Oil Viscosity Effect on Engine Operation

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I was just looking at a Chrysler 300C Hemi for a friend of mine, and ran into a P1521 code that my scanner couldn't define. Turns out, it's this:
Quote:
P1521–INCORRECT ENGINE OIL TYPE When Monitored: Engine Running. Set Condition: Using the oil pressure, oil temperature and other vital engine inputs the PCM can determine the engine oil viscosity. Incorrect viscosity will effect the operation of the MDS by delaying cylinder activation . Possible Causes INCORRECT ENGINEOIL TYPE ENGINE OIL CONTAMINATION ENGINE OIL Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Diagnostic Test 1. ACTIVE DTC NOTE: Review the customers oil change history. Ensure the customers is using the correct engine oil viscosity. If the incorrect oil is being used, change the oil, using the correct engine oil viscosity. Ignition on, engine off. With the scan tool, read DTCs. Is the DTC active at this time? Yes Go to 2 No Test Complete. 2. ENGINE OIL NOTE: If set along with P1521, repair any engine oil pressure or temperature DTCs first before continuing. The following conditions must be checked. OEM recommended oil viscosity is being used. Customer is following the oil change schedule. Check the engine oil for contamination. (i.e., fuel and/or engine coolant) Internal engine condition that may effect oil pressure. Were any of the above conditions found? Yes Repair as necessary. Perform the POWERTRAIN VERIFICATION TEST. No Change the engine oil using the correct oil viscosity. Perform the POWERTRAIN VERIFICATION TEST. If this was an early production vehicle I'd say check with a dealer on a TSB that was issued for this. But since you just had the engine rebuilt I suggest that you: 1. Verify oil viscosity used. 2. If incorrect oil was used, drain and refill with proper weight oil. 3. Insure that your oil pressure sensor has not been damaged during the repair work.
I guess this is one engine where you don't want to play around with alternative viscosities, or lose the MDS. He decided to pass on buying the car for other, more serious reasons, but this was an interesting thing I never knew about. I wonder if more engines with cylinder deactivation have the same feature.
 
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That is interesting! Thanks for posting it. Blows my mind. I saw a discussion on BITOG here once upon a time that an engine's sensors could deduce the viscosity from those pressure, temperature, etc. measurements on-board in real-time. Just googled in on the BITOG site: http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3706761/Re:_Viscosity_Measurement_by_T In that past discussion of it, I think they all missed the main way you could do this: Just measure the oil pressure drop from Point A to Point B in part of the oil circuit, and, knowing the temperature, higher pressure drop corresponds to more viscosity. (Analagous to electric resistance in a circuit.)
 
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I'm guessing the sensor reports something odd and that confuses the computer. It could be a bad sensor (but you make a lot more money chargin teh customer for an oil change) or something crazy like gear oil or kerosene causing the sensor to not be defective but still report odd data.
 

OVERKILL

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Originally Posted By: DoubleWasp
I guess this is one engine where you don't want to play around with alternative viscosities, or lose the MDS. He decided to pass on buying the car for other, more serious reasons, but this was an interesting thing I never knew about. I wonder if more engines with cylinder deactivation have the same feature.
Basically. You can get away with a slightly heavier oil (0w-30 or 5w-30, even 0w-40, which the SRT's and other 6.4L vehicles spec) but I'm sure it probably poops its pants if somebody puts 15w-40 or 20w-50 in it. The system expects a change in pressure (a range) as the oil temperature changes. An oil with poorer cold temperature characteristics and/or much higher than spec'd viscosity will subsequently trigger this code. It would be interesting to have more intimate knowledge of this PCM and see what the parameters are specifically in terms of ranges, as it would be a table just like the load/fuel table. Obviously wear and manufacturing variances must be accounted for so I'm sure the pressure/temp table is relatively generous.
 
