How to improve engine temperature?
05-20-2008, 04:50 PM
#16
Race Director
I found that water wetter with a lower % of antifreeze brought my temps down quite a bit......even on a 100 degree day with the a/c on it rarely goes over the 1/2 mark.....the highest I've ever seen is just below the 2nd white line
05-20-2008, 07:29 PM
#17
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If you search my posts from about 5 years ago you'll probably realize that your engine temp is EXACTLY where it's supposed to be. I owned 2 928s prior to my 91 and both ran with the temp gauge needle in the middle of the range. MANY later 928s run perfectly normally with the needle near or at the top white mark.
05-20-2008, 07:33 PM
#18
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Dr. Bob turned me on the water wetter. I was skeptical but I have to admit that it worked.
05-20-2008, 09:48 PM
#19
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At our little over-weekend fluid fest at Rob Edwards' place, lister Oscar M. showed off his pusher fan install, supplementing the S4 cooling fans from the front. He added a simple relay that triggers off the existing fan circuit, so the pusher has only one speed rather than the three speeds available on the pullers that Porsche installed.
05-21-2008, 12:59 AM
#20
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The "pusher fan install" you refer to, is that just the single-speed relay feature he added to the system or is there an additional fan (pusher) somehow installed? Forgive my ignorance on the subject if this is common knowledge.
05-21-2008, 02:05 AM
#22
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The combination that seems to work in never-ever-freezes Los Angeles is about 25-40% coolant in distilled water, with Water Wetter chaser. The low-dose coolant transfers heat better than the normally-recommended doses. the Water Wetter adds water pump lube as well as enhancing heat transfer.
05-21-2008, 11:51 AM
#23
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Do NOT use extra water wetter because it LOWERS the boiling point of the coolant mixture which is not a good thing....use as directed 
more is NOT BETTER ! Same with the coolant to water % too much antifreeze and it does not cool as well.
more is NOT BETTER ! Same with the coolant to water % too much antifreeze and it does not cool as well.
05-21-2008, 10:53 PM
#24
SteveG
To answer you question it is a little difficult as you mention that the temperature is a little over the centre of the gauge on your GTS? It would have been a little easer if you had given a temperature reading in degrees F or C.
Anyway, the specification for the thermostat in the WSM is that it begins to open at 85 + or - 2 degrees C and fully opens at 98 degrees C and the travel should be at least 8mm. The system is designed to operate at 0.9 to 1.15 bar pressure, which raises the boiling point of the cooling water well above 100 degrees C.
This boiling temperature can be calculated if you wish to have the full operating range or the cooling water before it turns into steam and the system starts to loose cooling capacity and blows off through the reservoir pressure release cap.
With these figures in mind the 87 degree thermostat valve disc will be well and truely closed against the thermostat housing "O" ring seat at 98 degrees C . The cooling system will now be getting full flow of water through the radiator for maximum cooling effect until the temperature of the cooling water starts to fall and the thermostat valve disc contracts off the housing seat until the thermostat reaches a stable state with some cooling water bye pass. This stable state is influenced by the ambient temperature, the speed of the car with forced air ingestion, the speed of the suction fans and the heat transferred by the combustion process into the engine jacket cooling water. The higher the speed the more heat transferred to the cooling water, but more forced air ingestion and higher fan speed.
By fitting a 75 degree thermostat, if the radiator and fans etc are working as designed, will actually lower the equiliberium state of the thermostat and reduce the operating temperature of the cooling water and therefore the operating temperature within the combustion chamber. In some instances too low a cooling effect can cause condensation on the lower section of the cyliner walls of the combustion chamber and it there is any sulphur present in the fuel, sulphuric acid can form. This is in extreme circumstance.
However if the radiator is dirty, externally and internally, and the heat transfer surface within the engine are encrusted in salt deposits the temperature can still raise until the cooling water boils and you loose cooling capacity and overheat the engine.
The fitting of a 75 degree C thermostat is therefore, in my opinion, a "band aid" approach to solving a more serious cooling problem and should not be taken as a permanent fix. I would suggest a total system clean as described above.
If you add the temperature control flaps as introduced on the 1987 S4s and then add the various controls such as:
Air intake temperature;
Radiator Temperature;
Automatic gear box temperature switch;
A/C pressure sensor switch; and the
A/C start up switch
all controlling the position of the flaps (closed, 30% and 100% opened) and the variable voltage supply to the cooling fans (fan speed) you can see why Porsche deleted the system from the late MY cars.
