81 XJ750 Oil Light

I recently had my oil warning light flickering under hard acceleration. I changed the oil and now the light only turns off at idle. I pulled the oil sensor and flushed it with PB Blaster in hopes that would help, but it didn't. My suspicion is that I have a plugged oil return line, but I really don't want to go digging into the engine. Do you have any ideas where I should start troubleshooting? Thanks.

 

To me, easiest troubleshooting step one would be test the sensor, or just replace it and see what happens. There are specs for the sensor floating around here somewhere.

Since the oil light comes on when pressing the starter switch, maybe there is something electrical going on.

Seems like that much of a problem in the oiling system would cause bigger problems - like bearings self destructing.

 

Is the connection from the sensor to the harness clean? Disconnect the wire from the sensor. If the light is on the wire must be grounding before the sensor.

 

I'm sorry I was unclear: at idle, the light is off. Around 5000rpm, the light comes on and stays on until the bike is stopped at idle for several seconds. My manual is 2500 miles away and the link I found here is broken, so finding the sensor connector and the specs is rather difficult.

 

The idea that oil is somehow not draining back down to the sump fast enough to so that the low oil level condition is triggered is interesting. I just can't imagine what sort of unholy sludgy mess the engine must be in order to make that happen.

What is the mileage on the engine? Any idea what the maintenance history might look like?

I suppose you could try an engine flush product (Berryman, LiquiMoly, etc.) and see if that improves anything.

 

Is the light coming on going uphill? Is the engine oil level low on the sight glass?

 

Rickcomatic stated The Yamaha Sender is a Float. When the Oil LEVEL dips below its limit ... the Switch closes and a Light comes on.
You will see the light come on if you run in weather cold enough to cool the Engine sufficiently to cause the Scavenged Oil to cling to cool surfaces and not drain back to the sump right away.

This was a condition that caused Virago's Oil Light Warnings to occur frequently.

 

Engine mileage is in the vicinity of 40,000 miles. It sat for some 20 years and I bought it with 4k. Once I took some bad advice and used an SF instead of an SJ oil. The oil is at or above the top line on the sight glass. I'm in a valley in Arizona, so no hills and no cool temps. I'll find some Seafoam and see if that does the trick.

 

Could the diode block be faulty? You can check the oil level sensor by removing it connect one probe of an ohmmeter to the sensor wire and the other probe to the sensors base. You should have continuity with the sensor in the normal operating position and no continuity with the sensor upside down.

 

Keep in mind - and for anyone reading in the future - there are two different kinds of oil level sensors for the XJs. One is normally open and one is normally closed. The bikes with atari style clusters are different than everything else, I think. Don’t recall which one is which. It is in the xj4ever catalog.

 

I had a crazy idea so I hooked my buddy's go pro to the highway bar and pointed it at the oil window and the oil is full of bubbles when the oil light triggers. When the light turns off, the oil in the window looks like a freshly poured Guinness. Which makes me thirsty, so I'm going to go ponder what might cause that, but I'm open to ideas and company.

 

I would change it.

 

What type of oil are you using? I use Shell 15/40 Rotella diesel oil . If your oil quantity sender is gummed up , you stated using PB Blaster . You should have used a solvent like brake cleaner .

 

I just put 10-30 Maxima Premium4 in it. I pulled out 10-40 Maxima Pro+, I had 10-30 Premium4 in it before that, Ran Valvoline 10-30 or 20-50 as weather appropriate for years before that. I caught all of them in the Guinness stage at some point, figured it wasn't a big deal because the light turned off quickly or was only on infrequently. It seems to me that the sensor is working just fine, but something is causing bubbles in the oil.

 

Is the crankcase breather inside the gear change cover blocked?

 

From my reading, this is supposed to be a one-way valve? Mine is certainly not any kind of one way from initial testing. It's bi -directional. I assume I need to remove the cover and investigate further. I'll post my findings this evening.

 

I couldn't find any issues under the side panel. The air/oil separator is clear and has no moving parts. I reduced the amount of oil to 3/4 in the sight glass on the center stand. I don't think that will do anything, but it's worth a try. I'll probably Seafoam it this weekend.

 

@Johnius - ever figure anything out?

 

I tossed in some Lucas oil cleaner stuff. I've put 90 miles on since then and added a small bit of oil. Seems to be worse when the oil is hot, but that's only speculation. The oil is definitely staying somewhere other than the sump. Sight gauge was good, went for a ride, oil light came on, stopped to check, no oil in the gauge, waited and watched the oil slowly refill the gauge.

