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oil sensor...temp- pressure sensors and wires

The old sensors (2 in 1) were basically the equivalent of combining the oil pressure sensor and the oil temp sender? So the first pic is the oil temp sensor
And the second pic is the combo sensor

Reason I ask, the current 2.2 rebuild has pressure switch pot up front by the oval breather cover, and the only available threaded port on the rear of the engine is where the oil temp sensor lives. I can remove that sensor (oil temp) and replace that with one of the combo sensors? That gives me both sensors using the one threaded port yes? Am I missing some thing?
On a related question...this engine had a cobbled wiring harness. The red/green wire for the pressure sensor is free as is the black wire for the oil temp sensor...but the wire for the oil pressure swithch ( the pot ) is missing. My diagrams show that wire as the red/black wire in the engine harness coming through the 14 pin plug. Is this correct?

Thanks

Speedo
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1974 911 coupe 2.7 "Ernie"
1971T-ST coupe 2.2 S "Gonzo"
1971 911 T targa 2.2T-2.4E "Sorg"
1970 914-6 2.7 (RS ?) Name-less
1966 R clone coupe 2.7 RS "Axel"
Old 04-08-2012, 09:10 PM
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Lars

I don't think Porsche ever made a combo oil temperature/pressure sensor.

The sensors in your second pic look like the thermal time switch that is threaded into the breather cover on the MFI engines.
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Old 04-09-2012, 02:08 AM
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The lower picture is of thermal time switches. They operate the cold start injector/valve while the starter motor is engaged below somewhere around 45 degrees ambient in usa specs, not celsius.

One terminal goes to the cold start injector from the starter motor solenoid primary wires and the other is a 12 volt heater element around the cold internal temp sensor that heats it up while trying to start the cold motor.
The pupose of the internal heater element is to heat up the sensor to simulate a warm motor and stop it from sending 12 volts to the cold start injector so it doesn't keep on spraying fuel flooding the motor if the cold motor won't start and you keep operating the starter motor trying to start it.
Old 04-09-2012, 06:18 AM
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Lars

What you can get is a combo oil pressure and idiot light sender. Put in front of engine where the idiot sender resides.

Or you can add, as Porsche did, one of at least two different fittings at the rear of the motor where the cam oil line fitting attaches to the block. The earlier version is just a short banjo fitting with an M10x1.0 female threaded end. Later Porsche switched to a largish steel block, rounded on several of its edges to fit, with a hole for the hollow bolt fitting down its center, and a 10mm threaded hole (some had a larger threaded hole for the larger OD pressure sender) in its top.

Each of these require a different length of threaded block fitting - longer as the pressure holder got wider. And require concomitantly shorter hoses going to the cams.

With your extensive collection of stuff, I suspect you have parts you can match up. And crush washers of about the right size also, one to go on either side of the holder piece. The motors from which you scavenged all those thermo-time switches probably had the parts needed.
Old 04-09-2012, 04:44 PM
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winter
 
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Lars, could you please post your solution, when you decide which way to go.

My ratty '75 targa (which joined you a few years ago on the Ned to Ward leg of your legendary CO drive) has a 2.2 carb'd engine installed by one of the previous owners.

I've never been able to sort out how to get the oil pressure gauge in the cockpit to function, although the idiot light does work, via the sensor at the front (towards the driver) of the engine.

I'd love to merely replace that sensor with a dual one, as you're seeking to do, and as Walt says is possible. Like your car, the wiring harness is a bit strange, and I think also I have a couple of loose wires, IIRC, the red/green one, but I'd have to look to confirm, as it's been a while.

Thanks, and good luck with the project. If you ever are in need of an extra pair of hands, shoot me a PM, I have a pretty flexible schedule and am now down in Boulder for the summer.

Cheers!
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Last edited by Winter; 04-09-2012 at 08:14 PM..
Old 04-09-2012, 08:11 PM
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Here is how I did the pressure sensor for my 3.0 install in a '73 chassis.

Similar to what Walt described.



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Old 04-10-2012, 01:53 AM
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That looks like clever usage of an ATE brass banjo fitting for the brake line on an old ATE M caliper.

