Oil light on!!

[California]

I doubt that the sender is at fault ....

This is one of the few idiosyncrasies of these elderly Yanmars. At around 40 years old the senders fail suddenly as he and I experienced, in my case right after an oil change. I've read in this Yanmar group of others too. So popping in an under $10 sender and hoping that fixes it, is a better diagnostic start compared to all the nonsense I worked through in that thread I referenced above where I started off suspecting worst-case and worked my way from complex to simple.

 

[kenmac]

If it's any help to ya. Before I sold mine, at low idle the oil light came on. I ordered a new sending unit and never had another issue

 

[clemsonfor]

I doubt that the sender is at fault; it's just a pressure switch that opens the ground circuit for the oil light, and if it fails it usually results in a light not going out condition.
Since it pulses at low rpm, it's likely that the oil pressure is getting low either through a worn pump, main bearings not holding pressure anymore, or some debris in the bypass valve that's bleeding off some pressure by not allowing it to close all the way.
Swapping out the sender is the easiest and least expensive first step in the troubleshooting process though.

After I cleaned it. It would be out below say 750rpm and out above it. Just seems strange. If things were worn it would show up as low pressure at 500 rpm just as much as 750 I would think? Anyway I'm just hoping.

Also if you read California post he had basically the same issue and had a bad sender. He verified with a huge as well. His sender was at fault.

I have one on the way. Says it will be at my farm Thursday so I will change it this weekend. Less than $8 for one with a screw terminal shipped to my house from Rock Auto. Don't even need to hack the wires.

 

[clemsonfor]

I suspect they may be getting trash in them or either just the connections breaking down or something overtime. As mentioned it's a 40 year old electrical part at this point in a very high vibration application. And if these are the same components that were originally designed for automotive applications, these have way less vibration. Smooth gas engine, suspension ride on asphalt. At least 5hats some of my thinking as well.

 

[clemsonfor]

Problem appears to have gone with a new sensor. I let it get warm at a high idle yesterday and the problem was there again at 750 rpm, not below or above. Today I swapped the new sensor in. Let it fastbidle till warm, maybe 15 mins or 20. Lowered it to 750 and lower , NO light! The old one the body of the sensor appeared to be loose in itself, the plastic part. Hopefully bit was just the old part wearing out, which it appears to be.

Here is a pic of the new sensor with application and part number listed if anyone wants to find it in the future. I looked through the various options listed for a universal one with the blade that could be removed and use the existing ring terminal with the screw on the new sensor. This brand from Rock Auto was the only one that appeared that way in the pictures of it.

 

[CoyPatton]

Thanks for the part no info.

 

[California]

Glad to hear the project turned out well!

 

[clemsonfor]

Glad to hear the project turned out well!

Thanks. Me too!

I bush hogged a few hours. Tractor was very well to operating temp it was in the 80s here today. I was in waist to chest high grass with the 5ft bush hog. Not light when I stopped and came down even to a 500rpm idle.