Oil spurting through breather on '76 911

[ejp]

Hello!

I'm trying to help a friend with a '76 911 that he recently inherited from his dad. When the warms the car up, the oil in the tank backs up and flows through the breather at the top of the sump and fouls the intake. He's checked the oil level and it seems to be correct, so it doesn't seem to be an issue with it being overfilled.

My thought is that there may be some sort of blockage in the oil system, but I don't understand the system well enough to know the common places to look.

Is this a common issue? Where should we be looking? Any advice would be appreciated.

[stownsen914]

First make sure the oil level is being checked with engine warm and idling. If checked cold / not running, it's easy to overfill and end up with what you describe.

If that checks out, you can also check for correct routing of breather hoses, and that they are not blocked or kinked. Crankcase should vent to tank, and tank (as you note) vents to intake.

[Tremelune]

Sounds like it has too much oil. At operating temp, checked with the car running, the oil should be halfway on the dipstick. 2/3 to 3/4 is fine, but is pushing it. At the "min" line is okay, but time to add a quart.

Let us know what the oil level is. My guess is that he checked it with the car off, trusted the dash gauge, or filled it to the "max" line on the dipstick.

[ejp]

Originally Posted by Tremelune

Sounds like it has too much oil. At operating temp, checked with the car running, the oil should be halfway on the dipstick. 2/3 to 3/4 is fine, but is pushing it. At the "min" line is okay, but time to add a quart.

Let us know what the oil level is. My guess is that he checked it with the car off, trusted the dash gauge, or filled it to the "max" line on the dipstick.

Thanks for the replies.

That was my first instinct and I suggested that it's most likely that the oil is overfilled. I explained the process for checking the oil level (full operating temp, with the engine idling and on level ground) and he said that the backup even happens when the oil in the sump is clearly low.

It does bring up the question - how much higher should the sump fill as the car heats up? He seems pretty sure that there is some sort of blockage somewhere in the system. Perhaps the way to test is to drain a few quarts out and run it up to operating temp?

[stownsen914]

You can get a lot of variation in level from car off to car running. Part is expansion of the oil, but the bigger reason is oil migrates from the tank to the engine when the engine is off. So checking cold or engine off (or trusting the gauge as mentioned above) can be way off from reality.

[stownsen914]

As for draining oil, if the tank is full cold, it wouldn't hurt to drain a couple quarts and try again. And just be ready to add if needed.

See if your friend remembers how many quarts were added at the last oil change (assuming one was done). Should take 9 ish for a typical oil change?

Or see if they may have simply added oil after checking the oil level when cold. If they did that, then drain however many were added and check again with engine running.

[Tremelune]

Hm. Perhaps a bunch of oil was in the front oil cooling section when the reading was taken, and when the external thermostat opened at ~190°F, it all poured back into the tank...I dunno.

I'm still banking on overfill and miscommunication...

[targa72e]

overfilled. There is not really a way for the tank to over flow without there being to much oil. When the car is running almost all the oil should be in the tank. There will be a little in the engine but the scavenge side of the oil pump that returns oil to the tank is much larger than pressure side.

john

[ejp]

Thanks again for the replies. My first instinct was overfilled too, and he insisted that it was low.on oil...I probably should have asked a third time before posting. He tells me that it needs an oil change anyway - and I'm having him start with 9 quarts.

Thanks again!

[fanaudical]

Definitely check for correct line routing at the oil tank. My '75 came to me with the line from the air box connected to the side of the tank and the line from the crankcase connected to the oil tank fill neck. It sucked oil.

But assuming lines are correct, it certainly sounds like it's overfilled...

[Gratefulporsche]

Hello everyone
It’s my car that my buddy posted about. I will keep you all posted. Thanks so much for being here

[fanaudical]

Welcome! I have found lots of help here. Post pics of the car!

[Bill Douglas]

Yes, it could be quite a quantity of oil is getting past the "non-return valve"? and backflowing into the sump. Then the tank is filled to the correct level on the dipstick. Once the engine is fired up the oil pump tries to pump it to the oil tank, but not enough room so out the breather instead. Good luck

[Gratefulporsche]

[rwest]

Great looking car, welcome to the board and I hope your problem is as simple as removing some oil.

Best,
Rutager

[75 911s]

Nice car!

[spuggy]

Originally Posted by Bill Douglas

Yes, it could be quite a quantity of oil is getting past the "non-return valve"?

Uh, "non-return valve"? Pretty sure there isn't one. At least from the factory.

If I leave my car sitting long enough, most all of the oil in the tank will seep past the oil pump and into the sump. Dry sump motorcycles with gear (as opposed to plunger/piston) oil pumps do the exact same thing, for the exact same reasons; clearances, time & gravity.

When I did a cold oil change (not my usual practice), I only got a quart out of the tank drain because the rest was in the sump...

[Bill Douglas]

Spuggy, I think your car needs fixing too.

My SC has almost nothing in the sump.

[spuggy]

Originally Posted by Bill Douglas

Spuggy, I think your car needs fixing too.

My SC has almost nothing in the sump.

LOL.

Sure, there should be relatively little oil in the sump overnight or after a week. Now go park your SC for six months to a year and tell me how much you can drain out of the sump.

Dry sump/gravity-fed oil reservoir design might be a relatively unusual configuration for cars, but it was the accepted norm for about 4 decades for sportier (higher output/larger displacement) motorcycle engines. Dry sump filling with oil when left unused because it seeps back into the motor is called "sumping" or "wet-sumping". It isn't some obscure quirk unique to 911s, and doesn't mean that there's anything wrong with it. Necessarily.

"They all do that sir". Some designs are more inherently prone to it than others.

[Gratefulporsche]

So I’m picking up the car today. It seems as though there was too much oil like the people have suggested. I’ll let you all know how the 20 mile trip back is to storage. Once again, thank you all so much for your help is greatly appreciated.