trying to find the correct fluid for my 1988 k100, i’m looking into mobil 1 75w90 synthetic? any recommendations or tips? i live in alabama (U.S) for reference so it won’t ever get too cold

My bikes are very happy to get Walmart full synthetic 75/90 GL5.  The GL5 is the important part.  It means it is for transmissions without brass or bronze synchronizers.

Same here on the Walmart full synthetic 75/90 GL5 available just about everywhere in 'merica with an occasional free freak show thrown in.

attached an image, i only added 3 quarts of oil to my k100 but everything says i need 4, but it’s right on the dot. is this okay or should i add the other quart?

You dont say if filter was changed as well, anyway fill to dot run engine for 5min or so allow to stand for 20/30mins check level add oil if required to dot on glass 

mmgee123 wrote:attached an image, i only added 3 quarts of oil to my k100 but everything says i need 4, but it’s right on the dot. is this okay or should i add the other quart?

As  you pour the new oil in, some may find its way over to the sight glass and fill it.  Because the oil is cold, it will have a tendency to hang in the glass.  As was mentioned by Moriarti, running the engine for a while will warm the oil so it will properly run out of the glass and show the proper level.

By Crazy Frog (Esteemed Forum Creator) from 2012.

Verified Oil Level Test Link

And here is a link to the K100 owners' manual courtesy of KBikeParts.com (see pages 18 & 69 of 94)

K100 Factory Owners' Manual

The first post is about transmission and final drive, not engine.

The transmission level is quite specific. It has to be measured with a dip stick. If you have the C spanner for rear suspension adjustment, its marked with the level mark. If not, a screwdriver with a non removable shaft [so it cant fall out into the transmission- dismantle it to get it back out] and its 116mm from the top handle.

Final drive uses the same oil, to the beginning of the filler plug threads.

1 litre is not sufficient to do both, together they take slightly more.

Point-Seven-five wrote:My bikes are very happy to get Walmart full synthetic 75/90 GL5.  The GL5 is the important part.  It means it is for transmissions without brass or bronze synchronizers.

 What are you guys in the USA paying for Red Line at Walmart? In Canada, 1L container is $38.95. Similarly, a 1L of Motul 75W-90 synthetic is approx $35. My Motul 90W mineral is $25 for a 2L jug.

92KK 84WW Olaf wrote:The first post is about transmission and final drive, not engine.

The transmission level is quite specific. It has to be measured with a dip stick. If you have the C spanner for rear suspension adjustment, its marked with the level mark. If not, a screwdriver with a non removable shaft [so it cant fall out into the transmission- dismantle it to get it back out] and its 116mm from the top handle.

Final drive uses the same oil, to the beginning of the filler plug threads.

1 litre is not sufficient to do both, together they take slightly more.

mmgee123attached an image, i only added 3 quarts of oil to my k100 but everything says i need 4, but it’s right on the dot. is this okay or should i add the other quart?
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The engine oil question is there amongst the posts.

Note: GL5 of your viscosity choice is 260cc (.3 qt/.26 litre maximum - page 70 of manual) in the final drive and 850cc +/- 5cc in the gearbox.

RS Rider wrote:

Point-Seven-five wrote:My bikes are very happy to get Walmart full synthetic 75/90 GL5.  The GL5 is the important part.  It means it is for transmissions without brass or bronze synchronizers.

 What are you guys in the USA paying for Red Line at Walmart? In Canada, 1L container is $38.95. Similarly, a 1L of Motul 75W-90 synthetic is approx $35. My Motul 90W mineral is $25 for a 2L jug.

I seem to recall spending about $8 a quart for the Walmart store brand the last time I bought it which was around 2 years ago. 

I have an ancestor or two who hail from Scotland so I have the Cheap Bastard gene.

Point-Seven-five wrote:

RS Rider wrote:

Point-Seven-five wrote:My bikes are very happy to get Walmart full synthetic 75/90 GL5.  The GL5 is the important part.  It means it is for transmissions without brass or bronze synchronizers.

