low oil quantity reading
12-17-2006, 09:09 PM
#1
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low oil quantity reading
Iv'e noticed that my "new" 87 carrera coupe shows oil quantity gage reading in the red when I first start in the morning. Then after about 5 minutes it goes to normal and stays there. Anybody have any idea why it does that and is it normal. Checked dip stick and it's full.
12-17-2006, 09:19 PM
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It is normal...so I am told....
The best reading will come after the oil has warmed to operating temp and you are on a level surface. However, I only rely on the actual measurement with the dip stick. Of course, you check the dip stick with the engine running.
12-18-2006, 01:01 AM
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Me too. I picked up my 911 in Kansas City and drove it around 1500 miles heading back to LA) before checking the oil at a gas station. The oil level kept showing low (in the red) and I was worried. I fumbled for the dip stick and it was at the minimum. I was concerned and quickly added 2 quarts. Not good but apparently no harm from what I can tell.
The only bummer is that I had a shop in KC do I valve adjustment and the right side is loud. I suspect I will have to have them adjusted again. I thought I was being smart as the 911 was right at 45k miles so I wanted it done before heading back to LA. Oh well.
The only bummer is that I had a shop in KC do I valve adjustment and the right side is loud. I suspect I will have to have them adjusted again. I thought I was being smart as the 911 was right at 45k miles so I wanted it done before heading back to LA. Oh well.
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12-18-2006, 02:04 AM
#9
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The engine is a dry sump, which means that oil is not pumped directly from the bottom of the engine, but rather it is pumped from an auxiliary oil tank that sits at the right rear fender. Oil is sucked from the bottom of the engine by a tandem oil pump. Oil, like any gas or liquid, expands or contracts depending on the temperature of it. The oil level will therefore show very different levels in that tank depending on the temperature. Furthermore, oil is thicker when it is cold, which means that more oil will be sitting at the bottom of the engine until the engine warms up. So the only way to check the oil in your car is after it has warmed up (for about 20 minutes) and with the engine running, on a level surface. And even then, the gauge might be off. The only surefire way to check the oil is with the dipstick
12-18-2006, 09:47 PM
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my concern was that the engine might be "wet sumping". somehow the oil might be draining back into the crankcase over night and reading red on the gage in the morning, then pumping back into the oil tank after startup and going to normal range on the gage But I obviously am quite mechanically illiterate regarding porsche engines. Thanks for all the comments
12-18-2006, 11:59 PM
#11
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Originally Posted by spad01
my concern was that the engine might be "wet sumping". somehow the oil might be draining back into the crankcase over night and reading red on the gage in the morning, then pumping back into the oil tank after startup and going to normal range on the gage But I obviously am quite mechanically illiterate regarding porsche engines. Thanks for all the comments
12-19-2006, 12:05 AM
#12
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Oil does trickle into the cylinders at night, sometimes, but only enough to cause an occasional puff of smoke. The gauge on the dash measures oil sitting in the external tank, not the sump. Keep in mind that when the motor is running, oil is simultaneously draining out of that tank and also being pumped into it. The float gauge is calibrated to be accurate when the car is sitting still on a level surface with the engine running at idle and the engine up to operating temperature (meaning it's been running for about half an hour).
Even so, you'll get slightly different readings based on just how hot the engine is. This actually doesn't have to do with the oil expanding. It has to do with the oil's viscocity improving as it warms up. It runs through all of its paths and passages more easily when everything is up to temp, and returns more quickly to re-fill the tank.
Oil does expand when it heats up, but it's very slight. You'd never be able to see a difference in the reading based on the amount it expands.
Even so, you'll get slightly different readings based on just how hot the engine is. This actually doesn't have to do with the oil expanding. It has to do with the oil's viscocity improving as it warms up. It runs through all of its paths and passages more easily when everything is up to temp, and returns more quickly to re-fill the tank.
Oil does expand when it heats up, but it's very slight. You'd never be able to see a difference in the reading based on the amount it expands.
12-19-2006, 12:15 AM
#14
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When you overfill, it gets sucked into the breather lines and the airbox. Then your intake is delivering oil and air to the combustion chambers. Understandably, the local mosquito population hates when this happens. 
12-19-2006, 01:14 AM
#15
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Originally Posted by JackOlsen
Oil does trickle into the cylinders at night, sometimes, but only enough to cause an occasional puff of smoke. The gauge on the dash measures oil sitting in the external tank, not the sump. Keep in mind that when the motor is running, oil is simultaneously draining out of that tank and also being pumped into it. The float gauge is calibrated to be accurate when the car is sitting still on a level surface with the engine running at idle and the engine up to operating temperature (meaning it's been running for about half an hour).
Even so, you'll get slightly different readings based on just how hot the engine is. This actually doesn't have to do with the oil expanding. It has to do with the oil's viscocity improving as it warms up. It runs through all of its paths and passages more easily when everything is up to temp, and returns more quickly to re-fill the tank.
Oil does expand when it heats up, but it's very slight. You'd never be able to see a difference in the reading based on the amount it expands.
Even so, you'll get slightly different readings based on just how hot the engine is. This actually doesn't have to do with the oil expanding. It has to do with the oil's viscocity improving as it warms up. It runs through all of its paths and passages more easily when everything is up to temp, and returns more quickly to re-fill the tank.
Oil does expand when it heats up, but it's very slight. You'd never be able to see a difference in the reading based on the amount it expands.
Your argument about the oil thinning out and draining faster into the bottom of the engine sump does explain how the oil level could change when the engine is hot versus cold. This is one reason why it is preferred to do oil changes when the engine is warm - the oil flow much faster.
But I'd like some more discussion on this oil expansion because if you do a search on here for "oil expansion" or "oil expand" you will see quite a few posts about how oil expands as the temperature increases...
Who is right? My physics background wants to agree with you. If you heat water, for example from 40F to 80F, it does expand, but you're right, it will be negligible and very difficult to measure. Since we're not talking about boiling or freezing points, then it would make sense that oil behaves the same way. But perhaps oil contains other components that causes it to expand and contract differently? I'd like to know if oil expands noticeably when going from, say, 60F to 190F.