Oil alarm comes on...now what?

[weinie]

Just when I think everything is just fine....

Oil alarm comes on today after about a half hour of motoring.

Engine is universal m18.
Oil level is fine. Oil and filter changed at the end of last season. Oil looks clean as it should. Engine seems fine otherwise.

Whats the procedure to diagnose and repair?
Do I replace the sender first?

 

[Donnybrook]

Take the wire off of the sender and see if alarm still goes off. If it does, then you have a short somewhere. Do you still have the original 8-pin connectors on the wiring harness? One by the engine and one by the control panel. Famous for electrical gremlins.

 

[weinie]

I doubt the issue is the wire. The alarm went quiet as i throttled up but returned as i let off the throttle.

I just started up the engine again, let it get to operating temp.....but now the alarm is silent... even at idle!!!

Whiskey Tango Foxtrot!!!!

 

[Charles Erwin]

Frank oil pressure sender (switch) failures are pretty rare. But -- a ground contact anyplace in the sender-to-alarm wire will trip the alarm and these faults are far more common.

So make sure the sender wire - the wire from sender to the alarm element - is completely intact. There can be no chafe to the motor block nor anyplace else either. Also, make sure that wire is well, cleanly, and firmly attached to the sender element itself.

Once you are dead certain there is no possibility the wire is exposed to ground via chafe or otherwise, only then you can imply a sender has failed.

If the wiring is spiffy, remove the sender, check for debris/trash at the oriface. Clean, reinstall, test before you go trekking off to the auto-parts retailer.

By the way -- do tell us what happens.

Charles

 

[finding41]

Last week the oil pressure gauge dropped on my Dakota truck while at idol on a scale. I shut it off right away and checked the oil.... Fine. I had to get off the scale so I started it up and the pressure went back to normal.... It stayed normal until I got to the next stop light and dropped.... I revved it up to about 3 grand and the needle climbed back up...
Hmm. I had just had the oil changed 4 days before (Jiffy Lube) and thought my be the cheap filter is plugged. So I went got a filter and spun it on and topped the oil back up.
Still the gauge would drop at idol...
So I called my mechanic.
He said check the wire and connection. (Fine) If that isn't it he said the sending unit has a small leak inside it. The loss in pressure is caused by lower oil pressure disengaging the gauge. When it is revved up it applies more pressure (not a lot more but enough to over come the internal gauge leak) and the gauge works.
Solution for me was a $12 gauge.

 

[centerline]

my vote goes to a failed oil pressure sender... i see a lot of them fail that very same way on equipment...
im not sure if that system uses a one wire sender or a two wire, but the one wire system is simple to test by removing the wire from the sender and grounding it to the block to see if it activates the light/buzzer. if it does then the wiring is good and the sender is junk... if it does not, the wiring is faulty.

 

[weinie]

my vote goes to a failed oil pressure sender... i see a lot of them fail that very same way on equipment...
im not sure if that system uses a one wire sender or a two wire, but the one wire system is simple to test by removing the wire from the sender and grounding it to the block to see if it activates the light/buzzer. if it does then the wiring is good and the sender is junk... if it does not, the wiring is faulty.

or are my bearing or pump shot?

As per my other engine thread, I am running about 1/4 of Marvel Mystery Oil. From some googleing, I've learned this may lower oil viscosity so that I'm running the equivalent of 10 weight oil rather than 15.

 

[Rob19574]

It sounds like its an oil viscosity issue here. I would change the oil again w/o the Marvel and see what happens. The alarm went on at low-RPM after 1/2 of run-time; it appears the heat lowered the viscosity enough to trigger the alarm at low RPM. And perhaps too your bearings are beyond their best-years but still hold enough pressure but under the above conditions, loose just enough to trigger the alarm.

I would check the sender and change the oil. 2 simple tasks to start with before you bring in a professional.

- Rob

 

[Stu Jackson]

weinie, good advice, but: don't ever do two things at one time, 'cuz you'll never know which one was the solution. Try one at a time and run the engine.

 

[Squidd]

You can get a cheap mechanical oil pressure "gauge" with the 1/8 plastic line and block adaptor ...(the kind the hot rodders use on cars) and check and see just what your oil pressure is doing...for about $20 at the auto parts store...

Hook it up where the sending unit is ...

Then you can decide if it's a bad sending unit, wire problem or you have something "deeper" to look into...