 What are you guys in the USA paying for Red Line at Walmart? In Canada, 1L container is $38.95. Similarly, a 1L of Motul 75W-90 synthetic is approx $35. My Motul 90W mineral is $25 for a 2L jug.

I seem to recall spending about $8 a quart for the Walmart store brand the last time I bought it which was around 2 years ago. 

I have an ancestor or two who hail from Scotland so I have the Cheap Bastard gene.

 $8 a quart? WOW! That's a huge difference in price. I wonder why that is?

As a cheap bastard I don't "waste" my money on "racing" lubes like Redline or Motul.  Rather I buy the Walmart store brand "Super Tech 75/90 full synthetic GL5" which my bikes are quite happy with.

75/140 in the transmission
75/90 in the final drive

I run Mobil 1 usually but I think any full synth would be fine

For smoother shifting add 25 grams (half a tube) of Liqui-Moly 2019 to the transmission oil.

duck wrote:75/140 in the transmission
75/90 in the final drive

I run Mobil 1 usually but I think any full synth would be fine

For smoother shifting add 25 grams (half a tube) of Liqui-Moly 2019 to the transmission oil.

Why the higher viscosity in the gear box? Is it due to its proximity to engine heat?

In a separate gearbox, there's no oil pump to push lubricant under pressure. So you can use hugh viscosity oil, that has better adhesive capacity and more resistance to the high forces applied on gears.
If you run your engine with 80w90 oil, it will loose a lot of power because of the succion resistance it implies, and will probably blow un the oil pump...

RS Rider wrote:Why the higher viscosity in the gear box? Is it due to its proximity to engine heat?

In the transmission case are more gears and shafts needing their lubrication to adhere during hard usage than in the rear drive. 75/140, as cited, is a viscosity for extended steep grade riding, track usage, or for those who like to think of themselves as racers but aren't.   The rest of us can use what BMW recommends in the rider's handbook.

As far as using 80w90 in the engine, don't use maple syrup in there either, no matter its color or how good it tastes.

75/140 shifts smoother. A 500 pound bike with only 75 hp has nothing to do with motorcycle racing.

Track days aren't necessarily racing days, duck.    The pretenders are doing their Brick redlining out on the public highways. They don't let 500lbs interfere with their destinies.

duck wrote:75/140 in the transmission
75/90 in the final drive

As well, in dry clutch Oilheads/Hexheads, & K1200RS/GT models with that superheated catalyst directly beneath it, we (various Pacific NW Beemer dealerships where I've worked) have recommended 75W140 in the gearbox - but not the final drive - for resistance to the heat and the fact that they do tend to shift slightly better. Sure, BMW specify GL5 75W90 or 80W90 in both locations, which is fine in any case.

I have also used 75W140 full synthetic GL5 in my two Airheads' gearboxes for many years.

Here's a link to an interesting (some of it outdated by now) article written by former BMWMOA tech writer Paul Glaves, about reasons for/against 75W140 & 75W90/80W90 gear oils, which was posted many years ago.

Paul Glaves article & customer receipt/complaint

Laitch wrote:
As far as using 80w90 in the engine, don't use maple syrup in there either, no matter its color or how good it tastes.

90 weight oil is not necessarily thicker than 50 weight.
The higher number identifies it as a gearbox oil, with certain characteristics (additives) that are appropriate for that use, and not for engines.

Check out this interesting chart.

Laitch wrote:Track days aren't necessarily racing days, duck.    The pretenders are doing their Brick redlining out on the public highways. They don't let 500lbs interfere with their destinies.

Mesmerising.  The K75 rider appeared to be the only one enjoying himself.  

Looked like lots of people with all the gear but no idea.

TacKler wrote:Mesmerising.  The K75 rider appeared to be the only one enjoying himself.  

Looked like lots of people with all the gear but no idea.

Nah. He just had to line up on the corners proper-like 'coz his brakes wasn't working and the red light was telling him not to fall off.








(I know I know. Just a busted brake switch somewhere)

That vid gives me flash backs to our KFest “Legends” ride at Castle Donnington…except we weren’t allowed to overtake and our speeds barely exceeded 40mph…which probably wouldn’t red line even in first gear.