RE: Oil temp vs water temp

["Louis" <louis@xxxxxxxxxxxx>]

What does it mean when it's said that the car should be up to operating
temperature before . . .?  My guess is it means the internal components
have warmed sufficiently - as measured by OIL temperature.

I base this assumption on the temperature gauges and the owners manual
of my 91 M5.  My instrument panel has two temperature gauges:  a water
temp gauge and an oil temp gauge.  The owner's manual states:  do not
exceed 4,000 RPM until the OIL temperature reaches 122 degrees F (50
degrees C).  The lowest temp indicated on the gauge is 120 degrees F.
In our moderate Southern California weather this normally takes between
3/4 and 1 1/2 miles of light throttle driving.  It generally takes about
4+ miles before the oil temp is up to full operating temp (on my car
it's the middle mark, 210 degrees).  As Scott Miller noted, the water
heats substantially faster than the oil.  Indeed, by the time the oil
temp gauge just moves above its lowest mark (120 degrees F) the water
temp is already at normal operating temp (the middle mark on the gauge).

While I don't have a clue (about many things), I would guess that the
variable redline in the tachometer of the new M5, which starts at 4,000
RPM and gradually raises to 7,000 RPM as the engine warms, is tied to
oil temp.  At least its starting point is the same as the admonition in
my owner's manual.  I would also guess that the temperature in the diff
and transmission parallels the engine temp as measured by the oil temp
when everything is working properly.

Bottom line, I use the oil temp gauge, which rises much slower than the
water temp gauge, as my guide to when I can make full use of the go
pedal.

Louis
91 M5
Original owner - 117K miles.
BMWCCA 89834

Clark Miller, in response to a prior post, expressed the following view
regarding what gets up to temp quicker, the oil or water:

>This does not make sense to me, but I can be convinced. The oil is in
>much closer proximity to the combustion process, and is subject to all
>the shearing action at the bearing journals and rubbing on, say, the
cam
>lobes. I would think the oil gets up to temp quicker than the water.
The
>water is circulated around for several minutes before the thermostat
>even opens to allow the radiator to do its work. But then again, I have
>never owned a car with both a water and an oil temp gauge. That said,
>back to the original question of when is the engine properly warmed up
>before proceeding to spirited driving, you must also take into account
>the tranny, the diff, and any other driveline components that depend on
>lubrication for protection. I would think that fifteen to twenty
minutes
>is a minimum. Fargo, NoDak, in February, probably more.

Scott Miller responded to Clark's comment:

Well, Clark, I've owned cars with both coolant and oil temp gauges.  On
those cars, the coolant warms up first, in just a few minutes (more or
less), while the oil takes longer.  Don't ask me to explain the physics
of
that, probably has something to do with oil viscosity or something?
But,
that's what happened.

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