Yet another overheating problem
10-10-2015, 11:58 PM
#1
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Yet another overheating problem
'83 with 68k miles (really), and years of storage - became mine yesterday. Please help me diagnose my overheating problem. I've hunted around the forum and gotten some hints, but nothing fits perfectly.
THE SITUATION
Ambient temp over 90degF.
Air conditioning ON.
Any speed, traffic or freeway.
THE PROBLEM
Gauge rises to the RED, warning illuminates.
Improves with heater ON (and I lose weight!).
Shut down for 30 minutes, and on start I see the OXS light and the car idles poorly. After a minute it runs fine.
THE CAR
No history
Coolant is green and at the proper level.
Radiator looks reasonably clean.
When I shut down the car hot and flip the fan, it spins about 90 degrees.
Belt tension feels about right.
No visible leaks, and coolant level doesn't drop.
CHOICES
Switch to an electric fan?
Pull and service the radiator?
Remove the thermostat (San Diego)?
Other tests?
THE SITUATION
Ambient temp over 90degF.
Air conditioning ON.
Any speed, traffic or freeway.
THE PROBLEM
Gauge rises to the RED, warning illuminates.
Improves with heater ON (and I lose weight!).
Shut down for 30 minutes, and on start I see the OXS light and the car idles poorly. After a minute it runs fine.
THE CAR
No history
Coolant is green and at the proper level.
Radiator looks reasonably clean.
When I shut down the car hot and flip the fan, it spins about 90 degrees.
Belt tension feels about right.
No visible leaks, and coolant level doesn't drop.
CHOICES
Switch to an electric fan?
Pull and service the radiator?
Remove the thermostat (San Diego)?
Other tests?
10-11-2015, 12:05 AM
#2
Vegas, Baby!
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If the fan isn't running, I'd fix that problem first, then change the thermostat. Make sure the water pump is pumping also. I've got an S4, not really familiar with the older models.
10-11-2015, 12:14 AM
#3
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The fan runs. I was checking the viscous coupling - if the car is hot and the fan spins freely, it needs fluid. In this case, the fan seems to be working properly.
Here in S Calif, it's okay to simply remove the thermostat. That slows down warm-up but increases coolant flow - and removes all doubt regarding faults.
I do not know how to check the water pump, but since I have no history on this car it might be wise to do the timing belt and pump right now.
Here in S Calif, it's okay to simply remove the thermostat. That slows down warm-up but increases coolant flow - and removes all doubt regarding faults.
I do not know how to check the water pump, but since I have no history on this car it might be wise to do the timing belt and pump right now.
10-11-2015, 12:18 AM
#4
Racer
If it overheats at freeway speeds I'm tempted to think the waterpump isn't circulating the coolant. When I bought my car there wasn't a belt for the fan and the electric fan didn't come on at all. It never overheated.
10-11-2015, 12:21 AM
#5
Team Owner
have you looked along the top edges of the Head Gaskets ?
see if you find white crusty deposits.
OR see if the HGs look fresh.
Remove the thermostat and place in boiling water see when it opens
see if you find white crusty deposits.
OR see if the HGs look fresh.
Remove the thermostat and place in boiling water see when it opens
10-11-2015, 01:39 AM
#6
Rennlist Member
The fan runs. I was checking the viscous coupling - if the car is hot and the fan spins freely, it needs fluid. In this case, the fan seems to be working properly.
Here in S Calif, it's okay to simply remove the thermostat. That slows down warm-up but increases coolant flow - and removes all doubt regarding faults.
Here in S Calif, it's okay to simply remove the thermostat. That slows down warm-up but increases coolant flow - and removes all doubt regarding faults.
Not recommended.
Things need to be at their designed temperatures. Not whatever temp can be managed with unlimited flow -and- dwell time in the radiator.
99.9999% sure your fan is empty. I sent you a PM.
10-11-2015, 02:49 AM
#7
Chronic Tool Dropper
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Do Not Remove The Thermostat.
