Coolant Light On
05-25-2006, 03:02 AM
#1
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Coolant Light On
Shortly after starting my car this evening, the coolant light came on. The engine was not yet warm. I watched the temperature guage and it didn't move above the usual reading (low normal). Assuming this must be a coolant level warning, I also watched the oil pressure on the premise that the oil pressure might increase if boosted by a head gasket leak. No change there either.
When I got home and shut it down, I opened the hood and checked the coolant level. It doesn't look to be down but I don't remember the level it was at previously. It is half way up the coolant tank when warm. The engine doesn't seem overly warm.
I checked the oil to determine if any coolant has entered the crank case. Oil (just changed a few days ago) is clean and uncontaminated (i.e. no milkshake appearance what so ever).
The manual suggests that if the light comes on, check if either of the fans are inoperative. Although not stated, this would seem to assume that the coolant light is accompanied by high temperature on the guage. It otherwise doesn't decribe what the light monitors. From some of the posted threads I now understand that the light is connected to a level sensor and a pressure sensor somewhere under the right front fender (at least on some models...mine?).
In the hope someone out there can deduce a diagnosis from my description above are:
1. Does the light indeed monitor both level and pressure? On my 1985 32V S?
2. What level should the coolant be at? Can coolant be lost from the system without there being an obvious external leak, coolant in the oil or coolant in the exhaust?
3. If the coolant level is not down, what can I do to determine the cause of the light coming on?
4. What risks should I be aware of in starting the car or driving it with the light on?
I don't want to assume that sensors have failed until I have confirmed that the system they monitor is working properly (pressure, level)
Thanks in advance.
When I got home and shut it down, I opened the hood and checked the coolant level. It doesn't look to be down but I don't remember the level it was at previously. It is half way up the coolant tank when warm. The engine doesn't seem overly warm.
I checked the oil to determine if any coolant has entered the crank case. Oil (just changed a few days ago) is clean and uncontaminated (i.e. no milkshake appearance what so ever).
The manual suggests that if the light comes on, check if either of the fans are inoperative. Although not stated, this would seem to assume that the coolant light is accompanied by high temperature on the guage. It otherwise doesn't decribe what the light monitors. From some of the posted threads I now understand that the light is connected to a level sensor and a pressure sensor somewhere under the right front fender (at least on some models...mine?).
In the hope someone out there can deduce a diagnosis from my description above are:
1. Does the light indeed monitor both level and pressure? On my 1985 32V S?
2. What level should the coolant be at? Can coolant be lost from the system without there being an obvious external leak, coolant in the oil or coolant in the exhaust?
3. If the coolant level is not down, what can I do to determine the cause of the light coming on?
4. What risks should I be aware of in starting the car or driving it with the light on?
I don't want to assume that sensors have failed until I have confirmed that the system they monitor is working properly (pressure, level)
Thanks in advance.
05-25-2006, 03:25 AM
#2
Team Owner
Hi the light may have come on from a lo coolant level but since you said that the level is halfway that seems to be about correct, however let the engine cool down the level will also go down then check it when its cold it should be at the seam on the tank, if you are indeed having to add coolant then the most obvious thing to do is replace the coolant cap if it is older than 1 year ,and inspect the coolant resivour it may have sprung a leak,and while your looking at the coolant tank look on top and disconnect the small white plug that goes to the level sensor, look for corrosion, there is also a possibility that the coolant level sensor has decided to quit working I have see where the float disintegrates and then the light will come on to see if the float is bad try looking into the tank if you cant see the float, then you will have to remove the tank securing screws and the windshield washer fill tube to move the tank out far enough to remove the sender,also you might want to remove the air cleaner assembly and check the right side rear of the engine where the heater control valve is connected the small hose to the valve it the most likely leak point. If the heater control valve is more that 4 years old it might be a good idea to replace it as the plastic can over time disintegrate inside the hose and then it will just slide out from a stress crack
Also just behind the top of the right shock mount there should be a hose that comes from the top of the thermostate housing and connects to a pressure valve try to remove the connector and see if it corroded, I am not for sure about your car having this pressure sender
the most likley possibilities bad sender, bad cap, bad tank, bad coolant line to heater valve or leaking heater valve, otherwise if the temp stays in the normal range and the level in the tank is at the seam and the fans are coming on you will probably be OK to drive the car without damaging anything , but check the heater valve for a leak
Also just behind the top of the right shock mount there should be a hose that comes from the top of the thermostate housing and connects to a pressure valve try to remove the connector and see if it corroded, I am not for sure about your car having this pressure sender
the most likley possibilities bad sender, bad cap, bad tank, bad coolant line to heater valve or leaking heater valve, otherwise if the temp stays in the normal range and the level in the tank is at the seam and the fans are coming on you will probably be OK to drive the car without damaging anything , but check the heater valve for a leak
05-25-2006, 11:06 AM
#3
Captain Obvious
Super User
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It could also be a faulty coolant level sensor or wiring. Mine dose this from time to time. If your coolant and temp level is normal, then don't worry too much aobut it.
