Druck Press - 0 PSI at Idle?

[samhigh]

Hi All,

Had the chance to really push my 2.7L for the first time, and observed the following.

Druck Press showing 0 PSI at idle
When I start the car, the druck/oil pressure jumps to 100, then falls down as the car warms up. Normal driving conditions the PSI varies from 20 up to 60 during acceleration. When cruising on the freeway, it will hover around 20/30 PSI.

Today however, the gauge would drop all the way down to around 0 PSI at idle, rising to maybe 30 PSI during acceleration. It was about 90 degrees outside, and engine temp was just shy of 210.

Is this normal? Oil pressure remained high the entire time, and a dipstick check at the end of the drive showed a full reading. Would the hard driving and high ambient temps cause this behavior?

Some significant smoking
After climbing in third gear for about 4 miles, stopped the car at the top of Malibu canyon and a stream of smoke was coming out of the engine bay pretty consistently for about five minutes. I know I have some oil blow-by, as I will see some wisps of smoke when checking the dipstick. But this was a lot more volume.

Any cause for concern? No significant loss in actual oil based upon both gauge and dipstick.

Thanks in advance.

[Eagledriver]

It sounds like your oil pressure is too low. If your car is stock, it has an early oil pump that was not as high capacity as later pumps. The zero at idle when hot is not a concern. The pressure should be at least 10PSI per thousand RPM. For example it should be 30 PSI at 3000 RPM. If you are not getting that much pressure then you should try to change things to get more pressure. Make sure the guage is correct. Might need to try a new guage sender. You can try a thicker oil (20W-50). You can put in cam oil line restrictors. You can rebuild your engine with an upgraded oil pump.

-Andy

[brads911sc]

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[donagain1]

Silly question, but have you checked your oil filter? If it's worked itelf even a wee bit loose, it might account for the loss of pressure, and seepage past the seal in that area is more than able to provide the engine bay smoke you noted. Don't ask how I know this!

[tuchan]

What oil are you running?

Over here in the Australian summer I run a Penrite 25-70, in the colder months I run 20-60. Going to those oils over a 20-50 has made a lot of difference in pressures. 3K RPM warm 3.0 it is sitting at near on 100 PSI, idle 20 PSI.

[samhigh]

Originally Posted by Eagledriver

It sounds like your oil pressure is too low. If your car is stock, it has an early oil pump that was not as high capacity as later pumps. The zero at idle when hot is not a concern. The pressure should be at least 10PSI per thousand RPM. For example it should be 30 PSI at 3000 RPM. If you are not getting that much pressure then you should try to change things to get more pressure. Make sure the guage is correct. Might need to try a new guage sender. You can try a thicker oil (20W-50). You can put in cam oil line restrictors. You can rebuild your engine with an upgraded oil pump.

-Andy

Thanks Andy. Currently running 20W-50. The gauge has always read kind of jerky (if that makes sense). But generally it seems to follow the 10 PSI for each 1k RPM. Will continue to monitor and identify where to begin troubleshooting.

[samhigh]

Originally Posted by donagain1

Silly question, but have you checked your oil filter? If it's worked itelf even a wee bit loose, it might account for the loss of pressure, and seepage past the seal in that area is more than able to provide the engine bay smoke you noted. Don't ask how I know this!

Oil filter was recently replaced, will ensure all connections are solid. It typically does not smoke though, and did not smoke any more later that day.

[samhigh]

Originally Posted by tuchan

What oil are you running?

Over here in the Australian summer I run a Penrite 25-70, in the colder months I run 20-60. Going to those oils over a 20-50 has made a lot of difference in pressures. 3K RPM warm 3.0 it is sitting at near on 100 PSI, idle 20 PSI.

Thanks, will check out some alternatives to 20W-50.

[Tidybuoy]

Are you sure it's at Zero? That's what I thought was the case with my car but it turned out that the first mark on the guage is 10psi. You can tell this if you have your car at idle and when it looks like zero, shut the car off and you will see the gauge moves about 1/4 inch lower.

Just a thought.

[samhigh]

Originally Posted by Tidybuoy

Are you sure it's at Zero? That's what I thought was the case with my car but it turned out that the first mark on the guage is 10psi. You can tell this if you have your car at idle and when it looks like zero, shut the car off and you will see the gauge moves about 1/4 inch lower.

Just a thought.

Good point, it definitely drops after turning the vehicle off. Will continue to monitor but at this point no longer horribly concerned.

Thanks all for your help.

[aigel]

You have to find out what's smoking. It may be related to the oil pressure, but it is not likely IMHO.

As far as the pressure goes, it has gone down over time significantly. That is not good. Either something wrong with your oil pump, pressure regulation or the clearances in your bottom end bearings.

