Oil Temp: How hot is too hot and why?

[fun2drive]

I am getting a 335i convertible BMW and it used synthetic Castrol oil. The normal operating temp according to my manual is 210-300 degrees F.
Normal temp will be between 240-255 F.
BMW says this will not shorten engine life.
I am old school and thought anything over 210 was a killer on oil. Also BMW uses the extended oil changes (15K) since they are changing the oil until it hits 50K then it is my responsibility.
I will be changing it well before 15K per change but I wanted some SAE or other tech pubs to help me understand how this elevated oil temp can be acceptable.

Looking for help on synthetic oils versus engine oil temp and oil life.
Thanks

 

[Buffman]

I'd have to say for a synthetic 240-255 should be fine for oil temps...

 

[SargeGTO]

Over 240 I freak out. Over 250 I start crying. Over 260 I pull over and start praying I didnt lunch an engine.

 

[double vanos]

I think a 100 percent PAO is in order here...if not Redlines' ester based oil! All on 5k OCI's naturally.

 

[TimVipond]

Fun2Drive -
From the Amsoil website:
2007 BMW 335i 3.0L 6-cyl Engine Code N54-B30 Turbo
Engine Oil
Grade 1......SM[1]
Series 2000 Synthetic 0W-30 Motor Oil
SAE 5W-30 Synthetic Motor Oil
SAE 5W-30 XL Synthetic Motor Oil
All Temps......5W-30[2]
1. To prevent potential engine damage, use only BMW
High Performance Synthetic Oil part No 07 51 0 017 866 or
equivalent. Refer to engine compartment oil change decal.
2. To prevent potential engine damage, use only BMW
High Performance Synthetic Oil part No 07 51 0 017 866 or
equivalent. Refer to engine compartment oil change decal.

The 3 Amsoil oils listed above are all synthetic. The XL is a petroleum synthetic, the other two are PolyAlphaOlefin synthetics and meet your BMW requirements and change intervals. Synthetic oils should be used when expected temperatures are over 230F as conventional oils could begin breaking down above that temperature.

And

to BITOG!

 

[TimVipond]

Fun2Drive - here is a primer on motor oil and filtration basics you may find helpful. http://www.amsoil.com/lit/g52.pdf .

 

[TeeDub]

The general rule of thumb is that for every 20F increase in oil temps, the rate of oxidation doubles. A typical engine may run oil temps in the 210F range, so if you are running consistent 250F temps, the oil is going to be oxidizing about four times as fast.

Even though this engine has a large sump, I'd stick to 5k-6k change intervals with the Syntec....

 

[Turbodriven]

I have been thinking about this a bit and as much as one needs the thin oil at startup, it appears to me that this is one of those applications where you actually need to forgo the cold start benefit. The standard fill in those cars is Castrol TXT 5w-30, which although a very good oil, I do feel will take a severe beating at those temps....not to mention 2 turbo's which make matters worse. My thinking is a 5w-50 from say FINA or Mobil would work well here. However I do also think this motor will shear oil at a rapid rate. I also see that these motors run the oil temps to 300C when driven hard, that is pretty hairy stuff.
I would most likely fit an oil cooler to bring the average operating temps to around 100C for normal driving and 120C on the track. Your thoughts?

 

[Merkava_4]

Quote:

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Synthetic oils should be used when expected temperatures are over 230F as conventional oils could begin breaking down above that temperature.

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That's what I was going to say - anything over 230 degrees Fahrenheit and you should start worrying.

 

[SpitfireS]

Quote:

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I am getting a 335i convertible BMW and it used synthetic Castrol oil. The normal operating temp according to my manual is 210-300 degrees F.
Normal temp will be between 240-255 F.

---

Does BMW spec oil temp in their manual?
Operating temp may also be coolant IMO.

What if an onwer just brings the car in for service at a BMW dealer (they have never heard of BITOG) and that dealer uses oil that BMW recommends (the dealer never heard of BITOG either

), would that car see premature engine failure?

 

[Buffman]

Quote:

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Synthetic oils should be used when expected temperatures are over 230F as conventional oils could begin breaking down above that temperature.

---

That's good to know. Im sure the oil temps were a lot cooler when my car was running 2.56s out back and on the highway (no factory oil cooler), but Im glad since I've had the car (and done mods of course) Im running a synthetic motor oil

 

[jmac]

Read AEHaas's papers and somewhere in there he mentions oil sump temps at track events aproaching 280-290-300 deg. F. All of these cars are using or should be using high end synthetics. There have been various posters from time to time relating thier experiences with street and race syn oils from RP, Mobil, Motul, Redline, etc at these events and drag race engines as well.

 

[Blue99]

Yes, temps over 230F are certainly high & will decrease the oxidative life of the oil.