05-25-2006, 11:16 AM
#4
Three Wheelin'
Originally Posted by Mrmerlin
Hi the light may have come on from a lo coolant level but since you said that the level is halfway that seems to be about correct, however let the engine cool down the level will also go down then check it when its cold it should be at the seam on the tank, if you are indeed having to add coolant then the most obvious thing to do is replace the coolant cap if it is older than 1 year ,and inspect the coolant resivour it may have sprung a leak,and while your looking at the coolant tank look on top and disconnect the small white plug that goes to the level sensor, look for corrosion, there is also a possibility that the coolant level sensor has decided to quit working I have see where the float disintegrates and then the light will come on to see if the float is bad try looking into the tank if you cant see the float, then you will have to remove the tank securing screws and the windshield washer fill tube to move the tank out far enough to remove the sender,also you might want to remove the air cleaner assembly and check the right side rear of the engine where the heater control valve is connected the small hose to the valve it the most likely leak point. If the heater control valve is more that 4 years old it might be a good idea to replace it as the plastic can over time disintegrate inside the hose and then it will just slide out from a stress crack
Also just behind the top of the right shock mount there should be a hose that comes from the top of the thermostate housing and connects to a pressure valve try to remove the connector and see if it corroded, I am not for sure about your car having this pressure sender
the most likley possibilities bad sender, bad cap, bad tank, bad coolant line to heater valve or leaking heater valve, otherwise if the temp stays in the normal range and the level in the tank is at the seam and the fans are coming on you will probably be OK to drive the car without damaging anything , but check the heater valve for a leak
Also just behind the top of the right shock mount there should be a hose that comes from the top of the thermostate housing and connects to a pressure valve try to remove the connector and see if it corroded, I am not for sure about your car having this pressure sender
the most likley possibilities bad sender, bad cap, bad tank, bad coolant line to heater valve or leaking heater valve, otherwise if the temp stays in the normal range and the level in the tank is at the seam and the fans are coming on you will probably be OK to drive the car without damaging anything , but check the heater valve for a leak
05-25-2006, 11:26 AM
#5
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There are two sensors which will cause the light to come on, one is the coolant level sensor the other is the coolant pressure switch.
To see which ssenosr is causing the problem, pressure switch you can just disconnect, coolent level I believe you need to short the connections.
Chris
To see which ssenosr is causing the problem, pressure switch you can just disconnect, coolent level I believe you need to short the connections.
Chris
05-25-2006, 11:29 AM
#6
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I find my coolant level sensor is quite sensitive to small changes. I have found that topping it up a small amount will do the trick. Easy solution to try first!
Glenn
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05-25-2006, 01:21 PM
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Coolant Light Fixed
Thank you everyone for your advice and input to my post. It now appears that the level was down a little and after topping it up the light has gone off. The warning system seems to be working as designed. I will keep my eye on the level and oil condition to ensure that I don't have an internal leak.
Thanks to all of your input I am now versed in the workings of yet another system on my 928 and will, in the furutre, be better able to differntiate between a warning and faulty warning sensor on this system.
Thanks to all of your input I am now versed in the workings of yet another system on my 928 and will, in the furutre, be better able to differntiate between a warning and faulty warning sensor on this system.
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06-07-2006, 03:28 AM
#8
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Just a little curiosity (my coolant light came on today):
Coolant pressure can kick the coolant light on at:
1. Low pressure condition
2. High pressure condition
3. Both.
If I ever put such light on a car, it would be low pressure condition. In that way, as temp goes up pressure should build up, otherwise there is a coolant leak somewhere. I always check it in my rally cars, and saved my *** once, pointing to a stone-hit damage in the radiator long before the high temp drama starts.
High pressure would point to faulty cap. Not bad info, either.
I must add some coolant every three months or so, and I wonder if it's a level problem or just a random condition that makes me check the coolant level and top it.
Thanks!
