Low RPM, Low Oil pressure then stalling.

[RRRUFF]

Need some help.  Yesterday Tucson was about 108 in the shade.  After driving around and engine temp high but within operating range,  the engine started to hesitate.  Applying some gas, brings the idle back up but if I release the gas RPM goes low and threatens to stall.  Conditions:  A/C on (did I say it was 108 deg in the shade?), at 3000RPMs oil pressure is at about 2 bars,  at idle 750RPM oil pressure goes about .6 bar.  Going to work that morning (88 deg outside) all was well.  Last year in August, same thing happened, I had attributed it to having just replaced the oil with Mobil 15W50 that morning and the incident happened that afternoon.  I immediately replaced the oil back to Mobil 1 0W40 the next day and no incident since.  This April, I replaced the oil with 5W40 Liqui Moly and have not had any problems until yesterday.  No other things have been done to the car that stands out being unique from the time this happened last summer.  I am getting ready to go back to Mobil 1 0W40 but I am at a loss as to why the oil viscosity might be causing this....or maybe it is something else like the MAF.  Any thoughts out there?

[Loren]

Exact model and year of your car please?

[BufordTJustice]

EDIT: I just read that you've got 5w-40 in the car now. Is the LM oil you're using A40 rated?

 

Mobil revised their 0w-40 formulation to make it even thinner than before (it starts at BARELY a 40-weight oil) and, if your temps are in the elevated range, this means you're essentially running a Xw-30 oil. The Mobil has also shown to sheer (lose viscosity) quickly. Add in some fuel dilution, and you could be rocking a 30-weight oil in terms of viscosity and not even know it.

 

How many miles on the oil in the crankcase? Lots of short trips?

 

Also, you may want to look at the updated (and backspec'd) oil pressure regulating spring and valve.

 

http://www.pelicanparts.com/catalog/SuperCat/0896/POR_0896_ENGOIL_pg5.htm#item14

 

Valve: 997-107-125-01-M100

 

Spring: 996-107-127-53-M100

 

If you haven't done this already, I recommend it. I gained about 1/4 BAR of oil pressure simply from doing the upgrade...and the parts are CHEAP. Easy to do while changing your oil, too.

 

Edited June 27, 2017 by BufordTJustice
Spelling

[RRRUFF]

On ‎6‎/‎27‎/‎2017 at 0:44 PM, Loren said:

Exact model and year of your car please?

Loren - the car is 2000, 996, convertible, with ~197K miles, underwent a DIY top-end rebuild 20K miles ago.

[RRRUFF]

On ‎6‎/‎27‎/‎2017 at 2:36 PM, BufordTJustice said:

EDIT: I just read that you've got 5w-40 in the car now. Is the LM oil you're using A40 rated?

 

Mobil revised their 0w-40 formulation to make it even thinner than before (it starts at BARELY a 40-weight oil) and, if your temps are in the elevated range, this means you're essentially running a Xw-30 oil. The Mobil has also shown to sheer (lose viscosity) quickly. Add in some fuel dilution, and you could be rocking a 30-weight oil in terms of viscosity and not even know it.

 

How many miles on the oil in the crankcase? Lots of short trips?

 

Also, you may want to look at the updated (and backspec'd) oil pressure regulating spring and valve.

 

http://www.pelicanparts.com/catalog/SuperCat/0896/POR_0896_ENGOIL_pg5.htm#item14

 

Valve: 997-107-125-01-M100

 

Spring: 996-107-127-53-M100

 

If you haven't done this already, I recommend it. I gained about 1/4 BAR of oil pressure simply from doing the upgrade...and the parts are CHEAP. Easy to do while changing your oil, too.

 

BufordTJustice - Liqui Moly 5W40 is A40 approved oil,  about 2K miles on the oil in the crankcase.  I did replace the spring and valve 20K miles ago during my DIY top-end rebuild.

Edited June 30, 2017 by RRRUFF

[BufordTJustice]

It's still possible that you may need more viscosity. Might want to look at Mobil-1 5w-50. It got up to 98 in the shade here in Orlando today and I can only imagine what another 10 degrees F would do to oil temps and film thickness. The fact that the issue disappears at anything but those high temps is a clue.

 

In fact, at 108 degrees, you could likely use Mobil-1 15w-50 and not get variocam errors! Yikes!

[RRRUFF]

10 minutes ago, BufordTJustice said:

It's still possible that you may need more viscosity. Might want to look at Mobil-1 5w-50. It got up to 98 in the shade here in Orlando today and I can only imagine what another 10 degrees F would do to oil temps and film thickness. The fact that the issue disappears at anything but those high temps is a clue.

 

In fact, at 108 degrees, you could likely use Mobil-1 15w-50 and not get variocam errors! Yikes!

Last year, when this happened the first time,  the oil was in fact Mobil 1 15W50.

[BufordTJustice]

Then you're going to want to have a look at the OP sensor, and then the oil pump mechanism itself.