Hey,

As everyone knows I've been having an oil leak that's not getting worse but it's most certainly not getting better. I plan on trying to tighten my valve cover tomorrow if I get a chance as the vast majority of the oil is on the upper cooling fins of the heads.

I noticed however that all these problems have surfaced after I switched to 5w40 from 10w40 at the recommendation of a friend who uses it in his CBR600RR. I've had two oil changes since then but the leak didn't show until the second (most recent) oil change.

So my question is this, could the oil weight be causing the problem? Could changing back to 10w40 fix it?

The problem is down to two surfaces not being mated and sealed.......nothing to do with the oil you use or its grades.

5w40 and 10w40 both have the same viscosity at operating temp so there is no difference there anyway 

Tightening the valve cover bolts on a GS will have little effect unless they are actually very loose, those are shoulder bolts and once tightened down to the shoulder they will not compress the gasket any further no matter how much more you tighten.  I've found valve cover gaskets to be good for about 30k miles at which time they need replaced to stop leaks.

I would not use a 5W-40, 5W-50, or 5W-anything oil in an air cooled motorcycle again, your friends CBR is liquid cooled with much better temperature control in the combustion area.  Also I've found that running multigrade oils in air cooled GS500s that range above 40 weight like 15W-50 or 20W-50 cause them to run hotter due to reduced flow of the cooling oil that carries heat from the combustion area to the sump.

Yes 5w40 and 10w40 oils both have the same viscosity at operating temps when they are new but after viscosity breakdown they do not.  Those long stringy molecules that are added to make them multigrade break down and after many miles a 10W-40 oil becomes a 10W- 25 or so.  Also bikes that use the same oil in the transmissions break down faster than in vehicles that don't due to those long molecules being chopped up by the gears.

Is that 5W-40 you're using a synthetic oil?  I put synthetic oil in my high mileage well worn CB750K years ago thinking a better oil might reduce oil consumption and it leaked several different places it didn't before so I changed it back and the new leaks stopped.

So my answer is oil weight can affect several things including running temp, oil usage, leakage, and winter start ups.  I've found the 15W-40 heavy duty dino oils like Rotella T to work best for me year around here in NE OH, been using them for over 120k GS500 miles now.  Used 15W-50 Mobil 1 full synthetic in my first GS for the first 50k of the 80k miles I had it.

Quote from: gsJack on May 26, 2013, 08:21:24 AM
Tightening the valve cover bolts on a GS will have little effect unless they are actually very loose, those are shoulder bolts and once tightened down to the shoulder they will not compress the gasket any further no matter how much more you tighten.  I've found valve cover gaskets to be good for about 30k miles at which time they need replaced to stop leaks.

I would not use a 5W-40, 5W-50, or 5W-anything oil in an air cooled motorcycle again, your friends CBR is liquid cooled with much better temperature control in the combustion area.  Also I've found that running multigrade oils in air cooled GS500s that range above 40 weight like 15W-50 or 20W-50 cause them to run hotter due to reduced flow of the cooling oil that carries heat from the combustion area to the sump.

Yes 5w40 and 10w40 oils both have the same viscosity at operating temps when they are new but after viscosity breakdown they do not.  Those long stringy molecules that are added to make them multigrade break down and after many miles a 10W-40 oil becomes a 10W- 25 or so.  Also bikes that use the same oil in the transmissions break down faster than in vehicles that don't due to those long molecules being chopped up by the gears.

Is that 5W-40 you're using a synthetic oil?  I put synthetic oil in my high mileage well worn CB750K years ago thinking a better oil might reduce oil consumption and it leaked several different places it didn't before so I changed it back and the new leaks stopped.

So my answer is oil weight can affect several things including running temp, oil usage, leakage, and winter start ups.  I've found the 15W-40 heavy duty dino oils like Rotella T to work best for me year around here in NE OH, been using them for over 120k GS500 miles now.  Used 15W-50 Mobil 1 full synthetic in my first GS for the first 50k of the 80k miles I had it.

Yeah, the oil im using now is a 5W-40 full synthetic Rotella T6. So you think that could be at the very least contributing to it? Is there anything special I need to do to go up a weight on oil other than drain the bike the best I can?

Will that 15W-40 work well in year-round summer weather of the west? I'm sorry if these seem like basic questions. I dont know much about oil.


The oil leak itself is all over the upper fins. I'm pretty sure oil can leak from only two places up there (tach cable/valve cover). What are the chances my valve cover seal is bad after only 15k miles?