No Oil Pressure when warm

Hello All,
I have a question about no/low oil pressure. Here is the Low down.

The Car: 2001 XC, 120K miles. Recently replaced turbo.

Background: The car recently began occasionally displaying the "no oil pressure safely stop.." message when the engine was warm and idling, usually as I was pulling into the garage at home. The display became more frequent, and I took it to the mechanic, where by he took off the oil pan, cleaned out the sludge, cleaned the oil pickup and we hoped for the best. About 10 miles later, the turbo blew, no warning lights at all, just heard the turbo whine a little and then a lot of smoke out the tail pipe.

Back to the mechanic, replaced the turbo, while the car was at the mechanic it was moved a few times, let idle for a time a few times, etc. no oil light. When the mechanic took the car for a test drive after installing the turbo everything was fine for about 10-15 miles, as he was pulling back in the shop, the no oil pressure warning light came on. He immediately shut down the car and has not driven it since.

I understand that when the oil gets warmer, it thins and oil pressure drops, but I am assuming that since the oil pressure is OK to begin with, mechanically oil is being pumped the way it should. I have searched the threads, and see that the O-ring in the oil pick-up could cause the drop in oil pressure.

The Question: Where else should I look for the loss in oil pressure? Could the pump not work as efficiently when warm?

Any help and advice would be greatly appreciated.

Thanks,

Sean

Oil thins when it warms - or thickens when it cools - depends where you start measuring...in a nutshell, the oil pump should pump enough oil that you develop 10 PSI per 1,000 RPM when the oil is at operating temperature (right about 100 C...). The warning on the dash comes on at 8 PSI (or close to that...way too late...). If you increase the viscosity, the pressure goes up (more resistance to flow). So, you'll have higher pressure cold than hot.

If the oil pressure is low, there are a couple of possibilities: 1. wrong viscosity, 2. failing pump, 3. blocked pick-up and 4. worn bearings.

But going over the description of your history, including frequent oil pressure warnings when hot lead me to think that worn bearings are most likely, because the pick-up was cleaned and the oil replaced. The turbo was the victim of low pressure - and the engine was operated repeatedly with low pressure.

What concerns me about your description was the "hope for the best"...he should have put a known good gauge on the engine (it's easy, pull the pressure sensor and attach there) to verify that the car had good pressure after doing the oil pan...if the o-ring was bad, then that would have shown up right then...and might have saved the turbo...

If the pump was failing, it would show up as low pressure when cold and warm...but since the car only warns you at extreme low pressure (like 8 PSI), the gauge is the only way to determine that...

Get a good oil pressure gauge on this thing and figure out what is going on before you destroy an engine too...

I believe it's your oil pump. Like Astro said, oil thins when it warms. A worn oil pump can pump a thicker, cold oil, but as the oil warms and thins, the pump has more slip and cannot pump up to the appropriate pressure.
Low pressure can be an indicator of worn bearings, but at 120K miles (while not brand new but not outrageous mileage), I would be surprised if they were that bad already. Is there any knocking or bad noises?
I'm an engineer for an oil and gas company, and we use positive displacement pumps to measure oil rates. But, if it is a light, thin oil, we will use a different device because the pd pump will have up to 5% inaccuracy (slip), and that's on a brand new pump.
If I were you, I would start on the simple items (sensor, o-ring) and then look at replacing the pump. Even better, replace all three items at once because every time you test to see if you fixed it and the warning light comes on, you are doing a bit of damage.

99% O rings - either sump to block or on the pick up pipe.
On mine @ 130K it was the pick up pipe which had a crimp on it, presumably from the factory.
I would replace them, then as said above, put a decent guage on it.

'No Oil Pressure' means No Oil Pressure! You and your mechanic cannot hope for the best.
Find another mechanic first, either an Authorized Volvo Dealer or an Independent with recommendations. Have the vehicle trailered to the new mechanic.
Have the source of the 'No Oil Pressure' found first before doing anything else.
Believe your indication until proven otherwise.-Dick

If it's a PO car, and you do not know oil change history (or type used) there is a good possibility of sludge.

The mechanic would (should) drop the pan and/or remove valve cover, and if sludge is present, replace the pickup tube/ring, clean pan & will possibly try to clean engine in other ways before proceeding to check pump, rings, etc. I'm wondering what caused your early turbo failure, which is usually caused by coking of oil (poor oil quality to begin with, coupled with too infrequent oil changes).

Couldn't hurt to AutoRx at some point, *probably past at this point.
Good luck,

Hey All,

Thanks to everyone for all the informative responses, I will be putting an oil pressure gauge on, any help on what it will indicate? What differences should we look for as far as temp and RPM variables? In essence how will the gauge indicate the cause of the low pressure?

Thanks again for all your help,

Sean

From the resources section: http://www.volvoxc.com/resources/how...e%20Sensor.pdf

you're looking for roughly 10 PSI/1000 RPM when the oil is warm. If the engine develops that, you have a bad sensor.

If you don't develop that - you have a mechanical problem as listed below. Pull the oil pan and begin the troubleshooting....You've already done the first step: cleaning the pan and pick-up of sludge. If it is still clean, then I would replace the pump and O-rings ... see where that gets you.

But with low oil pressure you will literally destroy the engine if it is driven that way...

2nd everything Astro said... Always gives excellent advice.

Hello, it is clear that low V70 oil pressure is normally caused by bad O-Rings.

My 2001 V70 turbo is causing me an awful lot of trouble.

I have just replaced all of mine, oil pickup, filter housing to cooler (both ends) and the sump to block o-rings. But it made no difference at all.

I drive two miles and the message appears telling me to stop.


Any other suggestions as to what could cause NO OIL PRESSURE?

I have had the pressure checked by the Volvo dealer and they confirmed it was low (cost £200 to confirm) they wanted about another £1000 to investigate further by removing the head !!

The O-rings were in a poor state, very brittle, and there was lots of sludge - it is now spotless and filled with fully synthetic 5W30

Any suggestions would be most welcome. I am 100% sure the new O-rings are in place.