Oil Pressure Vs. Oil Flow

[Scud]

Now that I have a functional oil pressure gauge on the LeMans, I'd like to know if my pressure readings make sense. As I understand it, oil flow is what we should truly be concerned about, but since that is hard to measure, oil pressure serves as an indicator of oil flow. Here's the data:

 

Cold Start:

Cold idle at about 1,200 RPM: about 15+PSI

 

After the bike warms up:

Idle: about 3 to 4 PSI

Steady speeds around 4,000 RPM: about 12 to 16 PSI

Accelerating: peak pressure about 25 PSI

 

Oil:

Maxima 10w-40 ProPlus 100% synthetic (10-40 is specified in 2003 manual) - I used a full gallon at the recent oil change, and the oil level is a bit higher than the dipstick "full" mark.

 

My cause for concern is that the pressure seems very low at hot idle - but since there is SOME pressure, there must also be oil flow. On my first ride with the new gauge, and my first stop for a traffic signal after the motor was fully warmed up, I noticed the pressure gauge needle dropped nearly to zero at idle - which made me nervous. But I can tell that it is registering something (3-4 PSI) and it bumps up with the slightest blip to the throttle.

 

FWIW - I put maybe 500-800 miles on while I was between gauges - so It's been working, but now I am just trying to understand the readings.

 

Questions:

Does it seem that I have any cause for concern? Is the big drop at idle between cold and hot because of the multi-viscosity of the oil? Would 20w-50 oil increase pressure slightly? Does anyone run 20w-50 (or thicker) oil in a 2003 or later motor? 

 

 

Correction/Edit: The 2003 manual calls for 5W-40 oil, even thinner.

Edited June 29, 2015 by Scud

[thumper]

Those numbers look quite low to me,

4000 rpm 16psi hot is not good.

Others may chime in but what you got would have me take a closer look.

[BMWDavid]

I think an old rule of thumb was 10 psi per 1,000 rpm. So at 4,000 rpm you should see at least 40 psi. This engine being a plain bearing engine certainly relies on oil pressure as well as sufficient flow.  

[stuarto49]

I have an actual mechanical oil pressure gauge on my 2001 V11 Sport.  When I bought the bike the OP light was malfunctioning and the previous owner had already ordered a replacement switch.  Once he gave me the new switch I used only the adapter (M_somehing to 1/8" FPT) and connected the real gauge, and put the new switch on shelf.  My gauge has a 0-100PSI range so it doesn't get 'nailed' when the bike is cold and the oil is thicker.  

 

When I start the bike from cold (summer here in VA) I read 65-75 PSI at fast idle.  Once the bike warms up, after some riding, I still get at least 12-15 PSI at slow idle, and right back up again to 50-60 PSI when taking off.  I believe the OEM pressure switch is set for 3-5 PSI.  I'm an engineer - GIVE ME DATA.   I also have digital voltmeters with one decimal point on all three of my bikes.  And I know exactly what's going on with the electrical systems.   On the Guzzi I saw 15-5 - 16 volts one day - I knew something was wrong.  The next time out it only showed 11.6V at any RPM.  I replaced the Rectifier / Regulator with an aftermarket unit.  Now it charges at 13.6 - 13.9 V, like it should.

 

Stuart

[Scud]

Thanks guys, for the input so far. I am not certain that the gauge is accurate. I had a different gauge and pressure sender on previously - all parts from Speedhut.  The prior one had a fault and would not read low pressures, but it showed much higher pressures at operating temperatures than I'm getting with the new gauge. The new gauge (which I paid extra to upgrade to) is supposed to be more accurate.

 

My opening post is what I remember from my short ride last evening, but I think I will take a pen and paper out for a little "research expedition." Empiricism shall prevail...

 

One more bit of info: before replacing the stock sender unit, I did notice some flickering of the stock oil warning light at hot idle. 

 

@stuart -

What oil are you using?

What are your other bikes? Maybe add them to your profile? Enquiring minds want to know...

[Scud]

Here's my fresh data:

 

Cold start, idle at about 1,250:  25 PSI

Warmed up a bit in the driveway, then rode the first mile or so: the 10PSI/1,000RPM ratio seemed pretty close, but I only took it up to about 4,000 RPM which yielded about 40 PSI. 

Then as the bike got warmer the pressure dropped.

 

After 2.5 miles to the gas station, I got the following readings with the bike stationary:

• idle about 1100:  about 4PSI
• 2000 RPM:  8 PSI
• 4,000 RPM:  20 PSI

Then I took a short section of freeway so I could monitor pressure at constant speed.

• 5,000 RPM:  pretty steady 20 PSI
• 6,000 RPM:  the needle moved between about 28 and 32 PSI

By the time I got home, the bike was good and hot, and the PSI readings were about the same as at the gas station, but a touch below 20 PSI at 4,000 RPM.

 

The previous oil change showed no metal, screen was clean. UNI oil filter screwed down tight (1 and 1/8 turns after contact).  The current oil is still golden-clean; the oil level is still up above the dipstick full mark (checked just now with bike level and stick screwed all the way in). 

 

Whatever is going on is not a new problem (if it is a problem).  If I only had an oil light, I would be blissfully ignorant of this. But now I have the data.......  

 

Anybody else running a pressure gauge with 10w-40 oil? 

