Oil pressure problems

[as400jockey]

I have a 98 S70 GLT with 301k. Bought in 2015 with 265k. Runs and looks great, despite living in New England.

Oil light was coming on at idle. Intermittent. I drove around all day last week without an issue, and then the next day it started again. If I leave the car idling for 25 min or so it'll start blinking again. Goes out with a small increase in rpm.

I replaced the pressure switch.

No joy.

I pulled the pan and did the seals in there. Thought maybe the pickup tube seal was letting air in.

No joy.

I pulled the oil pump. Cleaned it. Did not open up the pump. Relief valve seems to work, cleaned it. New gasket, o-ring and front crank seal.

No joy.

I attached a mechanical pressure gauge. Cold, idle is 90PSI, revving over 100. Seems high? Aftermarket oil cooler lines are weeping, will need to replace those.

Warm, idle is 20psi, revving jumps up to 50, 60...

Warm, idle at 20psi, but the needle bounces some. Gauge is connected with about 3 feet of rubber tubing, so that will attenuate the pressure changes somewhat and attenuate the needle bounce, but the needle bounces around +/- 2 psi. So I don't know what the real pressure bounce is.

Tried timing the bounces. Looks like around 200hz, so it could be synchronous with a cam (idle is ~800rpm, so cam is turning about 200rpm).

Oil pump is driven off the crank directly, so 200hz doesn't make sense for it to be the cause. I'm guessing a cam?

Plenty of oil flowing in the intake head (can see it under the cap).

I am reluctant to replace the oil pump.

Theories?

[as400jockey]

Seems unlikely that a cam bearing would cause such a sharp and short-lived drop in oil pressure as it hit some 'flat spot'.

But the pump... there are 11 teeth on the inner gear and 13 teeth on the outer gear. The inner gear rotates with the crank. The outer gear rotates more slowly - 11/13th the speed of the crank. Maybe this pressure drop only happens when a particular pair or two of inner teeth vs outer teeth match up. They match up only every 2/11 rotations (maybe 2/13... gotta think on that one). But 900rpm * 2 / 11 = 164hz. So maybe this is what I'm seeing. So maybe it is the pump. Maybe this makes more sense than it being a cam.

Thoughts?

[ignatz]

If it was my car, I would have gotten an oil analysis to see if lead levels were high....before I dropped the oil pan and re-o-ringed.
You can still get an oil analysis to see if the lead levels are high. Blackstone Labs will comment if you tell them the miles on the oil in the engine. Its only around $30.00.
At 300,000 miles, I'd want to know if the bearings were calling it quits!
If the analysis comes back fine, just keep driving it.

[as400jockey]

too late... there were multiple other issues with the car and my son took it to a local indy. he has since bought a 2016 camry and I have this one back in my collection. Fixing it up to sell it. It's had two oil changes in the last 500 miles and a couple engine flushes.

If I didn't already have too many cars I'd keep it to shoot for 400k.

[abscate]

I think the manual makes a reference to the oil light flickering at idle, going out when slightly revved, as being normal or at least acceptable , operation.

he has since bought a 2016 camry

Our sympathies



On edit

Snip from owners manual...below

If the light comes on while driving, stop the car and then stop the engine immediately and check the engine oil level. See page 124. If the light stays on after restart, have the car towed to the nearest authorized Volvo retailer. After hard driving, the light may come on occasionally when the engine is idling. This is normal, provided it goes off when the engine speed is increased.

[as400jockey]

Interesting... never seen that before. I have had a long line of volvos - 144, 145, 245 x 2, 740 x 2, v70, s70 x 2, s60, xc90 x 2 and never saw this symptom before.

The interesting thing is that 20psi at idle is very good. But the fact that the needle wobbles is troubling. The pressure should be steady. Something is causing it to drop, apparently below the 6 psi or so where the switch kicks in. The exact pressure is not known because the long rubber hose between the pressure switch port and the mechanical gauge is dampening it.

The cadence of the wobble indicates that it's not synchronous with engine rpm but rather some fraction of it. If it were 1/4 the engine speed then I'd say either a cam (rotates at 1/4 rpm) or a main or rod bearing when a particular cylinder is in the vacuum stroke or more likely the power stroke. Or the oil pump.

I found an oil pump on ebay for $100, so I'll try it. If that's not it then I think it's a 'live with it till it stops'. And with an average of 20psi at idle, I think it'll live a while yet.

I think that for giggles I'll disconnect the idle air controller and let it idle at a lower speed to see how the pressure needle behaves.

[abscate]

There is no way I would do an oil pump for this, to be honest.

I hate to turn this into an oil thread, but what weight are your running?

[as400jockey]

I was thinking the same thing, which is why I haven't changed the oil pump yet. But the list is getting shorter, and the only thing on the list after this are main, rod and cam bearings.

I typically use Mobil 1. This time I think it was 0w30. I don't think I want to go thicker because of the turbo.

It's not a steady, constant drop in oil pressure... there's a cadence to it. That's what's baffling.

The only other thing that changes when the oil warms up is the oil cooler thermostat. But for it to pulse like that would seem very unlikely.

[as400jockey]

I took a video of the pulsing oil pressure. Slowed it down so I could count. 59 pulses in 13 seconds, while the engine was running at 840 or 870rpm (Autel reported ECM engine speed - usually at 840, sometimes said 870).

59/13 x 60 = 272/min .

272/840 = .33 . One third. Hmmmm.

272/870 = .312.

Let's go with 840. This is pulsing at 1/3 the rate of the engine rpm.

1/3 is not the crank (1/1)... or the cams (1/2)... or the pistons (1/1)... or an intake or power stroke (1/2).. the only moving part I can think of is the oil pump.

fyi serp is removed.

ebay oil pump is on the way. I'll report back after I install.

[volvolugnut]

I believe you are making an error with the units. Hz is cycles per second, not cycles per minute. 59 pulses in 13 seconds is 4.54 cycles per second or 4.53 Hz.
volvolugnut