Michael Delaney

I recently ordered a 210 deg. thermoswitch for the front oil cooler oon my '91 C2. Before replacing it I checked it with a meter between the two contacts and it reads open. Checking the one on the car I found continuity between the two contacts. Is this thermoswitch defective, or does the 210 deg. t-switch(a BMW part) work differently? Any help out there? Thanks, Roy Eames

Adrian

Dear Roy,
You can only compare Porsche to Porsche I am afraid. It is possible to make the system use a normally open set of contacts or a normally closed set of contacts. You can open a circuit to make things work as well as to connect a circuit to make things work. Both are valid,
Ciao,
Adrian
911C4

Adrian

Dear Roy,
I just wanted to check that we are on the same page. You can email me privately if you wish. You have purchased a new oil temp sensor. The one used to activate the oil cooler fan.
I have checked the wiring diagram and you should read some resistance through this sensor. I think it is a PTC sensor which means the resistance increases as the temp increases so it will start as a short and the resistance will rise as the temp does. Now the BMW version may be a NTC or negative sensor which means the resistance starts high and goes low as the temp increases. Obviously they are not intechangeable. The oil temp sensor feeds the heating/aircon control unit which then activates the oil cooler fan relay at a specific temp. The thermostat valve which opens the oil cooler lines themselves is mechancial system.
Ciao,
Adrian
911C4

Michael Delaney

Adrian, Thanks for the reply. I understand that the circuit could work either way. My question, more clearly stated, is how does the switch work on my C2? Is the switch closed when cold and then opens upon reaching its temperature setting? Or the reverse? I thought it would be easier if someone could answer this for me than to remove it and check it physically by heating. Roy Eames 91 C2 Cab.

Adrian

Dear Roy,
I have received your private email and will respond. It is not a switch but temp sensor. Your test as written in the private email as you know confirms this.
What I would do and I am saying this for all to share because it may help others is to possibly install a resistor in series with the sensor and crank up the resistance a bit,
Ciao,
Adrian.
911C4

Pete911air

Roy and Adrian,
964 and 993 have a problem with the two speed resistor. Remove the relay and bridge with a jumper wire to see if you have low and high speed fan. Look at the wiring diagram for the correct terminals. The new resistors have a heatsink and won,t burn out anymore.
Pete.

Michael Delaney

Pete, I don't have access to a wiring diagram so if it's not too much trouble could you give me the numbers on the relay receptacle to jump? Also where physically on the car is this resistor located? Thanks,Roy

Pete911air

Roy,
Remove relay R04 (oil cooler)and jump terminals 3(30)and 5((87)high speed) also 3 and 7((87c)low speed)
Same test for relay R14 (a/c condensor fan)
Hope this will help.

Pete.

Pete911air

Roy,
If you have to replace the resistor, you would have to remove the right front wheel, inner fender and it is behind the oil cooler mounted to the sheetmetal.It takes about 2 hous to replace and it is not easy.
Pete.

E. J. - 993 Alumni

Hey Pete,

Same relay numbers and terminals for my 993?

Thanx,

Michael Delaney

Hi Pete, Finally found time to run the check you sent and happily found both hi and lo speed fan functions work with the jumper. If I'm thinking right this tells me the resistor is functioning correctly. Strongly suspect the thermosender as I am reading resistance across it when stone cold.(per Adrian) Have a new one on the way as well as a relay. Probably should have a spare relay anyway as I have found three of these on the car. As a curiosity, does this same relay that serves the rear blower motor also work on a hi/lo function? Thanks for your excellent info and instructions. Roy 91 C2 Cab

Pete911air

E.J.
EXACTLY THE SAME ON 993.
PETE.

E. J. - 993 Alumni

Thanx Pete

Roland Kunz

Hello

Yes the rear fresh air fan has two speeds.

The new resistors are also better protectet against corrosion.

Grüsse

Michael Delaney

Hi guys, Got my new oil cooler thermoresistor and relay for same today. Checked the resistor and it read 14.3 K ohms when cold. Installed the resistor and relay and wathced the car warm up. I left the fenderwell liner off so I could see the fan. When the temp gauge reached the first mark past warmup(still in lower half) the oil thermostat opened and began moving oil through the front cooler. When the temp gauge just passed level(halfway on the guage) the front cooler blower kicked on low speed. This brought the temp back down below the first mark past warmup, and stayed there.Assuming it would not get the fan to the high side until it got much warmer than the car was willing to.All this at idle.Then drove the car and everything is nice and cool. A succesful repair! Wouldn't have run this thread so long except I thought it would probably help someone out there. Thanks for the help,Adrian,Pete, and Roland. Great List. Roy Eames 91 C2 Cab