What does "oil - low pressure" light mean when it just barely starts coming on?

   / What does "oil - low pressure" light mean when it just barely starts coming on?
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#51  
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J

jpilk99

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several things could cause it.
1- Your oil sender unit is defective or close being defective. Sender is a normally closed switch by action of an internal spring. Upon start up, it maintains a closed circuit hence oil light pressure illuminating. As soon as pump start pumping oil, then the oil pressure will opens the switch and then oil pressure light will go out indicating pressure. Now this is for only "idiot light". The sender could also have a variable resistor, calibrated to digital or analog(needle) that actually shows pressure. This one is more preferable but mainly used on some automobiles more so than tractors.

2- If your oil level is low and you are in an incline (up or down) then you oil pick up tube and screen might suck some air while pumping, causing the pump to cavitate a bit, not making pressure and illuminating the low pressure light. A partially clogged screen can cause that and to clean that engine pan needs to be removed.

3- There is a very low possibility that your gear driven oil pump is damaged or has some restriction. This is very seldom a root cause but there is a possibility.

4- Check for loose wiring at the sending unit and also check all the fuses. Also check the connection at the back of tachometer.


By the way, I had to change my oil sending unit once 15 years ago. It was stuck closed.
Hi JC.

Coming back to this original post topic of the "oil pressure" light flickering under load. Just to confirm, (I'm 99% sure but need to confirm), the idiot light in my tach/mph is for when the oil pressure is too low, correct? I just changed my oil with Rotella & new filter and made sure the dipstick confirms proper fill level, which it does. Almost immediately, the oil pressure light is beginning to flicker when it takes on even a moderate load. I drove sideways across a gentle slope, so the machine was tipped mayyyyyyybe 10-15 degrees. It is hot as you know what out... Just weird that having owned this machine for about 10 years, I've never seen this issue.

I would have thought if the wiring or sending unit or any part of the overall apparatus was bad, it would either work or not work - not gently in between. Any thoughts/ideas?
 
   / What does "oil - low pressure" light mean when it just barely starts coming on? #52  

dieselscout80

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Have you tried putting a known good manual gauge on it to see what psi you are really getting?
 
   / What does "oil - low pressure" light mean when it just barely starts coming on?
  • Thread Starter
#53  
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jpilk99

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Have you tried putting a known good manual gauge on it to see what psi you are really getting?
I hadn't thought of that. Stupid me: Do a good search for "oil pressure gauge" that has an actual "read out", analog or digital, and wire it in place instead of the idiot light?
 
   / What does "oil - low pressure" light mean when it just barely starts coming on? #54  

JC-jetro

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Hi JC.

Coming back to this original post topic of the "oil pressure" light flickering under load. Just to confirm, (I'm 99% sure but need to confirm), the idiot light in my tach/mph is for when the oil pressure is too low, correct? I just changed my oil with Rotella & new filter and made sure the dipstick confirms proper fill level, which it does. Almost immediately, the oil pressure light is beginning to flicker when it takes on even a moderate load. I drove sideways across a gentle slope, so the machine was tipped mayyyyyyybe 10-15 degrees. It is hot as you know what out... Just weird that having owned this machine for about 10 years, I've never seen this issue.

I would have thought if the wiring or sending unit or any part of the overall apparatus was bad, it would either work or not work - not gently in between. Any thoughts/ideas?
Howdy JP,

The answer is yes but the light serves two distinct purposes.
1- it is a switch that is always on (making contacts against an internal spring) so when you put the key and turn on the ignition (not start position) then it verifies the electrical circuit is intact. That is a very important visual clue that at least the circuit all the way from ignition switch, idiot light the way to sender is not broken.
2- The spring has as certain amount of tension (stiffness) to match required operating pressure of your engine, so when the engine is running the oil pump pressure developed is greater than spring and the normally closed switch opens up and the oil pressure light turns off letting you know that oil is being pumped normally in the engine.
3- based on 1 and 2 then you first verify electrical is good by "light on" and then pressure is good by "light off"

In my case the innards of the sending unit was sticking and would work intermittently and replacement was my only choice as the sender is not repairerable. it had a ceramic body and I had to bust to take a look inside. If you have some electrical wire plugs in the circuit that is rusted or lose then it can work intermittently. Follow the wire from the sender as far as you can go short of opening the harness to check for lose or open. Like other gents suggested reading the pressure right the pressure gauge will eliminate engine oil pump problem. I think that is highly unlikely though. You can also bench test your sender by taking it off and put it a test light (has light and battery to check opn in a system) . Light should be on unless you manualy push back the face of the sender (opposite of the where the electrical lead is) and it should turn off then.

I ain't a betting man but bet you a buck it is the sender but do check before you buy another one. $27 from Fleabay below.
 
