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Discussion Starter · #1 ·
I bought a used Yanmar 3TNV70 engine for my gator, as I elaborated on in a prior post.

I have the engine installed and I have things hooked up to the stage where I can start the engine. The engine fired right up and runs good! I only ran it for about 5 seconds before I realized that the manual oil pressure gauge was reading zero! I removed that gauge and installed another one (both gauges are new) and same thing - no measureable oil pressure! I disconnected the microtubing for the gauge and left the free end open while I started the engine again - oil comes out of the tubing, but it is certainly not shooting out like it should. I believe oil pressure should be around 42psi minimum in these motors.

What is confusing me is that the "idiot light" for oil pressure does not illuminate (it SHOULD illuminate if there was no oil pressure, right?).

The oil level is correct and this is new oil. The seller had drained the oil for shipment, and so this engine has been "dry" for the last few months. Is it possible that there is an air bubble that needs to be burped out?

The only thing I did is put on a non-stock oil filter (it was an aftermarket filter that I had for my JD455. which has a similar Yanmar diesel).

Could the "wrong" oil filter be causing this? I do have an OEM filter on order.

I will not re-start the engine until I get that OEM filter on. In the meantime, any input regarding this perplexing situation would be greatly appreciated.

Main questions:

1. I should be able to measure about 40psi at idle in a gauge hooked up to a brass "tee" at the port for the oil pressure sender, right?
2. The idiot light should illuminate at what minimum psi?
3. Can a "wrong" oil filter be causing this lack of measureable oil pressure?
4. Would there ever be a need to "prime" the oil pump in these motors if one has sat "dry" for a few months?

Thanks!
 

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I believe the low oil switch specification is to open between 6-9 psi or 3-4 kPA. Anything less and the light should be on..

1. 40 psi might be a bit high if the engine is worn, but yes you should be able to measure pressure at this port.
2. Less than 6-9 psi. see above
3. Unlikely the oil filter.
4. Prime. Generally no, but if the pump is worn and it sat longer than you think all bets are off.
 

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I bought a used Yanmar 3TNV70 engine for my gator, as I elaborated on in a prior post.

I have the engine installed and I have things hooked up to the stage where I can start the engine. The engine fired right up and runs good! I only ran it for about 5 seconds before I realized that the manual oil pressure gauge was reading zero! I removed that gauge and installed another one (both gauges are new) and same thing - no measureable oil pressure! I disconnected the microtubing for the gauge and left the free end open while I started the engine again - oil comes out of the tubing, but it is certainly not shooting out like it should. I believe oil pressure should be around 42psi minimum in these motors.

What is confusing me is that the "idiot light" for oil pressure does not illuminate (it SHOULD illuminate if there was no oil pressure, right?).

The oil level is correct and this is new oil. The seller had drained the oil for shipment, and so this engine has been "dry" for the last few months. Is it possible that there is an air bubble that needs to be burped out?

The only thing I did is put on a non-stock oil filter (it was an aftermarket filter that I had for my JD455. which has a similar Yanmar diesel).

Could the "wrong" oil filter be causing this? I do have an OEM filter on order.

I will not re-start the engine until I get that OEM filter on. In the meantime, any input regarding this perplexing situation would be greatly appreciated.

Main questions:

1. I should be able to measure about 40psi at idle in a gauge hooked up to a brass "tee" at the port for the oil pressure sender, right?
2. The idiot light should illuminate at what minimum psi?
3. Can a "wrong" oil filter be causing this lack of measureable oil pressure?
4. Would there ever be a need to "prime" the oil pump in these motors if one has sat "dry" for a few months?

Thanks!
I'd try the oem filter first because it's cheap and known to be for that engine. I know its totally different but I had a Grasshopper zero turn that got an aftermarket Chinese one size fits all fuel filter on its last service. It started and ran fine but would pop and run rough while cutting. All I did was put the oem fuel filter on it and it was good as new. Not saying oem is always better, just saying at least it's right.
 

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Discussion Starter · #4 ·
Well, here is the follow up, and I am embarrassed to tell you that my BRAND NEW mechanical oil pressure gauges were faulty. How did I find this out? I borrowed a used mechanical gauge off of one of my farm tractors and hooked it up to the 3TNV70 oil pressure port and this gauge tells me that I'm actually getting 40psi at idle! Sorry to waste everyone's time with this worthless thread. I bought those gauges for cheap off of ebay. Lesson learned and onward with this project.
 

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Thanks for posting the outcome.
 
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