For the 928, this is very dangerous. The thermostat in the 928 modulates flow between the recirc loop through the block and the loop through the radiator. Removing the thermostat allows unrestricted flow through the least restrictive path back to pump suction, with only minimal flow through the radiator.
Heating at speed means low heat transfer through the radiator. The radiator may be plugged, water pump flow through the radiator reduced. Replace the thermostat plus the seals. Inspect the radiator with a mirror through the lower hose nozzle. Water pump is the Least Likely failure point for your symptoms.
For the 928, this is very dangerous. The thermostat in the 928 modulates flow between the recirc loop through the block and the loop through the radiator. Removing the thermostat allows unrestricted flow through the least restrictive path back to pump suction, with only minimal flow through the radiator.
Heating at speed means low heat transfer through the radiator. The radiator may be plugged, water pump flow through the radiator reduced. Replace the thermostat plus the seals. Inspect the radiator with a mirror through the lower hose nozzle. Water pump is the Least Likely failure point for your symptoms.
Last edited by dr bob; 10-12-2015 at 02:17 PM. Reason: Deleted wrong reference, updated language.
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10-11-2015, 10:41 AM
#8
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I have this same problem on my '89 GT except without the OxS light (oxygen sensor??). My car apparently also sat undriven for many years. I've thought through this problem a hundred times, and swapped out a few parts with no change in symptoms.
notaguru - questions....
1) do you also build heat with the AC off but running high revs (ir, 4k and over during "sporting" driving)?
2) will the engine temp climbstop or reverse itself if you leave the AC on but turn the system to blow heat too?
Mine builds heat running at high revs, but at cooler ambient temps (less than ~83*F), the engine temp stays right on the money no matter how hard I'm driving. That fact tells me that the cooling system is fundamentally working, just not at full capability, and so it cannot deal with higher than normal heat load of higher revs or higher load at high temps.
In any event, pull the t-stat and boil it to verify that it does in fact open. It's one of the easiest things to do and could in fact be the problem. Also, make sure that the t-stat O-ring and the seal on the opposite side are good and in place, because if it's not seated correctly and leaves a gap, some coolant flow could be diverted back to the engine instead of the radiator, diminishing cooling system capability. At this point, you may as well put a new t-stat in and eplace the o-ring and gasket too while you are at it.
But remember (everyone) that as long as the t-stat is opening, and the seals are in place, that's kind of the end of its potential involvement in the problem. Once the t-stat opens, it stays open, and additional heat build-up beyond that temp has nothing to do with the t-stat. You can replace it over and over and over (as I have) and you will not fix the problem. This is a problem of something else in the cooling system (WP, fans, radiator, nose vents) not doing its job correctly, or it is a problem of restricted coolant passages somewhere, or an open passage that should be closed (recirc path to the heads). I suspected my radiator was plugged up with deposits, constricting flow through the tubes, so I popped in one of the CSF all-aluminum rads that 928 Int'l had made - to absolutley no effect. I am going to step through the correct functionality of the cooling system to verify everything (both fans, nose vents, etc) is working correctly, hoping to find that the secondary fan isn't coming on when it is supposed to.
Since you do not know the maintenance history of the car, you should do the TB/WP/Tensioner service as soon as possible. Check if the WP appears to have been working correctly or not (my heat-build problem preceded and followed my TB/WP service), and of course replacing it may fix the problem or eliminate it as a possible cause.
If I can't find anything wrong with the operation of my fans or flaps, then the next step will be to bring my old radiator to a shop and have them remove a couple of the tube ends and rod it out to see if there are significant deposits in the tubes. If there are, then I will have to suspect that the coolant passages in the engine itself are restricted. If that's the case, I don't know what I can do!
notaguru - questions....
1) do you also build heat with the AC off but running high revs (ir, 4k and over during "sporting" driving)?
2) will the engine temp climbstop or reverse itself if you leave the AC on but turn the system to blow heat too?
