Forum bmwbike.com

As Single BMW have a «natural» propensity for overheating, I wondered if synthetic motor oil would be of any help.

While long distance riding by hot summer days, the oil (15W50) of my R 26 is inclined to turn in to vapour and escape, modestely, by the breather pipe.

Except the small loss of oil that result, I think lubrication my be of poor quality during these moments of high temperature.

As of what I understand synthetic oil, such as Motul, has a higher temperature working threshold, I wonder if it can be of any help.

Any body s'got any experience or knowlege about the mater ?

Thanks for any help or comment !

damien

Synthetic oil is superior, but if your motor is blowing visible fumes out of the breather, you have a problem - possibly worn rings. Synthetic oil cannot cure mechanical problems.

Allan,

Thanks for your comment.
You're right, synthetic oil will not cure anything !

But, as far as my R 26 is concerned, rings are OK, I checked it with a pressure-gauge on the sparkplug hole. I don't have the result value in mind, but it was pretty high. I also removed the cylinder, every thing is OK inside. Valve guides are also airproof as there is «Perfect Circle» rings around valve guides.

Any way, if it were mecanical weakness it'll not appears only on hot sommer days, when I ride for more then an hour between 80 and 100 km/h (that's on a freeway, where I don't go often, I recogn). It didn't appear as I ride on small roads, even in mountains. But the engine get very very hot indeed.
That's why I think it's only over-heating. And that's why I wonder if using a synthetic oil may help.

But I fear about high detergent capacity of synthetic oil, and may be agresivity on gasket, and may be points I don't know yet about.

Thanks again,
damien

Hi Damien,
As far as I know, on should expect oil consumption of 0.5 to 1.0ltr on 1000 km riding distance, depending on top speed /riding style. If you don't have one, consider installing the larger oil pan. It increases oil capacity by 0.25ltr to 1.5ltr. I frequently use my R26, also for longer rides at higher speed. And you can bet sure that it is pretty hot down here in the Philippines. The only situation my bike really hates is maneuvring in a traffic jam after a long and fast ride. But I guess that is a sure killer for every vintage vehicle.

Regards

Thorsten

Hi Thorsten !

Thanks for the comment.
On my R26, oil consumption is bellow half a liter per 1'000 km, and it must hapen only on these hot days when I ride long distance pretty «fast». Usualy I ride rather «cool».
You'll right, I'll have to consider to installe a larger oil pan. I was just wondering about loss of ground clearance.

«And you can bet sure that it is pretty hot down here in the Philippines»
I bellive you. (As a matter of fact, I never been to Philippin, but I remember Indonesia, and trafic jam in Jakarta. Been traveling over there years ago.)
By the way, which motor oil did you use ?
Thanks again.

Sincerly yours,
damien

Hi Damien,
What oil am I using? Was it 20W50 or 15W50? For sure it was 50. Never had any problems with ground clearance. Now what is considered fast for the R26? In the manual we find a permissable top speed of 110km/h for the rider in upright position, and 128 km/h in racing position. I guess that means downhill with the devil in your neck. After complete renovation including new bearings, crankshaft- and piston pin, cyl. rebore to 1st oversize, new piston, valve assembly , chain, etc., etc, and extended break in period, I've reached 120 on the speedometer but usually don't go beyond 100. The bike seems to feel most comfortable between 70 to 90 km. As they say: they were not built to be fast but to last.

Have fun

Thorsten

My understanding is that as long as your slingers have been recently cleaned there is only one negative aspect of synthetics. That negative is a side effect of synthetic's great ability to creep into the tiniest crevices. This provides great wear and corrosion protection but also means it finds leaks where conventional oil might not. It doesn't necessarily "attack" gaskets as someone suggested, it just finds its way past the marginal ones. My thinking is that this is a worthwhile trade off for an engine with clean slingers....more friction protection, less sludge, greater heat range, better low temperature flow.

Synthetic oil is OK to use. I used it from 1986 to 1991 in my R69S. But now I change the oil every 500 miles in my three oldies, so I use BMW 20W-50 oil because it is cheaper than synthetic.

Hi Allan !

As I understand, you improve lubrication, or at less secure it, by shorten by half the laps between oil changes.
It's probably whort thinking about it.

Thanks !
damien

Brad,

Thanks for this technical point !
It lighten the subject.

Sincerly yours,
damien