Castrol GTX High Mileage or Valvoline MaxLife Synthetic Blend in my 99 GMC Sierra

[vdd88]

with 154k miles? Which one would you prefer and why?
Currently I use MaxLife, and my truck eats one quart of oil every 3k miles
maybe switching from a synthetic blend to straight mineral oil will help?

[the rock]

i have always been told to not use synthetic oil in an engine with high mileage,because of the gaps formed from the high mileage wear.the synthetic oil will just slip right through these gaps and not protect the engine. just be safe and use the castrol gtx

[Molson02536]

Originally Posted by vdd88

with 154k miles? Which one would you prefer and why?
Currently I use MaxLife, and my truck eats one quart of oil every 3k miles
maybe switching from a synthetic blend to straight mineral oil will help?

Here is some information for the 2007 Sierra that my interest them on oil consumption:

The reason for the oil consumption in the 2007 Sierra is that these engines use low tension oil rings, nobody even makes standard tension rings for this application. Trust me I have seen piston tops and combustion chambers, that oil was going straight past the rings. There was no excessive cylinder wear, you could still see the crosshatch on the cylinder walls. Our solution was to send the replacement pistons out and have the 4mm oil grooves cut to 3/16" so we can install standard tension rings and reduce the oil consumption.

December GM service bulletin that outlines the suggested problem to why some of the 2007 5.3L consume oil. They are now, as of today, saying that they believe some of the engines have defective valve stems that have a nick or pit in them and this in turn causes them to take oil from the engine and burn it off- make sure they look at the December service bulletin and start the process for you- you may qualify for new heads with valves. Oh and the other thing also we have found is quite a few similar cases like yours, and the fault came down to the PCV baffle holes in the valve cover that the PCV is in. We need to replace the whole valve cover if we find an issue with them (plugged holes). We've done at least 10 of them at our speed shop and none have come back for the same issue.

Here is something you may be interested in knowing.

PIP 4574


Subject: Excessive Oil Consumption and/or Blue Exhaust Smoke

Models:
2007 Chevrolet Avalanche, Silverado, Suburban, Tahoe
2007 GMC Sierra, Yukon
with 5.3L Engine (RPO LC9 - VIN 3)

CONDITION/CONCERN:

Some customers may complain that their vehicle has been using approximately 1 quart of oil every 500-1,000 miles. In most cases, the customer will advise that this did not start until it accumulated approximately 30,000 miles or more.

If the spark plugs have been inspected, the technician would have found signs of oil consumption on one or more spark plugs. If they went on to perform a cylinder leakage test, static compression test, or the lifter and PCV baffle inspection from the latest version of PIP4492, they would find that none of these tests identified the cause of this concern.

In many cases, the engine may have had the rocker cover, cylinder heads, and/or oil control rings replaced only to come back with the same concern.

RECOMMENDATION/INSTRUCTIO NS:

If this concern is experienced, no repairs should be performed at this time because the cause of this concern is under investigation. This PI will be updated as soon as a procedure is available to help diagnose/repair this concern, which should be available by the end of this month (February 2009).


Matthew C. Edmiston
General Motors
District Service Manager Michigan

As for the oil in your 1999 Sierra with 150,000 miles. I would use the the optional SAE 10W30 oil and add Lucas engine oil additive to reduce the oil consumption till you get yours resolved. Check to make sure you have no leaks and chances are that your valve guilds my just be worn which is common and will need to be replaced. Good luck and hope this helps and note that synthetic oil has a way of destroying RTV gaskets.