Mine builds heat running at high revs, but at cooler ambient temps (less than ~83*F), the engine temp stays right on the money no matter how hard I'm driving. That fact tells me that the cooling system is fundamentally working, just not at full capability, and so it cannot deal with higher than normal heat load of higher revs or higher load at high temps.
In any event, pull the t-stat and boil it to verify that it does in fact open. It's one of the easiest things to do and could in fact be the problem. Also, make sure that the t-stat O-ring and the seal on the opposite side are good and in place, because if it's not seated correctly and leaves a gap, some coolant flow could be diverted back to the engine instead of the radiator, diminishing cooling system capability. At this point, you may as well put a new t-stat in and eplace the o-ring and gasket too while you are at it.
But remember (everyone) that as long as the t-stat is opening, and the seals are in place, that's kind of the end of its potential involvement in the problem. Once the t-stat opens, it stays open, and additional heat build-up beyond that temp has nothing to do with the t-stat. You can replace it over and over and over (as I have) and you will not fix the problem. This is a problem of something else in the cooling system (WP, fans, radiator, nose vents) not doing its job correctly, or it is a problem of restricted coolant passages somewhere, or an open passage that should be closed (recirc path to the heads). I suspected my radiator was plugged up with deposits, constricting flow through the tubes, so I popped in one of the CSF all-aluminum rads that 928 Int'l had made - to absolutley no effect. I am going to step through the correct functionality of the cooling system to verify everything (both fans, nose vents, etc) is working correctly, hoping to find that the secondary fan isn't coming on when it is supposed to.
Since you do not know the maintenance history of the car, you should do the TB/WP/Tensioner service as soon as possible. Check if the WP appears to have been working correctly or not (my heat-build problem preceded and followed my TB/WP service), and of course replacing it may fix the problem or eliminate it as a possible cause.
If I can't find anything wrong with the operation of my fans or flaps, then the next step will be to bring my old radiator to a shop and have them remove a couple of the tube ends and rod it out to see if there are significant deposits in the tubes. If there are, then I will have to suspect that the coolant passages in the engine itself are restricted. If that's the case, I don't know what I can do!
10-11-2015, 10:45 AM
#9
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Yes? No? Am I missing something?
10-11-2015, 11:48 AM
#10
Chronic Tool Dropper
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In the FWIW category...
For decades I played down the idea that a thermostat could fail. It's a simple mechanical device, with a temperature-sensitive wax plug that expands to push a piston that opens or closes the thermostat. What could go wrong? So when I started seeing symptoms similar to what the OP and GAZ describe, I went after the radiator first. After all, it's what actually carries the heat away. Radiators are subject to pluggage starting at the bottom, as the drop in temperature causes dissolved minerals to slowly precipitate out. Turns out my radiator was pristine inside, thanks I'm sure to religious coolant system maintenance and the correct coolant. Head-scratch. Water pump was then out for a TB service anyway, so I verified the impellor condition and clearance, which were both excellent. I swapped the rear seal for the thermostat (OP's early car doesn't have that...), but put the same thermostat back in. Same symptom with heating at higher speeds on hottest 95º+ days.
So the last thing done was a new thermostat, replacing the 75ºC unit accidentally wth 85ºC part. The new thermostat causes the temp needle to sit higher on the gauge, two needle-widths below the 190º mark, as I would expect from the 85ºC rating. The car warms up a LOT faster now, and once warmed up the needle goes no higher than that 190º mark on the hottest (100º+) days driving through the central valley of California in their summer heat. Other things happened too, with the cooling fans running a lot less, but I haven't got my head around why that might be. At the car's new home in the high desert of central Oregon, the extra engine temp is a plus when the mornings are cold, so that 85ºC thermostat will likely stay in there for a while.
For a decade or two I taught a course for industrial folks called "logical problem solving", which looked at applying some structure to the way we drill through symptoms to identify problems. My heating symptom diagnosis exercise was backwards because I --knew-- that the thermostats don't fail. So it was the second-easiest, lowest-cost possibility on the potential-culprits list, right after 'low coolant level'. Logically, it should have been the second thing on the list rather than the last. Good News is that I can keep the spare Behr new-in-box radiator new in the box in storage for a while. I'm comfortable that the other system components are working fine, after that full inspection.
