No oil pressure after rebuild – 1973 2.4t

[Swallowtail]

Hey guys,

I just finished the rebuild of my 2.4t engine. Today I tried to build oil pressure for the first time with the spark plugs removed. I used an external oil gauge but couldn’t get the needle to move at all.

I know there are a couple of threads with similar issues which I believe I have read. I hope to get some tips for my specific case anyways.

My car has no front oil cooler. I now have about 7.5l (8 quarts) of oil in the system. I have cranked to engine in 10sec intervals for 2 minutes.

After that I removed the oil filter. It was wet but had little oil in it. I guess that’s normal since it sits above the tank oil level.

I pre-filled to filter and cranked for another 2 minutes in 30sec intervals.

I then removed the oil sender unit and put a clear tube in it’s place. When cranking the engine oil comes out but but drains very fast back into the engine as soon as I stop.

I have connected the oil pressure gauge in place of the oil temperature sender (see picture). With the port open oil drains out. I guess it’s below the tank oil level.

The next thing I tried was pressurizing the tank with about 10 to 20psi while cranking the engine. This is something I read about but it was in reference to newer cars with the separate dip-stick. I do not know if I achieved the same thing by pressurizing the whole tank but it did not work (cranking for 30sec).

Next thing I would check would be the two pressure relief valves. Both are new since my case had the oil by-pass mod done. I believe I have installed them correctly but of course will check anyways. My car has a new 4 rib oil pump installed.

Another thing I tried was separating the oil return line from the hard line that runs under the gearbox. I was surprised that only a small of oil came out – shouldn’t the oil take drain empty here? I’m also not sure if the rubber line is routed correctly. Could air be trapped in the high spot (see picture)?

I was hoping to get some other ideas on how to proceed.

I also thought about adding more oil. What is the danger if I overfill? The breather drains into the oil tank and I have aftermarket air filters which are not connected to the tank/breather.

Thanks!

[stownsen914]

A couple thoughts ...
You shouldn't expect to see any oil in the filter at this point. The filter on 911 tanks is in the scavenge side of the system, so priming (including pre-filling the filter) there won't help the engine develop oil pressure. The scavenge and pressure sides of the oil system are separate.
You also shouldn't worry about air in the scavenge side of the oil system, or expect to see much oil there at this point. (I assume this is what you mean by the return line.)
Personally I would not pressurize your oil tank. You shouldn't need to do this, and it might damage something.
It looks like you are getting oil at the pressure sender. This is good. So I'm a little surprised you aren't seeing any pressure at all while cranking. It's possible you have air trapped somewhere and it needs to bleed out before you'll see oil pressure.

A couple questions:
Where are putting the clear tube to see oil? Same spot as the external pressure gauge?
Do you have a pressure gauge in your dash?


See the below post that has a diagram of an early 911 oil system. It may help with your troubleshooting.
Oil System Drawing

[Swallowtail]

Thanks for the quick reply! The diagram helps me a lot!

I'll put in here for reference.

I put the clear tube in the threads of the oil pressure sender (point 6 in the diagram). By now the sender unit is back in place of course.
My gauge is connected at point 14.

I do have a pressure gauge in my dash but it shows a constant 2 bar with the ignition on (no crank). I measured a resistance of 86 Ohms between the sender contact and ground. I haven't put much effort into diagnosing this so far. However I have tested the external gauge with pressurized air.

[proporsche]

1st, i`d start with the basic....when you have installed the engine did you have the oil cooler where it meet the S hose plugged? Also S hose at the oil tank ,did you have there plug...??
trust me it happens..i did that once ..drove me nuts for little until i remembered the plug in the inlet of the coil cooler ..
When you said you..Another thing I tried was separating the oil return line from the hard line that runs under the gearbox"
do you meant S hose? there is no oil line under the transmission..if yes and no oil came out look as i have mentioned on the oil tank....

Ivan

[Swallowtail]

Originally Posted by proporsche

1st, i`d start with the basic....when you have installed the engine did you have the oil cooler where it meet the S hose plugged? Also S hose at the oil tank ,did you have there plug...??

Thanks Ivan! Good idea but unfortunately I didn't use any plugs. Also oil is clearly flowing into the case

Originally Posted by proporsche

When you said you..Another thing I tried was separating the oil return line from the hard line that runs under the gearbox"
do you meant S hose? there is no oil line under the transmission..if yes and no oil came out look as i have mentioned on the oil tank....Ivan

I circled the connection I had separated below. This is a return line, no?

[Flat6pac]

I’m trying to understand
Do you have no flow or no oil pressure
Without spark plugs. Spin engine to raise oil flow and move pressure needle, which is right above the oil pump.
No movement, look at #3 to the left being knocked off location on assembly.
Been there, done that…
Bruce

[Swallowtail]

Hi Bruce,

I'm getting oil flow but no pressure while cranking. I'm not sure what exactly you're saying. By "pressure needle" are you referring to the oil pressure sender unit?

I'm still holding out hope for something not requiring a full tear down.

[proporsche]

in that case check as Bruce suggested...

[Swallowtail]

All right. Tomorrow I will first check the relief valves and if they are correct I will remove the oil cooler to check the seals (anybody know if that can be done with the engine in the car?)

Thank you all! Further ideas are always welcome, of course!

[proporsche]

yes if you have carbs ... you can do it in the engine in the car if CIS ,partial engine drop

Ivan

[Flat6pac]

Pressure needle on the dash..
Oil cooler seals aren’t the problem until warm. The thermostat keeps oil out of the cooler and the bottom is not leaking as the tank oil is right there, no pressure there.
Bruce

[Swallowtail]

Originally Posted by Flat6pac

Pressure needle on the dash..
Oil cooler seals aren’t the problem until warm. The thermostat keeps oil out of the cooler and the bottom is not leaking as the tank oil is right there, no pressure there.
Bruce

Oh, I figured by #3 you were referring to the oil cooler seals. Now I see the oil pump three are #3 as well.

Then I guess it's tear down time

[Flat6pac]

When you pull the oil screen it’s liable to have the seal laying there, even toward the chains
If the seal isn’t there, flashlight to see if it’s jammed off location.
I put aviation permatex lightly on the seal to hold in place.
Bruce

[proporsche]

Originally Posted by Flat6pac

When you pull the oil screen it’s liable to have the seal laying there, even toward the chains
If the seal isn’t there, flashlight to see if it’s jammed off location.
I put aviation permatex lightly on the seal to hold in place.
Bruce

that is a PITA..i always double, triple check those rings prior marrying the cases.....
covid times, assembling 930 at wife`s kitchen;-)
https://www.youtube.com/watch?v=2S0OuXyfIMU&t=2s


Ivan

[Swallowtail]

Good news! Found the issue.

When my machinist did oil-bypass mod he put an aluminum plug in the old hole. He obviously didn't remove the "leftover" stud that is present when cutting something to length on a lathe. This little stud protruded into the way of the pressure relief piston not allowing it to close.

I ground an old screwdriver into a long chisel and removed part of the stud. After putting everything together I got about 1bar of pressure while idling.

Just performed the first start and the engine is running perfect with good oil pressure!

[stownsen914]

Good sleuthing to find that, glad you got it sorted!

[PeteKz]

Good job.

[proporsche]

very very good ...
Ivan

[Gonbad]

Awesome Sauce!

[michelko]

what else may the mechanic have screwed up?
Hope no more issues