Quote:
Originally Posted by bcoats
OK thanks for all the feedback. I was running VR1 20/50 and was running much hotter than the Rotella T 15/40 running now, maybe the lighter oil took it way down? But a few weeks ago with the VR1 got it nice and hot, temps were just below middle hash mark on the dial and cooler lines were hot. Could oil weight make that big of a difference? Sounds like virob and I have very similar problems
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It's an air-cooled 911 in a cool climate. Assuming the gauge is reading correctly, you've already verified the thermostat is opening.
So. There's two thermostats, one internal and one external to the motor.
The internal one opens pretty quick, like a few seconds after a cold start - but you'll never notice this with a 5 bar pressure sender/gauge, like the one fitted to the SC and later cars.... On an earlier car, oil pressure reads high (120 PSI on mine) at first, then drops down (65 PSI or so) when the internal thermostat opens and starts returning oil/accepting new oil. This is at idle/fast idle with cold oil.
Below the regulated temperature, the external thermostat stays closed, and simply returns the oil to the tank. Seem to recall this is to protect the cooler from excess pressure.
At the regulated temperature (185-190 degrees, if memory serves), it opens and sends the oil through the external lines (which themselves serve as a heat sink/radiator) and to whatever cooler(s) are fitted to the end of them.
If the ability of the system to shed the excess heat is not exceeded, the system will simply regulate oil temperature to the thermostat setting - as designed... So, if the system can get rid of the excess, you'll never see temps above the thermostat setting.
The only reason oil temperature EVER climbs above the regulated temperature controlled by the thermostats is because there's more heat getting put into the oil than the cooling system can get rid of. Which is why you have a temperature gauge; so you can stop if the oil gets so hot it's about to damage stuff...
This freaked me out the first winter; with a turbo, I was used to seeing oil temps 10-15 degrees hotter. But when ambient was in the low 30's with a big-ass FMOC, the top line was barely warm (and only at the thermostat end), bottom line was stone cold and temp gauge read thermostat setting...
However. Put more heat into the system (like get into boost for a few miles), and oil temps would rise as expected, dropping back to the regulated temperature as soon as this heat could be shed (like within 400 yards of highway with a front-mount)
The 911 deals fairly well with temperatures when it's moving, especially in cooler climates. I'll bet your "spirited driving" translates to "air flow over the coolers" - and this, together with low ambient, simply means your oil doesn't get over the regulated temp.
Get stuck stationary in traffic for 20-30 minutes, and I'll bet the oil temps will rise significantly, because then the only cooling is from the engine fan, and the motor-mounted cooler, if you don't have a Carrera-style fan on the front cooler... I've seen hotter temps stuck in traffic (220-250) than I can hit or maintain on a track (sometimes as high as 210, but usually much lower).
One point to note; the regulated oil temperature is way less than the boiling point of water. So if you can never get the oil up to or over 212F, you're basically relying on keeping it "steaming" to get the water & condensation out of the oil. So you need to do that for longer to get rid of the water. Or change it more frequently.