2005 Buick LaCrosse, 3800 Series III, STP Full Synthetic 5w-30, 3204 miles,

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Here is the UOA for my 2005 Buick LaCrosse CXL with the 3800 Series III engine.

Oil: STP Full Synthetic, 5w30
OCI: 3204 miles
Engine miles: 153,260

I acquired this car in July to replace my previous '05 LaCrosse which had been totaled in an accident. This is my first UOA to check the health of the engine and establish a baseline. My goal is to get another 100,000 miles out of this vehicle.

Known History of the car: This car was built in January of 2005. According to Carfax, In March of 2005 it was sold to a person in a small town in Texas. This person owned the car from March 2005 through January 2020. and put about 122,000 miles on the car, averaging just under 9,000 miles a year. According to Carfax, the oil was changed every 4,000 miles at the local small town GM dealer, with other services performed according to manufacturer specifications at 50,000 and 100,000 miles.

According to maintenance records in the glovebox, the car suffered an overheating incident in August 2010, requiring a new water pump, coolant elbows, and intake manifold gasket replacement/upgrade performed at the dealer. Otherwise this appears to be the only significant repair other than normal wear/tear items like brakes.

The first owner traded the car back to the original dealer in January 2020. The car was then sold to a used car dealer in Independence, Missouri in February 2020, who then sold it to the second owner in June 2020.

The second owner kept the car from June 2020 through December 2021 and somehow put about 30,000 miles on the car in 18 months. There is no record on Carfax or in the glovebox of any maintenance being performed by the second owner.

In December 2021 the car was repossessed by the bank.

In April 2022 the car was auctioned to a used car dealer in Kansas City, Kansas. This dealer performed several repairs including new tires, new brakes, new shocks and struts, refreshing the transmission fluid, a new oil pan and pan gasket, and an oil change.

I purchased the car in July after my mechanic assessed it as being in good overall condition, although in need of more repairs including CV joints and more suspension work. He also advised another oil change since although the dealer had changed the oil and it looked clean, for some reason they had left the old filter on and said filter looked VERY old. The coolant was also looked stale and my mechanic said it probably dated back to the 2010 repair. We flushed that out and replaced with new.

Anyway, given all this and the possibility that the second owner did not treat the car well, I went with a short OCI and had a UOA done.
The results look OK to me except for elevated silicon, which could be from the new oil pan and gasket. I am glad to see the absence of coolant.

I do wonder about the loss of viscosity and the fuel dilution. Is STP oil a thin 5w30? For the winter I am running Pennzoil Platinum 5w30.

The car runs VERY well, gets 20 MPG in the city and 30 on the highway.
 

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With the flash point at 380°F, the fuel dilution is likely around 1.0-1.5%. It's more than a trace as Blackstone suggests. Their method for determining fuel dilution is less accurate than the GC used by other labs.

The KV100 of 8.98 cSt is in the 20 grade range (20 grade = 6.9 - 9.2 cSt) indicating a drop in viscosity. The most recent virgin analysis I have of this oil (2019) shows 10.65 cSt indicating a loss of 15.7% viscosity. If the fuel dilution is at 1%, that would account for ~0.5 cSt of that. The remainder is from permanent shear. It's important to note that the KV100 at 8.98 cSt likely includes some oxidative thickening as well. The viscosity has possibly dropped lower at some point in service. However, this is difficult to determine as Blackstone doesn't test for oxidation.

In the future, I recommend using Polaris Labs or WearCheck for used oil analysis as they can provide more accurate results for fuel dilution using GC and can test for oxidation. They also include TBN at no additional charge.

The TBN at 3.1 is fine. The bottom limit is 2.0.

The silicon is up a little indicating some dirt contamination. Around 5-10 ppm of that Si is found in the virgin form from an anti-foaming additive. The sources for dirt is typically from the intake / PCV system. However, like you said, it could also be leaching from silicone based sealant. Regardless, the amount isn't alarming. Just monitor with subsequent UOAs.

