Installed oil pressure gauge; interpreting data?

[TheBrian]

I recently installed an oil pressure gauge, and now it's got me thinking maybe I should be using synthetic.

 

When I start the engine cold, the needle on the gauge snaps to the right and sits at 80psi until the oil warms up a bit. It comes down to levels which seem fine, but it can take half my commute or longer for the oil to get up to temperature. Admittedly, it's a short commute.

 

I have a '96 EJ22. The service manual says the oil pump has a pressure relief valve that's supposed to operate at 71psi. Am I correct in assuming that when this valve is in operation, lubrication is compromised?

 

I'm running SuperTech (WalMart) 10w30. I was thinking of using Mobil1 0w30 or 5w30 at my next oil change, which is coming up before winter. I'd like your opinion.

[Snowman]

I'd switch to synthetic anyway, but that oil pressure reading doesn't seem unreasonable. Seldom should you be worried about too much oil pressure. Out of curiosity, what does it go down to when the engine is warm and at idle?

[forester2002s]

I wouldn't be too concerned with the observed PSI reading. Unless you bought a precision gauge, I would guess that the accuracy of a mass-produced pressure gauge could be in the order of + or - 20%.

 

So what does 80 psi mean, as opposed to say 60 psi? I don't know.

 

What is more useful, is to watch the position of the gauge over time. As you say, watch it as the engine warms up; and watch it over many miles and over many months or years, to see if the pressure degrades. And also after oil changes. And of course, if the pressure reading goes to zero, STOP THE ENGINE right away!

[TheBrian]

No, it's a cheap, mechanical Sunpro gauge. I figure when it reads 80 PSI, it probably should read the 71psi mentioned in the manual. It may not be accurate, but it does seem to be precise. Once it's warm, when I rev the engine at a stop light, it's like I have two tachometers. <img>

 

I installed a T-fitting, so both the gauge and the idiot light work. The fitting barely clears the alternator, but barely is good enough. I wonder how long before the nylon tube melts or gets brittle from sitting next to the alternator. I guess I'll replace it with copper if it melts.

 

Under the right conditions, my engine idles very low (like 500rpm). Oil pressure at 500rpm is very low, near zero on the gauge. Maybe 5 psi? But that's what you'd expect when pressure is about 26psi at 2000rpm and 55psi at 4000rpm.

 

What bothers me is how the gauge reads zero during cold cranking. Oil pressure probably *is* zero for the first two or three seconds.

[cookie]

I have used oil pressure guages for years and that is pretty normal. I am planning to put one on my Forester but that is one of the many things I have not gotten around to yet.

Engine don't have oil pressure until they run fast enough for the pump to work so don't worry about that. This is one of the reasons for wear they say, there are devices to pre lube your engine, but residual oil lubes it too.

For years engines did not have oil pumps and engines were lubed by splash or cups. In old steam engines like those on a Liberty Ship one of the crew's jobs was to lube the connecting rods. This job was called oiler.

Fairly low oil pressure at idle with a modern engine is pretty normal too. The less oil pressure the less resistance, hence better mileage and emissions.

The engine is being lubed just fine when the perssure regulator valve opens to prevent too much oil pressure, so don't worry about that either.

[zyewdall]

What bothers me is how the gauge reads zero during cold cranking. Oil pressure probably *is* zero for the first two or three seconds.

 

That is the reason to switch to synthetic IMO. I've noticed that mine starts easier in subzero weather with synthetic 5W40, and getting the oil to the engine sooner is probably good for it.

[nipper]

I wouldn't be too concerned with the observed PSI reading. Unless you bought a precision gauge, I would guess that the accuracy of a mass-produced pressure gauge could be in the order of + or - 20%.

 

So what does 80 psi mean, as opposed to say 60 psi? I don't know.

 

What is more useful, is to watch the position of the gauge over time. As you say, watch it as the engine warms up; and watch it over many miles and over many months or years, to see if the pressure degrades. And also after oil changes. And of course, if the pressure reading goes to zero, STOP THE ENGINE right away!

 

Gauges or most innacurate at the bottom 15% and top 15% of thier posted scale. You get what you pay for in gauges ( I used to calibrate them). I have never seen any gauge that was so badly out (new out of the box) that it was junk. There is such a thing as too high an oil pressure, but that is usually due to an inferior oil filter (again dont buy cheap). Have seen oil filters burst due to pressure bypass failure in the filters, but internally inside the car, it doesnt matter. Oil is thick when cold.

Synthetic vs non is discussion that goes round and round and i see no difference, especially now with so many blends out there.

nipper

[frag]

No, it's a cheap, mechanical Sunpro gauge. I figure when it reads 80 PSI, it probably should read the 71psi mentioned in the manual. It may not be accurate, but it does seem to be precise. Once it's warm, when I rev the engine at a stop light, it's like I have two tachometers. <img>

 

I installed a T-fitting, so both the gauge and the idiot light work. The fitting barely clears the alternator, but barely is good enough. I wonder how long before the nylon tube melts or gets brittle from sitting next to the alternator. I guess I'll replace it with copper if it melts.

 

Under the right conditions, my engine idles very low (like 500rpm). Oil pressure at 500rpm is very low, near zero on the gauge. Maybe 5 psi? But that's what you'd expect when pressure is about 26psi at 2000rpm and 55psi at 4000rpm.

 

What bothers me is how the gauge reads zero during cold cranking. Oil pressure probably *is* zero for the first two or three seconds.

1) I get the same kind of readings at startup and I have the same car.

2) Made the install just as you did with a T fitting.

3) I have a copper tube but it's hard to thread around obstacles and it also gets brittle with heat and age. I've read there is a teflon with stainless mesh tube available.

4) My idle speed is around 700 rpm and the gauge reads 10 psi then.

[nipper]

You really need a guage that reads 1-15 psi to read oil pressure during cranking (and dont let the car start), this is nothing to worry about at this time. There is always a fine film of oil on the surfaces, and thats good enough for starting. as soon as the car fires off you get oil pressure, Now if you had zero sitting at a red light i would worry.

 

Sometimes we worry way to much about things.

 

 

nipper

[jib]

1) 3) I have a copper tube but it's hard to thread around obstacles and it also gets brittle with heat and age. I've read there is a teflon with stainless mesh tube available.

 

Nylon oil pressure tubing is inexpensive and is easy to install.

 

Jack

[cookie]

The only failure I have ever had was with the nylon tube. It does make a mess.

I have used copper tubeing with no problem many times, and I think the best is steel tubeing with a brake line type flexible section on the end toward the engine.

That said the last Jeep I had I just used the nylon with no problem, and I will probably do it again with the Subaru.

[nipper]

 

I have a '96 EJ22. The service manual says the oil pump has a pressure relief valve that's supposed to operate at 71psi. Am I correct in assuming that when this valve is in operation, lubrication is compromised?

 

 

If lubrication was compromised we wouldnt get over 200K out of the bottom end of the car. Lubrication is not compromised... It just doesnt dump all the pressure.. if its over 71 psi, the bypass in the oilpump cracks open to releive pressure.

 

nipper