What oil is reccomended for a K100. A friend told me synthetic is good but it has to be for motorcycles and not for cars. Is that true?
Thanks, Doug

Ask your friend why he is certain this oil has to be for motorbikes. He might then give you a half answer because he doesn't really know. His intentions are probably well-meant, however. There is good in using caution.

Our bikes have a separate from the oil sump, automotive-style dry clutch and therefore do not require the additives and such that swim in the usual motorbike marketed oils which share a spinning grinding gearbox, vital bearing surfaces of the engine bearings, and particles sluffing off the clutch plates. Several years ago there were some changes made to 'car' oils which were designed to have an effect on overall fuel economy in the larger market. With that in mind I shy away from the lower viscosity 'economy' or 'energy conserving' oils such as 10W30, 10W40 and the like. The oil's container will have a small circular label clearly showing that the oil within is such. Most heavier grade oils are not considered 'energy conserving'. Any chemical engineer-types care to elaborate?

A quality car (or even diesel once in a while if you want to give it a good internal cleaning) oil with the appropriate viscosity due to the temperatures in your region will suffice. I use a 15W50 and change the filter and oil at the same time at intervals of about 6,000 to 7,000 kms. Others here might be able to elaborate on their personal choices too.

I was wondering the same, i have just put castrol gtx in mine with a new filter. My thinking was 25 years ago castrol gtx was proberbly the main oil for bikes and cars, i might be wrong though?

I use Valvoline 20W50 and a new filter every 5,000k's. A new filter at each oil change might be a bit of overkill, but that's me.

I've also used GTX for years and have had no problems.

People swear by synthetics, but in my opinion, a good quality oil (correct viscosity) and filter changed regularly and you can't go wrong.

In my old Ford Falcon I change the oil (Valvoline) and filter every 10,000k's and it's still going strong at 330,000k's.

Well I was going to use a Castrol synthetic 20W50 so it sounds like that will work fine.
Thanks for the info, Doug

Caltex Delo Silver 15W40 is my choice. It has a high detergent addive pack as well as a high zinc content (solid lubricant). It is 1 of only a handful of recommended alternative oils by Caterpillar for their modern hi-tch engines used in our fleet at my work place (off road mine haul trucks).
I keeps the engine internal very clean and flows quickly around a cold engine. Both very important attributes, as most damage is done to engines when they are cold.
5000 K's oil change intervals, with a genuine filter. Warm it up, keep it loaded and ride it quickly !

I use the very very cheapest 15W50 mineral I can get hands onto. You can make a whole philosophy about it, but in the end all that mumbojumbo that the companies are trying to sell us is not worth the mony, if your changing your oil and filter on a regular basis and if your not riding at 8000/min constantly... just my 2 cents

Dennis gets my vote, the recommendations by BMW for 20/50 was based upon oils of yesteryear and I would be going thinner nowadays and I do believe in synthetic. If one uses full synthetic I would be happy to use 5/50 or even 0/40 in temperate climates.
Regards,
K-BIKE

I use Neste 20W50 which meets the requirements, recommended by bmw, i.e. API SF/CC

There you go, Doug, lots of good and differing opinions on oil usage.

It's true that too much attention is paid to the slick marketing of oils (as in all things from bread to politicians), and it's difficult to find an oil with the proper rating these days that's bad for our K bikes.

I consider the use of synthetic engine oils, which are premium oils, this way:
if you are the sort of person who owns a vehicle for a very long time, accumulate high mileage, in a harsh climate (cold and hot), and you use the bike to its fullest, then perhaps synthetic is for you. But if you are the type to buy a bike and own it only for a coupla years, then trade it in or sell it, then the extra money spent on synthetic oils by you is only really a benefit to the person who ends up with your bike secondhand, down the track. It is a long-term investment, because it 'tends' to make an engine last longer, all controllable variables considered.

On a different note, I use fully synthetic hypoid GL5 in my gearbox and final drive, but that's another subject.

Dino vs Synthetic - Lots of information is available but I look at it this way,.. oil performs 2 basic functions - it keeps 2 surfaces apart and it dissipates heat. Additives help manage things such as soot saturation, acid attack, sludge removal etc.
Mineral oils (Dino) of today are more than capable of performing under normal conditions, i.e. normal loads and sensible temperatures. Synyhetics are engineered to be able to provide better protection under extreme conditions, for example, higher loads and extreme heat. All this of course, comes at a cost.
A K Bike engine is not highly stressed, in fact it is very much over-engineered, that's why they are so durable. There are no extreme temperatures generated within the engine due to the excellent cooling system design, high oil volume (secondary cooling) and the use of technologies such as hard-chromed crankshaft journals and Nickasil cylinder linings, both low friction designs in themselves.
So, for me, my money goes into buying a good mineral oil and changing it, along with the filter, a little more often.
I prefer to leave the use of synthetic products to those in need, like in an air-cooled engines where elevated cylinder head temperatures (alone) shorten mineral oil life. For example, a Volkswagen type 1 engine under heavy conditions can reach 250 degrees Celsius at the cylinder heads (I used to build them for a hobby). Not high peformance by any means, but they live for longer with the synthetic products.
My logic only of course, but there's a lot to be lost in playing with oils, and (often) not a lot to be gained.

I used to rally a 1973 Hillman Avenger on a very small bubget for over 20 years. In the 80's we used Castrol GTX 20w50 and changed it every few events. Then before one event my brother brought a can of I think Valvoline 10W40 semi synthetic. I asked him where the F... he was going with 10 bloody 40 when we were having trouble keeping the oil pressure above 15 psi at tickover when the engine was hot with 20-50. Of course being the night before the event, and not having anything else we had no other choice only to use it. Imagine my surprise after coming off the first stage and stopping at the time car to get our finish time I looked at the oil pressure at idle and it was over 20 psi. Running at full throttle the oil pressure was also higher than before. From that we concluded that the semi synthetic was holding its viscosity better than the mineral oil of higher viscosity when hot.
After that we always used 10W40 semi in it (not always Valvoline) even though the engine was built in the seventies with less tight tolerences than more modern engines.
I use any 10W40 semi synthetic I can get in the K, the cheaper the better.

For me price isn't a huge thing since I always buy a few gallons of Castrol Synthetic for about $24.00 per gallon at Canadian Tire when it's on sale. Thanks again for all the info. My conclusion is use the right viscosity, change it often, and don't cruise all day at the red-line. From what Dennis said, since the motor seems to be over-engineered you don't hear of them seizing up after 30,000 clicks from the wrong oil. low oil or dirty oil maybe but not the wrong brand or even weight.
But I'll stick with my Castrol (or maybe whatever I have around).
Thanks again, Doug

Just a word of caution. It seems that sythetic oils have better cleaning abilities. This often results in leaking seals when you change from a mineral oil to a synthetic. Somehow that oil dissolves some of the crud build up at the seals and what previously kept an already worn seal tight (the crud) now suddenly isn't there anymore. Therefore some will tell you that changing over to synthetic is bad for the engine. Actually it isn't, but might lead to discovering some issues. It's great for cleaning your sprag clutch though ;-)