Oil pressure or volume?

alniki · 03-26-2009, 11:23 PM

Would the engine be running just fine if oil pressure and temperature are both within normal range but the oil volume is only half or less as manufacturer suggested?

Any personal experience? Thanks!

DRACO A5OG · DRACO A5OG's Garage

Do you mean Oil Level?

If Oil Level, do not trust the Guage, it is only a guide. You should check level with engine at normal running temps and then keep her on and check the level at the dip stick.

In your car, while you accelerate, the oil level will go down to red. This is normal. At stop the needle will bump back up to where it should be. If she stays at red all the time would indicate oil level is too low. Again check as stated in the manual.

alniki · 03-27-2009, 12:26 AM

Thanks! I mean the total oil volume of 13 Qt. as suggested by the manufacturer, not where the needle lies in the gauge.

Newsboy · Newsboy's Garage

If your oil pressure is O.K. , your probably O.K. But why would you want to run the car on 6 Quarts? This leaves only a few quarts in your oil tank. Is this just a hypothetical question?

T77911S · 03-27-2009, 03:21 AM

i never fill mine all the way up. if i was going to track the car i would for the extra cooling.

alniki · 03-27-2009, 04:48 AM

Sadly, it's a real-life question for my engine. A few days ago when I slowed down from 5000+ rpm on the 2nd gear for a stop light, there was a strange whining sound from the engine bay which changed to a horrible loud knocking sound as the rpm dropped. I stopped the engine, checked the engine bay for loose parts (I just did a cleaning job for the fan/alternator a few days before), nothing! Restarted the engine, the knocking sound was still there. Since it's only a few blocks from my home, I limped back. While parking, the engine stopped, probably due to low rpm on releasing clutch, and would not crank again. Took it to a garage on a flatbed, the mechanic ran the starter for a couple seconds, it cranked. He said he never heard of such strange sound from a 911. Tried again, it would not crank. Drained oil from engine case, got about 2 quarts only and there was a small pyramid of metal shaving on the oil plug. . Drained the oil tank, no oil there. The mechanic thought the engine crank probably seized due to lack of oil.

Sounds logical except that the oil pressure was always more than 4 bar at 5000 rpm and the oil light only blinked now and then at idle. The engine ran pretty smooth after injector replacement but it probably consumed as much oil as before. Engine rebuild seems inevitable anyway but I'd like to know if there is other possibility or what parts will need to be replaced beforehand.

ossiblue · 03-27-2009, 06:17 AM

Reading your last post, I audibly moaned. Sadly, I think your mechanic is spot on. Pressure can still be high with low volume--there's only about 3-4 quarts of oil in the block when running anyway--but the cooling ability and lubing breakdown caused by overheated oil is likely what doomed your engine and those elements are provided by the volume of oil circulating through the cooler and tank. Hope I'm wrong, but looks like you've got a rebuild in your future.

T77911S · 03-27-2009, 07:05 AM

check to make sure a rocker shaft did not come out or you dropped a valve. you can pull the plugs and verify that each piston is moving. turn it over by hand and see how it feels. i would do some more investigating before i wrote it off.

DRACO A5OG · DRACO A5OG's Garage

Can you post a video of the sound and where you suspect it is coming from?

alniki · 03-27-2009, 05:08 PM

Car has been in the garage waiting for engine drop and disassembly in a couple weeks. I was suspecting a cracked flywheel, a low probability, or broken clutch due to the strange sound before the findings from oil drainage. I'll tell you the 'autopsy' results then but any comments are welcome before that :-)

alniki · 03-29-2009, 07:56 AM

Quote:

Originally Posted by ossiblue

Pressure can still be high with low volume--there's only about 3-4 quarts of oil in the block when running anyway--but the cooling ability and lubing breakdown caused by overheated oil is likely what doomed your engine and those elements are provided by the volume of oil circulating through the cooler and tank.

If there's only about 3-4 quarts of oil in the block when running then I guess the crank is probably fine as my oil temp was OK.

Since the spark plug of cyl #6 was always oily, either the valve guide or the piston ring was no good and probably broke at high rev, hence the metal shavings at the drain plug. As the knocking sound likely was not from a seized crank and the engine did crank intermittently after the break, it's probably a problem other than the crank. Just a guess before disassembly, we'll see.

T77911S · 03-29-2009, 08:21 AM

since you have drained the oil, go ahead and pull the valve covers and check the rockers. i had a rocker shaft come out once, sounded like i dropped a valve. very loud knock. i removed the valve cover just to look and found the shaft had come lose. put it back in and all was fine. i thought for sure my motor was gone.
also look for broken valve springs.
pull the plugs and turn the motor over with a wrench. put a wooden dole in the plug hole to veryify the piston goes up and down, just in case you thru a rod.

i dont like that you said the oil light blinked at idle. if you do a rebuild, replace the oil pump.

ossiblue · 03-29-2009, 08:26 AM

Quote:

Originally Posted by alniki

Since the spark plug of cyl #6 was always oily, either the valve guide or the piston ring was no good and probably broke at high rev, hence the metal shavings at the drain plug. As the knocking sound likely was not from a seized crank and the engine did crank intermittently after the break, it's probably a problem other than the crank. Just a guess before disassembly, we'll see.

That, too, is a real possibility and a less expensive fix. I hope you're right and be sure to let us know.
BTW, do you know why there was virtually no oil in your tank? Could you have blown out that much while driving?

alniki · 03-29-2009, 04:58 PM

This motor had been consuming a lot of oil for the last two years. I planned to rebuild it myself when I got the working space and since it's a weekend fun driver I thought there's no emergency to do it right away and just replaced the oily spark plug frequently. The exhaust did have a strong burned oil smell at idle, on the other hand I also revved the motor pretty hard everytime I drove it -- that's the way to enjoy a 911, IMO

The motor did not leak, so the oil was mostly consumed through the combustion chamber, I think. Actually, the oil light never blinked when there's enough oil (but still not up to the level of the lower mark on the check stick or to raise the oil gauge needle) and once it blinked at hard cornering or braking, I add a quart to the oil tank. That had worked just fine until I read the owner's manual, a PDF from a nice Pelican, and learned that occasional oil light blink at idle is normal, then I probably became a bit sloppy at adding oil and just monitored oil pressure and temperature.

The engine is now in a specialist garage. When it's to be disassemled I'll be there to check the rocker arms and shafts first. At the least or best, a top-end is needed considering the heavy oil consumption.

Thanks for all your comments!

alniki · 05:08 PM

Engine dropped and intake removed. The engine case was broken at the upper part. Looking down through the hole, the crank bearing surface was exposed and dented. The rod #5 was not clearly seen, probably dropped to the case bottom. The wrench said it's the first time he saw a broken 3.2 case. Catastrophic and an infamous record. The man who broke the tank of Deutschland, instead of Bank of England

Now looking for a swap engine.

ossiblue · 04-06-2009, 07:10 AM

Sorry about the bad news, you can believe all of us were hoping for something far less "fatal." As you probably know, there are many engines offfered here, so keep those eyes peeled, and good luck.