OEL to Dipstick Comparison
 

1980 911 SC US spec


I have a question that’s a little involved. I just completed a major service in which I removed the CIS system to replace the airbox. I also installed SSI heat exchangers, which required rerouting the oil lines, and removed the valve covers to set the valve lash. During all this I drained the oil at several points, including some of the main oil lines. This is my first oil change since I bought the car, so I tried 10L of oil for the refill. It ultimately took 12L to get to the middle of dipstick when up to temperature.

My question concerns the OEL gauge. When I first acquired the car, the OEL gauge moved a lot when driving and it rested around the 1/2 mark. I think the oil level was too high because the intake had considerable oil residue in it. After this full service, I used 20w50 oil. The OEL gauge is now resting a little above the red mark and will occasionally move up to about the 1/2 mark. The dipstick read the middle between min and max on the dipstick. Should I be concerned about the lack of movement on the OEL gauge and the resting level fairly low?

Those OEL gauges are notoriously inaccurate. You do know the car should be at operating temp, at idle and resting level. I just rely on the dipstick but the float is relatively easy to replace if you want to go that route.

Thanks, Walt. That’s what I was hoping to confirm—that the OEL gauge is not precise. I am checking the oil with the engine up to temperature and on a level surface.

I find that my Oel gauge may not be accurate, but it is consistent. Keep in mind that the oil level in the tank changes depending on RPM and whether you are driving straight and level or hustling through the curves. But if you are cruising down the highway at constant speed, it should be consistent.

The owner's manual has the ungarbled word. The oil level gauge should only be read when

• oil is up to operating temperature range
• motor running, idling for at least 30 seconds
• car parked, on completely level surface

Exactly the same conditions under which the dipstick reading is accurate.

I top off the oil with motor running, looking through the rear window at the oil level gauge, allow a few seconds for reading to stabilize, then double-check the dipstick.

They've always corresponded 100%. Every time. If yours doesn't, it's not working correctly.

When you're moving, the oil gauge should be completely ignored because it's entirely meaningless. It can vary anywhere between empty and 1/3 full, seemingly at random.

But it's very handy to check the oil level if you're sitting on the level at a red light.