Operating temp for a '74 911 2.7L engine
 

Facts: super clean 1974 911 2.7L with 30k on high quality rebuilt engine. All recommended upgrades done [airbox with pop-off valve, 11 blade fan, high-output alternator, high strength studs and time-serts, Carrera chain tensioners, aux oil cooler (w/ thermostat & fan, etc.)]

Question: I installed the auxiliary oil cooler to keep the engine temp down to prevent the stud pulling problem and in advance of reactivating the after market A/C this late Spring. As it stands, the car is operating at around 130 degrees on days when the outside air temp is around 80 degrees. Is this running too cool? What is the optimum operating temp (including when the A/C will be on 100 degree + days) and finally what is the true "danger zone" – the gauge goes up to 300 degrees, but I know that around 225 to 250 you are looking for trouble.

Might do a search. Hardly any issue has seen more attention. 180-210 is the proper range; 130 is too cool to dissipate water etc in the oil. 220-230 every now and then is fine; 250 isn't. Engine life drops quickly when oil temps consistently exceed 210.

Could one of your oil thermostats be stuck open?

I've read that at least 180 to burn the carbon off the plugs.

Any time it gets over 200 I start to worry.

My car has kept under 210 since I sorted out the ignition timing and adjusted the valves.

What's your gas miliage when running so cool?

Do you smell gas or burn more oil?

Vdd
 

Thanks for the info on the temp range - very helpful. Gas mileage is good (around 25 to 27 city), no gas or oil smell. I wondered if the problem could be in the distance I drive in the AM and PM (10 miles/25 minutes each way in stop and go traffic - mostly stop), but even in drives to Santa Barbara (somewhere over the speed limit and in the hills) it does not get to 180 degrees unless the day is very hot. As I noted the gauge is working fine. Could it be the auxiliary oil cooler (even when the fan is off) is dissipating the heat too efficiently?

stuck T-stat. or bad sending unit/gauge. the T-stat should bring the temp up to the 180 mark then regulate there no matter how many or how big an oil cooler.

I have 74 2.7 that I did a high quality rebuild on. I have a 28 row brass oil cooler in the front, which doesn't have a fan.

With outside temperatures 80 or under my oil temp goes to 190 (which is thermostat opening) and stays there all day long. Even if I am driving agressive.

When the air temp is 90 to 100, the oil temp goes to 200 to 205 for normal driving and 210 for the periods I drive aggressive.

Thanks, I will do another check on the thermostat and sending unit/gauge. Maybe I need to drive her harder. What should I expect once I reactivate the aftermarket A/C. Will the extra load bring up the oil temp significantly? How much of and should I expect to see? Perhaps a moot point if the oil cooler is kicking in at 190 degrees - and keeping it there - but I'd like to know if I should except to see the A/C bring up the temp up a lot quicker.

I also have a fairly recent rebuild, an external oil cooler, and I drive surface streets every day for about 20 to 25 minutes (no freeways on this route). My temp also stays fairly low with this type of driving, especially on cooler days at this time of year. Longer drives, and harder driving bring the temps up to normal (180 to 200 max). VDD - after you drive your 25 minutes, feel the external oil cooler lines to see if the thermostat for the cooler is even opening. It wouldn't surprise me to find that the lines are still cold, and no oil is circulating through the external cooler yet. As far as A/C is concerned - never had it. It doesn't get hot enough around here to need it.

Thanks, Rex. So even when the days that are around 75 to 80 degrees you are hovering around 130 degrees on the oil temp on your regular drive (25 min/25 mile) drive? To your question, the lines to the aux oil cooler are pretty cool. From the others posts, I'm sensing the running cool issue is not a result of the aux oil cooler.

That only happens one day at the end of July around here - so I'll have to wait to tell you :D. On hot days my car gets up to 180 degrees.

Tonight, on the way home, it took more than 10 minutes for the temp gauge to even move. It sits below 120, and it was probably 15 minutes or more before I saw the gauge move. After 25 minutes of driving, the temp got up to about 145 degrees. The outside air temp was probably 40 degrees.

As you said, you may have an issue - either with your engine oil thermostat or your sending unit or your gauge.

what moneymanager said. 130 is way too cool, something is wrong....guage, sender, wiring, etc. Rex, I think that 180 is low for a hot day. I think that you should get to 180-190 regularly during normal dirving, once the engine is warmed...10 minutes or so and i would expect higher..maybe 200-210 on a warm day and a bit higher with higher speeds. 250 is too damn hot!!!