Hopefully this is a new twist to an old topic.

I asked a pretty smart buddy of mine about his theory why a GS500 might consume oil, and he wrote back,

"Depending upon the design of the vent system, high rpm can vaporize oil  in
the crankcase and blow it out the breather .  Unless the rings or valve guides are worn on your GS, you shouldn't experience oil consumption at  low revs."

OK, consistent with what I read here I guess, though I haven't actually found an explanation in my quick search.  Then I asked if he thought the oil cooler addition on the "F" would help alleviate that.  His response (and he's not a GS expert) was,

"Afaik, the cooler was added because the newer engine runs hotter.  This may
be partly due to the fairing, but most likely the EPA was the culprit. Cooling the oil won't stop the vaporization, it's usually a rev thing.  All bikes are different, YMMV."

So I'm wondering,
(1) does his first explanation jibe with conventional wisdom of our site gurus?
(2) What about on the GS500F.  Anybody with one have lower oil consumption, or is this a constant among the GS500 twins?  And does the new engine really run hotter by design (maybe for EPA regs)?

I'm only trying to understand the bike better.  Thanks for any info/opinions, and sorry if I missed some of the answers on my abbreviated search.

--Mike D.

The GS, even if flogged hard, doesn't blow too much oil out of the crank case breather. Its at the very top of the cylinder head away from most of the oil churning.

Oil consumption is almost all from piston blow by because the GS has an air cooled engine. As such it has to be built "looser" than an equivelent water cooled motor, because you have a greater temperature range the bike has to be able to tolerate.  When cold the pistons are very loose in the bores and you get alot of blow by. When the cyliders heat up and expand, clearances get tighter, but are still loose by modern liquid cooled standards. Things get worse as the cylinders and rings get worn.

Just a fact of life for air cooled engines...

OK another question... where does it go from here... I am refering to the 45K mile 89, ok Its seen high rpm's and its got oil useage... OK a quart in 250 miles... and actually it seems to reduce with thicker oil... ao maybe that vaporisation factor does happen... anyway what will eventually happen in mine... would I foul plugs, will it stop making power and be barely able to get under way on its own power... what... BTW I have never fouled a plug on it and it still makes enough power to make a good 100 mph, and give me 42-45 mpg.
Cool.
Srinath.

Overbore kit.

Suzuki sells +1 mm pistons and rings as a "maintainence item".  
Have the cylinders honed out to the proper diameter, install new pistons and rings and she'll be better than new.

Well I was asking more along the lines of what will happen eventually... If I leave it be... which is most likely to happen... till it wont get up my driveway... which is gently up hill BTW... That is when what to do is even comming up... else its getting flogged as it is.
Cool.
Srinath.

Yes, eventually it won't run worth a shaZam! because of loss of compression and drowning in its own oil...

OK but it wont like catastrophically seize up at high speed or anything like that right...
Cool.
Srinath.

No the exact opposite. It will be overlubed and strangled on oil and unburnt mixture.  Unless of course things get so loose that the piston crown or skirt starts dragging on the cylinder wall...

If the bike is showing signs of needing the cylinders done, I'd just bite the bullet and do it. Besides being cool and will bump up the performance of the bike, it won't cost that much if you factor in the amount you'd save on the wasted gas, oil, spark plugs otherwise used up by trying to wring out a few more miles out of a bad engine.

Also think of the crap you are flinging into the air too...

Flinging... ha ha... If suzuki built it and they homologuated it... I am not realy going to make any changed to it as long as its going down the damn road...
If they did want it to be cleaner they should homologate it better... Have had enough crap from poorly designed and badly enforced rules ... if I can get away I will ... BTW they dont want it to use less oil either... they want oil companies making money... use oil, use gas and buy bigger and bigger vehicles... OK I am doing only 1 of the 3... so I am really hurting them.
If I could only buy a hummer instead of my GS, and drive it everywhere and convert the GS into a track only 2 stroke and race it there every day using 105 race gas... that will make me their sweetheart.... but hey we cant all be perfect...
Cool.
Srinath.

He is right about the rpm.  It's the same for most engines.
I'm riding the GS to work for the last two weeks and at same speeds before that and the oil level has not changed in almost 500 miles.

se that's the thing... my plugs are never oil fouled. I doubt I will ever have the bike go off the deep end... see the oil coating on the cyl wall gets thicker and thicker... as my rings and bore get worn and clearances go up... isn't it going to stop wearing at one point cos there is no ring to wall contact...
Cool.
Srinath.

and don't forget..that turd still has 150 # compression each cylinder!!!!!!

can't be tooo worn out

That turd is going to get flogged til it cries...
Cool.
Srinath.

with budda riding it....it's crying.... :mrgreen: