911 oil filter thread sizing (for sandwich plate)

Alexandphoto · 12-26-2021, 01:42 AM

I’m going to be putting some aftermarket gauges on my car for oil pressure and oil temperature, and I’m looking to do this via a sandwich plate on the oil filter housing as I believe that’s going to be the best point to tap in at.

Does anybody know the sizing of the oil filter threads/pitch? I’ve been searching and haven’t found a concrete result.

1976 911 S

Thank you

stownsen914 · 12-26-2021, 04:14 AM

The oil filter won't be the best place for measuring oil temp or pressure on a 911. The 911 is a dry sump motor, and the filter is on the scavenge side of the system. Pressure there is less relevant to the overall health of the engine, and the oil temp there will be hotter as well as it's the "spent" oil that's just been pulled from the sump.

You'll be better off measuring at the factory measurement locations for pressure and temp on the engine block. It'll be important to match the senders to the gauges you're planning to use. You might be able to find adapters to use aftermarket ones in the factory locations if that's the direction you prefer to go.

hcoles · 12-26-2021, 05:09 AM

Doesn't the car already have pressure and temperature? Re. temperature you can get a gauge that reads in Fahrenheit. I suppose something like that for pressure is out there or could be made up for you. Maybe I'm not familiar with a 76 S

HarryD · 12-26-2021, 10:23 AM

Your car should already have gauges for temperature and pressure. The sensors are on the motor. The temperature transmitter should be on the right side of the blower fan. The pressure transmitter should be in the same place or at the back of the motor in the triangle of death.

In my 1973, this is the location of the transmitters (near the blower motor). I do not have a oil pressure switch. The big can is the pressure transmitter and the small one is the temperature transmitter:

Per the PET, for your car, item 28 is the temperature sender. Item 47 is the pressure transmitter. Item 49 is the oil pressure switch.

HarryD · 12-26-2021, 10:32 AM

Quote:

Originally Posted by stownsen914

The oil filter won't be the best place for measuring oil temp or pressure on a 911. The 911 is a dry sump motor, and the filter is on the scavenge side of the system. Pressure there is less relevant to the overall health of the engine, and the oil temp there will be hotter as well as it's the "spent" oil that's just been pulled from the sump.

You'll be better off measuring at the factory measurement locations for pressure and temp on the engine block. It'll be important to match the senders to the gauges you're planning to use. You might be able to find adapters to use aftermarket ones in the factory locations if that's the direction you prefer to go.

Just to pile on. The oil that passes through the oil filter may have been cooled by the external motor cooler, if installed.

As noted above, the pressure at the oil filter is meaningless as it is not the pressure inside the motor.

This drawing is helpful.

Quote:

Originally Posted by HarryD

… snip…

This is a diagram of the oil flow in your 911:

Note there are two circulation loops.

They are as follows when at operating temperatures:

Scavenge Side: From the engine sump, through the scavenge side of the pump (if equipped, to the external oil cooler), through the filter and into the tank.

Pressure side: From the tank, into the pump, through the engine mounted cooler, to the cams, crankshaft, carrera tensioners and into the engine sump.

Walt Fricke · 12-26-2021, 10:18 PM

Alex - trust what these guys said. The pressure where you were thinking of getting it is not useful for anything (you want to see what the bearings are seeing), and the same with the temperature unless you are perhaps intending to do some kind of engineering study of cooling efficiencies, for which you'd need to gather temperatures at a number of other places.

Alexandphoto · 12-28-2021, 01:07 AM

Thank you all for the great advice, really appreciate it. Lucky I asked before diving head first into the sandwich plate!

Great call about the suggested location too. I would like to retain the factory gauges and add these as an additional reference item, just in case the factory gauges ever play up. They already do in fact, when turning the headlights on the temp will jump ~20F

I have installed one of the MOCAL/SETRAN external oil cooler kits available through pelican parts, and I’m now exploring the possibility of using an appropriate AN fitting with NPT port, just before the thermostat. I believe that would allow for a valid reading?

That way there would be 2 points in the oil system where both pressure and temp are measured.

Alexandphoto · 12-28-2021, 01:09 AM

Actually, looking through the diagram that was shared that may still be the scavenge side and not as relevant for pressure.

For temperature I suspect it would still be valid though?

