968 temperature issue

[tek_121]

Hi all, I have a little problem with my 968, the temperature gauge is going from down to top all the time. It goes (like on a watch) from 8pm to 10pm, as soon as it get hot.

I'm not leaking any fluid, but I see that there a bit of coolant missing in the expension tank.

could somebody point me in a direction? head gasket, thermostat???

[krystar]

bleed the coolant system first.

[ernie9944]

How long ago was your water pump -thermostat done ,could very well be a sticking thermostat or faulty water pump but like suggested bleed the systeme first.You could also pressure test the rad if any leaks it will show up,both hoses coming out of your expension tank & all hoses (motor to the rad) should be check for small leaks,you'll be surprise how a small coolant leak will go undetected.Hope it's nothing serious .

[tek_121]

I did bleed the coolant already, no leaks found.
water pump and thermostat are original. don't really want to undo the entire water pump for nothing! Is there a way to know if she's working fine. Thermostat is not a big issue, not to expensive and easy to change, right?

[krystar]

how many times did ya bleed it....being serious. usually takes 2-3 times to get all the air out. did you turn on the heater when u bled it?

thermostat change isn't that big a job. u just gotta squeeze in there with a pair of angled snap ring pliers.

what do u mean "original"? like...it's never been changed since the car left the factory? if that's the case, it's probably due for a change.

[tek_121]

Ya did bleed it 3 times.
yes heater was on...

Yes I meant never been changed!!! damn it, didn't want to do that yet!

So your all pretty sure it's not the head gasket at least?

Originally Posted by krystar

how many times did ya bleed it....being serious. usually takes 2-3 times to get all the air out. did you turn on the heater when u bled it?

thermostat change isn't that big a job. u just gotta squeeze in there with a pair of angled snap ring pliers.

what do u mean "original"? like...it's never been changed since the car left the factory? if that's the case, it's probably due for a change.

[tek_121]

How could I test the water pump just to be sure before changing it?

Originally Posted by krystar

how many times did ya bleed it....being serious. usually takes 2-3 times to get all the air out. did you turn on the heater when u bled it?

thermostat change isn't that big a job. u just gotta squeeze in there with a pair of angled snap ring pliers.

what do u mean "original"? like...it's never been changed since the car left the factory? if that's the case, it's probably due for a change.

[krystar]

is coolant disappearing from the expansion tank?

another possiblity is that the engine is running fine but it's the gauge that's malfunctioning

[tek_121]

Yes coolant is disappearing from the expansion tank. So i guess it's not the gauge?!?

Originally Posted by krystar

is coolant disappearing from the expansion tank?

another possiblity is that the engine is running fine but it's the gauge that's malfunctioning

[ernie9944]

Just one question how many miles on the car

[mxfrank]

While I'm new to Porsche, I'm something of a specialist in cooling systems. Here are my suggestions.

- Before you start, there should be a large bubble of air in your expansion tank: fluid should be between min and max when the engine is cold. Don't be thinking that it needs to be full to the brim.

- The first thing I'd do is ascertain what the true temperature reading is. This can be done in several ways, the most accurate being to measure the temperature at the block fitting for the upper radiator hose. You can do this with an infrared thermometer if you have one. If not, I can supply inexpensive temperature strips which will do what you need (contact me offline)

- Next would be to confirm the temperature reading on the body of the water pump (not the thermostat neck).

- If the temperature is stable, the problem is in one of three areas: the temperature sender, the wiring, or the gauge itself.

- If your temperature is really fluctuating, The next thing you want to do is feel up your lower radiator hose. Squeeze it, knead it, test it by touch. This is the low pressure side of the system. When the engine rpm increases, a pressure drops and a weak hose can collapse choking off coolant flow, only to rebound when the rpm's drop.

- If the temperature is most unstable at the water pump, then the problem is your thermostat. Porsche uses a peculiar design in which the thermostat is located on the low pressure side of the system. The "normal" path for coolant is to circulate endlessly around the block. The thermostat senses when the recycled coolant is too hot, and changes the flow path so that fresh coolant is drawn from the cold side of the radiator. If you can picture this, the thermostat sits between the hottest water in the system and the coolest. When the thermostat opens, allowing cool water into the block, it sort of douses itself. To make this work, the thermostat is designed with "high hysteresis", which is to say, it closes slowly. As it ages, it tends to lose this property, and can motorboat between full open and full closed. This could also be caused if your fans are "stuck" on, creating too much of a temperature drop.

- If none of this has located your problem, you're probably stuck replacing the pump and thermostat (I know this car well enough to know to do these together)

Mike

[tek_121]

61 000 milles... why?

Originally Posted by ernie9944

Just one question how many miles on the car

[tek_121]

Thanks MXFRANK, i'll do all your reco's tonight... and I'll let you know.
great post, thanks again...

Originally Posted by mxfrank

While I'm new to Porsche, I'm something of a specialist in cooling systems. Here are my suggestions.

- Before you start, there should be a large bubble of air in your expansion tank: fluid should be between min and max when the engine is cold. Don't be thinking that it needs to be full to the brim.

