Oil Analysis - Viscosity Question
 

I just received my second oil analysis. First analysis was done when oil had around 4000 miles, second analysis was done around 3800 miles. First analysis was Mobil 1 0w40, second analysis was Motul X-Max 8100 0w40. Two different oils. Both times, oil viscosity came in lower than expected (61 and 10.5 where they should have been 65-75 and 11.6-14.5). The fuel and antifreeze amounts are nonexistent. All other metals are excellent, all below universal averages.

Blackstone's explanation is this engine might be just shearing oil and they say this is okay. I searched the forum for similar issues but apart from a 997 mezger engine shearing oil, I didnt find any here in the 9A1 engine. Wanted ask for everyone's opinion.

I’ve read that Mobil 1 0-40 does tend to shear over time.

Right. Thats why I switched to Motul X-Max 8100. The numbers did improve slightly but they were still low.

10.24 became 10.52 and 60.1 became 61.1. Not the improvement I was hoping for.

Before anyone recommends 5w50, my car’s user manual only says to use either 0w40 or 5w40. There is no more 5w50. My car is a 2019 GT3RS, its not an OPF car either. I’m not sure if 5w40 would make a difference.

I drive the car year around including cold temps as low as 20-30F (but not lower). It is kept in garage that never goes below 45F but I cant guarantee that there will never be a day where I might have to park it outside in a super cold day and start it.

Does it have better viscosity then Motul?

Is 5w40 ok to use in my ambient temp environment?

As a control, what is the viscosity of a virgin sample of both oils? Might be useful to check that before blaming the engine. If it truly is shearing a bit, is this clinically relevant at such a short OCI?

I can try to do this. I was looking at my oil reports of the C7 ZR1 that uses the same 0w40 Mobil 1 oil and its viscosity numbers are also low, borderline above minimum (11.4, 11.2, 64, 64,5, etc).

Since the 5w50 has been dropped from the manual, I dont know what other option I have other than changing the oil every 2,000 miles?

Is 5w40 better than 0w40 in this regard? Any way to know how much better its viscosity is?

I also read in various threads that people say “if ambient is 50F or more use 5w40”, why is this? The manual says -25F or more. Thats a big temp difference.

I like this recommendation. For clarity, use the 4100 since it's A40 approved. The #4010 is C40 approved for our new 992 GT3s. I just ordered 10 liters from FCP Euro and will hand carry to my dealership in early November for an oil change prior to winter storage.

The 5W50 and 5W40 are both good to -13 degrees. Colder than -13 requires 0W40. And not many here do that! LOL:)

What you have to remember is, with only 2 oil changes, is that you still have a lot of the factory fill Mobil that is very prone to high temp & high pressure sheer. Motul did a reformulation a few years ago and their viscosity breakdown is similar to Mobil's. Many times different oil brands don't play well with each other. Their additive packages fight each other, and show poor results for a couple oil changes until the cross pollination is removed/reduced.

If I were you, I'd try to find a way to use Mobil 5W50 (A40 approved) or switch over to the Liqui Moly. Also reduce your OCI (oil change interval) to about 2,000 miles until your viscosity numbers improve as the factory Mobil and Motul wash out. As the UOAs improve, slowly increase your OCI.

Here’s my UOA on a 2018 GT3 6MT. This is with 3,466 km on this oil, about 11 months. Does this simply mean that there’s no shearing and the viscosity is within limits or that I am changing it too soon? I think it would be important to do a before/after UOA on oil from the same bottle to be sure the viscosity drop is due to the engine.


https://cimg0.ibsrv.net/gimg/rennlis...109d0b674.jpeg

Which oil was this? How do you use the car? Do you drive it hard? Thats 2100 miles. Most likely oil didnt shear yet.

Thanks LexVan for your response. I exchanged emails with Blackstone who strongly believes this viscosity being low is nowhere near a cause for alarm. They said some engines do this and its perfectly fine. TBN showing 7.1 in my case indicates oil is still healthy. In fact they say when oil starts going bad, it turns much thicker and viscosity shoots higher.

With that said, I have a question about 5w40 oil. If the first number is only the viscosity in cold then wouldnt a 5w40 and 0w40 shear the same amount and be the same oil? Furthermore, an engine has probably the worst metal wear in cold start. Wouldnt you want the thinnest but safest oil during cold starts?

Or 5w40 oil is simply a thicker oil and will shear less?

I also dont know anything about liquimoly. Are they better than Motul?

And if I switch oil brands, wouldnt this cross contamination issue you raise will even be worse since now there will be 3 oil that were switched?

Not sure if the below works on all cars, particularly those that have a thermostat-controlled oil heat exchanger, but it might still work on your car:

One way to solve that problem is to buy twice as much oil as you need for the oil change, but just one filter. Perform the oil change while the engine is still warm, not changing the filter, and then run the engine for a minute or two with the fresh oil. Rev the engine a small amount to not more than 3,000 RPM occasionally during this time. Perform 2nd oil change, this time, changing the filter as well.

The engine will have such a small amount of residual old oil that a variance of contamination won’t show up on any UOA test.

I think you’re right, but it’s a little more complicated. The thinner oils (first number) have to use more additives in order to make them behave like a thicker oil when hot. And these additives tend to be consumed when used. So, a 5W40 oil has some advantages (requiring less additive), but the thinner oils can protect better in very cold weather.

I was never very good at Chemistry in school…😄

I think both Motul and Liqui-Moly are excellent. Motul is French and Liqui-Moly is German - kinda like comparing wines…

I read through all the tech data and see that the liqui moly viscosity is somehow lower than both 0w40 and 5w40 and the motul 5w40 viscosity is quite a bit higher (14.2 vs 12.9) than liqui moly. I dont know if Motul simply shears quicker and drops to 10s whereas liqui moly stays at 12.9.