With 928 winter hibernation season approaching, I'm getting ready for a full service immediately prior to sleepy time, one that includes oil and coolant replacement. The five-year coolant is now two years old in the car, and a fresh charge means that the car won't sit with possibly low-pH fluid in the galleys.
For decades I played down the idea that a thermostat could fail. It's a simple mechanical device, with a temperature-sensitive wax plug that expands to push a piston that opens or closes the thermostat. What could go wrong? So when I started seeing symptoms similar to what the OP and GAZ describe, I went after the radiator first. After all, it's what actually carries the heat away. Radiators are subject to pluggage starting at the bottom, as the drop in temperature causes dissolved minerals to slowly precipitate out. Turns out my radiator was pristine inside, thanks I'm sure to religious coolant system maintenance and the correct coolant. Head-scratch. Water pump was then out for a TB service anyway, so I verified the impellor condition and clearance, which were both excellent. I swapped the rear seal for the thermostat (OP's early car doesn't have that...), but put the same thermostat back in. Same symptom with heating at higher speeds on hottest 95º+ days.
So the last thing done was a new thermostat, replacing the 75ºC unit accidentally wth 85ºC part. The new thermostat causes the temp needle to sit higher on the gauge, two needle-widths below the 190º mark, as I would expect from the 85ºC rating. The car warms up a LOT faster now, and once warmed up the needle goes no higher than that 190º mark on the hottest (100º+) days driving through the central valley of California in their summer heat. Other things happened too, with the cooling fans running a lot less, but I haven't got my head around why that might be. At the car's new home in the high desert of central Oregon, the extra engine temp is a plus when the mornings are cold, so that 85ºC thermostat will likely stay in there for a while.
For a decade or two I taught a course for industrial folks called "logical problem solving", which looked at applying some structure to the way we drill through symptoms to identify problems. My heating symptom diagnosis exercise was backwards because I --knew-- that the thermostats don't fail. So it was the second-easiest, lowest-cost possibility on the potential-culprits list, right after 'low coolant level'. Logically, it should have been the second thing on the list rather than the last. Good News is that I can keep the spare Behr new-in-box radiator new in the box in storage for a while. I'm comfortable that the other system components are working fine, after that full inspection.
With 928 winter hibernation season approaching, I'm getting ready for a full service immediately prior to sleepy time, one that includes oil and coolant replacement. The five-year coolant is now two years old in the car, and a fresh charge means that the car won't sit with possibly low-pH fluid in the galleys.
10-11-2015, 12:00 PM
#11
Chronic Tool Dropper
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As I have always understood it, the t-stat does not regulate the engine temperature - it stays closed to get the engine up to operating temp, then it opens and stays open, and the cooligng system regulates the engine temperature at a temp higher than the t-stat opens.
Yes? No? Am I missing something?
Yes? No? Am I missing something?
In the early (pre-'91) S4 cars especially, there's a combination of thermostat, cooling fan and flap controls woring to manage engine temp. Ultimately though, the thermostat manages coolant flow to keep the temperature just right. Fans and flaps play supporting roles.
In the OP's car, cooling fan operation is available to provide airflow when the car isn't moving fast enough to force adequate air through the radiator. Heating at speed may be an airflow problem due to partial airflow obstruction, but that's seldom solved by cooling fans.
10-11-2015, 02:45 PM
#12
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just so no one else happens to read this.....THAT IS NOT TRUE for a 928 !!! running with no thermostat will cause it to overheat......actually much like this car is doing right now !!
10-11-2015, 08:22 PM
#14
Rennlist Member
Those are all good factual posts, but if notaguru and I have the same problem (and it certainly seemslike we do), and I have had three t-stats and seals in my car with no change in the problem, and my car still does what his does, and he (most likely) will confirm that he has a t-stat in his car, we are still nowhere.
We need some next-level thinking here...
We need some next-level thinking here...