Time for a new oil pressure thread

[Skunksmash]

Well I guess its time for a new oil pressure thread. Why not. I don't often get time to work on my truck, so if anyone is wondering that's why my threads are sometimes about the same thing, 3 or 4 months apart.

So to get to the point:

What is good oil pressure for a TBI 350? I put in a new gauge because the old one got kind of sloppy even after replacing the sending units. New gauge seems to work much better, but now I realized that I don't even know where the oil pressure is supposed to be. At idle, the gauge says about 25psi. When revved to 3000rpm, it goes up to about 51. At 2000rpm its halfway between 25 and 50. Does this seem about right?

[geezer#99]

Nothing wrong with that pressure. You want 10 psi per 1000 rpm.
If you want an accurate reading, install a mechanical gauge.

[donut]

I'd say your good. Rule of thumb I've been told is 10 psi per 1000 rpm.

This can vary depending on engine condition, weight of oil, and accuracy of gauge.

[kalbert]

10 psi/1000 rpm is a good rule of thumb. The factory guage isn't calibrated to anything and is more a pass/fail indicator than a guage. If the needle moves off the rest, you have oil pressure. If not, the sender is bad, the guage is bad, or the motor is bad. A factory guage that fluctuates a lot is usually caused by a bad sender. To get an accurate reading pick up a mechanical guage and screw it on. It doesn't have to be an automotive guage, the guage and assorted fittings tool set from the parts store is all you need. They might even rent it to you for the afternoon.

[Skunksmash]

Originally Posted by geezer#99

Nothing wrong with that pressure. You want 10 psi per 1000 rpm.
If you want an accurate reading, install a mechanical gauge.

Well see I've had some mechanical gauges on other stuff and they're always within 1 or two PSI of each other. I looked into it when I bought the gauge a while back. Autometer doesn't seem to think it makes much of a difference. It might actually be the other way around sometimes. For example my dad's diving gauge for air is mech and its always 200lbs give or take. The dive computer is 5lbs give or take and its of course electrical. I think the whole mech being more accurate than electric is a myth. Unless someone can offer up some proof? I'd be interested to read about it.

[bilfman]

I don't think the post responders are referring to dive gauges or auto meter gauges. They are giving you their response based on the possible inaccuracy of 30 year old gm gauges and sometimes even newer ones . Debating electric over mech is another thread altogether. Confirming accuracy of an electric gauge that is around 30 years old with a new mechanical one just makes good sense.

[Skunksmash]

So when yall say that it should make 10psi for every 1000rpm...

Does that mean that at 1000 rpm, the engine should be making about 10psi? Or is there some other number for the baseline?

For example, if I rev up the engine to 3000rpm, the new gauge says 45psi. So taking that into account, it doesn't exactly match up with 10psi for every 1000rpm. Just trying to make sure I'm doing everything right.

[donut]

Your good.
Pressure will vary, 10 psi per 1000 is a guideline.

Pressure can be vastly different on an old engine running 10w-30 versus a fresh rebuild running 20w-50.
Will also vary depending on if the oil is hot or cold.

[Skunksmash]

Thanks! That always seemed low to me, having only 10 psi at idle. But oh well.

Perhaps I should think about putting on a new oil pump? I know a lot of guys will do that just to pick up some oil pressure.

[Tx Firefighter]

Low oil pressure on an older engine is caused by worn bearings rather than worn oil pump. Oil pumps hardly wear at all. They're made out of steel and iron. Engine bearings are designed to be sacrificial. They are meant to wear, hence their construction is much softer metal than crankshafts and camshafts.

[Skunksmash]

Should my engine be idling at 25psi? I noticed tonight that its doing that. Goes up to about 53psi when you give it the gas and it gets up to about 2,000rpm. At 700rpm, the oil pressure looks to be about 12psi.

I'm mentioning this because its a little bit different from what I posted earlier. I was wrong about a couple things. This oil pressure gauge has a learning curve because it goes all the way up to 100psi, but the stock one only went to 60. So I'm still working out exactly how it should be behaving.

[donut]

It's reading oil pressure and not "pegged".
Mine will peg at 60 when it's cold. Warmed up it will drop some. Is it accurate? Obviously not, however it's not on my list of priorities as it will warn me of a failure, and the engine is not clattering at idle. In my mind, adequate oil pressure. This is a bone stock '86 with 110k miles.

Other than the gauge readings, any other oiling issues? Is the gauge somewhat correct?
If it bugs you that bad, return the gauge to where you bought it, and try with another.
Other than that, enjoy the ride.

[Skunksmash]

Yeah i see what you're saying. I just like accuracy. I had no idea it was so hard to get an accurate oil pressure gauge. Then again, maybe its perfectly accurate.

[50seven]

Oil pressure is about where it should be for a well used sbc.

Tx Firefighter explained it well oil pressure is developed from the tolerances of the crank and especially the cam bearings. The more they are worn the lower the oil pressure.

IMO 25psi is just fine at idle.

Use better high mileage oil with some wear additives and turn up the stereo.

[Skunksmash]

I have seen a guy change the old oil pump on his old ford and gain some oil pressure back. Now of course that's a ford and they're different as they maintain a constant oil pressure whereas the chevys goes up and down. I don't know if its some kind of different design, or if its just different where ford meters the pressure.

Has anybody else ever done this? Maybe you don't do it on chevys. Mine doesn't really seem to need it but oh well

[Tx Firefighter]

There's really not much to wear inside of an oil pump. It's an iron housing with two gears inside of it. There's one spring in there but that it.



A retired engineer from Buick once told me that they were the single best lubricated component inside an engine and wear was negligible over the lifespan of a vehicle. Very much unlike rod/main/cam bearings. An oil pump should last through several engine rebuilds.

[Skunksmash]

You always see people replacing them. That is what made me question.

Like on Horsepower TV and 'Trucks' and all those shows. Then they'll weld on the siphon tube. But thanks for the explanation. Explains why mine isn't dead after all these years.

Perhaps some people's pumps wear out if they didn't change the oil often enough? Maybe there is an external factor that could kill an oil pump, or reduce its efficiency

[kalbert]

A worn out oil pump is a rare thing. Like they just don't wear out. Not our iron gears in an iron body ones anyway. Low oil pressure is caused by worn out bearings. The whole oiling system is basically a controlled oil leak. The oil pump pushes oil to all the bearings, where it leaks out between the surfaces and drops back to the pan to get pumped around again. When those bearings get worn down they leak too much and the oil pressure gets low. Eventually enough oil is leaking that not enough is making it to the last parts in the pipeline, that bearing at the end of the line then goes dry and bad things happen.