10W-30 in 4.8

sheridan · November 19, 2003

I've got an '02 Z71 with the 4.8 and the piston-slap option (no charge-hehe). Went to the jiffy lube the other day and they put in 10W-30, even though the filler cap says 5W-30 only. Being a nice guy, I said just leave it in there and I'll see if its really a problem and bring it back if it is (couldn't see how it could be).

Thing is, it has almost completely eliminated the cold-start piston slap. Are there warranty issues or good reasons for me to go back to 5W? The bad side is I haven't collected my 100K warranty yet. Thanks in advance for any insight.

HDChuck01 · November 19, 2003

I think it just depends on how cold it gets there where you are. I believe 5-30 is for colder temp protection and if it stopped your piston slap using 10-30 i would go with the heavier oil. Just my thought

Butch 02 Denali · November 19, 2003

10-30w is fine to run all year. The only reason to go back to 5-30 is if the temp where you are drops below 0 degrees. I am a very much convinced that if people had run 10-30 after the first oil change that 90% of them wouldn't have CSK now. I have 12k miles on my 02 Sierra Denali with absolutly no noise, 16.5k miles on the wifes 5.3 Avalanche with no noises, and had 17k miles on my 2000 Sierra 5.3 that i traded, with absolutly no noise. I attribute this to 10-30 oil and a molly additive.

Butch 02 Sierra Denali

sheridan · November 19, 2003

Thanks guys. I'm in Nashville, and teens is about as cold as we see. Why does the cap say 5W-30 only? If it won't hurt anything, I'm fine to stay with the 10W.

SilveradoWV · November 19, 2003

There should be a temp chart in the book!

97whitez71 · November 19, 2003

I was just reading through the November 2003 GM Tech Link and came across this:

"For 2003 L36 and L67 engines, the vehicle owner’s manual recommends 10W30 motor oil, while the engine oil fill cap may state to use 5W30 motor oil.

For the 2003 model year, 10W30 or 5W30 motor oil is appropriate for the L36/L67 3800 applications. The use of either 10W30 or 5W30 motor oil will provide necessary lubrication for engine component wear protection."

I thought this might help set your mind at ease.

JayMan · November 20, 2003

I use Mobil 1 0W-30 in winter (Can get to -40 where I live!) and Mobil 1 10W-30 in summer. I'm not sure if oil alone will cure piston slap, as that usually won't go away until the motor is warmed up (2-5 minutes).

If you're having trouble with those hydraulic roller lifters not pumping up quickly, a synthetic oil will really help here. Don't forget the oil pump is now at the front of the crank, so the oil has to be sucked up that long oil pickup tube all the way to the front of the motor.

Here is a quote from my official Helm shop manual, page 0-44:

"The recommended oil viscosity is SAE 5W-30 ... Engine oil viscosity (thickness) has an effect on the fuel economy and the cold-weather operation (starting and oil flow) ... However, higher temperature weather condition require higher viscosity engine oils for satisfactory lubrication. When the temperature is consistently above 0F (-18C), SAE 10W-30 can be used. SAE 20W-50 or oils of other viscosity rating or quality designations are NOT recommended in any Trucks at any time."

That said, a guy I know uses Amsoil AMO 10W-40 High Performance year round, and his Vortec 5.3 is QUIET. His Vortec 4.8 used to give the knock-knock when first started, with Amsoil AMO it doesn't.

How is your oil pressure when first started?? That's all I would worry about.

TROYROBO · November 20, 2003

i run 10w30 year round here in east tennessee----no problems so far and no knocks--i believe that if you drive it like you stole it then you do not get any knocking--none in mine so far--just my 2 cts-- by the way -welcome aboard

JayMan · November 20, 2003

Thanks for the welcome!

Main thing is you actually LOOK AFTER the thing!

If there really is a mechanical problem, it'll blow up quickly. A friend of mine bought a new Dodge Diplomat (1983? 1984?) and with 400km on the odo, floored it to pass a pulp truck. Blew the motor.