The wear metals are unremarkable.

The only thing that concerns me a little is the KV100. While fuel is present, it's not enough to drop the viscosity that low. The main reason for the drop in viscosity into the 20 grade range is from permanent shear. Still though, the oil did its job as the wear metals are still low. I would probably change the PP 5W-30 at a similar 3,200-3,500 mile interval with another UOA, just to monitor the silicon and fuel content, and then potentially extend OCIs afterwards depending on how it looks.
 

KansasBuickFan

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What could be causing the shear? I am just learning to understand this stuff and was under the impression that the 3800 was usually gentle on oil.
 
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The GM 3800 has always been a little hard on oil in terms of shear. This is why GM recommended 10W-30 in them up until the Series III came out. By the time the Series III came out, 5W-30 had improved to the point that shear isn’t much of a concern. Long story short, 10W-30 may be more shear stable in these engines.
 

KansasBuickFan

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My plan is to replace the current PP 5w30 at 3400 miles or so, or in mid-April, whichever comes first. I was considering a frankenblend of some odds/ends PP 5w30 and Quaker State 5w30 I have lying around. But I could also try something else.

In my old LaCrosse I had excellent results with Pennzoil High Mileage 5w30 but that engine had a few oil leaks and this one doesn't. That engine was up to 208,000 trouble-free miles until it was totaled.
 
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Permanent shear is mostly due to the viscosity index improver (VII) polymer losing viscosity under load. It undergoes temporary and permanent shear. The cheaper shelf oils tend to use lower viscosity (4-6 cSt) base oils with more VII to make up the viscosity for a 30 grade. VII polymers have a shear stability index (SSI) that reflects how much viscosity the polymer loses, relative to the base oil viscosity, when a load is applied. It's common for cheaper oils to use a cheap olefin copolymer (OCP) for VII with a SSI of 35-50%.

Let's say this oil has a base oil viscosity of ~6.25 cSt. The remainder is made up of the VII to make it to 10.6 cSt which is 4.35 cSt gap. If the VII has a permanent shear of 35%...

4.35 x 0.35 = 1.52
10.6 - 1.52 = 9.08 cSt

So the oil would be expected to shear from 10.6 cSt to 9.08 cSt with use. Add in the little bit of fuel dilution, some oxidative thickening correction, you arrive at your 8.98 cSt.

These engines can be hard on the oil. My MIL has a 2003 Buick LaCrosse with the 3800 which I currently have Mobil 1 FS Euro 0W-40 in with 1 quart of High Performance Lubricants Engine Cleaner SAE 30. I don't like the rather low bar set by API so I tend to look at ACEA standards for better oils. Pennzoil Platinum Euro 5W-30, Castrol Edge Euro 5W-30, or Mobil 1 FS Euro 0W-40 would be where I'd look.
 

ls1mike

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My plan is to replace the current PP 5w30 at 3400 miles or so, or in mid-April, whichever comes first. I was considering a frankenblend of some odds/ends PP 5w30 and Quaker State 5w30 I have lying around. But I could also try something else.

In my old LaCrosse I had excellent results with Pennzoil High Mileage 5w30 but that engine had a few oil leaks and this one doesn't. That engine was up to 208,000 trouble-free miles until it was totaled.
We have the same car in my family, we are at 135,000 miles on it. Excellent runner. I am running Quaker state 5W-30 in ours. Seems to work well. I did the intake gasket when I first picked up the car. It was at 130,000 and had never been done. Question sort off topic, I need to do the shocks and struts and was wonder what you are running on yours.
 

KansasBuickFan

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We have the same car in my family, we are at 135,000 miles on it. Excellent runner. I am running Quaker state 5W-30 in ours. Seems to work well. I did the intake gasket when I first picked up the car. It was at 130,000 and had never been done. Question sort off topic, I need to do the shocks and struts and was wonder what you are running on yours.

