How to test an oil pressure sensor?

[neil1967]

The oil pressure sensor on my perkins 4108 always reads the same (about 65psi if I recall correctly), irrespective of load, hours run etc. Although the engine is running fine, I'm slightly suspicious - surely there should be some variation? Other than replacing the sender, is there anyway of checking the sender or the gauge?

Neil

 

[lw395]

Either swap it for another gauge, or somehow tee the sender into something like a tyre pump with gauge?
You can get adaptors on ebay.

I'd expect the pressure to drop a little from cold to hot, by virtue of the way it's regulated and the viscosity of the oil.

 

[Trundlebug]

Does the pressure even read the same at idle when the engine is hot?
It is unusual if that is the case, even fairly new engines display some pressure drop at idle.

Perhaps you have an engine in very fine fettle.
If you're concerned you could always buy a new sensor or gauge, fairly standard from most motor factors and only a few quid.

 

[David2452]

Generally speaking you can check them with a decent multimeter, resistances vary on gauge range but for instance a 0 psi to 80 psi sender should read 10Ω at 0 psi, 95Ω at 40 psi and 180Ω at 80 psi. Other ranges are similar, e.g. they will be 10Ω at minimum gauge and 180Ω at maximum gauge. A US gauge will be 240Ω at 0 psi, dropping to about 33Ω at maximum, so different readings and upside down.
Similarly you can test the gauge by applying current via suitable resistor, I use a variable pot that I have marked for testing gauges, rudder indicators and the like, but resistors can be had for coppers form Maplins

 

[VicS]

The oil pressure sensor on my perkins 4108 always reads the same (about 65psi if I recall correctly), irrespective of load, hours run etc. Although the engine is running fine, I'm slightly suspicious - surely there should be some variation? Other than replacing the sender, is there anyway of checking the sender or the gauge?

Neil

Presumably it reads zero when the engine is not running ??? If so and reads in the order of 65psi when it is running I would suggest all is well. Don't fix what's not broken

 

[danielefua]

Presumably it reads zero when the engine is not running ??? If so and reads in the order of 65psi when it is running I would suggest all is well. Don't fix what's not broken

I agree with Vic!
Moreover if your 4.108 is like mine, there is also an independent oil pressure switch that will turn on a buzzer and a lamp if something happens to go really wrong.

Daniel

 

[Billjratt]

My 4108 is stable at about 60 PSI once pressure is up, you can see it stepping up from zero as the engine starts.
On mine the separate switch is normally open, and closes when the pressure rises (opposite to what you would expect, or are used to in a car engine)
I believe it was originally intended to delay load on startup when the engine was driving a generator. I had to wire a flashing LED through its dropper resistor so it was shorted when the oil pressure came up in order for the warning light to make sense.

 

[neil1967]

I'll look into it a bit more - while I fully endorse the 'if it's not broke don't fix it approach', I don't know it's not broke! Yes the gauge reads zero before starting, and 60-65 PSI when running, but it doesn't seem to build up pressure - it's all or nothing. Some good pointers though, thanks

Neil