First oil change from 15w40 to 5w30

I wanted to provide an update following the recent oil change on my 2014 SSV. After purchasing the vehicle in April with 103,000 miles on the odometer, I noticed it had consumed a quart and a half of oil over 3,000 miles. Based on the maintenance department's practice of switching the vehicles to 15w40 oil at 90k miles, I sought your advice on whether to continue with this grade.

The consensus on this forum was to revert to 5w30, which I did, opting for Mobile1 5w30 full synthetic paired with a Wix filter. I'm pleased to report that there has been no change in the oil pressure readings post-change.

I plan to monitor the oil consumption closely and will provide updates on this thread as I accumulate more miles. Your advice has been invaluable, and I appreciate the collective wisdom of this community.

Thank you once again for your guidance.

It's not just switching from 15W40 (which is patently ridiculous unless you already live in year round desert heat) to 5W30.

You will find different brands of 5W30 will be consumed at different rates.

I check my oil every weekend. Once the engine consumes 1/2 a quart, it's time to change oil and filter, regardless of what the Oil Life Monitor thinks.
After all, the oil just told me!

Some oils resist consumption better than others - and no, it's not as simple as 'full synthetic' vs 'synthetic blend'.

Before I start whinging about how you didn't mention which 15W40 the previous 'maintenance dept' switched to -
bet you they can't or won't tell you which brand & version of 15W40, huh?
Let me try to be helpful by saying, make sure you have the UPDATED valve covers - maybe the previous 'maintenance dept' didn't bother.

Marky Dissod said:

It's not just switching from 15W40 (which is patently ridiculous unless you already live in year round desert heat) to 5W30.

You will find different brands of 5W30 will be consumed at different rates.

I check my oil every weekend. Once the engine consumes 1/2 a quart, it's time to change oil and filter, regardless of what the Oil Life Monitor thinks.
After all, the oil just told me!

Some oils resist consumption better than others - and no, it's not as simple as 'full synthetic' vs 'synthetic blend'.

Before I start whinging about how you didn't mention which 15W40 the previous 'maintenance dept' switched to -
bet you they can't or won't tell you which brand & version of 15W40, huh?
Let me try to be helpful by saying, make sure you have the UPDATED valve covers - maybe the previous 'maintenance dept' didn't bother.

Click to expand...

I purchased the SSV from an auction and spoke with the maintenance crew upon pickup. They were unable to confirm the brand of oil in the drums, though they speculated it might be Rotella T4.

For this oil change, I used Mobil 1 5W-30, primarily because I also use it for another truck with a 6.0 engine and can conveniently purchase it from Costco. Thank you for suggesting trying different brands.

I’m uncertain about the cause of the oil consumption, as there are no visible oil leaks under the truck.
I collected a sample of the old oil and sent it to the lab for analysis.

thank you for the advice, I am going to look into the valve covers next, how do I tell if they are an updated version?

I know there's more than one Mobil1 5W30.
I used to be big on Pennzoil Platinum or Ultra Platinum, or Quaker State Euro or Ultimate Protection Full Synthetic.
I've since switched to Valvoline Restore & Protect, because I'm a sucker for the idea that this oil might actually clean the engine.

ChevySSR said:

I collected a sample of the old oil and sent it to the lab for analysis.

Click to expand...

Respect. You obviously take this more seriously than someone who keeps posting til they read what they want to read.
Oil analysis kicks @$$.

Been a while since I owned a GMT900, but I know there are updated part numbers for the younger valvecovers with improved PCV circulation,
I know my old GMC YXL did NOT get them (I was too busy as a livery driver driving all over NYC / NJ / PA / CT),
and I remember that I had to change oil every 3200-3500 miles to avoid oil consumption -
except this one time when I used a 'raceboy' oil whose brand & type escape me, it went about 4100 miles, but was not worth the price.

Hope what I said to you on Apr 26 helped.