Carrera oil cooler/oil level

[logan2z]

We've all been programmed to check our oil level at the dipstick when the car is up to operating temperature and idling on level ground. What I'm hoping someone can clarify for me is this: it is often suggested to only check the oil once the oil lines to the front-mounted oil cooler are warm enough for the external thermostat to open and send oil to the external cooler. Is this simply so the oil can be checked when the entire oil system is in 'the loop'? Some threads seem to suggest that there will be more oil in the engine and less in the tank before the external thermostat is open, so an accurate oil level will only be obtained once the tstat opens. I don't quite understand how that can be the case given my (poor) understanding of the Carrera oil system outlined in this diagram:



Can someone explain why there would be relatively little oil in the tank prior to the external tstat opening?

[ossiblue]

Originally Posted by logan2z

We've all been programmed to check our oil level at the dipstick when the car is up to operating temperature and idling on level ground. What I'm hoping someone can clarify for me is this: it is often suggested to only check the oil once the oil lines to the front-mounted oil cooler are warm enough for the external thermostat to open and send oil to the external cooler. Is this simply so the oil can be checked when the entire oil system is in 'the loop'? Some threads seem to suggest that there will be more oil in the engine and less in the tank before the external thermostat is open, so an accurate oil level will only be obtained once the tstat opens. I don't quite understand how that can be the case given my (poor) understanding of the Carrera oil system outlined in this diagram:



Can someone explain why there would be relatively little oil in the tank prior to the external tstat opening?

Here is the way the system works:

The line from the engine to the front cooler is always open through the thermostat. Contratry to what some believe, when the thermostat is closed, it blocks the return oil from flowing into the tank and opens the bypass. The bypass in the thermostat allows cold oil to bypass the path to the front (currently filled with cold, non-circulating oil), and return directly to the tank. When the stat heats up, the return line is opened and the bypass is closed, allowing the oil to circulate through the long path to the cooler and back to the tank.

That being said, if you don't run your engine, you will get a false reading on the stick as oil will tend to settle in the sump. If the engine was warm, running and the system pressurized, you will get an accurate reading even if the external cooler is not open as the loop is "full" of oil.

[Goth]

What I'm hoping someone can clarify for me is this: it is often suggested to only check the oil once the oil lines to the front-mounted oil cooler are warm enough for the external thermostat to open and send oil to the external cooler.

I think this would apply if the loop forward of the thermostat had been opened up for some reason, or, perhaps if the engine sat drained of oil for an extended period of time.

Just my 2 cents...

[GH85Carrera]

The other reason to wait until the engine temp is up to normal is the oil expands when hot. I would love to see MythBusters test how much 12 quarts of oil expands from 85 degrees to 185 degrees.

[Manitop]

The extent to which a liquid increases in volume per one
degree Fahrenheit or Centigrade is defined as it’s
coefficient of expansion. For example, the coefficient of
expansion of gasoline is approximately 0.0006 per one
degree Fahrenheit, mineral oil is similar. I haven't found the coefficient of expansion for motor oil, but it would likely be similar So a 100 degree change in temp would cause 12 quarts to expand to 12.7 quarts, assuming this coefficient of expansion near .0006.

[robert walsh]

Why do the rpm's drop when you open the oil filler cap and why does the volume on the dip stick change change after several mineuts of sitting? I understand waiting 2-3 mins on level ground, but wait 4-5 and I get a better reading, at least higher.

[robert walsh]

I do know that openning a persurized system will drop rpm's I am confussed about the length of time it takes to get an accurate level reading when the engine is up to full operating temp?

[boyt911sc]

Originally Posted by ossiblue

Here is the way the system works:

The line from the engine to the front cooler is always open through the thermostat. Contratry to what some believe, when the thermostat is closed, it blocks the return oil from flowing into the tank and opens the bypass. The bypass in the thermostat allows cold oil to bypass the path to the front (currently filled with cold, non-circulating oil), and return directly to the tank. When the stat heats up, the return line is opened and the bypass is closed, allowing the oil to circulate through the long path to the cooler and back to the tank.

