Oil temp question

[bcoats]

Hello fellow Pelicans,

I have a bit of an odd one, most oil posts are about how to lower oil temp but this is the other way around! I have a 1979 911SC 3.0, 964 cams, SSI's, Weber carbs and old style trombone cooler. Had the car out today in Seattle, about 53 degrees, did some spirited driving, felt like I got her nice and warmed up for about an hour. My temp gauge wasn't near 9 O'Clock and the thermostat never opened as my front cooler lines were stone cold. Also, even this past summer, on a 90 degree day I didn't see 9 O'Clock. This seems odd the oil temp isn't hitting the 184 or whatever the ideal temps are but could it be more air flow around the motor with less clutter with carbs and SSI's? Last bit of info, I recently changed the oil and notice a bunch of sludge and moisture. I don't drive the car unless I'm getting her nice and hot so not an errand car, made me wonder if my old oil every really got hot?

Bryce

[fintstone]

It is more likely that your gauge is reading low...and your thermostat is stuck...than your thermostat not opening on a 90 degree day with some spirited driving.

[virob]

I'm new to the 911. Have only had the car a couple months, and I'm also in the PNW. Even after a hour of spirited driving I haven't gotten the temp gauge more than halfway between the first 2 marks. Most of the time it's barely past the first mark. I have yet to get it to operating temp, including driving from Tacoma to Blaine. I replaced the temp sensor because it was leaking which made no difference. I did an oil change with Brad Penn 20w50, and it seems like I am getting higher temps, but still well below ideal operating temp, not sure why that would make a difference.

I was going to wait and see what the temps are like in the summer. If it is still low, I might try a lower weight oil.

[Jdub]

Temp sensors are matched to gauges, so do be sure you got the sensor meant for the gauge you have. I know this after replacing my SC's bar gauge with a numeric item.

[Bob Kontak]

Originally Posted by virob

Even after a hour of spirited driving I haven't gotten the temp gauge more than halfway between the first 2 marks. Most of the time it's barely past the first mark.

Which marks are the first two marks? Base and first mark or 1st and 2nd mark after the base (cold) mark?

[fanaudical]

I went through this following my rebuild. It's important to get the oil warm to burn out the sludge.

It's important to verify the oil gauge is correct. I used a long thermometer into the oil tank filler when hot to validate the gauge temp. (I figured a few degrees difference was OK.)

Once I determined the oil temp was indeed low, I checked front oil cooler line temps. One line would get warm. That lead me to believe my external thermostat was stuck open (which it was). I also had reason to remove my CIS and so changed engine thermostat as well.

[virob]

Originally Posted by Bob Kontak

Which marks are the first two marks? Base and first mark or 1st and 2nd mark after the base (cold) mark?

Base and first mark for me. Most of the time it is barely above base

[Jdub]

You are running approx. 190 at the "first mark" if memory serves.

[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

[spuggy]

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

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.

[GH85Carrera]

Water will evaporate rapidly even at temps well below 212.

185 is plenty to get all the water out of the system, it does not have to boil.

Last winter I was driving my 911 in COLD weather. Low single digits and after an hour of just driving around the oil temp was just 110 or 120. It would not warm up enough to push the engine hard enough to get warm. I had to keep it below 3,500 RPM.

[virob]

I haven't been getting concerned about it, considering I have only so far driven the car at 10C (50F) ambient temps or less. It is also tricky to figure out what the true oil temp is from the gauge with only a few lines.

But, if you go to this site 911 Gauge module overlays that supplies numbered module overlays for the oil temp gauge and I take the B overlay and put it over the B gauge (which is the one I have), I would have to say that my typical max reading would correspond to about 180F, which is about halfway between the base and the first mark on my gauge. Assuming that my thermostat is functioning properly and opening at 184F, than this would suggest that everything is working as it is supposed to. That sometimes (probably correlated to lower ambient temps) the car isn't getting to 180F and when it does, the cooling system is not being over taxed and is keeping oil temp at the 180F level. As we get into spring/summer and ambient temps increase, I will be curious to see if this changes