 

It seems to me that up in the cam case would be the only place you could hide that much oil for that long.

Is the solvent helping at all?

 

I don't know if this applies to our bikes so take this with a grain of salt, but in my mazda car for example, if the oil level is too high, the bottom of the crank will be in the oil. When the crank starts spinning, because it is submerged in oil, it will "whip" the oil into a frothy mess like you are describing. I was told this is a reason as to why you wouldnt want to put more oil in then necessary. With that in mind, the obvious fix is to drain all the old oil out, and only put the recommended amount. My bike calls for 2.5L, so I put in 2,5L, check the sight glass to make sure it shows up, then go....

 

Could be you overfilled it, the oil got frothy, which causes the oil level sensor act weird, giving you a light. Just an idea

 

I think I have a combination of that it was overfilled, but I overfilled it because I ran it to saturate the filter and the oil got trapped in the cam area. I reduced the oil level and I'm going to keep running it gently with the solvent in it and see what happens. Pretty concerned the passage is plugged well enough I need to break of the gaskets loose and perform an endoscopy. It's being loaded onto a trailer to go back east, so I won't get to ride for about a week.

 

If it's any consolation, I'm beginning to have a similar situation with my '81 XJ550RH Seca, with almost 51,000 miles. The low-oil light comes on intermittently, low speed or high speed, and resting oil level is 7/8 full in the sight glass (so not overfilled).
Over my 22 years of ownership, I've changed oil regularly. Top-end work has always revealed clean-as-a-whistle passageways, and no sludge anywhere.
I don't remember ever replacing my oil-level sending unit. So between the possibility of a failing wiring connection or ground (which I'll look for) and just the ravages of time and heat beating against a 42-year-old sending unit, I'll try cleaning mine (like you did).
But if that doesn't help, I'll probably just save up my pennies and figure the $300 (ouch!) for a new sending unit is probably the next logical step.

 

I've changed the oil again and the light turns on about 3 minutes into idle and just doesn't shut off. The oil level drops below minimum in the window and the sump isn't refilling until it sits for a while. Is my oil too thick? I looked at the oil diagrams, and from what I can tell, the pump moves oil to the cams, where it drops back down the timing chain guides into the sump. So it doesn't make any sense to me that the oil would be inhibited on it's return from there. But it also gets pumped into the transmission, and I don't know how it gets back to the sump from there. At this point, I'm afraid I'm going to blow the motor and so I'm not riding, which defeats the purpose of the bike...

 

Your oil quantity sensor needs to be removed and cleaned out , it has a float inside . To remove drain the oil, your exhaust will need to be removed. There are two 10mm bolts and disconnect wires, carefully twist and sensor can be worked out. Spray it down there are three holes in top use carb cleaner and let it air dry throughly, and reinstall.

 

Already did this. The oil level is dropping to nil in the window.

 

Have you checked the oil level switch wiring it is not chaffed and grounding to the frame? Unlikely but worth checking.

 

Transmission is partly visible with sump removed. Transmission is splash lubricated.

 

Or he could dose the oil with Seafoam and ride for a few days before an oil change.

 

New oil with about 40 minutes of run time, I'm not happy with whatever is going on. So I did exploratory surgery. I pulled the oil filter and tried running a guitar string up the journals. But the journals don't... do what I thought. So I opened the bottom cross tube of the oil system and it was GROSS https://photos.app.goo.gl/w6FT6gRvq9dKjDq17. So I pulled the valve cover and... it's full of clean oil https://photos.app.goo.gl/4kJraS6NStRZRkd17 , https://photos.app.goo.gl/BAcBgGQ1TzDSVNiv7 I tried putting a guitar string through the cam oil holes and into the journals only to get stymied again by what I assume is a sharp turn in the journal. The engine is making ferrous metal, but it isn't from the cams as there is no scarring on any lobes. I'll check the pots before I seal up the valve cover again. I'm... flummoxed.

 

https://photos.app.goo.gl/n71DWensHR9VoXxg6 I grabbed a video and then I got to wondering maybe one (or both) of my checkballs are bad? If the overpressure ball in the pump got stuck, would this happen? What if the filter ball was too weak and was forced open?

