A serious oil pressure question

Pennzoil motor oil
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djlinux64

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Hello,

This subforum gets the most attention so I figure by posting here I have the largest user exposure. This is a rather general question that might be extrapolated to other engines as well so it is not off-topic. I have a 250cc four stroke, liquid cooled engine with a 15,000 rpm red line and an oil pressure gauge that I installed in between the bottom end and the top end. The oil pump picks up oil from the sump and then pushes it through the bottom end then it makes its way up to the top end. Along the way it is measured by the oil pressure switch, if I am reading things correctly. I replaced the factory oil switch with an actual gauge. The manual states that I need to make 50 psi @ 4000 rpm @ 194 F, but I have not been getting anywhere close to those numbers at that temperature and angular velocity. I believe my oil pump is working fine because at 8300 rpm I am making 75 psi, the amount the pump is rated for. That is an indicator that the pump is functional and my gauge is reading correctly. That's why I believe this is a viscosity problem. Right now I am using 1.8 quarts of Redline 10w-40 and 0.2 quart make up of Castrol GTX 20w-50. At 4000 rpm @ 194F I am only getting 18 psi! Should I switch up to 20w-50 or even - dare I say it - straight 50 weight? Please advise!
 
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I know it isn't a Santa Fe I'm giving you a comparison is all..

At Idle (700 RPM) I make 10-12 PSI at 212oF (100oC)

If you can't make the proper PSI at the temperatures with the proper oil weight specified as stated in your service manual then I would repair the problem causing it (Most likely a bad oil pump) and not switch to a thicker oil to bandaid the problem.
 
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The oil pump is fine. The issue is viscosity. The oil pumps in these engines are not failure prone and I will not replace it due to insufficient funds and time. Because the engine is so small the oil pump is too. Temperature has a lot to do with my running viscosity because of this. On a very cold start, I do get up to 40 psi at 4000 rpm. After that it goes downhill.
 
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How many hours on the bike? It sounds like the motor is getting a bit worn, either the oil pump or the bearings or both.
Also at the temperature the 10W40 is at it should act the same as straight 40 weight so going to a straight 50 weight shouldn't do to much except make the bike hard to start when its cold.

Do you actually spend anytime at all @4000rpm? Since the pressure is good at useful rpms you might be able to run it for a long time with some 20W50 in there?

Also don't these little engines destroy oil viscosity quickly? Like 5 or 6 hours in race conditions? Maybe the 10W40 is 10W15 now?
 
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What make of motor,how many hrs/mi?What does the manufacturer specify?
Is this is a bike engine that may share the oil with the transmission?Does new oil have any effect on the psi?

High mileage/hrs and high revving engines sometimes have lower oil pressure because of increased bearing clearance due to wear.
I'm not saying that's the case here but its one possibility.
 
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The manual states that I need to make 50 psi @ 4000 rpm @ 194 F, but I have not been getting anywhere close to those numbers at that temperature and angular velocity. I believe my oil pump is working fine because at 8300 rpm I am making 75 psi, the amount the pump is rated for. That is an indicator that the pump is functional and my gauge is reading correctly. That's why I believe this is a viscosity problem. Right now I am using 1.8 quarts of Redline 10w-40 and 0.2 quart make up of Castrol GTX 20w-50. At 4000 rpm @ 194F I am only getting 18 psi! Should I switch up to 20w-50 or even - dare I say it - straight 50 weight? Please advise!



Was the gauge install before the last oil change or at some intermediate point? Is this a mixed sump (engine and trans)? Lots of bikes start out at one visc and decay to a lower visc in the meat grinder.
 
I wonder if the location of the oil pressure tap is part of the problem. I do believe pressure is reduced the farther you get from the pump, assuming bleed off points in between. It may be that if you check pressure immediately after the pump, you will get higher readings. Just thinking out loud. I am not a mechanic or particularly knowledgable in this topic.
 
18psi at 4,000rpm and 73psi at 8300rpm is not right. It's more than a viscosity issue. You're getting over 3 times more pressure from double the rpm. Not to mention you're waaaay below spec at 4,000.

I'm not familiar with your setup but I would start looking for a partially always open bypass valve if it has one. That's the only thing I can think of that would give the correct high rpm readings with super low low/mid rpm readings.
 
Originally Posted By: BuickGN
18psi at 4,000rpm and 73psi at 8300rpm is not right. It's more than a viscosity issue. You're getting over 3 times more pressure from double the rpm. Not to mention you're waaaay below spec at 4,000.

I'm not familiar with your setup but I would start looking for a partially always open bypass valve if it has one. That's the only thing I can think of that would give the correct high rpm readings with super low low/mid rpm readings.



I concur, that's the only explanation that I can think of.
 
Not sure about the hours, but it has approx 23,000 miles on it and 300 miles on the 10W40 oil.

I am truly stumped. I actually added some pre-load washers to the pressure relief spring this morning to raise my pressure. The relief normally opens at 65 psi. The relief must be closed for the pressure to reach 75 psi. The relief cannot be open especially to meet the pressure numbers I see at the top end.
 
What kind of oil filter does this use?A spin on?Have you tried a different filter?Some bike oil pumps can easily reach 100lbs at low RPM,my CBR1100 has 98lb @ 4,000 warm.It could easily hit the 75lbs pressure relief point at such high RPM even if the bearing were worn a little or the housing was scored.

Pressure relief valve malfunctions usually show up as low across the board readings or no pressure at all.Anything is possible i suppose from a loose pick-up to a scored pump housing,loose bearings,some odd ball pressure relief valve problem,a plugged filter(it would have to be really plugged).
 
Originally Posted By: Trav
What kind of oil filter does this use?A spin on?Have you tried a different filter?Some bike oil pumps can easily reach 100lbs at low RPM,my CBR1100 has 98lb @ 4,000 warm.It could easily hit the 75lbs pressure relief point at such high RPM even if the bearing were worn a little or the housing was scored.

Pressure relief valve malfunctions usually show up as low across the board readings or no pressure at all.Anything is possible i suppose from a loose pick-up to a scored pump housing,loose bearings,some odd ball pressure relief valve problem,a plugged filter(it would have to be really plugged).


You raise an extremely good point. It uses a cartridge filter. I am going to change oil filters right now and hope for the best.
 
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From your description, the bike sounds like a Kawasaki Ninja 250. Just a guess.
 
Correct, it is a Kawasaki EX250 fitted with a pressure gauge. Zero fuel dilution (no fuel smell and thick oil comes out) and zero coolant in oil (no milky residue). I just changed the filter and topped it off with 1/4 quart of Castrol Syntec 5w-50. PSI is up from 18 psi to 30-35 at the manual spec 4000 rpm @ 50 psi @ 194F. Still have to go another 20 psi. I believe this means I might have to start using 60 weight oil. Does that make any sense? What do the oil masters think?
 
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