Oil pressure light question

[Sonny]

My oil pressure gauge (autometer mechanical gauge) went from 60/30 (cruise/idle) normal to 20/5 psi today but my oil light never came on. It’s operational and lights up briefly at start up so I know it works. I want to verify if the autometer gauge is bad. What is the low oil pressure that would activate the stock light to come on? I have a 1978 360. It never knocked, runs fine, and the temp maintained 180. It was a quart low, but the autometer gauge still reads low even after adding a quart.

 

[khryslerkid]

What is the low oil pressure that would activate the stock light to come on?

Zero oil pressure is when they come on.

Or ten minutes after the tow truck gets there.
Go with a mechanical if you can. And you could still use a electric light for the "attention getter".

 

[Steve Garner]

Switches are calibrated somewhere between 5 and 9 psi. I think that most that I've seen in the parts catalogues are 9

 

[khryslerkid]

I re-read and see you do have a mechanical guage.
You could rent a oil pressure guage from you local parts store and compare the numbers.

Have you changed what weight oil you normally use. Defective oil filter?

Does the pressure increase when letting off the gas when going down hill?

Could be a gummy or stuck pressure valve in the oil pump. Weak or broken spring. They can be removed from the outside of the pump for cleaning and inspection while on the car.

If the valves, rockers, are quite then you know you are getting some oil pressure.

How many miles on your engine?

Just throwing some things out there.

 

[HT413]

Typically the oem sending units turn the light on below 9psi, but there are replacements available as high as 20 psi. Probably safe to assume yours is in the 9psi ballpark, which would mean that it should have lit up when your gauge read 5. But even in the unlikely event that you have a 20psi sender, it should still have turned on. So something might be wrong with the gauge (boy is that rare though).

First I’d prime the pump with a drill and record what pressure you see. Then replace the capillary tube and retest. If it’s the same, replace the gauge and retest.

If it’s still the same, then you really do have an oil pressure problem and then I’d start with the pump then perhaps look for a lifter.

 

[Sonny]

I re-read and see you do have a mechanical guage.
You could rent a oil pressure guage from you local parts store and compare the numbers.

Have you changed what weight oil you normally use. Defective oil filter?

Does the pressure increase when letting off the gas when going down hill?

Could be a gummy or stuck pressure valve in the oil pump. Weak or broken spring. They can be removed from the outside of the pump for cleaning and inspection while on the car.

If the valves, rockers, are quite then you know you are getting some oil pressure.

How many miles on your engine?

Just throwing some things out there.

I did an oil change last night an filter change too to rule out plugged filter. Will crank it up this am.

 

[Sonny]

I re-read and see you do have a mechanical guage.
You could rent a oil pressure guage from you local parts store and compare the numbers.

Have you changed what weight oil you normally use. Defective oil filter?

Does the pressure increase when letting off the gas when going down hill?

Could be a gummy or stuck pressure valve in the oil pump. Weak or broken spring. They can be removed from the outside of the pump for cleaning and inspection while on the car.

If the valves, rockers, are quite then you know you are getting some oil pressure.

How many miles on your engine?

Just throwing some things out there.

Is it possible to remove and replace the oil pan while still in the car (laying on the ground)?

 

[HT413]

I did an oil change last night an filter change too to rule out plugged filter. Will crank it up this am.

Don’t start the car. Get a priming tool and use that to trouble shoot some basic stuff first.

 

[HT413]

Is it possible to remove and replace the oil pan while still in the car (laying on the ground)?

Yeah you can pull the pan on the car.

 

[Wietse]

Your mechanical gauge will have an engine oil feed line on it right?
Maybe disconnect it and makes sure it is not blocked.

Other option is to change the gauge for another one and check again.

 

[Sonny]

Your mechanical gauge will have an engine oil feed line on it right?
Maybe disconnect it and makes sure it is not blocked.

Other option is to change the gauge for another one and check again.

Changed the gauge and tubing, oil and filter. About the same. 10 psi at idle and 40psi at about 4000 rpm. I’m hearing a knocking/rattle under distributor. 3 weeks ago I replaced the cam gear/oil pump shaft and it’s brass block bushing. Wonder if something is going on there? My oil tubing is connected to the electric sending unit block located under the coil above this area. ?

 

[Wietse]

Ok, well that was the simple thing i could think of first.
Regardless of the drive gear being good or worn, it will run the same rpm. (increase/decrease with engine speed obviously)
Next thing i could think of is a worn pump, being gears or housing causing a pressure loss.
Or as said, the pressure relief valve is passing.

Any pressure difference between cold and hot oil? (dunno what is the ambient temperature where you live?)
With hot oil you should see lower pressures.

 

[Sonny]

Ok, well that was the simple thing i could think of first.
Regardless of the drive gear being good or worn, it will run the same rpm. (increase/decrease with engine speed obviously)
Next thing i could think of is a worn pump, being gears or housing causing a pressure loss.
Or as said, the pressure relief valve is passing.

Any pressure difference between cold and hot oil? (dunno what is the ambient temperature where you live?)
With hot oil you should see lower pressures.

I’m in Florida so never under 40 degrees very often. It’s kept 30/60 psi since I installed the engine 5 months ago. I’ve driven it in 98 degree temps and no effect really to speak of with pressure. Drove it to Charlotte and back, 60psi highway all day. I’m gonna pull the pan and replace the oil pump. I’m hearing some rattling noise in that area.

 

[Fran Blacker]

Maybe your pump is loose and pissing oil.

 

[Wietse]

Does a '78 engine have an internal pump?
Well, yeah if there is noise observed from there pump could be loose indeed.

 

[Sonny]

Does a '78 engine have an internal pump?
Well, yeah if there is noise observed from there pump could be loose indeed.

That’s what I’m thinking too. I remember the gasket was hanging out and reading lots of opinion about gasket or no gasket. I took it off to add the new pickup tube. It could be loose.

 

[Fran Blacker]

That’s what I’m thinking too. I remember the gasket was hanging out and reading lots of opinion about gasket or no gasket. I took it off to add the new pickup tube. It could be loose.

If the bolts are loose I'd safety wire them.

 

[Wietse]

If the bolts are loose I'd safety wire them.

Or use Loctite!

 

[Sonny]

Or use Loctite!

Blue or red?

 

[khryslerkid]

That’s what I’m thinking too. I remember the gasket was hanging out and reading lots of opinion about gasket or no gasket. I took it off to add the new pickup tube. It could be loose.

Sounds like you're on to something. Could you pull the dizzy and do a inspection of the shaft again before pulling the pan?

Sorry about my last post, talking about a external oil pump. Re-read and see you're working with a small block. Will make an optometrist appt. Tuesday.

Good luck on your findings!