Anyone see this before.

Wiith the oil pressure guage now atached permenantly, I am having fun watching how the oil pressure behaves.

When the oil is cold, on startup, at idle the oil pressure is really high 70 - 80 psi, increase revs to 2000 and the needle comes down to 40 or 50. Let go back to idle and the needle goes back up around 80.

When hot it works correctly with more revs increasing the pressure so I am not really worried, but out of interest, anyone any idea of why this would happen?

Regards
BMF

High hysteresis in pressure regulator?

Curious, do you still have the 20W-50 oil in the engine you tried while troubleshooting or are you back to 10W-40 again?

Sounds like you're good to go now.   

Still the 20 w 50, i think this  winter I will split the case and check the bypas vavle and bearings.  When very hot pressure can drop to low 30s psi at 3000 revs.

Oil pressure relief valve??

Cookie

Quote from: bmf on July 12, 2013, 08:25:25 AM
Still the 20 w 50, i think this  winter I will split the case and check the bypas vavle and bearings.  When very hot pressure can drop to low 30s psi at 3000 revs.

Air getting drawn in?

Sorry meant to say pressure release valve......

Would air come in from low oil? (Oil level is fine) or is there another mechanism??

I wouldn't worry too much about that 30 psi at 3000 rpm when very hot.  Spec is 28-71 psi at 140 F (60 C) and that is not very hot, actually it's not really hot enough.  Oil is best run at near or just over the boiling point of water (212F) to boil off the water which collects  in it.  Somewhere around 240-250F it gets too hot.

Keep in mind the GS500 runs hotter with the 20W-50 oil than it does with 10W-40 oil.  The cooling oil flow from head to sump is greate with the lighter oil. Would be interesting to see this same info with 10W-40 or 15W-40 oil in it rather than 20W-50, I doubt it would be so dramatic.

Quote from: bmf on July 11, 2013, 02:07:55 PM
When the oil is cold, on startup, at idle the oil pressure is really high 70 - 80 psi, increase revs to 2000 and the needle comes down to 40 or 50. Let go back to idle and the needle goes back up around 80.

There is a physical relationship between pressure, flow, and viscosity.

See here..... http://en.wikipedia.org/wiki/Pressure_drop

Perhaps when the oil is cold its too viscous to be pumped at a high flow rate and instead is just churning up in the pump without going down the line and generating pressure 

Ideally you need to make comparisons with another engine to find out if what you are seeing is indeed normal or abnormal behaviour but if you are following Suzuki's procedure and seeing the sort of figures they quote I doubt there is much of an issue.

Air ingress on the suction side of the pump could also give rise to the symptoms described. Were all the case mating surfaces correctly sealed and were the o-rings on the rear of the pump in good order when you did the recent rebuild?

Quote from: sledge on July 13, 2013, 09:04:45 AMPerhaps when the oil is cold its too viscous to be pumped at a high flow rate and instead is just churning up in the pump without going down the line and generating pressure 

The oil filter has a bypass valve. When oil pressure gets too high, that valve opens up, allowing oil to bypass the filter. That's most likely the source of the pressure drop.

Not quite.

Filter bypass valves maintain engine oil pressure when they open, not reduce it. However a sticking oil regulator could give rise to the problem, as previously mentioned, but to get to it on the GS5 means splitting the cases.

The fact remains though that the figures the OP is seeing are within spec and we don't yet know if fluctuating pressures are normal