However if the system is working correctly it controlls the temperature in the engine on my vehicle to around 89 degrees C with minimal variation in temperature for hot or cold weather conditions and in stop/start traffic. I like the system, but then I'm a techno freak?
Tails 1990 928S4 Auto
Tails 1990 928S4 Auto
To answer you question it is a little difficult as you mention that the temperature is a little over the centre of the gauge on your GTS? It would have been a little easer if you had given a temperature reading in degrees F or C.
Anyway, the specification for the thermostat in the WSM is that it begins to open at 85 + or - 2 degrees C and fully opens at 98 degrees C and the travel should be at least 8mm. The system is designed to operate at 0.9 to 1.15 bar pressure, which raises the boiling point of the cooling water well above 100 degrees C.
This boiling temperature can be calculated if you wish to have the full operating range or the cooling water before it turns into steam and the system starts to loose cooling capacity and blows off through the reservoir pressure release cap.
With these figures in mind the 87 degree thermostat valve disc will be well and truely closed against the thermostat housing "O" ring seat at 98 degrees C . The cooling system will now be getting full flow of water through the radiator for maximum cooling effect until the temperature of the cooling water starts to fall and the thermostat valve disc contracts off the housing seat until the thermostat reaches a stable state with some cooling water bye pass. This stable state is influenced by the ambient temperature, the speed of the car with forced air ingestion, the speed of the suction fans and the heat transferred by the combustion process into the engine jacket cooling water. The higher the speed the more heat transferred to the cooling water, but more forced air ingestion and higher fan speed.
By fitting a 75 degree thermostat, if the radiator and fans etc are working as designed, will actually lower the equiliberium state of the thermostat and reduce the operating temperature of the cooling water and therefore the operating temperature within the combustion chamber. In some instances too low a cooling effect can cause condensation on the lower section of the cyliner walls of the combustion chamber and it there is any sulphur present in the fuel, sulphuric acid can form. This is in extreme circumstance.
However if the radiator is dirty, externally and internally, and the heat transfer surface within the engine are encrusted in salt deposits the temperature can still raise until the cooling water boils and you loose cooling capacity and overheat the engine.
The fitting of a 75 degree C thermostat is therefore, in my opinion, a "band aid" approach to solving a more serious cooling problem and should not be taken as a permanent fix. I would suggest a total system clean as described above.
If you add the temperature control flaps as introduced on the 1987 S4s and then add the various controls such as:
Air intake temperature;
Radiator Temperature;
Automatic gear box temperature switch;
A/C pressure sensor switch; and the
A/C start up switch
all controlling the position of the flaps (closed, 30% and 100% opened) and the variable voltage supply to the cooling fans (fan speed) you can see why Porsche deleted the system from the late MY cars.
However if the system is working correctly it controlls the temperature in the engine on my vehicle to around 89 degrees C with minimal variation in temperature for hot or cold weather conditions and in stop/start traffic. I like the system, but then I'm a techno freak?
Tails 1990 928S4 Auto
Tails 1990 928S4 Auto
05-22-2008, 04:08 PM
#25
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I have an electric fan waiting to be installed. It replaces the belt driven fan most of us have in their cars. The reason I bought it was:
1. overheating engine in summer hot traffic jam, resulting in blown head gasket (car had new wp and thermostat)
2. not sure if fan clutch is as good as it should be
3. newer 928's also have electric fans
4. it seems more logical to help making more cfm at low speeds. At high speeds there will be enough. Strangely the mechanical fan will run at modest speed while creeping through traffic and at high speed when there is already plenty of wind.
1. overheating engine in summer hot traffic jam, resulting in blown head gasket (car had new wp and thermostat)
2. not sure if fan clutch is as good as it should be
3. newer 928's also have electric fans
4. it seems more logical to help making more cfm at low speeds. At high speeds there will be enough. Strangely the mechanical fan will run at modest speed while creeping through traffic and at high speed when there is already plenty of wind.
05-22-2008, 05:08 PM
#26
Chronic Tool Dropper
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The car in question already has the dual electric fans (pullers) from the factory, so no fan clutch to worry about.
The original cooling system was very robust, lots of capacity to shed heat in the toughest environments. Remember that the car was tested in everything from arctic cold to mideast desert summer days before release. So we start looking for "what's changed?" when cooliong system questions come up.
