Optimum 911 oil temp?

[speeder]

Being fairly new to this board, this is my first topic posting-yahoo!
I've read the entire cool-collar postings and they are friggin' hilarious. Let's just say that I'm a card-carrying member of the sceptic's society as well as gear-head.
Question: what is optimum 911 oil temp? I have seen a few different opinions on this. Roland has written that "needle straight" (horizontal) is good. That would be about 225-230F on my SC. I do know that cooler is definitely better,(to a point), this seems hotter than optimum to me but not in danger zone- however, the more buffer you have between O.T. and D.Z. the better, right?
Suffice it to say that I am pretty obsessed with cooling on this car as I live in hot place w/traffic. When I bought it in beginning of summer it had stock trombone cooler and worked OK until I got in hot traffic and really needed it to work. Then temp would go to 250+F. I installed new carrera oil cooler,(radiator),in front and car runs at 200-210F, goes up to maybe 225F in stop/go hot traffic. I'm happy as a pig in cool-collar, but still wonder about OPTIMUM oil temp. Anyone really know? Hope this ain't to long-winded. Thanks,

Denis Hartigan '82 SC coupe------------------


[This message has been edited by speeder (edited 08-16-2001).]

[This message has been edited by speeder (edited 08-16-2001).]

[Bill Verburg]

For racing where the oil is changed every week 180-190F, for street use where oil is changed once or twice a year 212-220F. Doesn't matter if dino or synthetic is used. Most of the problems with 911 oil are condensates that never get boiled off. Newer cars can tolerate higher oil temps than older, for emissions reasons they are designed to run hotter.

------------------
Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page



[This message has been edited by Bill Verburg (edited 08-16-2001).]

[911pcars]

As Bill says, the minimum temperature is to get hot enough to burn off water condensation (always created in a cold running engine); that would be around 212 deg.F (boiling point of water). If your gauge reads 240, I don't think you'll have a problem with sludge and acids formed by a cold engine.

However, if your oil temp. gauge reads "only" 190-210 deg., does this mean the oil is not hot enough to burn off water vapor? No. The oil gauge reads the oil temp. at the location of the sending unit. Engine oil is either hotter or cooler than the oil at the sender. Oil will be hottest when it circulates through the cylinder/cylinder head around the combusion chambers/valve guides and coolest as it exits your engine or external oil cooler. Combustion chamber temperatures can get up to 1400 deg. in a turbo.; all others maybe 1200 deg.F. Warm enough?

What this means is when your oil temp. gauge is at 230-240, some of your oil is cooler than this and some is hotter. What's the range? +-10? +-15? 25? Don't know, but that's why you don't want to see high gauge temperatures. It's an indication your engine is running ..... hot. Probably hotter than you think.

Sherwood Lee
http://members.rennlist.org/911pcars

[Colby]

Ok, I've always been leary if (on rare occasion, such as rush hour in 100deg temps)the oil temp creeps near 250deg. Anything below that, especially with Mobil 1 in there, is ok. I average 190-210 summertime driving. Now how about too low? In the winter I rarely get much above 180, if that. Possible my thermostat is sticking? Should I be concerned with these too low of oil temps in the winter?

Colby

[Bill Verburg]

Colby, assuming that you have a pre 964 engine. You have 2 thermostats one internal and one external they both open at the same temp 80C(~180F) is the spec. That is the coolest normal temp for any of our air cooled engines. Condensates will evaporate in time at these temps, that is one reason long trips and highway driving are better, wear wise, than short trips. It's just that as the temp increases the time to boil off condensates decreases.

As Sherwood has indicated, the oil temperature sender is right at the end of the main oil gallery from the crankshaft, oil goes from there to the tensioners and cams and then to the sump/scavange pumps. As such it is a good AVERAGE indicator of oil temp. The internal thermostat however receives oil directly from the pump, probably the coolest oil anywhere inside of the engine. The effect of this is 2 temp plateaus the first at ~180F the second somewhat higher(~210) due to the later opening of the external thermostat.

With a late car using the newest sealing technology short excursions to 250F aren't really much of an issue, though they do take a toll on guides and will eventually lead to problems in that area. Another good reason to use synthetic oil.