Coolant pressure can kick the coolant light on at:
1. Low pressure condition
2. High pressure condition
3. Both.
If I ever put such light on a car, it would be low pressure condition. In that way, as temp goes up pressure should build up, otherwise there is a coolant leak somewhere. I always check it in my rally cars, and saved my *** once, pointing to a stone-hit damage in the radiator long before the high temp drama starts.
High pressure would point to faulty cap. Not bad info, either.
I must add some coolant every three months or so, and I wonder if it's a level problem or just a random condition that makes me check the coolant level and top it.
Thanks!
06-07-2006, 04:28 AM
#9
Rennlist Member
I had the impression that the pressure switch did not activate the coolant level warning by itself, but it simply serves as an indicator for the central warning unit to remember that the coolant was low while cold. I posted the relavant tech doc page here but I'm still not 100% clear on what the intent was.
The way I read it, if low coolant is detected then pressure is detected, then so long as the pressure switch remains closed the warning system will "remember" that the coolant was low, even if the sender says otherwise later on if the car is restarted while warm. I assume that the whole thing then resets if the car sits long enough for the pressure switch to open. What I still don't get is, how does it know the difference between that scenario and one where you simply open the cap(and relieve pressure) while hot and add coolant.
The way I read it, if low coolant is detected then pressure is detected, then so long as the pressure switch remains closed the warning system will "remember" that the coolant was low, even if the sender says otherwise later on if the car is restarted while warm. I assume that the whole thing then resets if the car sits long enough for the pressure switch to open. What I still don't get is, how does it know the difference between that scenario and one where you simply open the cap(and relieve pressure) while hot and add coolant.
06-07-2006, 09:58 AM
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Man, it was clearer before reading the tech note! 
Now, one just know that it's something related to turning engine off and on to clear the light. The funny thing is I switch engine off and on and light does not come! (exactly was this was intended to avoid?)
Oh, well.
Now, one just know that it's something related to turning engine off and on to clear the light. The funny thing is I switch engine off and on and light does not come! (exactly was this was intended to avoid?)
Oh, well.
06-07-2006, 11:21 AM
#11
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The warning system assumes that the cooling system is fully functional - that is, that the cooling system will hold pressure.
If the coolant is low, and the pressure switch is open (no pressure), the coolant low warning is set. When the engine is warmed, the coolant pressure switch will be set (normal operation).
If you shut the car down to go into the liquor store, when you come back, the coolant level switch will probably be closed, due to the expansion of the (slightly low) coolant. But - if the pressure switch is still closed (engine still warm), the warning system will remember that the coolant was low, and will set the low coolant warning again.
When the pressure disappears, it is because either the engine has gotten cold or because you opened the pressure cap to add coolant - or at least to look at the level.
When the engine is cranked, the pressure switch is now open. If you added coolant, the level switch will be open, and no warning will be set. If the coolant is still low, the warning will be set again.
The idea is to give you low coolant warnings every time that you crank the engine until you fix the problem.
The only real question - Why didn't Porsche put a level warning on the place that it is really needed - the auto transmission fluid?
If the coolant is low, and the pressure switch is open (no pressure), the coolant low warning is set. When the engine is warmed, the coolant pressure switch will be set (normal operation).
If you shut the car down to go into the liquor store, when you come back, the coolant level switch will probably be closed, due to the expansion of the (slightly low) coolant. But - if the pressure switch is still closed (engine still warm), the warning system will remember that the coolant was low, and will set the low coolant warning again.
When the pressure disappears, it is because either the engine has gotten cold or because you opened the pressure cap to add coolant - or at least to look at the level.
When the engine is cranked, the pressure switch is now open. If you added coolant, the level switch will be open, and no warning will be set. If the coolant is still low, the warning will be set again.
The idea is to give you low coolant warnings every time that you crank the engine until you fix the problem.
The only real question - Why didn't Porsche put a level warning on the place that it is really needed - the auto transmission fluid?
06-07-2006, 11:25 AM
#12
Rennlist Member
Originally Posted by WallyP
Why didn't Porsche put a level warning on the place that it is really needed - the auto transmission fluid?
07-13-2006, 11:30 AM
#15
Do the early cars have a coolent pressure sensor? My 79 manual has no reference to such a sensor and neither does the WSM.
I am currently having a problem with the coolent light. The level sensor measures open circuit (as it should) and the tank is at the proper level. Light still comes on and stays on after the central warning light is cleared. The next step would be some fault in the central warning module?
I am currently having a problem with the coolent light. The level sensor measures open circuit (as it should) and the tank is at the proper level. Light still comes on and stays on after the central warning light is cleared. The next step would be some fault in the central warning module?