First candidate for consideration is the radiator. S4's are getting to 20 years old now, so there's a lot of time in service. Even the most gentle driving means that coolant and water are hot in one place and cool in another in the system, and the place where it cools is a prime candidate area for every posible mineral salt to drop out of solution and plate on the exposed cooler material. If you question how well your radiator is flowing and cooling, buy/borrow/use your IR temp gun to look at the temps at the corners of the radiator with everything up to temp. If the bottom inch or four of the radiator is noticeably colder, it's quite likely that there's a bunch of hard sedimentation in there blocking coolant flow.
Second candidate is fan performance. Again, 20 years of service on them, and as the radiator has become restricted the fans end up running more and more to compensate. Of course they run whenever the AC is on, in slow traffic, and in line at Starbucks too. If they don't run at full speed when needed, coolant temps will result from the lower airflow. You just won't notice the deterioration until the car starts overheating. The fan motors are used in other cars so you may find parts or low-miles motors available. A few cases have come through where the power feeds from battery to the fan were left loose during service/cleaning/whatever, then resulting in loss of fan function and overheating.
S4 cars up until '90 or so had temp control flaps in the grill that sometimes (very rarely) malfunction and stick in the closed position. Verify that they are open when the engine is off, and pull the fuse for the position setting motor. That way they won't move.
A "colder" thermostat won't keep the car from overheating, but it will keep it from warming up adequately. In the S4+ cars, there's a risk of having the thermostat, fan and flap controllers fight to keep the engine at the right temp. There is no good reason to use a colder thermostat except to get some driver comfort with the position of the gauge needle. Bring on your arguments, I'm ready.
Factory water pumps seldom if ever fail. There are a few that have, but they fail catastrophically, either with a metal impellor grinding the pump housing, or a plastic impellor that spins slower than the shaft and doesn't pump enough coolant. There are cheap rebuilts and some Asian imports on Ebay that fail in infancy, so don't go that route.
Use the correct coolant for your engine and the climate you are in. Put in enough to get the freeze protection you need and no more.
Use distilled water to blend with the coolant. It cuts down a lot on the salt deposits in the radiator and in the coolant jackets in the motor.
Flush the block completely when you change coolant. That means the galley drain bolts are out and a lot of water is flushed through.
Use Water Wetter. It works.
Don't forget to replace the coolant hoses, the heater valve and the coolant bottle cap regularly. The hoses are probably safe to do every other timing belt change. The heater valve and the coolant bottle cap get replaced at every coolant change.
The coolant bottle are getting old and tired, and more prone to cracking in places you may or may not be able to see. Buy a new one and a bullet. Bite the bullet, and install the new tank with the new hoses and cap and coolant and Water Wetter.
End tanks on the radiator leak as the temp gradients across the ends of the radiator change. Biggest gradient shows up between the top of the pass side tank with incoming engine coolant, and the bottom of that same tank where flow is blocked by the salt deposits. You can replace and reseal the tanks, generally a job for a radiator specialist who can also clean all the crud out of the lower tubes, and the oil and trans coolers if they are in there. If you decide to pull the radiator yopurself, remember that you MUST counterhold the fittings in the tank (32mm flat wrench), or risk twisting the fittings in the tank and rupturing the fluid cooler inside.
928 Int'l sells a very nice aluminum one-piece radiator for less than the price of a new Behr factory radiator.
The original cooling system was very robust, lots of capacity to shed heat in the toughest environments. Remember that the car was tested in everything from arctic cold to mideast desert summer days before release. So we start looking for "what's changed?" when cooliong system questions come up.
First candidate for consideration is the radiator. S4's are getting to 20 years old now, so there's a lot of time in service. Even the most gentle driving means that coolant and water are hot in one place and cool in another in the system, and the place where it cools is a prime candidate area for every posible mineral salt to drop out of solution and plate on the exposed cooler material. If you question how well your radiator is flowing and cooling, buy/borrow/use your IR temp gun to look at the temps at the corners of the radiator with everything up to temp. If the bottom inch or four of the radiator is noticeably colder, it's quite likely that there's a bunch of hard sedimentation in there blocking coolant flow.
Second candidate is fan performance. Again, 20 years of service on them, and as the radiator has become restricted the fans end up running more and more to compensate. Of course they run whenever the AC is on, in slow traffic, and in line at Starbucks too. If they don't run at full speed when needed, coolant temps will result from the lower airflow. You just won't notice the deterioration until the car starts overheating. The fan motors are used in other cars so you may find parts or low-miles motors available. A few cases have come through where the power feeds from battery to the fan were left loose during service/cleaning/whatever, then resulting in loss of fan function and overheating.
