Lightweight Oil

I Have a 2000 Bonneville, with the 3.8 V6 engine. My manual says to use 10W-30, could 5w-30 cause any damage to my engine?

No…, not unless it’s damaged or worn out already…

Both are 30 weights at operating temperature, the only difference is the winter viscosity which is lower for the 5w, but that 5w is still thicker than either oil at 30 so the thinnest either will get is 30. Won’t do any harm.

Yeah …as was said they’re close to the same hot viscosity. It’s the cold properties that are different. The 10w-30 will show the same limits on stress in the Cold Cranking Simulator at +5F above what 5w-30 does.

Even if it did mean “weight” a 10 weight oil is EXTREMELY thick at -25F …while the thirty range is EXTREMELY THIN at 212F. The average consumer is looking at a room temperature quart of oil and imagining it getting thicker as it warms and thinning out as it gets colder. The stuff never gets thinner. It just reacts within certain limits of pumpability and doesn’t turn into a gel that fractures like you were trying to egg beat form up jello.

Multivisc fluid “react” like a lighter fluid at extremely cold temps and “simulate” heavier fluids at higher temps. They do this with VII (viscosity index improvers). The actual base stock (all except additives) is a 20 grade. The polymers coil up when cold and stretch out when hot to “simulate” a heavier fluid. As they shear, the oil tends to start heading back toward its base stock viscosity. 10w-30 tends to shear less since it requires less doping to achieve its target spec.

Are you sure it doesn’t say to use 10-30 in the summer and 5-30 in the winter? While I don’t disagree with anyone, I just use what the book says to use. So I use 5-20 in one, 5-30 in another, and 10-30 in another. No big deal.

I own a 2000 Impala, and the owner manual specifically states that if the car is equipped with a 3.4 engine use 5-30W oil, if the car is equipped with a 3.8 engine use 10-30W. So there must be a reason GM specified 10-30W for the 3800 engine within the normal temperature range. So why deviate from what the owners manual specifies? Especially sense there is no price difference in the oil.

I believe my manual says the same thing, amc. The reason I ask is I noticed my engine making some noise like it was low on oil and my gauge fluctuating quite a bit. I was advised to change the oil to a heavier weight and the noise started to go away. Then within a week the engine threw a rod and destroyed the car. I’m trying to figure out if the lighter weight oil in the car may have had something to do with it. I also notice that I never had any problems with it over the winter, it just recently happened once the weather started to warm up. I don’t know so I thought maybe somebody smarter out there could tell me.

Nope! Won’t harm a thing! As a matter of fact, it’s better!

The first number on the oil bottle is the winter weight. (5W/10W). This indicates how the oil will flow when the engine is started cold above freezing. The higher the weight of the oil for winter weight means it builds pressure quickly but flows poorly. Take a bottle of maple syrup and fill your mouth. Now blow that maple syrup out of your mouth thru a straw. It flows quickly with little pressure. Now take and fill your mouth with 100% molasses and try blowing that thru the straw. A lot of pressure but very little flow. And that’s how oils work on cold starts.

I run 5W-30 regular oils in all my vehicles all year long because I want instant lubrication on cold starts. Except for the Mazda. It has a turbo so it gets Mobil1.