That being said, if you don't run your engine, you will get a false reading on the stick as oil will tend to settle in the sump. If the engine was warm, running and the system pressurized, you will get an accurate reading even if the external cooler is not open as the loop is "full" of oil.

L.J.,

Well said. The explanation is clear and concise!!!! Many misunderstood how the auxiliary thermostat works. I wanted to add something to the discussion but it will be just redundantly unnecessary since you have covered the topic very well. This is the kind of information that makes this technical forum very valuable.

Tony

[snbush67]

Originally Posted by robert walsh

Why do the rpm's drop when you open the oil filler cap and why does the volume on the dip stick change change after several mineuts of sitting? I understand waiting 2-3 mins on level ground, but wait 4-5 and I get a better reading, at least higher.

When the oil cap is opened it releases the pressure and vacuum at the air box and lowers the RPMs.

This is an easy way to tell if your CIS has a vacuum leak somewhere, if you remove the oil cap and the rpms don't drop your engine is adjusted to idle to high or you have a vacuum leak at the cap or somewhere else.

On an engine requiring no vacuum the rpms should not change when the oil cap is removed.

Edit: I just read your other post about oil level, I dont know why your level would increase with time.

Shane

[CCM911]

As for the oil level increase. Since we are dealing with a dry sump, more oil is circulated through the system from the oil-tank as the revs increase. This causes the level in the oil-tank to drop. Yet when returning to idle, there is less oil volume being circulated, with the "excess" seen as a higher oil level in the tank. Did you ever notice that the oil level gauge gets higher at a stop-light?

At least tht is my understanding.

[GH85Carrera]

Originally Posted by Manitop

The extent to which a liquid increases in volume per one
degree Fahrenheit or Centigrade is defined as it’s
coefficient of expansion. For example, the coefficient of
expansion of gasoline is approximately 0.0006 per one
degree Fahrenheit, mineral oil is similar. I haven't found the coefficient of expansion for motor oil, but it would likely be similar So a 100 degree change in temp would cause 12 quarts to expand to 12.7 quarts, assuming this coefficient of expansion near .0006.

OK, that is interesting. 3/4 of a quart overfill could cause problems. That is one reason I always run my 911 at the point right between the high and low marks. To heat the oil from 95 degrees to 195 degrees is pretty easy on a warm day with normal driving. I have seen 230 degrees before.

[MJP]

I run my 3.0 at the min point on the dipstick when warm, but still end up with a little oil showing up in the airbox. I've never been able to figure out why, I just live with it.

[THECARREAPER]

this discussion has lead me to ask a question that has been bugging the crap out of me.

i own an 85 targa, and an 87 Turbolook slopenose. i am in southern Georgia, and i have yet to see the temp gauges on either car go above 180. the puzzling thing is that the oil cooler lines, as well at the thermostats themselves are always cold to the touch. we even shot one of them with a laser temp gun, and it was like 50F, as it was in the 30's outside.

even during long drives on the warmer days, both of my cars run nice and cool. both have cat bypass pipes.

is this normal for winter time?

i have only owned these two cars a few months, but i have had several 911s, and had them during the hot Georgia summer months.


it just seems to me the oil lines should get warm. or at least one of them.

what are the chances of having two 911's at the same time with stuck oil thermostats!

[tcar]

Originally Posted by GH85Carrera

The other reason to wait until the engine temp is up to normal is the oil expands when hot. I would love to see MythBusters test how much 12 quarts of oil expands from 85 degrees to 185 degrees.

This is the MAIN (ONLY) reason you only check the oil when it's up to operating temperature.

Oil increases in volume a good bit when it gets hot, as GH85... said.

And when you check the oil, dipstick or gauge, you are only checking the VOLUME of the oil.

The gauge and the dipstick are both calibrated to hot oil volume.

I couldn't find a guide to how much it expands, though.