Engine temperature and synthetic

[hjsbmw]

I recently switched to synthetic engine oil: Mobil 1 V-Twin 20W-50. I had used BMW's 20W-50 petroleum-based stock before. I have 18k on the bike. I notice that the temperature gauge is more up now. I used to see 4 bars (first notch on the display) almost exclusively, except when doing extended Interstate riding or when caught at many red lights. In the latter cases it went up to 5 bars. Now, I see 5 bars frequently during regular cruising after the bike is heated up. This is actually the case at slightly lower ambient temperatures now (80s-90s) compared to just a few weeks ago (90s-100s) when I still had the conventional oil in. Did you experience a similar increase in temperature when switching?

The only other difference I can think of is that I used a Mann oil filter from Beemer Boneyard as opposed to the OEM BMW filter I had used before.

I was expecting the engine to have better cooling with synthetic. Is what's displayed the oil temperature or the actual engine temperature? Any ideas or opinions?

[deilenberger]

What you're seeing, according to what I've read, is the oil temperature. There are 2 head temperature readings that you can read with the GS-911 (they both read exactly the same when I've tried it, which makes me think there may only be one of them, and I'm not sure where it is OR if is is the oil temp sensor.) If you look at: http://www.realoem.com/bmw/showparts.do ... g=61&fg=31 - #7 appears to be the engine temperature sensor. #17 is ambient temperature for the OBC. (Of interest is #16 - which I believe is the oil level sensor for bikes so equipped - like the GS and RT models.. we don't have it..)

Anyway - the diagram above makes me think there is only one temperature sensor. The service manual refers to it as an oil temperature sensor, so..

The filter should make no difference - that's on a different circuit from the cooling circuit. The engine has two oil pumps (in one housing - see: http://www.realoem.com/bmw/showparts.do ... g=11&fg=35) - one for lubrication and one for the cooling system. The cooling system also has a thermostat that cuts out the oil radiator when the engine is cold to help the oil heat up faster. (Thermostat is #15 in: http://www.realoem.com/bmw/showparts.do ... g=11&fg=35 - and note the two pickups for the two sections of the oil pump.)

If you mean you're seeing one bar above the first larger bar - that's about normal for my bike in almost any conditions. I can't actually recall what it ran with dino oil since it only had that in it the first 6,000 miles - I switched to BMW synthetic at the 6k service. I have on rare occasions seen the temp go beyond that - but it was in stop/go traffic in 95F temps. I was roasting, but the engine seemed happy enough.

FWIW - with the engine displaying 1 bar above the larger bar - the GS-911 read about 185F for temperature. If that's oil temperature it is fine - and actually quite conservative for a synthetic oil (good ones start to burn or carbonize at > 400F..)

[blueviewlaguna]

#9 (in my 2nd image below) is the temp sensor (#6 in the RealOEM listing) located in the left head only (right head has a bare threaded blind hole), Since it just threads into a dry metal hole it could only be Cylinder head temp. #7 in the RealOEM listing is the oil pressure sensor located on the left side of the block near the oil level window.

Seems there is no Oil temp sensor on this motor.

[deilenberger]

I think you read the RealOEM listing wrong, to quote:

07 Temperature sensor 1 11117672505 $31.39

The oil pressure sensor is #4 in that diagram:

04 OIL PRESSURE SWITCH 0,15 BAR 1 12617686501 $15.80

The factory DVD (REP-ROM) refers to an "oil temperature sensor".. and in section "12 61 010 Replacing oil temperature sensor" shows it located near the oil cooler pipe on the right side of the engine (output side of the oil cooling circuit..):

• Disconnect plug (1) from the oil temperature sensor.
• Remove oil temperature sensor (2).

BTW - I found this description by using the RT to search on, for some reason LOTS more of the repair procedures are outlined and illustrated on the RT listings then on the R listings.

Also found this on REPRom:
12 62 001 Replace temperature sensor

• Disconnect the plug of the temperature sensor.
• Remove temperature sensor (1), using socket wrench insert (No. 12 4 611).

So - question is - does the R12R have the oil temperature sensor, and what is the dash display showing? Gonna have to go out to the bike and see if this sensor is there..

Hang on.. (luckily, the bike is only about 20' away..) YUP. One is right where it's shown, just ahead of the oil cooler pipe.

I'll have to hook the GS-911 up to the bike again and see if it can read the oil temperature readings, and try to correlate them to the dash display. Looks as if we have two temp sensors - head AND oil. Oh, dunno the reason REALOEM doesn't show the head temperature sensor (bet it's #6, but it's not shown on REALOem as being on our bikes..) Lemme make sure it is.. (heading back to the bike..) Yup - it's there.

[hjsbmw]

Thanks for the replies. I didn't know we had a separate oil temp sensor. I had looked for temp sensors on the cylinders before and found only one on the right side. The left has the thread for it but is empty. It seems other models, such as the R1200S have the left side sensor.

Be that as it may, I was hoping the displayed temp may be the oil temp. Meaning, higher temp corresponds to more heat being washed off/absorbed by the oil. That might be a good thing.

If it is the cylinders, i.e. the metal, getting hotter then I'd interpret that as bad, i.e. there being more friction (somewhat hard to believe) or worse heat absorption by the oil. The latter would sound like an argument against using synthetic.

[blueviewlaguna]

Yep, I should have noticed the tiny nib from the bottom of the RealOem #7 that would have given it away as a temp sensor - sure looks just like the #4 oil sensor other than that.

So the Cylinder head temp sensor must be for the Engine Control Unit, with the oil temp sensor in your diagram feeding the dash gauge - good, I was hoping it had an oil temp sensor.

[deilenberger]

I was thinking about why RealOEM didn't show the oil temp sensor. Wonder if it's only used on bikes with OBC? Anyone have a non-OBC bike here? I recall hearing that they didn't have the fuel level indicator (just a low fuel warning light) - do they also not have a temperature indication (aside from the engine light)?

Yup - that's gotta be it. I looked it up for an R12RT: http://www.realoem.com/bmw/showparts.do ... g=61&fg=31 - #6 is shown as a temperature sensor. In that case - if the non-OBC bike has no temperature display, then it looks like BMW does use the head temperature for the display.

Mysteries abound..

[blueviewlaguna]

I wonder then, if not having a cylinder head temp sensor on the right side exposes the engine to any damage scenario due to a right side overheat (injector clogged, causing a lean burn - etc). Maybe the non-OBC models have a right side for the gauge, with a left for the ECU?

[vroomr]

Isn't the Mobil V-Twin oil intended for bikes with wet clutches? I believe such motorcycle oils are less slippery than the non-motorcycle stuff the R can use. Perhaps this has something to do with it.

From a Mobil FAQ explaining the difference between passenger car and motorcycle synthetic:

Additive packages balanced differently for motorcycle engine and transmission operation. For passenger vehicles, fuel economy and emission system protection are higher priorities. These require low phosphorus systems and the use of friction modifiers. Motorcycle oils do not require friction modifiers for fuel economy and for better clutch friction less/no friction modifier is optimum. Motorcycle oils allow the use of higher levels of antiwear additives such as ZDDP (phosphorous).

[websterize]

Did you experience a similar increase in temperature when switching?

I switched to synthetic at 6,000 miles, and the engine temperature readouts have stayed about the same — four to six bars in mostly city commuting. I'm at about 8,000 miles.