Proper oil pressure question

[Huicho417]

Does 25 oil pressure sound ok when cruising at 2800 rpm on the highway? Car ran great and maintained that oil pressure driving about 65 mph. The car is a 67 coronet with lightly modified 318 and 727 torqueflite. Rear end is 8 3/4” with 2.94 gears.

 

[ruffcut]

Rule of thumb is 10 pounds for every one thousand rpms

 

[Runcharger]

I'd prefer to see 40. Must be worn a bit, it won't kill it though. What weight oil is that with?

 

[beanhead]

IMO I wouldn't be happy with only 25 at that cruise rpm. Granted you're not loading the engine much, but still...factory pressure spec is 20 psi minimum at 500 RPM, 45-65 psi at 1000 RPM...for all stock V8s (except HEMI, which was allowed 15psi@ 500 rpm).
What's the condition/mileage of the engine, and what are the clearances? You might just need a thicker oil for the build.

 

[Huicho417]

I’m using 10W 30 oil. About a year ago I gave the engine a good refresh with all new seals, gaskets and rebuilt the heads. I constantly check the mercury inches is vacuum and it’s all good there. Should I use a different oil viscosity?

 

[beanhead]

I’m using 10W 30 oil. About a year ago I gave the engine a good refresh with all new seals, gaskets and rebuilt the heads. I constantly check the mercury inches is vacuum and it’s all good there. Should I use a different oil viscosity?

10-30 *should* be fine if the rods and mains are near stock..but if you aren't sure about the clearances it won't hurt to try a heavier oil and see if the pressure comes up.

 

[Runcharger]

Hot in Texas lately. I think I'd try 20-50 in it and see how much that brings it up.

 

[gtx6970]

If the climate can take it,
I would run a straight 30 or 40 weight and see what it nets

But 25 is a tad low for cruise speed / rpm

Whats it got at idle ?

 

[diesel_lv]

As said above, rule of thumb minimum is usually 10 psi per 1k rpm. So that is livable. Does it climb as rpm goes up proportionately? If so, n it stays "close" to 10 psi per 1k, I'd say you're ok. Does it still have a functioning oil pressure light? Apparently you have a guage, if the lights not coming on either or even flickering, I'd still say you're ok.

 

[Huicho417]

Yes light is still connected and never comes on, except before initial startup. So I know it works. Oil pressure does go up with rpm increase. When the engine is cool it does start at about 50-60 psi oil pressure. After about 30-40 minutes driving I get the psi I mentioned initially. The gauge is a aftermarket electronic Bosch, I think I need I’ll check the wiring on it as well.

 

[Huicho417]

Quick update on this. I found a mechanical gauge and installed it on the car to compare to electrical gauge. When initially started both start at about 60 to 65 psi on oil pressure. At idle the mechanical shows about 10 psi and l electronic almost at 0. Took it back on the highway and at about 60mph 2500rpm the mechanical wast at about 35 psi and electric still only at about 25 psi. The mechanical gauge was also very steady and easy to read. On the other hand the electric was still jumping around and at times even lower that 0 which was obviously not correct. I’m almost tempted to replace the interior electric with the mechanical. But don’t like the idea of running a small tube with hot oil to inside the car. Either the electronic sender is bad or I have issues with the wiring which I have already triple check the ground and power supply. Any suggestion on a goo electronic gauge the one I have is a Bosch. Thanks in advance

 

[diesel_lv]

Quick update on this. I found a mechanical gauge and installed it on the car to compare to electrical gauge. When initially started both start at about 60 to 65 psi on oil pressure. At idle the mechanical shows about 10 psi and l electronic almost at 0. Took it back on the highway and at about 60mph 2500rpm the mechanical wast at about 35 psi and electric still only at about 25 psi. The mechanical gauge was also very steady and easy to read. On the other hand the electric was still jumping around and at times even lower that 0 which was obviously not correct. I’m almost tempted to replace the interior electric with the mechanical. But don’t like the idea of running a small tube with hot oil to inside the car. Either the electronic sender is bad or I have issues with the wiring which I have already triple check the ground and power supply. Any suggestion on a goo electronic gauge the one I have is a Bosch. Thanks in advance

Don't use digital. They try to give every little nuance of a reading making them jumpy. Get an electric guage w a dial indicator that uses a stepper motor in it. It will read smooth. And of course the new sending unit that is designed w that gauge.

 

[Ranger16]

But don’t like the idea of running a small tube with hot oil to inside the car.

Use copper tubing and you should not have any problems.

 

[Bob Benson]

Hot in Texas lately. I think I'd try 20-50 in it and see how much that brings it up.

20W-50 is too high to use, even here in south Texas. Your motor s not designed to run that heavy an oil, 20W-40 is highest I would ever consider, ever.

 

[dvw]

Remember pressure is resistance to flow. Thick oil raises pressure by restricting flow. Straight weight is old school. A5wX or 10wX is your best bet. A stock pump can put out over 200 psi fully blocked. So why is your pressure low? I'd bet lifter bores, bearing clearances are worn some. Would I worry about it? Nope In hot areas of the country oil temps will run hotter. This will make the oil thinner. A 5w40 or 10W40 wouldn't be a terrible idea. But the increase in pressure won't be dramatic. Oil flow keeps bearings cool. To be honest your number looks about normal with bearing clearances on the higher side of the spec with a stock pump.
Doug

 

[padam]

Use copper tubing and you should not have any problems.

I don’t think copper tubing should be used on a car. It is too susceptible to cracking.

 

[RGAZ]

I don’t think copper tubing should be used on a car. It is too susceptible to cracking.

I think he meant nickel-copper like used in custom brake lines.

RGAZ

 

[diesel_lv]

I think he meant nickel-copper like used in custom brake lines.

RGAZ

This stuff, which is meant to be run inside cars for oil pressure. Been using it on cars/trucks/boats for more than 40 yrs without a problem.

 

[padam]

This stuff, which is meant to be run inside cars for oil pressure. Been using it on cars/trucks/boats for more than 40 yrs without a problem. View attachment 1350554

That looks good to me.
The reason I said that is that I used to use copper lines for coolant on cnc machines.
If the machine had a lot of chatter and vibration it would cause the copper line to crack.
I don’t think you will see it on high end race cars.

 

[moes]

I've been using copper oil lines for years on my motors. Never seen a problem with lines breaking or leaking on my cars or friends, plastic lines, yes. Just make sure you leave a little coil of line at the motor and at the gauge.