Yeah, the dealer didn't have much choice but replace the 318. That 'ole rustbucket is STILL running!

toboyca · November 27, 2003

I have an 03 Suburban ... with the 5.3L, had my initial oil change @ 1000 Mi... filled it up with synthetic 10/30 Castrol syntec... No problems. Reason for the early change... wanted to switched to synthetic & convert grades from 5/30 to 10/30. Everything's cool ...

JayMan · November 27, 2003

Good choice! Depending on how you drive, after 500-1000 miles the thing is broken in. That's a good time to change the oil and filter to get all the crap out.

If you have a problem, you should know by then.

Lance Link · November 27, 2003

I've run Castrol 10w/30 in my Z-71 since new, changed every 3,000 miles. Just turned 100,000 miles and it still runs perfectly- never had piston slap. I live in Maine but keep the truck (and every other vehicle I own) in a heated shop every night. I also run the same oil in the Yukon and the Willy's, as well as my '94 Nissan SE-R which is about to turn 200,000 miles, still all-original including the clutch.

MrQuadrasteer · November 27, 2003

10-30w is fine to run all year. The only reason to go back to 5-30 is if the temp where you are drops below 0 degrees. I am a very much convinced that if people had run 10-30 after the first oil change that 90% of them wouldn't have CSK now. I have 12k miles on my 02 Sierra Denali with absolutly no noise, 16.5k miles on the wifes 5.3 Avalanche with no noises, and had 17k miles on my 2000 Sierra 5.3 that i traded, with absolutly no noise. I attribute this to 10-30 oil and a molly additive.

Butch 02 Sierra Denali

I couldn't agree more. 5w-30 is water 'round these parts...

Changed my oil at 1000m with Castrol 10w-30, again at 3000, and now at 3900, smoothest, quietest motor I've ever had .

I've kinda gotten away from synthetics. The price, and the stuff FINDS leaks. Every motor I've run it in has been fine, change to syn and few months later.... dribbles. I hate leaky motors.

I've always used Castrol, 20/50 in my air-cooled bikes, 10/40 in my cars and liquid cooled bikes, 10/30 in the truck. Thinking of trying 10/40 this summer...

Castrol GTX = good stuff .

JayMan · November 28, 2003

Well, I already covered this in another post, but here goes:

I've never had a new engine (Car, truck, tractor, skidder, Class 8 truck) leak due to a synthetic that was run FROM NEW. That said, I would NEVER take an older vehicle and switch to synthetic.

Synthetic oils have much higher detergent levels. They will actually clean out a motor. That is where the trouble is, especially if you use a Dinosaur Oil with that magic "seal conditioner."

As a specific example, the Eaton Dana HP-40 single reduction tandem axles can be equipped with Spicer LMS hubs. With factory fill synthetic gear oil, or a synthetic on their approved list, you have a 3 year/300,000 mile warranty against leaks/failure, with recommended drains of 250,000 miles.

According to Eaton Dana TSB #TMIB-0130 , the tandem and/or LMS hubs must be switched to a synthetic within the first 5,000 miles if factory filled with Dinosaur Oil. Even then, you MUST change the seals when switching back to an approved synthetic.

Otherwise, the seals leak and gear oil pees all over your brakes. Eaton is leery of changing to synthetic after 5,000 miles of service as the gunk has already built up inside the axle.

In a motor, Dinosaur Oil will create varnish, sludge, and carbon deposits, no matter how often you change it. Against a rotating surface on a seal, these deposits grind away the seal, but the deposits sort of make their own seal.

Change to a synthetic motor oil, and the extra detergents will dissolve a lot of the gunk. You then get leaks.

I broke in my GMC for 1600km / 1000mi and changed everything to synthetic. No leaks, average oil consumption of 1 qt / 6200 miles, no problems. The plastic oil filler cap is spotless.