 

On the 900, there's an oil feed gallery on the lower left of the engine (assuming the 750 lump is the same) stick a pressure gauge in there on a flexy pipe if necessary and see what the bearing feed pressure is like.
Take the valve cover off and eyeball the amount of oil being flung to the top - use old towels to safeguard everything around if you rev it up.

 

FWIW my 750 SECA does about the same thing with respect to the OIL warning for the past few months. Buzz the motor to the 9500 point and its lights on for however long it wants (days) then buzz it again and the light is out. I suspect it's the oil getting whipped up and the float in the sender sinks getting stuck on whatever is in the unit until another hard buzz of vibrations shakes it loose. Pressure is good and the level is always kept at the top line of the glass so I just live with it. I've done the Sea Foam thing and nothing really changed and at the moment I'm running 10W40 dino oil with 2/3 can of the STP zinc oil treatment. For all I know it could be a chunk of chain guide stuck in the sender unit or something sticky on the float post itself.
With my engine running the oil level is just above the first line on the glass and with everything moving around I consider this normal. If you like I can snap a couple of photos of stopped and running levels to compare with.

 

Drop the exhaust , drain the oil and remove oil sending unit, flush it out with carb ir brake cleaner , let it dry . Reinstall and reinstall the exhaust system . Refill with fresh oil it is only way fix this . The sending unit float gets gummed up from overdue oil changes and using various types of oil as many previous owners of bikes might not have been up on maintenance.

 

And just FYI the Atari uses normally closed switches and will indicate the fault on an open circuit.

 

https://photos.app.goo.gl/r71mWBViRHgeju9BA soooo... if my oil pump strainer had all this in it, could that be a problem? /sarcasm I also soaked the level sensor in carb cleaner

 

And here's the pics that didn't link properly in my earlier posts

 

Are those black bits plastic?

 

They're very brittle if they are. I think they're carbonized oil. They break into powdery brown chunks, like if you left a Hershey bar in your saddle bag and then put it in the fridge.

 

Plastic wouldn't break down like that I think. Great it is not bits of the alternator, starter chain guide.

 

And a pic of mine running at idle and not running oil level

As it should be right?

I think I would consider replacing it since you cleaned it earlier with PB blaster - or maybe carb cleaner will do a better job?

My guess is those black bits are chain guide

 

Those are the exact levels in my 81 SECA 750 and right on target according to the factory service manual.

The bits may not be broken chain guide but old oil deposits sometimes called "coffee grounds", dino oil that was run beyond its thermal limits and breaking down or coking in the pan itself. This was common with older eastern crude conventional oils that had higher phosphorus levels, eastern oils were far higher in paraffin than southern oils (older Pennzoil for example) and different detergents that would precipitate the coked deposits out and settle at the cooler areas. I don't recall the exact name for this but I covered it at the Onan tech school during the late 80's, automakers also had numerous issues with plugged oil pickups during the 80's and into the 90's before reformulated oils and synthetic blends became the norm, we also "ran out" of eastern Pennsylvania crude and Pennzoil became part of Ashland oil.

 

Thanks for your help, everyone. Thanks for letting me vent and process here, too. After reassembly, the test drive showed no issues. Hopefully the holiday today allows for a longer run.

 

After getting good and warm (around 30 minutes), the light starts going on and off again. I did a compression check and everything is showing 95-100psi (cold). I have oil along the cylinder head gasket. I'm thinking that the cylinder head gasket is bad and is pushing air into the oil system, creating bubbles in the sump which cause the light. My thought is to run it until it's hot and recheck the compression to see if the metal is moving just enough to make the gasket leak more.

 

Hot compression check is 75-80psi. Is it normal to lose compression when the engine is hot?

 

No.

 

Not that much anyway, 20-25 PSI is a lot considering the overall displacement of each cylinder. The factory manual states a cranking compression of 156 PSI +/-14 PSI and this should be done at room temperature. Do another compression check only this time pump two or three ML of oil into the cylinders and check again, higher numbers will indicate worn rings/walls.
If the head gasket was blown that cylinder would show a significant drop in compression compared to the others and the oil would smell like combustion/exhaust if it was on the feeder, that cylinder would also burn oil as it would seep in at idle & light loading.

 

20 psi gained with a couple mL of oil... looks like it's time for a top-end rebuild kit. :-(

 

Bummer. I guess the good news is that if you pull the engine from the bike, you will be able to fully clean and inspect the oiling system.