High DRUCK & low Oil when cold: problem?

[Hendog]

Should I be concerned when I start out with high Druck (4 to 4.5)pressure and low oil reading until it warms up? Dipstick shows propper oil level. Could the sending units be cold and inaccurate? Any others experience this? I'm driving '87 Carrera. Once it warms up, the oil level is right up there where it should be and the pressure is at 1 bar while idling. A fairly recent thread dealt with oil level only, but I've since taken notice of the pressure as well. Thoughts?

[VaSteve]

The pressure is high because the oil is cold and isn't flowing easy like it does when it's hot. The level is low because the thermostat hasn't opened to the front cooler and thus all the oil in the lines hasn't been "counted."*

Proper oil check procedure to check the stick when the engine is warmed up and RUNNING. A pain? yes, but gives the accurate reading.

*Someone can ring in with the proper techincal terms for this

[Hendog]

Thanks for the quick reply VaSteve. I kind of figured it was something of that nature but I just wanted to compare with others...just to be on the safe side.

And I do check oil while warm with engine running.

[masraum]

As the oil heats up it expands, usually not very noticeable in a car with only 4 or 5 quarts, but since we have close to 14 quarts of oil the expansion is noticeable. When the oil is cold it's thicker so it creates more pressure, as it heats it becomes thinner and so the pressure decreases. This is completely normal. You should notice similar behavior in any engine, but it will be less obvious.

Completely normal, nothing to worry about.

[grant lyon]

Both are normal effects, relax.
Pressure.
Viscosity: the degree to which a fluid resists flow under and applied force. Oil is more viscous when cold vs hot, hence greater oil pressure at cold -- the thicker (cold) oil tends not flow as readily compared to hot.
Volume.
Oil, like many substances, expands with heating and contracts as it goes colder. The term is coefficient of thermal expansion (CTE). The only way to get a consistent volume measurement is to determine volume at a set temperature. This is why you check oil at the dipstick with warmed-up ~180° oil temperature.

[Hendog]

I appreciate the replies. That little bit of "gnawing" in the back of my mind has been quelled. Thanks.

[Formerly Steve Wilkinson]

By the way, "druck" means pressure in German. You don't have "4.5 druck pressure," you have 4.5 bars of druck, or pressure, i.e. about 65 psi of oil pressure.

Stephan