Good job! I've seen people use those on the 10x1 threaded fittings on the back left corner of some older longneck 930 Garretson intercooler end tanks so the overboost sensor and wastegate hose can be mounted pointed downwards or off to the side so the rear wiper motor won't hit or scrape them when closing the rear lid.
Old 04-10-2012, 08:49 AM
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Well, the banjo fitting holding an oil pressure sender is a 911 part according to the 1972-3 Porsche Parts catalog. Maybe only on the S, or the E and S? I should have been able to figure that out from the catalog, but couldn't.

My guess is that the earlier S models used it as well. The VDO combined idiot switch and oil pressure sender I think was used on VWs, though it can work on 911s as easily.
Old 04-10-2012, 09:21 PM
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OK, Walt, you've got me very interested in the VW solution (apologies to Speedo for jumping in on this thread, not my intent to highjack it, but I'm really curious about this solution).

So, if I understand you correctly, I replace the "idiot" oil pressure switch with the VW part, I can then also get my pressure gauge up and running. Engine, is a 2.2.

One issue is that I think I still have the '75 guages and wiring harness.

But maybe a better and faster/easier solution than adding tubing, etc., to come up with Tom1394racing's fix?

I'll look into the VDO sender, but any help on posting the part number or link to the actual item that will definitely work on the Porsche 2.2 engine would be appreciated/

Thanks, Lars, for letting me join in on your thread. Let me know which direction you end up taking.

Cheers, all!
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Old 04-12-2012, 10:23 AM
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winter
 
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Is it this one?

German Supply - Parts for VolkswagenŽ Cars - VDO Oil Pressure Sender (Dual Pole) 80 PSI

I'm not seeing it yet on our host's site, but just started looking. Goes without saying I'll buy it from Pelican if they carry it. . . regardless if it's a few bucks more or not.

Cheers!
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Last edited by Winter; 04-12-2012 at 10:27 AM..
Old 04-12-2012, 10:25 AM
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I think, but do not know for sure, that the 2.2 OP gauges would be 150 psi or 10 bar.

Because the senders come in different flavors, I deduce that the 75 psi resistance of the sender is higher for the 5 bar/75 psi sender than it is for the 10 bar/150 psi sender.

And from that I deduce (a logician would say I infer, and he would be right) that the gauges are the same electronically, and simply have different scales on their face plates.

So a nominal 80 psi sender would read 150 psi when the actual oil pressure was 75 psi.

If the VDO dual senders don't come in a 150 psi flavor, a guy could use an 80 or a 75 if he changed his gauge face.

It is my surmise that Porsche, with the advent of the SCs, dropped the gauge face from 10 bar to 5 bar so its customers would not be as alarmed over the small movement the needle made up from 0 at hot idle. They had learned that the oil pressures were never going to be over 75 psi, so why have full pressure at half gauge? Something like that. And had VDO make senders to go with this.

For those interested in the inner workings of these gauges, they are a nice electronic design. The battery voltage is split (divided?) between the resistance of the coil which moves the gauge needle and the resistance of the sender. Which is why high resistance (such as when it is infinite because the sender got disconnected) means the needle pegs because all the current is flowing through that coil. I understand that this kind of meter retains its accuracy no matter what the battery voltage is. So the gauge works as well at 11 volts as at 15, and so does not vary with the state of charge of the battery, how well the alternator works, how many accessories are dragging the voltage down, and so on. But maybe I have that wrong.
Old 04-12-2012, 02:20 PM
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Googling around, I found an assertion that all VOD senders (unless specially noted) are 180 ohms full scale. Thus I assume that a 75 or 80 psi sender reaches full scale sooner. Because it has a weaker internal spring resisting movement of its diaphragm, or different leverage on a spring somewhere, and so on.

JEGS has an M10/1.00 dual contact gauge at 150 psi, with a 7 psi idiot setting, at its part number 918-360023. I think the 360023 number is the VDO part number.
Old 04-12-2012, 02:39 PM
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Thanks, Walt. Interesting to learn more about how these senders and gauges work. It's something I've not really explored, and your insights are helpful.

Thanks for letting me jump in here, Speedo. My offer of extra hands stands if you need any help.

And thanks again to Walt for sharing his knowledge. I'll keep you guys posted as to my solution.

Cheers!
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Old 04-13-2012, 02:23 PM
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