S4 cars up until '90 or so had temp control flaps in the grill that sometimes (very rarely) malfunction and stick in the closed position. Verify that they are open when the engine is off, and pull the fuse for the position setting motor. That way they won't move.
A "colder" thermostat won't keep the car from overheating, but it will keep it from warming up adequately. In the S4+ cars, there's a risk of having the thermostat, fan and flap controllers fight to keep the engine at the right temp. There is no good reason to use a colder thermostat except to get some driver comfort with the position of the gauge needle. Bring on your arguments, I'm ready.
Factory water pumps seldom if ever fail. There are a few that have, but they fail catastrophically, either with a metal impellor grinding the pump housing, or a plastic impellor that spins slower than the shaft and doesn't pump enough coolant. There are cheap rebuilts and some Asian imports on Ebay that fail in infancy, so don't go that route.
Use the correct coolant for your engine and the climate you are in. Put in enough to get the freeze protection you need and no more.
Use distilled water to blend with the coolant. It cuts down a lot on the salt deposits in the radiator and in the coolant jackets in the motor.
Flush the block completely when you change coolant. That means the galley drain bolts are out and a lot of water is flushed through.
Use Water Wetter. It works.
Don't forget to replace the coolant hoses, the heater valve and the coolant bottle cap regularly. The hoses are probably safe to do every other timing belt change. The heater valve and the coolant bottle cap get replaced at every coolant change.
The coolant bottle are getting old and tired, and more prone to cracking in places you may or may not be able to see. Buy a new one and a bullet. Bite the bullet, and install the new tank with the new hoses and cap and coolant and Water Wetter.
End tanks on the radiator leak as the temp gradients across the ends of the radiator change. Biggest gradient shows up between the top of the pass side tank with incoming engine coolant, and the bottom of that same tank where flow is blocked by the salt deposits. You can replace and reseal the tanks, generally a job for a radiator specialist who can also clean all the crud out of the lower tubes, and the oil and trans coolers if they are in there. If you decide to pull the radiator yopurself, remember that you MUST counterhold the fittings in the tank (32mm flat wrench), or risk twisting the fittings in the tank and rupturing the fluid cooler inside.
928 Int'l sells a very nice aluminum one-piece radiator for less than the price of a new Behr factory radiator.
05-22-2008, 05:22 PM
#27
Rest in Peace
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I use Water Wetter, and in 106 degrees in Fresno, CA two years back it worked fantastic!
http://www.redlineoil.com/products_coolant.asp
http://www.redlineoil.com/products_coolant.asp
05-22-2008, 05:38 PM
#28
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Originally Posted by Dr. Bob
Put in enough to get the freeze protection you need and no more.
Last edited by Charley B; 05-22-2008 at 09:42 PM.
05-22-2008, 05:40 PM
#29
Rennlist Member
Tails, my question was not about the GTS and no reference was made to middle of the range in my question. Must have been another poster. I was just concerned that the '85 was running too cool; it used to run above the middle but now is well below it. I've had another mechanic point that out (an engine could be too cool), but it was about another car, and at least one poster here says you can't run a 928 too cool. This needs more research I think. Isnt' there some sort of optimum range for ignition?
05-22-2008, 07:38 PM
#30
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Hotter cylinder temps are good for emissions, and mileage. Hotter is more efficient because less heat energy is absorbed by the coolant, and the oil is thinner.
Cooler cylinder temps are good for power, if you can take advantage of the increased ignition advance. A cooler intake makes a world of difference, too.
The engine oil thermostat is (87C).
75C t-stats had a factory part number, 928 106 129 16 (Behr 116 200 00 15). I wonder if they were used in hot climates, or if 75C was the norm, unless it was a cool climate, which then got the 83C, 928 106 129 17. PET shows the 75C, -89, and the 83C, 90-.
More tips for staying cool (for power):
-Remove the rear hood seal from the firewall
-Cover the radiators to keep the intake cool
Cooler cylinder temps are good for power, if you can take advantage of the increased ignition advance. A cooler intake makes a world of difference, too.
The engine oil thermostat is (87C).
75C t-stats had a factory part number, 928 106 129 16 (Behr 116 200 00 15). I wonder if they were used in hot climates, or if 75C was the norm, unless it was a cool climate, which then got the 83C, 928 106 129 17. PET shows the 75C, -89, and the 83C, 90-.
More tips for staying cool (for power):
-Remove the rear hood seal from the firewall
-Cover the radiators to keep the intake cool