If it has always been low, you may install the restrictors to the cam oiling and bring up the bottom end pressure significantly. I liked this mod on my SC even though it has been debated if this may not hurt the top end.

G

[Alan Lindquist]

Here's my experience. 1980 SC. Got the car in 2004 with 121K miles on it. It's been a daily driver and now has 250K miles on it. No internal engine work that I know of. Cyl #2 is low on compression so I have blow-by.

The oil pressure running 20-50 is dependent on age and temperature. As the oil thins from heat or combustion contamination the oil pressure responds with a lower reading. When the oil is new and it's 60 degrees F outside, I get 10 points per 1,000 RPM after warming up and a bottom reading at idle. When the oil is due for a change and it's 98 degrees F outside and I'm hauling a$$ in 3rd gear up a long grade, I'm going to end up running less than 10 points per 1,000 RPM until the motor cools off. And idle is definitely showing no life on the gauge.

My point it, it's a worn motor but it's running and the pressures have been consistent for over 120K miles of wear.

These gauges are cool, but they're just indicators. You'd have to get inside the motor to really determine what is going on. That's a big chore. But if you're going to run it hard you may need to do that.

The smoke? When you run that hard and hot your'e going to have some leaks that hit the exhaust pipe. Some are solvable and some are part of the engine rebuild process. I'm living with a case leak after solving three of the traditional leaks.

[samhigh]

Originally Posted by aigel

As far as the pressure goes, it has gone down over time significantly. That is not good.

G

I will continue to monitor, but as of right now it just read low for the first time this weekend.

[samhigh]

Originally Posted by Alan Lindquist

The oil pressure running 20-50 is dependent on age and temperature. As the oil thins from heat or combustion contamination the oil pressure responds with a lower reading. When the oil is new and it's 60 degrees F outside, I get 10 points per 1,000 RPM after warming up and a bottom reading at idle. When the oil is due for a change and it's 98 degrees F outside and I'm hauling a$$ in 3rd gear up a long grade, I'm going to end up running less than 10 points per 1,000 RPM until the motor cools off. And idle is definitely showing no life on the gauge.

My point it, it's a worn motor but it's running and the pressures have been consistent for over 120K miles of wear.

These gauges are cool, but they're just indicators. You'd have to get inside the motor to really determine what is going on. That's a big chore. But if you're going to run it hard you may need to do that.

The smoke? When you run that hard and hot your'e going to have some leaks that hit the exhaust pipe. Some are solvable and some are part of the engine rebuild process. I'm living with a case leak after solving three of the traditional leaks.

Very helpful, thanks Alan. Seems logical the oil pressure would go down with higher temps and harder driving.

The car is actually running great, so I have no reason to think a critical failure is imminent. Would like to get a year out of this 2.7 before starting the project of purchasing and rebuilding a complete 3.2.

[aigel]

Originally Posted by samhigh

Seems logical the oil pressure would go down with higher temps and harder driving.

Indeed - the viscosity will be much lower and hence it can't build the same pressure as it will be slipping through the clearances before building pressure.

If you had a sudden reduction in idle pressure as you describe, you should see if your measurements are correct. Hook up a manual gauge and check. Do you know where the pressure gauge sender is? It is fairly easily accessible.

An engine would run like a champ with oil pressure issues, until it starts to seize, so don't take it running great as an indication of general oiling system health.

May not be a bad idea to invest a few hundred bucks and take it to the shop for a go-over and have them check the oil pressure.

G

[Bill Verburg]

I have no idea if there is a problem or not, but especially on the older cars from the early '70s idle oil pressure is quite low, the low pressure light is often(normally) on.

The spec is warm oil 80*C/176*F, 5k rpm, oil pressure should be above 4bar/59psi but should not exceed 77bar/103psi

another rule of thumb 10 to 14psi per 1000 rpms

[Tippy]

Sounds like either your oil pressure sender or oil pressure gauge may have died or a loose connection between them.

Can't imagine major pressure loss without knocking.

[manbridge 74]

Not trying to knock the guy with 19,000 posts, but for reference, my 74 with 89K original miles has no issues maintaining 10-15psi at 1000RPM idle at 210F.

Stick another gauge on there?

Is idle speed correct?

Any low oil pressure warning light flashes?

[efhughes3]

Originally Posted by samhigh

Is this normal? Oil pressure remained high the entire time, and a dipstick check at the end of the drive showed a full reading. Would the hard driving and high ambient temps cause this behavior?

Why are you contradicting yourself? You say you have low pressure, but then you say oil pressure remained high the entire time. What does this mean?

A- I'd stick with good 20w-50 oil.
B- I'd troubleshoot before driving it any further. If there is a problem-it will be expensive if you let it go too long. It's probably something simple, sender-gauge-wiring.