But keep in mind, if the GF-4 certification is on the bottle of the oil in your crankcase, it has passed the Sequence IIIG test which exposes the oil to 300F degrees for 100 hrs at 3600 rpm.

The test engine is a GM 3.8L V6, and allowable make-up oil is somewhere around 4-5 quarts.

 

[Hokiefyd]

I thought I read/understood that conventional oils were "good" for the upper 200s to 300 degrees before severely breaking down...and if you had oil temperatures exceeding that, synthetics were necessary. It sounds like most people here don't consider conventional oil safe at those temperatures.

The regulated testing conditions (300F @ 100 hours) is reassuring though. I always like to trust science/instrumented testing.

 

[mbcoops]

I had temps up to 270-280f in my 05 cooper S on the track while running RL 5-30. I'm going to put in RL 50 weight racing oil for my next track day in hopes of keeping temps down a bit.

mb

 

[Bobert]

I've seen temps at 245F in my VR6 during the summer on the highway @ 80mph with AC on. Drove the car for hours and hours at that temp. Been using M1 for awhile now, so I really don't worry with synthetic.

In fact I think the original VR6's that came out had a warning in the manual saying pull over at 293F. I'm sure many conventional's can handle that temp, but I wouldn't want to do it for long though, yikes.

 

[fun2drive]

BMW has an external oil cooler on cars that have the sport package and manual. I see no reason why that external oil cooler should not be put on this car as well. I would have purchased the sport package but to be honest the sport seats are uncomfortable for my body type.

I am going to push BMW to add the external cooler but until that happens I will plan to use the spec'ed BMW oil for warranty purposes alone and I will change the factory oil out at about 3-4 K just to get out whatever was in there.

I have not been able to discover where the sensor is for the oil temp reading but if it is in the sump then I am getting a true hot running oil. BMW knows all this and designed the car to run hot but my concern is that engine life even with synthetics will be sacrificed. I keep my cars a long time 10-12 years and don't want to see this thing chew bearing up after 50K when it is my problem rather then BMWs problem.
I guess it is reassuring that the synthetic that BMW uses will hold up to elevated temps. I live in Florida and summer temps on the road are over a 100 F at times.
My guess is that the temps I saw at ambient 55-60 F (240-245 low speed) will be a linear climb when ambient temps are 95 (285 F). I hope I am wronb but I should know in about 6 weeks when we get that hot soon.
Appreciate the suggestions and help.

 

[Bobert]

My folks X3 has the same motor as your 335i except it's naturally aspirated. The manual specs 5w-30 or 5w-40 synthetic. Since your 335i will see temps north of 240F, I would move to a 5w-40..

Castrol makes a 5w-40 which meets many VW and BMW specs, available at Autozone, also VW/BMW dealers. Another choice is M1 TDT 5w-40 which is Mobil's best oil (identical to Delvac 1). It doesn't have all the fancy approvals if warranty issues are a concern, but is a superb oil. It is also a PAO based oil unlike many of the other grades of M1.

 

[unDummy]

Reasonable oil temps are acceptable if flow is acceptable and pressure isn't lost. I would think that there is surplus of both in that BMW engine.

The 'synthetic' seems to be insurance policy for the 'temp' and 'OCI'.

Definitely install the cooler, especially if the OEM has an optional one. To me, OEM cost cutting is pretty pathetic.

Using the 40wt oils is an easy choice. The 0w, 5w, 10w, and 15w, --40wt full synthetics are excellent choices even if they don't have certain OEM cert's.

The 15k blind OCI is foolish. I'm beginning to see more and more sludged 'lower cost of maintenance' higher priced vehicles. Enjoy those free 15k oil changes and seriously consider changing the oil in 7.5k increments in between dealer free changes.

Florida weather won't add to fuel dilution and moisture issues that us northerners deal with. I see no reason why you would need to change it out before 7.5k miles. But, if you don't drive much, you should still change your oil out at least once a year.

Since some engine families suffer oil consumption, make an effort to keep the oil topped off. Low oil level will exaggerate oil temps. Exercise that dipstick every 1k and top off in ounces if needed.

Even thought there isn't a need to dump the factory fill early, I'll always recommend an early new vehicle rinse oil change with a couple short OCI's prior to picking the interval you decide on.

A UOA/TBN/PCs is an easy way to see if your OCI and OEM filtration are acceptable.

Depending on oil sump capacity and driving style, even though I don't care for extended or 15k OCI's, it is still a possibility and may be acceptable(engine overengineering). This is easily verified with the mentioned UOA.

 

[onion]

I can't tell you about a BMW, but I can tell you that most industrial diesel engines will set a code and de-rate the engine when the oil temperature gets around 235 degrees F. Depending on how the ECM is set up, many will shut the engine down if the oil temp stays above 235 F for more than a few minutes.

If you're seeing oil temperatures in excess of 240, then I would definitely run synthetic and investigate an engine oil cooler.