 

I've got a trip planned in a few days and intend to take the LeMans (along with the Husky) to the mountains.  Don't want to take it if I have a problem.

[Scud]

Doing a little reading on the topic, I chanced upon a discussion forum for automotive engineers. It seems they don't really concern themselves with pressure very much. One engineer said "...any positive number should be acceptable. Customary minimum numbers are basically safety factors." Another talked about differences in pressure due to different weights of oils - and said the differences don't matter so long as there is enough flow. Another actually talked about how thinner oil and lower pressures can be better... because they flow more volume through the bearings.

 

I'm no engineer, but I found this short discussion very interesting - and counterintuitive. I have always assumed that more pressure is generally better.

 

http://www.eng-tips.com/viewthread.cfm?qid=354922

 

It got me thinking, the 2003 engine has oil sprayers. That's two more exit points for oil - and sprayers would seem to take more flow than bearings (my assumption), but I think the oil pump is the same as earlier models. Considering that, combined with thinner oil than used in the early V11s, one could reasonably expect the 2003 and later engines to run at lower pressures.

 

Anybody running a pressure gauge on a 2003 or later bike?

[stewgnu]

I wonder has anyone got a copy of Guzziology?  I'd have thought there would be info on this subject in there.

 

Stew

[thumper]

Pull the sump and please check your oil filter.

Check the gasket, look for particles in the sump.

Something is wrong, check the big easy things first.

May be just that simple, oil filter loose, cross threaded two or no gasket.

I do hose clamp my filter, found it loose once.

[JBBenson]

Keep in mind that oil is hard to wash off, and a thin film remains even if the pump were to stop working for a short period.

 

The most wear on an engine occurs at start-up, when the oil on the walls of the cylinders have been draining for a while. But, there is still a thin film there, otherwise you would wreck your motor when starting, right?

 

I have never measured the oil pressure on my 2001 Sport, but when I do the valves, I can see oil flowing to the heads while I turn the motor over to find TDC. 

 

So, I guess it is working.

[Scud]

Thanks. I had the sump off recently (I've only had the bike a couple months) and all was good. Verified clean surface for the UFI filter, good gasket, etc. I just ordered a WIX filter to have on hand in case I need to get into the engine again. 

 

I know the oil-pressure topic has come up frequently, and I just reviewed this thread:

 

http://www.v11lemans.com/forums/index.php?showtopic=17027&page=1

 

However, given that I had much higher pressure readings with the previous gauge, it seems like it's time for me to buy an external, mechanical gauge that I could use on any vehicle. If I can run that in tandem with my new, electronic pressure gauge it will help with the diagnosis.

[Scud]

Took it out again last evening - 60 miles without incident. The pressure held constant at 40 PSI / 4000 RPM for the first couple miles - then I actually watched it drop while I maintained constant speed and warmed up the bike. Given that the system is capable of holding high pressure with cold oil (I saw close to 60 max PSI) and lower pressure with hot oil, it seems there is not a mechanical problem.  I have put a lot miles on it the last few months without being aware of the exact pressure readings - including some pretty hard running in the heat, and no problems/noises.

 

Here is what I've surmised from reading too much...

 

Pure, 100% synthetic oils (like the Maxima I am using) do produce lower pressures. This is because the synthetic molecules are all the same shape, whereas the organic molecule shapres are diverse. The diversity in shape creates more back-pressure as they all squeeze through tight bearing clearances. This is also why synthetic oils are considered slipperier - and perhaps also why they are more prone to seepage. Some things I read talked about pressure drops up to 10PSI when compared to organic oils.

 

Piston sprayers (as installed on 2003 and later V11s) reduce oil pressure - sort of like when you turn on multiple faucets in your home. There is still sufficient flow, but there is less back pressure because the 2003 engines have two more "faucets" open than earlier engines.

 

 

 

While I think the "alarm bells" are no longer ringing, I'm still interested in comparative data.

 

Who's got a pressure gauge on a 2003 or later engine? What oil are you using and what pressures do you see?

[thumper]

4000 rpm 40psi if you are happy with it have fun and go.

Still seems a bit low and if oil pressure is marginal it will never get better or correct itself.

It's bleeding somewhere.

[Bjorn]

4000 rpm 40psi if you are happy with it have fun and go.

Still seems a bit low and if oil pressure is marginal it will never get better or correct itself.

It's bleeding somewhere.

 

Do you have a oil pressure gauge as well? Just curious why Scuds numbers are ''wrong''?

[Scud]

I'm not sure that I'm happy (or unhappy) with the pressure readings. But I am sure that if I had only a warning light that I would be ignorant of the pressure readings, and not have even started this thread, I would just be riding the bike (as I have been doing).

 

What I'm trying to do is to figure out what makes sense. The above-referenced conversation (post #7) on the automotive engineer site really challenged my thinking.

 

Of course, I am not disputing the need for oil pressure and proper lubrication. But as I am currently understanding it, a high oil pressure number just shows how much the oil is being held back, not how much it is flowing. The idea that a lower pressure number can be good - and can indicate more oil flow and better cooling - is new to me. The "bleeding somewhere" could be fast flow through all the places the oil is supposed to go, which would be good.

 

So - I'm not trying to be right, and certainly not trying to do harm, just trying to learn by paying attention to the data. Hopefully we can get a direct comparison with someone else's experience.