So thanks for pushing me (inadvertently) to actually looking at my own car.
So thanks for pushing me (inadvertently) to actually looking at my own car.
05-02-2018, 07:23 PM
#36
Rennlist
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Here's my "rule of thumb" about the gauge:
When a proper cooling system and the gauge working correctly (A/C off), the gauge will hover 2 needle widths below the third white line. The fans should come on (at the low speed) 1-2 needle widths below this line and should shut off 2-3 needle widths below the white line. The fans should run for 30-45 seconds, depending on how hot it is outside.
Any car that actually sits on the white line needs some attention....either to the gauge or the cooling system.
When a proper cooling system and the gauge working correctly (A/C off), the gauge will hover 2 needle widths below the third white line. The fans should come on (at the low speed) 1-2 needle widths below this line and should shut off 2-3 needle widths below the white line. The fans should run for 30-45 seconds, depending on how hot it is outside.
Any car that actually sits on the white line needs some attention....either to the gauge or the cooling system.
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
05-02-2018, 07:32 PM
#37
Three Wheelin'
Thread Starter
Any car that actually sits on the white line needs some attention....either to the gauge or the cooling system.
between one needle width below that white line, and can get to one needle width about. (just noticed I have a radiator cap with a torn off
rubber gasket...if that means anything?_)
05-02-2018, 08:53 PM
#41
Rennlist Member
If youre not reaching boiling point, more pressure adds no benefit. It only increases boiling point.
Ive had a cut hose where ive daily driven for days with the cap off, no change in gauge reading.
05-02-2018, 11:23 PM
#42
Rennlist
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guessing that my gauge and system are good: being in a very hot and humid climate, (and with the blockage issue resolved) my needle floats
between one needle width below that white line, and can get to one needle width about. (just noticed I have a radiator cap with a torn off
rubber gasket...if that means anything?_)
between one needle width below that white line, and can get to one needle width about. (just noticed I have a radiator cap with a torn off
rubber gasket...if that means anything?_)
Get a Behr cap, not some generic Stant cap.
05-02-2018, 11:30 PM
#43
Rennlist
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The relationship between the fan switch and the thermostat is a finely tuned "dance". Change one without the other and the fans can run constantly.
928's, in general, do not have overheating problems....even in crazy high temperatures. Don't overthink it or play car designer/engineer.
Make it work stock and forget it.
05-03-2018, 08:04 AM
#44
Three Wheelin'
Thread Starter
[QUOTE][928's, in general, do not have overheating problems....even in crazy high temperatures. Don't overthink it or play car designer/engineer./QUOTE]
I completely agree! the reason I tend to overthink the cooling system, is that I have had many cars with inadequate cooling systems let me down
to catastrophic results; one example, (of many!) was a 1972 3.0CS. Poor head design, inadequate radiator, and lousy fan and fan clutch. back when
there was no internet, and sites like this, I was on my own. took a lot of trial and error, but finally got it right. (I loved that car)
good to hear, overheating is NOT an inherent issue with this one
I completely agree! the reason I tend to overthink the cooling system, is that I have had many cars with inadequate cooling systems let me down
to catastrophic results; one example, (of many!) was a 1972 3.0CS. Poor head design, inadequate radiator, and lousy fan and fan clutch. back when
there was no internet, and sites like this, I was on my own. took a lot of trial and error, but finally got it right. (I loved that car)
good to hear, overheating is NOT an inherent issue with this one
06-03-2018, 03:57 AM
#45
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Great thread guys! Lots to learn... never enough! I took my S4 for a short ride yesterday (it happens less and less frequently...); it was a sunny day, approx 90F temp and I turned A/C on. I realized that pretty soon all the tree fans were running (I was driving in town, modest traffic conditions, slow speed anyhow); the A/C fan was on and off intermittently, almost continuously. As soon as I switched off the A/C that fan stopped (obviously...). Coolant temp on the gauge was OK, right in the middle... when I returned and parked the cab back in the garage the fans kept running for long time (far beyond what I would consider normal, say they run for at least 5-6 more minutes. IS this normal? I use the car very rarely but I remember that the fans kept running for a while with the engine off even in wintertime.
A friend of mine, much more expert than I am on 928 (He owns a GTS) told me that the cooling fan Electronic MU deals with loads of variables, and that abnormal cooling fans behavior could also be due to transmission oil level being low (or old)... my AT oil is certainly not old, but I do have a leak from the trans oil pan and wonder if oil level could be low,,,, did not check recently.
A friend of mine, much more expert than I am on 928 (He owns a GTS) told me that the cooling fan Electronic MU deals with loads of variables, and that abnormal cooling fans behavior could also be due to transmission oil level being low (or old)... my AT oil is certainly not old, but I do have a leak from the trans oil pan and wonder if oil level could be low,,,, did not check recently.