Maybe pressure I could get from another spot

'78 SC · '78 SC's Garage

Quote:

Originally Posted by Alexandphoto

...
I would like to retain the factory gauges and add these as an additional reference item, just in case the factory gauges ever play up. They already do in fact, when turning the headlights on the temp will jump ~20F
...

Sounds like you have an electrical problem, likely bad ground. I would address that first.

Alexandphoto · 12-28-2021, 04:04 AM

Quote:

Originally Posted by '78 SC

Sounds like you have an electrical problem, likely bad ground. I would address that first.

It is on the to do list!

But as I am intending to get onto track, I will be adding additional gauges either way. Just trying to figure out the best way to do it.

The more temp/pressure data the better I think!

'78 SC · '78 SC's Garage

Quote:

Originally Posted by Alexandphoto

...
But as I am intending to get onto track, I will be adding additional gauges either way. Just trying to figure out the best way to do it.

The more temp/pressure data the better I think!

My bigger issue was seeing the dinky stock light while focused on driving. I replaced the clock with a more visible light.

The light is a standard LED trailer light. I connected it to the normal warning light via a relay.

HarryD · 12-28-2021, 10:23 AM

Quote:

Originally Posted by Alexandphoto

Actually, looking through the diagram that was shared that may still be the scavenge side and not as relevant for pressure.

For temperature I suspect it would still be valid though?

Maybe pressure I could get from another spot

All the factory locations are on the pressure side.

Walt Fricke · 12-28-2021, 07:48 PM

As others noted, if you fix the electrical problems which are causing your gauges to move when they shouldn't, you won't need duplicate gauges. I can't say I have ever seen this in a race car. In a professional setup there is often some duplication of critical functions - like spark coils or fuel pumps. But not instrumentation.

The stock gauges are basically trouble free. The temperature sensors never, as far as I can tell, never fail. No moving parts. The oil pressure sensor will eventually literally wear out - a moving contact slides along a wire winding, and eventually will wear the wire through. When the slider reaches that point the gauge will peg. So you will know to replace it. The gauges themselves are also pretty much trouble free. With respect, you are looking in the wrong direction here.

78SC has the same idiot light as I do on my highly modified 911 track car - mine is a trailer brake or tail light (but, being 30 years old, not LED, but it once did its job). The light in the instrument cluster isn't going to get your attention as well as you would like on the track.

The stock idiot light comes on only below just a couple of pounds of pressure. That is way too low for track use. The way to deal with this is to purchase an idiot light sender which closes its switch at 15 or 20 psi. Autometer makes one of those, and you can purchase an adapter to deal with the thread differences. That, along with a better warning light, is what you want. It is hard enough to look at the gauges you have often - looking at two isn't going to work well.

I improved the warning light for the alternator/fan by using a multi-colored flashing LED in parallel with the stock instrument light. Hard to ignore. An other blinking light is to remind me that I haven't switched my video camera on. Drill a small hole in the dash by the instruments where it stares you in the face and hold the LED in with a rubber grommet. You could do the same for an idiot light - or using LED technology, replace the clock with something solid state. Blinking really works - you might miss a standing yellow, but not a waving one. Just Google flashing LED.

If you like electronics, you could consider using an Arduino or the like, or spare channels on one of the various track data systems to set off any variety of warnings and digital displays with much more resolution than the stock gauges - plus you could record and graph the data. The typical sensors for this kind of instrumentation use 5VDC, but these days that is trivial to supply. For oil pressure, just tap the block (part 50 in the diagram) the pressure sensor screws into, and add the sensor. This will allow you to use whatever thread your sensor has. For oil temp, you might purchase the engine breather cover (the thing your breather hose connects to before it goes over to the oil tank) for a later model which has a bung for a sensor. You will get the temperature of the oil mist which flies around inside the engine, and that will be more than adequate, even if it will differ from what the stock sensor measures. Porsche uses that temperature on later models for various purposes.

Here is an instrument you might consider purchasing immediately, though: a volt meter. Lots of options, but an inexpensive one with no installation issues is one which plugs into your cigarette lighter. What you will see is that you are getting a voltage drop when you switch on your lights. I think it is pretty normal to see a drop of maybe a couple of 10ths of a volt. But not enough to affect your gauges. This will help you figure out if you have bad grounds, or something which draws more current than it should (not too likely, though), or maybe an issue with the alternator or the voltage regulator. I think your VR is still the old coil and relay type, and not solid state, and hence subject to points wear. Easy to replace with a more modern solid state one.