Why does the M3 tolerate 300 F. Oil Temps?

Emission · Emission's Garage

This photo is from the BMW E46 M3 (current model) owner's manual. It talks about the "normal" oil operating temp of 175 - 250 F. Then it mentions during performance-oriented driving not to exceed 300 F...

I know the rule around here is "250 is just too damn hot...", but why would a water-cooled car be more tolerant of the high temps? Why did Porsche put the "red" zone on my oil temp gauge at nearly 300 F?

Neilk · 07-02-2003, 09:13 AM

Because it also water cooled??? Not sure but sounds like a good answer

dad911 · 07-02-2003, 09:13 AM

Is that oil or water temperature?

Emission · Emission's Garage

The pic is the Tach and Oil Temp gauge.

Chuck Moreland · 07-02-2003, 09:20 AM

I'm sure the M3 is also equipped with synthetic oil which breaks down at higher temp.

Even if you run synthetic consider that oil is a prime cooling medium in the 911. Spot engine temps, specifically head temps, are much higher than oil temps. A cool supply of oil is used to help keep these components from getting too hot.

The M3 uses water to control engine temps.

dotorg · 07-02-2003, 09:23 AM

Part of it is synthetic, very light oil. My S4 is the same thing... 225 is normal winter temps, 250 is normal summer temps. 300 is "time to pit in and cool off" at the track.

1fastredsc · 07-02-2003, 09:25 AM

Water cooling involves having either water jackets or water ports running along the side of cylinders and through the heads. The reason for there high temp oil capabilities is because the oil's not responsible for cooling the motor. And since the water transfers heat extremely well, it means that the cylinder and head temp can be closely monitored and therefore closer tolerances can be accepted. Oil/air cooling means that the cylinder and heads are cooled by air, and the pistons are cooled by the oil. The relative temp of the oil in proportion to cylinder/head temps is much different than a water cooled engine so an oil temp of the same degree as that stated would mean, for an air cooled motor, that the cylinder and head are hella hot.

speeder · 07-02-2003, 09:28 AM

That would be the first water cooled car I have ever seen w/ an oil temp guage. I would think that one guage, (coolant), would give you engine temp, no?

dotorg · 07-02-2003, 09:33 AM

My car has a coolant temp gauge (that largely does nothing useful -- its always right at the middle), and an oil temp gauge.

Emission · Emission's Garage

The M3 runs special synthetic 10W-60 oil.

I found that on most modern water-cooled cars, the water temp stays very stable, while the oil temp fluctuates depending on the driving conditions. With the modern "dumbing up" of car instrumentation, very few cars (the M3 being one exception) have oil temp gauges. There is even some debate whether or not modern electronics give a false "perfect reading" on the water temp when, in fact, it may be running a bit hot (climbing a long grade, etc...) so not to alarm the driver.

Emission · Emission's Garage

Quote:

Originally posted by 1fastredsc
Water cooling involves having either water jackets or water ports running along the side of cylinders and through the heads. The reason for there high temp oil capabilities is because the oil's not responsible for cooling the motor. And since the water transfers heat extremely well, it means that the cylinder and head temp can be closely monitored and therefore closer tolerances can be accepted. Oil/air cooling means that the cylinder and heads are cooled by air, and the pistons are cooled by the oil. The relative temp of the oil in proportion to cylinder/head temps is much different than a water cooled engine so an oil temp of the same degree as that stated would mean, for an air cooled motor, that the cylinder and head are hella hot.

Excellent answer, and I am assuming you are correct (it makes sense).

Chuck Moreland · 07-02-2003, 09:44 AM

The 10w-60 would be part of it too. It will retain viscosity at higher temp than 20w-50, check the table here that shows viscosity vs. temp.
http://www.elephantracing.com/techtopic/oiltemperature.htm

Where do you get 10w-60?

Emission · Emission's Garage

Quote:

Originally posted by Chuck Moreland

Where do you get 10w-60?

According to the guys at the M3 board:

"For all S54 engines, (E46M3 or S54 Mcoupe/roadster) it's 10w-60, and not just any 10w-60. It must be Castrol TWS Motorsport, Castrol RS, or Veedol Synthetic Z in that weight."

I'd hope the dealer sells it. Funny thing about BMW dealers and synthetic oil - it is cheaper at the dealer than at your local auto parts store!

I wonder how it would run in our cars? I am running Mobil 1 15W-50 now...

KTL · 07-02-2003, 10:07 AM

http://www.sunoco.be/uk/ProductInfo/synturoRacing10w60.html

http://www.castrol.de/produkte/a_auto/a_motorenoele/details_rs10w60.html

Guess you'll have to have k9handler get you some Castrol from Germany? You sure don't wanna get raped at the BMW dealer!!!

Pelican should be able to get it, no? It has BMW part number 07-510-009-420

It's in the second column, top of the page here:

http://www.sts.sae.org/servicetech/july-2001/tech-tidbits-01.pdf

1fastredsc · 07-02-2003, 10:28 AM

Maybe the oil fluctuates and water doesn't because the water only disipates the heat tranfered from the cylinders and pistons. Therefore if the oil is the only thing that comes in contact with the pistons, and under hard load the pistons get very hot, logic would say that the oil gets hot as well.

david lipman · 07-02-2003, 11:22 AM

Interesting thread.

Incidentally, I think that the owners manual from my 1977 2.7 says not to exceed 300 degrees as well. 300 degrees may be bad for the engine, but gradually damaging. Maybeabove that is almost instantly fatal?

Also, doesn't oil get to the heads on our cars via the camshaft?

Elombard · 07-02-2003, 12:03 PM

I wonder if it could have anything to do with where the temp is taken? If the sensor is at the hottest possible point than 300is safe. IF it is not - as in a 911, then the heads are much hotter i.e. too damn hot. Just a thought. I remember crewing for a rally team that ran an RX-7. They were very mindful of the oil temps and never went over 225 I think. Rotaries may be different though.

banjomike · banjomike's Garage

I guess it makes sense that if the oil's only job is lubricating, then it could get a good deal hotter.

In conductive and convective heat transfer the heat that can be moved is directly proportional to the temperature difference. So if your piston is 350deg and your oil is 300deg then it can only removes half as much heat as it would if the oil were 250deg.

When my Dad got a 993 and I learned how much oil was in there, I laughed. I knew that that car was not 'air cooled' any more than the ford next door. It was 'oil cooled'.

Maybe the M3 needs a oil/coolant intercooler like in a 944. With my 944 I never once had to think about engine temperature except during warmup.

Gus Berges · 07-02-2003, 12:54 PM

My car also has a coolant gauge and an oil temp gauge. Regular driving, temps are near 230. When driven "hard", temps rise to near 275. I use the Castrol 10-60 oil. Local dealer wants $28/qt

but I get it at the Castrol distributor for $14/ qt.

I have the S50B32 engine (Euro spec M 3.2) and when BMW had issues with the new S54 engines (M3s) then they issued a oil specification change to the same oil I use (as per BMW reccomendation).

Emission · Emission's Garage

Quote:

Originally posted by Gus Berges
"I use the Castrol 10-60 oil. Local dealer wants $28/qt but I get it at the Castrol distributor for $14/ qt. "

Hmmm... I guess Mobil 1 @ $4.50/quart starts looking CHEAP!

Even at $14/qt, an oil change will be $150!