I'm not sure, the shocks and struts work was done by the used car dealer before I bought my car. My mechanic checked it and said the work had been done correctly, which was my main concern given the dealer's sloppiness with not changing the old oil filter and leaving in the stale coolant, but I'm not sure what parts/brands was used for the shocks/struts.
 

KansasBuickFan

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Permanent shear is mostly due to the viscosity index improver (VII) polymer losing viscosity under load. It undergoes temporary and permanent shear. The cheaper shelf oils tend to use lower viscosity (4-6 cSt) base oils with more VII to make up the viscosity for a 30 grade. VII polymers have a shear stability index (SSI) that reflects how much viscosity the polymer loses, relative to the base oil viscosity, when a load is applied. It's common for cheaper oils to use a cheap olefin copolymer (OCP) for VII with a SSI of 35-50%.

Let's say this oil has a base oil viscosity of ~6.25 cSt. The remainder is made up of the VII to make it to 10.6 cSt which is 4.35 cSt gap. If the VII has a permanent shear of 35%...

4.35 x 0.35 = 1.52
10.6 - 1.52 = 9.08 cSt

So the oil would be expected to shear from 10.6 cSt to 9.08 cSt with use. Add in the little bit of fuel dilution, some oxidative thickening correction, you arrive at your 8.98 cSt.

These engines can be hard on the oil. My MIL has a 2003 Buick LaCrosse with the 3800 which I currently have Mobil 1 FS Euro 0W-40 in with 1 quart of High Performance Lubricants Engine Cleaner SAE 30. I don't like the rather low bar set by API so I tend to look at ACEA standards for better oils. Pennzoil Platinum Euro 5W-30, Castrol Edge Euro 5W-30, or Mobil 1 FS Euro 0W-40 would be where I'd look.

I was considering the Pennzoil Platinum Euro L 5w30 for summer but I don't know much about Euro oils or how well it would match with a 17-year-old 3800 engine. I was also considering Pennzoil Platinum High Mileage given the good results this gave me in my previous LaCrosse, but this one isn't a leaker, yet, so I wasn't sure.

I'm likely overthinking it. Any name brand oil I pick of the correct viscosity will be a better-quality oil than what was available in 2005 when the engine came off the line.
 

ls1mike

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I was considering the Pennzoil Platinum Euro L 5w30 for summer but I don't know much about Euro oils or how well it would match with a 17-year-old 3800 engine. I was also considering Pennzoil Platinum High Mileage given the good results this gave me in my previous LaCrosse, but this one isn't a leaker, yet, so I wasn't sure.

I'm likely overthinking it. Any name brand oil I pick of the correct viscosity will be a better-quality oil than what was available in 2005 when the engine came off the line.
Exactly. I used to run a full synthetic in 3800s, but the semi seems to do well in my current one.
 
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I was considering the Pennzoil Platinum Euro L 5w30 for summer but I don't know much about Euro oils or how well it would match with a 17-year-old 3800 engine. I was also considering Pennzoil Platinum High Mileage given the good results this gave me in my previous LaCrosse, but this one isn't a leaker, yet, so I wasn't sure.

I'm likely overthinking it. Any name brand oil I pick of the correct viscosity will be a better-quality oil than what was available in 2005 when the engine came off the line.

The Euro oils are held to a higher standard than the API oils in most cases. The A3/B4 oils, like the Pennzoil Platinum Euro 5W-30, are required to have an HTHS of ≥3.5 cP and a TBN of ≥10. The price usually isn't much different.

Like you said though, any oil will be an improvement over what was available in 2005.
 
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The coolant elbows were actually a design flaw with these engines. The block and radiator would drain of coolant before you would even have a warning of temp rising. Fortunately we caught ours before it decided to give up.
Our 2007 GP had 260K+ miles on it when it was totaled for vandalism. That car still ran like a top after using M1 0W40 for years.
 
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