Excess oil in sump

[welshdragon]

2.7 1977 911
When draining the oil there was so much from the sump when all the info says the majority of the oil is in the tank. And as the oil tank will fill when the engine has been running can you tell me what stops the oil returning back into the sump when the engine is not running.
Is it that the clearances in the bearings are to small to allow the oil to drain back into the sump under gravity if so I may have to much clearance in the bearings?
Any help very welcome 🏴󠁧󠁢󠁷󠁬󠁳󠁿

[dannobee]

It slowly drains back through the oil pump gears.

[welshdragon]

Originally Posted by dannobee

It slowly drains back through the oil pump gears.

Thanks for your reply
Does that explain why the oil level reads low on the gauge when you start the engine and rises after a time
Also do you know if the oil pumps are prone to wear
Thank you

[Mark Salvetti]

I don't think the oil pumps are particularly prone to wear. Unless you have huge mileage on that car, it's probably OK. Are you thinking if the pump was worn it would be more likely to allow the oil to drain back?

Some cars just do that. Rothsport sells a check valve to prevent it.

I think the oil level being low at startup is more a function of temperature. The oil expands about 10% when it gets to operating temperature, which on a 911 means expansion adds over a quart in volume.

Mark

[stownsen914]

Equalizing of the oil level in the tank with that of the engine sump is a common issue on older 911s as dannobee noted. And yes the tank level will be measurably low when this happens. Unless your engine is leaking, or oil is getting somewhere you don't want it (it can get to the muffler in some cases and make a smoke bomb), don't worry about it.

[GH85Carrera]

Originally Posted by welshdragon

Thanks for your reply
Does that explain why the oil level reads low on the gauge when you start the engine and rises after a time
Also do you know if the oil pumps are prone to wear
Thank you

No.

The level on the gauge is useless, until the engine is warmed up to operating temps. Don't bother checking the oil level on the gauge, or the dipstick until the engine is warm, and at idle for 60 seconds on flat ground. Get the level between the two marks on the dipstick at that point. Don't fill the tank to the top mark, that is overfull.

[timmy2]

Lots of oil in the sump if you don’t drain it while hot as recommended.
Hot oil change is what the published info is based on.
Drains back from the tank over time.
When hot, lots come from the tank, not so much from the sump.

[DerkPerk]

So if the oil drains back to the sump, and you can drain the sump during the oil change, why does it need to be hot?


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[Zuffenwerker]

Hot oil changes are always good because theoretically there could be things in the oil that settle when cold but come out of the drain plug more easily when hot. On the new 911s it’s important to drain hot otherwise it will take forever to do a proper oil change.

[Alan L]

You should always drain oil hot. Never cold unless there is some compulsory reason - failed engine that needs to come out. Cold oil is like treacle. You will leave a whole lot behind and any gunk that is stuck to it. it doesn't need to be full temp, but very warm is a lot better than cold.
Alan

[DerkPerk]

I fully understand changing warm oil is better, and following that practice in all my vehicles. Jeep, truck, DD, air and water cooled P-cars. I was more curious on the topic of why the oil migrating from the tank to sump once cool and if it gets trapped in the motor somewhere of cool.


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[Mark Salvetti]

There is actually a lot of oil trapped inside the oil lines and engine nooks and crannies. The capacity is what, 12.5 quarts? But an oil change typically only requires 10 quarts to refill.

Mark

[Alan L]

Yes - for a 911 there is only a partial oil change. Unless you want to drain the lines at the thermostat.
But the oil tank is the highest part in the system, so at rest some oil is always going to drain to the lowest point - crankcase. Longer been sitting, more in crankcase. Something to remember if you suddenly decide to set the valve clearances. The exhaust valve covers will almost certainly be holding back a small tide of oil. You can lift that side of the car to avoid being swamped, or run it for a couple of minutes to pump some out, without the engine getting warm, or better, both. Or drain the stuff in the crankcase first.
Alan