2011 GMC Sierra 1500 slt, 76,000 miles, I decided to change the engine oil from dexos to full synthetic, used amsoil XL 5w-30 synthetic, I believe the dexos gm oil is a 50/50 blend. So with about 40% oil life left I had to put add 1.5 quarts of oil. Should I go back to the 50/50 blend? I have heard that this shouldn't go back to regular oil after using synthetic, but the previous oil was 50% synthetic.

 

Can't believe no one else has had this problem, had to recently add another 1/2 quart making it 2 quarts. So I have seen some mention the fact that when going to full synthetic it may use some oil until about the 3rd or 4th oil change. It is not leaking oil anywhere on the engine, so it must be burning oil.

 

What I think you are actually looking at is the difference between additive packages. It is not so much of a conventional to full synthetic issue or a synthetic blend to full synthetic issue. This could have happened in going from say one of the Pennzoil full synthetic oils to one of the Mobil 1 oils as well. Even though you are (and likely have been) using quality oils, there are still some differences between the additive packages especially when going from one of the "mainstream" oils to a boutique oil like Amsoil,

Yes, you should a decrease in oil consumption as you keep driving. Jut curious how much Amsoil are you consuming per 1000 miles?

 

4419 miles used 2.5 quarts of oil.

 

OK, you are only using about 1 quart per 1800 miles which in the realm of things is not really bad.

I know some consider 1 quart every 1000 miles to be OK, but when you go along with essentially zero consumption and then all of a sudden bingo, oil consumption. I don't know what your oil change intervals have been, or how long you plan to go between oil changes with the Amsoil, but I am fairly confident that like others have seen, your oil consumption with Amsoil will go down and possibly disappear completely the longer you use it - provided there is nothing mechanically causing the increased oil consumption (like a leaky gasket or seal, clogged PCV passage, etc.).

If no mechanical issues, then this is quite likely the result of a different oil's additive package cleaning up deposits that your previous oils left behind. All oils will do this to some extent, and some people will change oil brands every so often to get around this "perceived issue". Me, I'm too lazy to look for alternate oils to use so I keep using Havoline Conventional 5w30 because over the last 45 or so years, I've never had a problem with it. However, now that Havoline Conventional is no longer available in the 5w30 flavor, as soon as my stockpile dwindles down, I'll switch over to Havoline ProDS full synthetic, and heck I might even see some increased oil consumption for awhile due to the change in additive package.

Good luck!

 

Thank you so much for your prompt reply, after doing some research I have found that this a common problem when switching from 50/50 blend to full synthetic and you are probably right with the additives that are used in Amsoil being a better or high grade of oil, so listed below are 2 of the other products that may or should be used in conjunction with the upgrade. I didn’t want to give up on the fact that I changed from a dexos 50/50 blend to a higher grade of oil, but like you say and it sounds like you know what you’re talking about that the additives could be the cause of the oil consumption problem and would have to give additional time to give it a fair chance. Also as you can see that I am probably not going to put more than 6 or 7000 miles this year on the truck. The oil was changed in 01/07/20. Also the mileage dropped from around 16 mpg to around 13mpg. < this is on the first oil change though. But I can see that there may be improvement after a couple of oil changes and using the listed products to clean the engine. Imagine that you would think that changing to a better grade of oil wold increase everything right from the first oil change, but never gave much thought to the other factors that may be involved.







[img]file:///C:/Users/twodo/AppData/Local/Temp/msohtmlclip1/01/clip_image001.jpg[/img]

Engine and Transmission Flush

16-oz. Bottles (FLSHCN-EA)

Qty: 1

$9.35

[img]file:///C:/Users/twodo/AppData/Local/Temp/msohtmlclip1/01/clip_image002.jpg[/img]

P.i. Performance Improver Gasoline Additive

12-oz. Bottles (APICN-EA)

Qty: 1

$10.65

 

Regarding your drop in gas mileage, that is likely caused by things other than the oil you are using. The first things that come to mind, considering your truck's age and mileage, are lazy oxygen sensors, worn spark plugs, and "poor driving habits" remembered by the PCM.

O2 sensors are known to get lazy with age and high mileage, so you might want to consider changing them. I would go with one of these three brands - ACDelco, Denso or Delphi. My choice between these three brands would be based on cost from rockauto.com.

Spark plugs, well, your truck is going on 10 years old and has over 75,000 miles on it, so to me, that's close enough to 100,000 miles to consider changing (assuming you have not yet changed them). I would go with the ACDelco 41-162 iridium plugs that were originally installed at the factory. It's know that these 5.3 L engines are awfully picky when it comes to spark plugs, so using what the factory used is best.

Now for the PCM and it's memory. The easiest way to handle the PCM is to pull the fuses for the PCM and let it sit for about an hour so it forgets all the "bad things" it's learned over the last 10 years or so. This way the PCM can relearn your good driving habits and increase your gas mileage. It works more often than not, so you really have nothing to lose in trying it.

Now for the chemicals, I really can't say one way or the other if they are worthwhile. In my case, I'll pour in a bottle of Techron Complete to keep the fuel injectors clean. Years ago, I used to replace 1 quart of motor oil with 1 quart of Rislone when I did an oil change during the coldest months of the year, but I stopped doing that about 10 years ago because motor oils had taken a quantum leap in overall quality and low temperature flow characteristics.

If you followed the oil life monitor on your truck for oil changes (at the minimum), I don't really think you need to worry about having a dirty engine and the need to clean it up. It's pretty amazing how today's oils will keep an engine clean when the manufacturers oil change recommendations are followed.

Good luck!

 

I changed the plugs < iridium and wires at 67K, O2 sensors look pretty easy to replace, but I don't know if I would do that myself, I would if I had a lift. I will try the pcm reset. I do follow the oil life monitor for the oil changes.
I purchased a gallon of mobile 1 synthetic to fill what oil im using now instead of the more expensive amsoil.

 

OK on the changing of the spark plugs. Regarding the O2 sensors, it's not a tough job to do - just jack up each side, remove the front tires and that will give you access to the O2 sensors. Use an O2 socket and a decent sided breaker bar to remove the sensors after you have run the engine a couple of minutes so the area around the O2 sensors gets hot enough to slightly expand. They can often be TIGHT. If you can, spray the threads with some Kroil or PB-Blaster a few hours before running the engine for the minute or two and that can help too.

OK on following the oil life monitor and using the Mobil 1 to top off in place of Amsoil. Neither oil will mind.

 

At 96,524.00 miles this truck is still using oil, I don’t know how much cause haven’t been keeping track of it, seems every time I check it I have to add oil.
The pcv valve was mentioned in a previous post, I have never changed that, only to find out recently that you have to change the whole valve cover because the pcv valve can’t be removed.
Thats brilliant.