------------------
Bill Verburg
My Home Page My Pelican Gallery page My Porsche Owners Gallery Page

[speeder]

Not to get off topic, but related-how exactly is synthetic oil an advantage at 250F? I am familiar with superiority of synthetic oil at much higher temps; one of the reasons I've never used it in my older cars,(80s BMW & Porsche),besides cost and leaking fear, is the simple fact that my engines would self-destruct from overheating long before this advantage kicks in.
I may still switch for other reasons, but I do not understand advantage at 250-275F. Wouldn't high-quality mineral-based oil(SH 20-50),still be together at this temp? I was under impression that it breaks down at much higher temp. I realise that this is a furious debate on board,(and elsewhere),but some pretty respected techs have told me,"don't worry- your engine will blow up way before this thermal-breakdown advantage kicks in". Anyone?

[911pcars]

Speeder,
I think we owners of air-cooled engines are more concerned with engine temperature due to the narrow cooling margins we have as we only have oil and air to dissipate excess heat .... not the most efficient cooling mediums. Water-cooled engines, while having a decided weight penalty, have this add'l medium and thus have more cooling capacity before critical "meltdown" begins.

We focus on oil temperatures because there's a direct relationship to the temperature of engine parts. Engine parts that overheat can expand at greater-than-designed limits and either decrease important clearances (galling and seizure) or increase important clearances (excessive wear, pounding). Aluminum, steel and other "precious" metals in our Pcar engines expand at different rates and engineers design their relationship to be symbiotic at a design temperature. Increasing this temperature beyond these limits shortens component life.

On this fine edge between longevity and mass destruction, a good lubricating oil can stave off meltdown or any of a number of destructive engine scenarios. Thus, if you happen to run your car under extreme conditions, you will want any and all cooling capacity to be there for you otherwise you'd better shut it down. If modern engines are designed to run hotter using better materials and design, then the oil should be up to the task. Whether one has to run synthetics or not is a judgement call based upon your driving and operating conditions. Following the manufacturer's recommendations is usually the prudent thing to do. Others may err on the conservative side by not operating at extreme temperatures, gain additional cooling capacity (increase oil cooler capacity, increase air volume, insulate, increase heat rejection, etc.) or use a synthetic for those "just in case" moments.


Sherwood Lee
http://members.rennlist.org/911pcars

[Doug Zielke]

Originally posted by speeder:
....but some pretty respected techs have told me,"don't worry- your engine will blow up way before this thermal-breakdown advantage kicks in". Anyone?....

Nonsense.
A better quality oil will give long-term benefits in the form of decreased wear on all components.

Oil (even synthetic) is cheap. Motors (especially Porsche motors) are expensive. Why not use the very best oil you can find.



------------------
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
The Blue Bomber's Website

[Roland Kunz]

Hello

Cold starts are the "real" engine killers.

The water does cock at 100°C at NN ( normal nought/ seelevel ). But it will cock at 60°C in the alps ( 2000 m abouve NN )

The oil industrie made giant steps in the last years but be aware that modern oils are made for modern engines. Or better say the engine technology follows the oil ability.

Most other cars will read the oiltemperature in the oilpan witch is some 10-20°C lower then the oiltemperature in the main gallery.

Right now I try to get detailed informations and hope to catch MR Thieringer ( Former Porsche engenier and made the TAG F1 cooling moved to MCC ) or Mr Schweizer ( Freelance expert for race parts and cooling specialist, AMG/HWA is his main costumer ) to write a specific article from first hand.

Right now I´m stuffed with many books and mmany theoretical stuff, to much to understand in several days as most off them is pure thermodynamics.

Sorry I´m only a mechanic.

Right now it looks like the aircooled engines use the oil as a heat sink ( or heat pipe ) but don´t "cool" with the oil. I´m not saying they don´t use the oil to cool the engine but the oiltemperature is not "direct" relatet to the engine temperature as it reacts to slow and carries to less BTU.
There are to much differences beetween Water and Oilcooling to say they follow the same principle.

( Hope you understand why I look for some real experts who have the knowledge in the small finger )

But give me some time to get deeper into that story. Just an other worm can to open.

Grüsse

[kepperly]

Roland,
"Your,re the man"!!!
Keith