Low oil pressure at low revvs


Active member
Hi Folks,

got a JD 455 with 23HP Yanmar 3 cyl diesel.
I bought it with 900 hours on the clock, it now has about 1100.

The low oil pressure light on the dash comes on at low revvs.
As it warms up it needs more and more revvs to get the light to go out.
I bought it with this fault and got a good deal because of it, I have been using it with the fault, just keep the revvs up!

I cant believe that the engine has adequate wear in it to lose oil pressure with only 1000 hours on the clock! It doesnt burn any oil or anything and sounds sweet!

Weak oil pressure switch maybe, or does anyone know if there is a pressure adjust valve on this engine?


Super Moderator
Staff member
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For some reason the oil pressure sensors that Yanmar used don't last forever.

You can screw in a temporary gauge if you want to verify the sender (BSP threads) but the solution is simpler: replace the sensor.

Take the old one into an auto parts house and match it by eye to one for a Nissan/Honda/Subaru of similar age. Problem solved. BTDT. Expect under $10 (7 lbs??? I don't have a key to represent that) for the sensor. Yanmar used some parts same as Nissan's for off-the-shelf stuff like this and the radiator cap, etc.

I added a temporary gauge with a T while keeping the suspect sender. It showed 18psi minimum at slowest hot idle, and 30 or better above that idle - with the bad sender still lighting the lamp. This is the 1981 Yanmar, 24 hp.


Active member
£16.79+vat. I will head down the auto factors tomorrow and see if I can fetch a generic one as you suggest Cali. Got to be a good starting point. Fingers crossed it will solve the problem when it arrives.
I had a kubota do the same thing, oil light was on all the time. Bought it cheap, replaced the switch and sold it well.

The sump has got a bit crack in it too, but it doesnt seem to leak very much. The oil level hasnt gone down since last autumn.


Active member
Fitted a new switch, still lighting up. Pretty sure it must actually have low pressure. I also noticed that no oil tickled out of the hole when I took the switch out. Usually a bit of oil runs out.

Sounds like I had better take the sump off......