flatsixcrazy

Hi,
Last month my 964 cab is telling that my oil temp is extremely high (it went from o to max in 2 seconds, right after start up) even though the car has not been started in a week. The natural diagnosis is the oil temp sensor on the engine block, next to the oil pressure sensor. I ordered a new oil temp sensor from Sunset Porsche and replaced the old one yesterday. I was disappointed to find out that it did not fix the problem. My next logical step is to look at the oil temp gauge itself. Am I in the right diagnostic mode?, or should I be looking at something different i.e a fuse or something. The gauge seems to be fine since I am showing a good oil pressure on the gauge (2 bars). Please le me know what I should be looking at next?. Thanks. AN

Arjan B.

Oil hot in two seconds is wierd, yo have to check to oil filter etc. with a heat gun [a kind of laser gun which you point on the heat source]to be sure if the oil is really hot. I think it's a electrical problem you have. Normally with the thermostat closed, it takes between 10 and 15 minutes to open it at normal use.

Adrian

The oil temp sensor is a NTC thermistor. What I recommend is that you substitute it with a variable resistor and see what happens. You start at around 4 K ohms and work your way down. Full scale deflection of the indicator indicates a short in the wiring somewhere or an indicator fault.
Max temp in 2 seconds is clearly a wiring, sensor or indicator problem. I would also advise you remove the new sensor and resistance check it. Apply someheat and watch the resistance drop.
My guess is a wiring problem actually. There is no separate fuse for this system and full scale movement tells me you are powered.
I advise you try the resistance checks first because indicator faults are quite rare. I always like to try and prove an expensive part has failed first.
Ciao,
Adrian
964C4

flatsixcrazy

Thanks Arjan and Adrian
I'll do the heat check on the sensors as you advised. AN


Arjan,
Where in Holland do you live? I used to live in Friesland for a short period when I was growing up. I still have my adopted families and a biological sister in Groningen. I visit them every other year. Beautiful country with incrediblely nice people. AN

ian c - u.k

don't these guages read "full" when the earth is disconnected ???????

Arjan B.

Flatsixcrazy,

In the Enschede Area, Overijssel. Nice country?? Hmmm not that great, I am more impressed by your Country. My wife is not interested enough, otherwise I would try to immigrate to the USA. I think there are more chances for us. Now I am in the USA once or twice a year. Always great to be there.

flatsixcrazy

Ian,
How do check the ground integrity of the gauge?. I've checked the sensor and will pull out the gauge tonight. Is there a way for me to check if the gauge is grounded?. Thanks. AN

ian c - u.k

what happens when you disconnect the wire from the sensor ??

i am pretty certain these guages read max when they sense no sensor .

if i remember right , the sensor is a 1 wire connection ??
if it is , then the thread of the sensor screwing into the engine finds earth .

flatsixcrazy

Ian,
When the wire is disconnected from the sensor, the indicator does not give any reading,( i.e the needle did not move when I start the engine). There is only one wire (green/black stripe) connects to the sensor. The green/black stripe wire comes from the same wire bundles as the oil pressure sensors. When I pulled the gauge out, the the electrical connector in the back of the guage, that correspond to the oil temp indicator, does have a few electrical wires to it, along with a brown wire which I assume is the ground or earth. The other wires are for the check engine lights, and the ABS lights and other purposes. I am trying to find a way to test the indicator if it is functioning. I may have to crack open the gauge and take a look inside to see if there are any corrosion in the circuits. The gauge has 135K miles on it, maybe, it's time for it to go **** up?. If you or anyone know of a way to test this gauge, please let me know. Thanks in advance. AN

ian c - u.k

first , you need to get a meter and check continuity in the green wire (from guage to sensor)
then continuity betwween brown at guage and chassis earth .

then continuity betwween "nut-shaped" bottom of sensor and chassis .

if all these are ok , i would remove sensor , clean threads and re-fit .

if all else fails , you could try a "swap meet" with another local porsche owner to try his sensor , then guage etc.

sorry , but i do not know how to test the guage itself , only to eliminate wiring faults , then try the guage in another car !!!

flatsixcrazy

Ian,
That's great help already. It gives me a starting point. I am a medical researcher, so naturally, I am very poorly at using electrical theories. I am going to try your sugestions and report back to you guys in couples of days. By checking for continuity, you mean I should turn on the ignition, connect one probe to the electrical wire and the other probe to the sensor?. If there is electrical continuity, the meter should register 12V?. Thanks so much. AN

ian c - u.k

no !!!!!!!!!!!!!!!!!!!

does your meter have a function that beeps / buzzes / whips the needle when you touch the probes together ??

if not , buy/borrow/steal one that does

checking continuity of a wire is the same function as testing a bulb , fuse etc.

the meter sends a signal to one probe , which you put on say 1 spade of a bulb . then you put the other probe on the other spade .
if the filament in the bulb is ok , then a circuit will be made and you meter will tell you you have "continuity" !!
ie. the fuse has not blown , the bulb has not blown , there are no breaks in the legnth of wire .

did you ever have a go at threading that loop over the funny shaped bent piece of welding rod at a school summer fair ???
the thing that buzzes/flashes when you touch ???
............................ continuity !!!

ian c - u.k

oh , and obviously , if nothing happens , no buzzes , bleeps , needle movement etc. then you have no continuity , ( blown bulb,fuse,broken circuit etc.)

what meter have you got ??
pm me if you like

ian