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Discussion Starter · #1 ·
Hello all. I have a question about my oil warning light on a 97 Monster 750. I have had the light come on, intermittently, for about a month or two. It is extremely sporadic and only seems to come on at idle/low RPM and then it turns off if I rev it up a little bit (no tach; maybe 2k RPM it goes off?)

Sometimes it flickers and lights up only barely, and it seems to flicker off when I rev it up (eg, it doesn't just shut off). I have changed the oil (no filings or metal/plastic bits in the oil) and the engine itself makes absolutely no abnormal noises. The light issue has happened before and after the oil change, so I figure if the motor was REALLY starved for oil, it would have seized or, at least, I would have found evidence of a failed bearing when I changed the oil; neither of which occurred.

I do have an intermittent, very grabby (and grindy; making a sound like you're walking on gravel) clutch upon launch in 1st gear and, especially, when the bike is cold, but that has been an issue since I purchased the bike and occurred before the light started coming on.

Yes, I believe there is plenty of oil in it; it sits right between the lines on the sight glass.

Anyway, I have two theories. 1, the oil pump has something wrong and just has a little bit of low pressure at idle that goes away when revved (just like an old American V8 motor) or, 2, it has something to do with the electrical system. The bike has a rear tail light integrator and I am almost positive this warning light started illuminating when I removed the front turn signals. They were all busted up, care of the wonderful folks parking in my neighborhood and constantly knocking my motorcycle over, so I just removed them. When I did so, I also noticed that the turn signal indicator light began only illuminating faintly when I turned the turn signal on. So, I was thinking, perhaps, it was just due to an electrical low voltage, which also would make sense that it goes away when I rev it up.

I have ridden it for quite a few miles with no abnormal sounds or issues with the motor and it is a very intermittent issue, so I'm a bit confused as to what might be causing it. Anyone else had this issue or have an idea what it might be?

Thanks for the help, everyone.

B
 

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Old Wizard
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Oil pressure is the lowest when the oil is least viscous; when the engine is up to temperature and turning the oil pump at its lowest rpm, at idle.

It's also the highest ambient temperature outside so the engine is running at a higher temperature now since the cooling air is hotter. Your Owners Manual suggests a higher viscosity oil be used if you anticipate hot weather.


So the lowest oil pressure will be at idle when the engine is hot and should be at least 16psi. This number will above 36psi when the engine is cold and be 60 - 80 psi around 4,000rpm.

The oil light is connected to a pressure sensor which causes it to light up when the oil pressure drops below a threshold pressure. These sensors have been seen to trigger the light at too low a pressure and need to be replaced if necessary.

It's not unusual to see the light come on at idle, but when if fails to extinguish at a slightly higher rpm or at a progressively higher rpm over time, it becomes a cause for concern.

As a first step, you should carefully straighten any oil cooler radiator fins that are bent from road debris so you get the maximum cooling from the unit. After you straighten them, attach some protective screening to prevent future damage.

If you don’t see any improvement, it would be unwise to just continue to ride it knowing that the oil pressure could actually be marginally low. The expensive consequences include failed bearings and engine seizures.

Since there’s a chance that the pressure sensor is faulty, hook up a pressure gauge to where the sender mounts and check the pressure.
 

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Discussion Starter · #3 ·
Awesome. It is kinda what I thought as well, but I just wanted to ping the group to see if it was potentially a known problem and my search wasn't turning much up.

Thank you very much for the reply.

B
 

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just out of curiosity, what viscosity oil are you using? my 2000 M750 calls for 20w-50 for any weather above freezing, and I use exactly that at all times.
I only ask because its possible that you might just be using too thin of an oil
 

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Discussion Starter · #5 ·
I'm 98% sure I got 20w-50. I know that's what I was going for when I picked it up for the oil change. But, I don't want to say 100%, because there is always the possibility that I grabbed the wrong one.

However, I also had the light coming on when I had the previous oil running in the bike; and it was not always on. I think there is the potential the pressure sender is bad or, perhaps, something is going out; but I had no mentionable material in the screen or drainpan when I changed the oil last.

One oddity, however; the new oil got pretty black again within a hundred or so miles. I'm not sure if, possibly, this is a ring issue that's allowing too much blow-by, or what. The oil did not smell like gas, but who knows.
 
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