   / What does "oil - low pressure" light mean when it just barely starts coming on?
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jpilk99

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Howdy JP,

The answer is yes but the light serves two distinct purposes.
1- it is a switch that is always on (making contacts against an internal spring) so when you put the key and turn on the ignition (not start position) then it verifies the electrical circuit is intact. That is a very important visual clue that at least the circuit all the way from ignition switch, idiot light the way to sender is not broken.
2- The spring has as certain amount of tension (stiffness) to match required operating pressure of your engine, so when the engine is running the oil pump pressure developed is greater than spring and the normally closed switch opens up and the oil pressure light turns off letting you know that oil is being pumped normally in the engine.
3- based on 1 and 2 then you first verify electrical is good by "light on" and then pressure is good by "light off"

In my case the innards of the sending unit was sticking and would work intermittently and replacement was my only choice as the sender is not repairerable. it had a ceramic body and I had to bust to take a look inside. If you have some electrical wire plugs in the circuit that is rusted or lose then it can work intermittently. Follow the wire from the sender as far as you can go short of opening the harness to check for lose or open. Like other gents suggested reading the pressure right the pressure gauge will eliminate engine oil pump problem. I think that is highly unlikely though. You can also bench test your sender by taking it off and put it a test light (has light and battery to check opn in a system) . Light should be on unless you manualy push back the face of the sender (opposite of the where the electrical lead is) and it should turn off then.

I ain't a betting man but bet you a buck it is the sender but do check before you buy another one. $27 from Fleabay below.
I understood pretty much everything you said, JC, especially at the end where you said it's likely the sender. If that's the case, then the sender is just failing (if I understand correctly):

The light comes on when I turn the key to 'ignition on'
When the machine starts up, the light goes off
So, it functions well/accurately at startup and idle. But when under decent load, the light begins to flicker. When just driving across flat surfaces, no flicker. But up a hill or dragging a wagon full of wood, it flickers. And the odd thing is, when the flickering was happening before I changed the oil today, it would take 10-15 minutes of decent use (up and down the hills around my property about 7 or 8 times, then flickering going up hill at low idle as load increased significantly). Now, with brand new oil/filter/proper level ...the light flickers within a minute or two under very little load. Could it be the Rotella, that is was "T6" SAE15W40?
 
   / What does "oil - low pressure" light mean when it just barely starts coming on? #56  

JC-jetro

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I understood pretty much everything you said, JC, especially at the end where you said it's likely the sender. If that's the case, then the sender is just failing (if I understand correctly):

The light comes on when I turn the key to 'ignition on'
When the machine starts up, the light goes off
So, it functions well/accurately at startup and idle. But when under decent load, the light begins to flicker. When just driving across flat surfaces, no flicker. But up a hill or dragging a wagon full of wood, it flickers. And the odd thing is, when the flickering was happening before I changed the oil today, it would take 10-15 minutes of decent use (up and down the hills around my property about 7 or 8 times, then flickering going up hill at low idle as load increased significantly). Now, with brand new oil/filter/proper level ...the light flickers within a minute or two under very little load. Could it be the Rotella, that is was "T6" SAE15W40?

It is pretty dang strange but there is always a reason for things. We can't always find it right away but we can eliminate possibilities one by one.

Changing the oil and full up to dip stick should have not negative effect going up / down or side ways. The oil pump is gear driven and it might be getting tired and not being able to pump @ rated flow or pressure.The only way to check it is to plumb a hose to where the sender is and check it by a gauge that could read under 50 psi. That will be the least intrusive way. Anything else is much more difficult and costly specially comparing to 10 minutes of work and gambling $27. You oil is perfectly fine and other than two oil changes with NH brand , all the other changes I have done was with Rotella and never had an issue. You can bench test like I said but can test for on and off but not for flickering. Flickering most probably is caused by lose wiring and more importantly bad sender. Keep us posted as I really like to know how you end up fixing it.

One last thing, if you have junk built up in the oil pan next to oil pick up might cause bit suction issue at the pick up screen to the oil pump. You can drop the oil pan off to check the pick up screen but still I think $27 is a cheaper gamble.
 
   / What does "oil - low pressure" light mean when it just barely starts coming on?
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jpilk99

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New Sender, here I come. Thank you!!!
 
   / What does "oil - low pressure" light mean when it just barely starts coming on? #58  

flyerdan

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This is a tough one - it's not the sender or the wiring or it would be sporadic all the time, it's not worn main bearings failing to hold pressure or it would only flicker at idle and go out with a few hundred more rpm.
A partial obstruction of the screen, or loose pickup tube allowing suction or cavitation would make sense, but it should occur at higher rpms regardless of load.
 
   / What does "oil - low pressure" light mean when it just barely starts coming on? #59  

JC-jetro

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This is a tough one - it's not the sender or the wiring or it would be sporadic all the time, it's not worn main bearings failing to hold pressure or it would only flicker at idle and go out with a few hundred more rpm.
A partial obstruction of the screen, or loose pickup tube allowing suction or cavitation would make sense, but it should occur at higher rpms regardless of load.
Yup, everything will be costly to figure out for sure. $27 might be wasted but to me that's a cheap gamble. Again, reading a pressure with external analog gauge is doable and sender can be bench tested. internal engine issue leading to low pressure requires a tear down and that is doable and will not be cheap either.
 
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   / What does "oil - low pressure" light mean when it just barely starts coming on? #60  

JC-jetro

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New Sender, here I come. Thank you!!!
I hope that's a cure. It is a very educated guess and cheapest to tackle among other possibilities.
 
 
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