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Originally Posted By: OVERKILL
Basically. You can get away with a slightly heavier oil (0w-30 or 5w-30, even 0w-40, which the SRT's and other 6.4L vehicles spec) but I'm sure it probably poops its pants if somebody puts 15w-40 or 20w-50 in it.
Wondered about that too. As on oil warms up, it naturally is thick for a while, and the hydraulic circuits in the MDS must handle it.
Originally Posted By: OVERKILL
The system expects a change in pressure (a range) as the oil temperature changes. .....
I can see that. At a given RPM and temperature, there should be an acceptable range of oil pressure. Higher visc oils will have higher pressure. Now what would be nice if the Chrysler Hemi system could tell us if fuel dilution or shearing has reduced our oil to water visc (and hence time to change because Mr. Stribeck would not be happy.)
 
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My question is: Is this P1521 Code being triggered only if the oil is too thin then? As OVERKILL said, higher visc oils than 5w-20 don't usually trip it. The OP's copied notes do mention possible cause of "oil contamination". Edit: Garak and used_oil's responses typed in same time as my question here.
 
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In another thread years I posted the effects on oil pressure at a given engine rpm and oil temp' with various oil grades ranging from 0W-20 to 5W-50. Not surprisingly there is quite a range. Once one becomes familiar with the combined OP and OT characteristics of an engine you should be able to predict pretty accurately the viscosity of any oil is using without knowing in advance. More importantly, when running the specified oil, you'll know first hand if something is affecting the oils viscosity such as oil shear, fuel dilution or defective oil itself (rare with premium brands but does happen).
 
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No news here, this has been discussed on the Mopar forums ad-nauseum. Its just about as much a religious war as M1 vs Pennzoil vs. Royal Purple vs Amsoil is here. :-p The hardware is the same in the 6.4 that uses 0w40, but the PCM tolerances can be programmed differently. Also, it has to be pretty wildly out of spec to trip an error, as there is a lot of variation in oils when they're new, and more as they age. PLENTY of people get away with running things up to 0w40 in 5.7 Hemis that spec 5w20, because just a whole lot of people still think its always better to run 5w30. But I'm sure there's the odd car out there that will spit an error with a 5w30. I would actually tend to avoid a used car that spit that error, because I would be suspicious that an unrelated problem (worn bearings, worn oil pump, or heaven forbid rotated bearing partially blocking a passage) might be putting the pressure out of range. I'd certainly consider it a warning flag if my own car did it and I hadn't changed grades.
 

DoubleWasp

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The fuel dilution being mentioned as a possible culprit would seem to indicate that it's looking for oil insufficient to create appropriate pressure, as opposed to too thick. I would assume that the relief valve, and possibly the pump could deal with oil pressure being too high. These are all just theories, though.
 

DoubleWasp

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Originally Posted By: 440Magnum
No news here, this has been discussed on the Mopar forums ad-nauseum. Its just about as much a religious war as M1 vs Pennzoil vs. Royal Purple vs Amsoil is here. :-p The hardware is the same in the 6.4 that uses 0w40, but the PCM tolerances can be programmed differently. Also, it has to be pretty wildly out of spec to trip an error, as there is a lot of variation in oils when they're new, and more as they age. PLENTY of people get away with running things up to 0w40 in 5.7 Hemis that spec 5w20, because just a whole lot of people still think its always better to run 5w30. But I'm sure there's the odd car out there that will spit an error with a 5w30. I would actually tend to avoid a used car that spit that error, because I would be suspicious that an unrelated problem (worn bearings, worn oil pump, or heaven forbid rotated bearing partially blocking a passage) might be putting the pressure out of range. I'd certainly consider it a warning flag if my own car did it and I hadn't changed grades.
My major concern as well. Not like I can change the oil and see what happens. Better to walk away. Greater concern were the 4 roached undersized tires. Those are the act of of an owner who no longer cares about their car. I can only assume the rest of the maintenanceon the car suffered as badly. He was asking premium money for it to top it off.
 
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Originally Posted By: CATERHAM
In another thread years I posted the effects on oil pressure at a given engine rpm and oil temp' with various oil grades ranging from 0W-20 to 5W-50.
That brings up another important question. One would think the code would be set off by something being amiss with respect to operational viscosity, which may not correlate all that well with SAE grade. In any case, 440Magnum's and DoubleWasp's points do make a lot of sense.
 
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