- The first thing I'd do is ascertain what the true temperature reading is. This can be done in several ways, the most accurate being to measure the temperature at the block fitting for the upper radiator hose. You can do this with an infrared thermometer if you have one. If not, I can supply inexpensive temperature strips which will do what you need (contact me offline)

- Next would be to confirm the temperature reading on the body of the water pump (not the thermostat neck).

- If the temperature is stable, the problem is in one of three areas: the temperature sender, the wiring, or the gauge itself.

- If your temperature is really fluctuating, The next thing you want to do is feel up your lower radiator hose. Squeeze it, knead it, test it by touch. This is the low pressure side of the system. When the engine rpm increases, a pressure drops and a weak hose can collapse choking off coolant flow, only to rebound when the rpm's drop.

- If the temperature is most unstable at the water pump, then the problem is your thermostat. Porsche uses a peculiar design in which the thermostat is located on the low pressure side of the system. The "normal" path for coolant is to circulate endlessly around the block. The thermostat senses when the recycled coolant is too hot, and changes the flow path so that fresh coolant is drawn from the cold side of the radiator. If you can picture this, the thermostat sits between the hottest water in the system and the coolest. When the thermostat opens, allowing cool water into the block, it sort of douses itself. To make this work, the thermostat is designed with "high hysteresis", which is to say, it closes slowly. As it ages, it tends to lose this property, and can motorboat between full open and full closed. This could also be caused if your fans are "stuck" on, creating too much of a temperature drop.

- If none of this has located your problem, you're probably stuck replacing the pump and thermostat (I know this car well enough to know to do these together)

Mike

[968 GUY]

You stated that coolant was "disappearing" from coolant tank. I'm guessing that means you have to keep adding fluid. You also stated that there were no leaks found during pressure check. Did you test the cap also? Did the pressure drop during the test? Have you noticed anything strange about your oil? You could drain a little after it has sat to see if there is any water. Coolant does flow thru the throttle body and leaks could be easily missed there. Is the gauge fluxing wildly or steadily? Good call on bleeding several times. If coolant has to be added continuously, with no visible leaks, ouch! Also, check the heater valve and piping for that closely. Bleed, bleed, bleed...check and check again for leaks, sometimes the car has to get hot for leaks to show up, and check wiring to coolant temp sensor. (there are 2, one for DME, one for gauge). I know most of these things are probably obvious, and you may have done most of them, just throwing in all in case something was missed.
Good luck...keep us posted, always looking for solutions to problems others have found for the crazy 968.

[flash968]

also, the fans are 2 speed - the low speed fans should come on at the "8 o'clock" line and the high speed fans should come on at about the "10 o'clock" line

if the fan temp switch is bad (very common) you could lose the low speed fans - this would allow the coolant to rise to the high speed temp before the fans kick on

the fan temp switch is located immediately below the driver side upper radiator hose, has a 3 pin connector on it, and is a pain in the butt to remove with the hose in place, requiring a 30mm wrench or socket - the tank is plastic, so do not over torque

the switch is inexpensive - there is also a low temp switch available, and is highly recommended for warmer areas - check the new parts listing here on this site

this would not account for any changes in coolant level, unless you were pushing it out the top of the reservoir

as to the bleeding of the system, first, make sure you have a bleed screw and not just a regular bolt in there - then, make sure the engine is fully warmed up (thermostat open), the heater is set to its highest temp, and the heater fan is on, before cracking the bleed screw

[smokin_944]

Originally Posted by ernie9944

How long ago was your water pump -thermostat done ,could very well be a sticking thermostat or faulty water pump but like suggested bleed the systeme first.You could also pressure test the rad if any leaks it will show up,both hoses coming out of your expension tank & all hoses (motor to the rad) should be check for small leaks,you'll be surprise how a small coolant leak will go undetected.Hope it's nothing serious .

A pressure test is necessary in this case. I believe Ernie is right. You have to be able to explain the coolant leak. After the pressure test, well... the next alternatives are not so good. I would then check the therm a royal PITA...

[tek_121]

Next alternative being head gasket or worst?!?!

Originally Posted by smokin_944

A pressure test is necessary in this case. I believe Ernie is right. You have to be able to explain the coolant leak. After the pressure test, well... the next alternatives are not so good. I would then check the therm a royal PITA...

[tek_121]

What would be the worst case scenario guys?

[flash968]

warped head or cracked block would be the worst thing i could think of

first, eliminate the obvious things that can cause your problem

verify bleeding with proper method described above
verify proper fan operation
verify pressure
verify REAL temperature (not what the dash says)
eliminate possibilities of leaks

then, if none of those things show you the problem, do a leakdown test to see if it's the gasket

[ernie9944]

Originally Posted by tek_121

Next alternative being head gasket or worst?!?!

I think your putting the cart in front of the horse trying to figure the worst case scenario ,first go througth the check liste provided by Flash & don't forget the all important radiator cap.A bum one will cause a lot of problems with your cooling system get it test. Once again look for small leaks specially around your thermo fan switch,saying this cause it happen to me not on the 968 but on the 944 .Was only leaking when driving around once stop the darn thing will disappear into the nigth,on mine the gasket was gone Thermo fan location as seen with trims & air boxe remove ,upper left of the rad.