When to measure your engine oil?

I have recently changed my oil and appears that I have added 0.2 quarts more than I should. Now when the engine is cold and I check my oil the measurement of the oil is right on, leaving one bar on the top of the scale, however if the engine is warm all of the bars are light. My question is, when shall the oil be measured, when the engine is warm or cold? Also, should I remove some of the oil?

I always measure it cold.

Oil level should be measured when the engine is cold. I do it each time before I start the engine from cold; just turn the key to the first position and wait about 6 seconds for a reading. It's easy to overfill because it's only about a quart from the bottom mark to the top. I like to run the oil at the next bar down from where yours shows with a cold engine. It takes only 7 quarts of new oil after a drain to get there. That provides plenty of room for expansion when warmed up. Your fill may be right at the top with no problem, or may be just a bit too much (the gauge is not very precise). If you start at the full mark and get it really warm, as one would on track, it will expand to be too much.

Measure the oil when the engine is cold and on a level surface. Also, check your oil in the same place so that you get the most consistant reading.

Thank you all for your feedback! I let out almost 1/2 quart of oil, leaving me with the oil level indicator 1 bar below the max limit indicator. This way it should have plenty of space to expand when it heats up.

F1 - I believe you are now running your oil about 1/2 quart too low. Oil really doesn't expand that much that you should be worried about it showing over the fill line every once in a while, as long as most of the time it is showing full up to the line when cold. The fact that you drained 1/2 qt. and it now shows one segment below the top horizontal line, shows it had the right level at the time you drained it. Another thing to consider, is that oil picks up contaminants and moisture as it ages, and will often show as full before you start the car, then if you go on a drive of an hour or so on a nice warm day, if you measure the oil after that, you'll find it showing lower than when you started because the moisture has evaporated out of the system. Each segment represents .4 liters (0.42267528 qt.) so, now you are running that much low. The three segments between the min. and max. horizontal lines represent 1.268 qts. brad

Thanks Beez! Given that I always had the oil level one bar below the Max Line indicator I think that it would be OK if I leave it at this level. After my initial oil change the only time the indicator was at the Max Line level was when the engine was cold, whenever it heated up just a little bit it was over the Max level. I'll be monitoring the oil level and see how it changes and if needed I'll add another .200 quart.

F1: I disagree with brad on this one. Your oil level after draining is just where I want mine; I don't regard it as a half-quart too low at all. I also have an alternative explanation for why the oil level reads higher when the engine is cold than when warmed. After the car sits overnight, the oil has run down from the engine parts to collect at the bottom. Your oil reading should be the highest at this time. Driving the car moves oil up into the engine for lubrication. After a drive, it may take several hours for the oil to drain back down again, so oil level measures on a warmed engine should read less than those on a cold engine.

Jim - You're correct that it does takes some time for all of the oil to return to the "integrated" sump below the motor, but because it's a pressurized/pumped system, it really only takes about 30 minutes for the oil to return to the sump and therefore be able to get an accurate level measurement. The 1999 996s have both the dash gauge and a dipstick, and I spent some time comparing the two, and after about 30 minutes, the level on the dipstick never went any higher, no matter how long I waited after that. As far as the level for running - I guess we'll have to agree to disagree. I don't understand why one would want to run this car 1/2 quart low all the time. I've been very careful with this and have kept it at the top line for a year and 20k miles, and never experienced it going above that line because of expansion, nor have I had any trouble on the track with blowing oil out the back because it sloshed up into the intake runners. brad

brad: Just as having your oil at the full line is comfortable for you, having it .4 (or .5) qt, below the full line is comfortable for me. It's not .4 qt too low, but .4 qt below the full line, with still another half-quart or so to go before more oil is needed. Either way, the engine still gets all the lubrication it needs. From previous reports on CC, it seems more people have over-filled than under-filled. You may be right about the CS not spewing it's hot oil in the engine compartment like the air-cooled 911s did, but one such experience on track led me to keep the oil level below full. I'd like having both the oil level guage and a dip stick. The CS guage may be accurate, but it's not as precise as measures from a dip stick, not that such precision is really needed.

Jim - I agree, the comfort zone is most important - either way, there's plenty of oil in the system. I'd like to see the return of the the dipstick, too... It took me a while to get used to not having one with the 996 turbo , but as it turns out, the gauge on the turbo was quite accurate - probably owing to the turbo's, real dry sump system like the old 911s . You measured the oil the same way as the air-cooled cars, at operating temp with the motor at idle. It was great, because you could add some while car was running, then take another reading, and it would show you where the current level is. made it easy to keep things topped-up. brad

dip stick why can't we use a dip stick from another pcar ? Seems that any dip stick would work if we could measure and mark the stick at full and 1 qt low. JDH

Two problems. First, not only are all Caymans mid-engine, but they are also "hidden-engine" -- there's no easy access to the engine without putting it on a lift or unbolting panels after pulling carpet sections. Second, a dipstick requires a hole that goes all the way down to the "integrated" sump. Without the access such a hole would provide, there's no way for a dipstick to reach the oil to provide a reading. Sadly, there are no such holes available on our engines, and I can't imagine someone drilling a new hole just to provide access for a dipstick (at a minimum, it would void your warranty ).