 

[weinie]

Changed oil and filter today using rotella 15w40 straight up.

Motored out for about 15 mins till the engine was nice and hot

Dropped down to idle speed and alarm goes off. Throttle back up to 1500 rpms and it goes off. Go back to idle and ...alarm.

Sitting here at the dock watching the boats go by in 10 knots of wind.

 

[Squidd]

Again, a mechanical gauge will tell you what the OP actually is, if there is a mechanical problem ...or the sending unit is just popping off early...

Although it does look more like worn bearings at this point, it's still cheaper to test that a motor tear down...

 

[weinie]

Access to the sender is virtually impossible. The alternator and the starter will need to be removed to get to it.

Ive already ordered a sender online but I might just go to harbor freight to pick up an oil pressure gauge. Its just that in order to test, im going to have to take off the alt and starter, attach the gauge hose, then put back the alt and starter and then start the engine.

It might, however, tell me what actually is going on with the pressure.

 

[Benny17441]

Sunds to me like a faulty sender. Testing the sender can be difficult for the DIY so I would just replace it and see what happens.

 

[weinie]

I agree. Im think im just going to replace the sender and see what happens.

If it the new sensor is still triggering the alarm, i will know my summer is done.

 

[weinie]

So i just replaced the sender today. It was a real pain removing and reinstalling the alternator and starter plus I had to borrow large diameter sockets that would fit the senders.

I got the engine nice and hot by running it in gear at the dock and when i dropped down to idle speed, there was no alarm!

(Of course the alarm went off when I shut the engine).

Hopefully, another problem solved!

Thanks all for the tips.

 

[Rich Stidger]

Congratulations!

 

[Jim 5757]

Sorry fellas, but Squidd is correct. Real nice that your alarm dosen't go off now, but what is the oil pressure???? You do not - cannot know unless you put a gauge on it! I'm sure it's a PITA, but is it worth trashing your engine?

Just sayin...

 

[Steve Dion]

What good does that gauge do for you when you are watching the wind, traffic and other happenings. It is not xlike an automobile where this stuff is right in front of your face. While I like the analog/digital reference there is no guarantee that they are accurate either. Having an alarm with a mechanical reference is the best of both worlds. As far as I am concerned, the audible alarm is your primary defence against a fried engine.

 

[weinie]

Sorry fellas, but Squidd is correct. Real nice that your alarm dosen't go off now, but what is the oil pressure???? You do not - cannot know unless you put a gauge on it! I'm sure it's a PITA, but is it worth trashing your engine?

Just sayin...

Every hose type oil gauge I have seen are scaled from about 0 to 100psi. The service manual for my engine specifies the pressure at idle speed to be just 10 psi with the sender to trigger at just 6-8 psi!
Therefore, any gauge I use will have that has a error factor of just 2 or 3 percent (of the whole 0 to 100 psi scale) will give me information that is misleading. I would expect this error to be much more magnified at the very low end of the gauge's scale... i.e. less than 10 psi; right were I need to be the most concerned! In other words, if I measure 10 psi on the gauge, the pressure might actually be just 7 psi, if there is a 3% error factor. (Once again, by percent error, I am referring to a percent of the total range of the scale, not 3 percent of the measured value, which I don't think is far flung assumption).

On the other hand, the sender which I bought to replace the broken one, is designed to trigger at 7-8 psi. If I assume the sender is functioning correctly, I know it should trigger if my engine's oil pressure drops below this number. If it doesn't trigger, I know I have at least 7 psi. This is the same number I could expect to see if I hooked up the gauge above and it was off by just 3 percent!

Now, I know the new sender triggers at 0 psi (engine off) and doesn't at idle speed. If it was off by say, a much larger 40% error, it would "measure" about a 3 psi difference, the same as a 0 to 100 psi hose gauge with a just a 3% error!

And, the new sender came from Kubota, the original builder of the universal engine, so I am putting my trust in it.

Also, the original sender, when I removed it, showed obvious signs of corrosion at the wire connection. The ring terminal was connected by a phillips screw which rusted to the point that I destroyed the screw head trying to remove the wire. So I ended up just cutting the wire instead and putting on a new connector. Just one more reason to suspect a bad sender.

ETA: for the TL;DR set:

Without a precision hose gauge designed to measure at psi ranges at about 10psi, a new sender is a more precise measuring tool than an off the shelf gauge.