1976 Temperature Gauge At Maximum

[Bill Jennings]

The Temperature Gauge (Numbered) goes directly to maximum when you turn on the ignition whether the wire from the sendor is connected or not. Does that mean the Gauge is faulty rather than the sender or could it be a wiring fault?

[JohnJL]

Check your ground connections at the gauge and sender.

[Autoban]

I'm not sure what the resistor value is for the sender unit when the car is cold. You may can look it up somewhere. First thing is to measure the wire coming from the sensor and see if it is either open (not good because there is a short somewhere) or no reading at all (not good because the wire might be broken and has lost contact). This way you can narrow it down to either sender (plus wire to the gauge) or the gauge.

[Bill Jennings]

I have just replaced the sender with part number 90164163200 which I am told is the right sender for a UK supplied 1976 Carrera 3.0 and fixed a damaged part of the wire between the sender and the gauge. I read on here that the sender needs to be matched to the gauge do I have the wrong sender? Now the gauge is showing approx 100f when the engine is cold then rises very quickly to above 300f with the engine running. I have checked the engine temperature just below the sender with an infra red thermometer when the gauge shows 300f and the thermometer says it is about 190f. Does anyone know what the resistance should be across the sender to ground? Is there anything else I can test. My gauge is a numbered gauge by the way with graduations from 80f to 340f.

[spuggy]

Originally Posted by Bill Jennings

I have just replaced the sender with part number 90164163200 which I am told is the right sender for a UK supplied 1976 Carrera 3.0

Pretty sure that's the correct sender for 74-76 and SC, but wrong for a '77, 3.0/3.3 930 or a 3.2 Carrera - or, rather, wrong for the gauges originally fitted to those cars.

For '76, PET lists 901.641.632.00.

For 77-, PET lists 911.606.112.00 for 911/81/85/94, or 930/02/52/53/54.

Changes back to the 901.641.632.00 part for the SC, changes back again to the 911.606.112.00 for the 3.2.

All 3.0 and 3.3 turbos had the same part - 911.606.112.00.

See these threads:

Which Temp Guage sender required??
Hot Hot Hot !

Originally Posted by Bill Jennings

My gauge is a numbered gauge by the way with graduations from 80f to 340f.

So is mine - but mine is a 1977.

I'm pretty sure 1977 is the only year with a gauge that goes to 340. The '77 gauge requires a different sender to the 74-76 and 78 up (until Carrera) N/A cars. Fun, eh?

Try taking it out and checking the #'s on the back.

When you say yours is a "1976" car - are you sure it's not a car manufactured in last part of 1976 for the 1977 MY? That could be to 1977 spec, even with an earlier build date.

That's not even considering someone swapping the gauge later, or the factory running out of the older parts and opening the bin of new parts early.

[spuggy]

Originally Posted by spuggy

I'm pretty sure 1977 is the only year with a gauge that goes to 340. The '77 gauge requires a different sender to the 74-76 and 78 up (until Carrera) N/A cars. Fun, eh?

Try taking it out and checking the #'s on the back.

Hmm. I just checked my spare 1977 gauge - and the date stamp on the temperature portion is kind of debatable for the month, depending on the angle you look at it from. However, the date stamp on all the other gauges from the same car (including the 0-140 PSI pressure gauge in the same instrument) have "111" in the triangle, with "10/76" underneath (my car has a build date of May 1977 on the VIN sticker).

Unfortunately, none have visible part #'s on the back...

[Bill Jennings]

I finally thought of checking the obvious-- the part number on the original sender in the car which is 91160611200. I also looked at the Porsche Certificate of Authenticity that the PO obtained:
Model Year 1977, Production Completion Date 4/1/1976, Date of Registration 1/5/1976, Chassis 9117600150, Engine number 6670193, Transmission number 170836.

Can a January 1976 build date really be a 1977 model?

Any way will order another new sender.

[Autoban]

spuggy, I used to work for VDO and was in charge of oil pressure sender production. The stamp on the back of your gauge indicates that Inspector "111" inspected your gauge and it was manufactures in October 1976. Every quality Inspector was assigned a specific number so we were able to trace back who inspected the product.

Bill, your sender has to match the gauge to make sure the resistor values are correct. You mentioned that you replaced a piece of bad wire. This could cause the gauge to go to the max. scale. Have you tried your old sensor after you fixed the wire?

Juergen

[Bill Jennings]

Juergen,
Yes repaired the wire before removing original sender (it still went straight to max with cold motor)and I still have to trace another fault in the wiring that showed up after changing to the wrong sender. The gauge now has an intermittent shake to the needle which I am assuming is a dodgy connection at the 14 pin connector, or another damaged part of the snder wire.

[Autoban]

It sounds like your gauge is reacting the way it should and the problem is in the wire and connection between the gauge and the sensor. I don't remember the resistor value of the sensor when the engine is cold. If you find a specification somewhere with the resistor value you could purchase a cheap resistor of that particular value and install it between the wire that hooks up to the sensor and ground and see what your reading is. The gauge should show "cold". If not, then you have to trace it all the way back to the gauge.

Juergen

[Bill Jennings]

Juergen,
With old 77 sender gauge goes straight to top and stays there engine hot or cold.
With brand new 76 sender gauge starts at 80f then quickly rises to maximum within a few minutes driving. My conclusion 77 sender is correct but kapupt. 76 sender works fine but wrong mismatched sender.
Wiring fault is frayed wire or loose connection that intermittently interupts signal to gauge and makes gauge needle shake slightly. The fault I fixed was frayed wire between sender and 14 pin plug in engine compartment. I have tried running new wire from sender to gauge as a test with both senders which made no difference to gauge behaviour except it removed the intermittent signal fault.

Note To Self:
The Carrera 3.0 seems to be made from different year parts, some parts from previous years, some carried over to later years and some just for the Carrera 3.0

I could have avoided buying two senders just by pulling the original sender and checking the part number before ordering. However it could have only been a wiring fault as the wiring is in poor condition.

I'm thinking starting a Carrea 3.0 thread where other Carrera 3.0 owners can list the differences of these unique cars.

[Bill Jennings]

I still haven't fixed this temp gauge and have not had much luck finding an instrument repair shop here in Oz.
Symptoms are unchanged, max reading as soon as ignition turned on except for very occasionally it reads normally for about 5 min from cold then suddenly jumps to max. The needle may also spike (shake) during this short time of apparent normal operation. I have repaired a frayed wire from sender to 14 pin connector at engine dist board and also tried running an external wire from sender to grn/blk connection at gauge. It still reads at max with the external wire attached. I also have two new senders with different part numbers and it may be possible they are both the wrong one.

I am unsure if my connection's to the gauge are correct as the bentley wiring diagram does not match my wiring (see pic below). The bentley shows 4 red/blk wires to the right hand pole, grn/blk from sender to the top pole and another wire going to ground from the lefthand pole.
My gauge has 2 red/blk left pole, green top pole and grn/blk from sender right hand pole.
I'm taking the orientation literally as I compare wiring diagram to the back of the gauge.

I am also unsure where the wire goes from the 14 pin connector at engine dist board. Does it go straight to another 14 pin connector at the front firewall?

It getting hot here (opposite season to USA) so must get this gauge working.

Cheers Bill

[Bill Jennings]

Here is the wiring diagram I have!

[jmod]

Hi Bill,

The Haynes diagram (circuit 77) looks much more like your wiring.

[86 911 Targa]

Bill,

Here is the CKT for our '86 which is identical to yours:



You should only have continuity.

[smithcarloso]

your sender has to match the gauge to make sure the resistor values are correct.