Low Oil pressure after warmed up

[Mekanix]

Its in the Haynes manual on page 115.

Pressure should be high for this engine,

Here is what it says.
"
Run the engine at 2000 rpm for 10 minutes to warm it up.
Then run the engine at 3000 rpm,
Pressure should be 42.7 to 78.2 PSI.

A pressure reading lower than specified may be caused by a worn pump, a blocked oil strainer or oil filer element. OR installing it backwards !! ( long story )
"
A slow decrease over time is indicative of bearings wearing out.

I'm going between internal leak, pressure regulator weak spring, or faulty pressure sensor. I've seen all 3 do this on mine.


Roller bearing engines run on low pressure high volume. So 5-7 psi is normal for those.

[bwanna]

Thanks so much! Maybe I should get a haynes manual?

That gives me something to work with!

[Mekanix]

Thanks so much! Maybe I should get a haynes manual?

That gives me something to work with!

Its on his site, Listed as GS400-450 and 250, There is two on there, I sent him the two I had and I think he already had them on the second page of manuals.

Also get the gs500 manual. Nearly everything is applicable if not more advanced in terms of knowledge and experience. I mean the oldest manual is still 7 years newer than the one made the year of your bike.

[bwanna]

So I installed a permanent oil pressure gauge as suggested earlier.

Average max pressure during warmup is about 70psi, with cruising pressure about 50psi and idle drops to about 35-40ps. So this correlates to what the manuals indicate.

After warmup things change. Once the things are hot avg cruise pressure is about 40psi with idle dropping to 0psi... with light coming on.

As mentioned earlier, if I let the bike sit for just a few minutes, the light goes off, but the gauge still shows 0 psi at idle. I chock this reading to the fact that the gauge has about 8 inches of hose to the side plug.

SOOOO... any ideas on what I can check? ... tests I can do to determine the cause?

Thanks,

[GregT]

tests - no,not really. causes IMO in order of probability...

Sticking pressure relief valve - sorry but this is an engine strip to get to it, not accessible from outside...

Worn pump - this is accessible but involves removing the clutch.

Those two i'd pick as most likely causes. If you pull the pump, don't forget to renew the O rings sealing it.

[tkent02]

Bad O rings leaking between the pump and the case maybe, or between the upper and lower case.
What oil are you using?

I'd look around the oil filter first, just because it's easy.

[hjfisk]

Being this is a plain bearing engine, it could be worn bearings. Is there ever any noise,or does the engine seem to struggle at all when this happens ?

[tkent02]

Being this is a plain bearing engine, it could be worn bearings. Is there ever any noise,or does the engine seem to struggle at all when this happens ?

Have seen low pressure from bad bearings, but never zero, even with very loose old bearings rattling away constantly. Have you?
Hopefully that's not it. But if it is something which requires splitting the cases to fix, you can leave the head and cylinders in place, flip the engine over and take the lower case off of the upper.