Oil weight change in different seasons

[84gmcsierra]

I have an 84 GMC Sierra and just had another engine put in, and the mechanic said run 30 weight in it all the time. I usually do 40 weight, of 15w40 Rotella since it is a used engine. I live in Arizona so would it hurt to go to a 15w40 all the time, and go up to a 20w50 in the summer or just stay with one weight?

 

[Titan]

Of course it won't hurt. But it also won't help.

 

[Hohn]

Just stay with the 15w-40 year round. There’s no utility in changing viscosity for seasons, certainly not in Arizona.

 

[fozzdesy2001]

I say go for it with an original engine that old

 

[tblt44]

5w30 or 10w30 would be fine or run a 0w40 Euro or 5w40 Euro oil it would work good also and help with cold starts

 

[The_Jeff]

15w40 is more than enough.

 

[RDY4WAR]

Choose which one is actually the better oil. Just because it's a narrower multi-grade doesn't automatically mean better quality. In many cases, it's the opposite to an extent. If you notice a 5W-40 has similar Noack and HTHS (relative to KV100) to the 15W-40 version, you're better off with the 5W-40. Such a case tends indicate the use of cheaper, lower quality base oils and VII in the 15W-40. Narrow multi-grades like 10W-30 and 15W-40 can be formulated cheaper and still meet the grade. Since the major brands are all in a race to the bottom (including Shell... see my avatar), they happily exploit the lower production cost. (with no corresponding drop in retail cost, of course)

 

[DanL13]

Maybe if you lived somewhere that it actually got cold you’d have a case to change with the season. Keep running that Rotella.

 

[Rand]

Where in AZ? Flagstaff is different than Phoenix.

 

[Hohn]

Choose which one is actually the better oil. Just because it's a narrower multi-grade doesn't automatically mean better quality. In many cases, it's the opposite to an extent. If you notice a 5W-40 has similar Noack and HTHS (relative to KV100) to the 15W-40 version, you're better off with the 5W-40. Such a case tends indicate the use of cheaper, lower quality base oils and VII in the 15W-40. Narrow multi-grades like 10W-30 and 15W-40 can be formulated cheaper and still meet the grade. Since the major brands are all in a race to the bottom (including Shell... see my avatar), they happily exploit the lower production cost. (with no corresponding drop in retail cost, of course)

While this is all true, there are some market pressures that restrain their ability to make the oils as cheap as possible. Oxidation resistance being a big one because there’s relentless pressure to extend OCIs with the cheapest possible oils.

So in terms of cost-per-unit-oxidation-resistance, the current crop of diesel spec oils blows away most other blends only because it’s prioritized so highly within the formulation budget.

There are some solid 15w-40s out there. My current favorite for gas engines would be Delvac 1300 Super in 15w-40. It’s a blend with an API SP rating along with about every diesel rating on earth.

Valvoline Premium Blue One Solution in 15w-40 is also a very good oil with API SN Plus in addition to all the diesel ratings. They have a full synthetic HD oil in 15w 40 that is API SN (not plus).

Delo 400 XLE SB is 15w-40 and rated API SN.
Delo 400 XSP 15w-40 is full synthetic and API SN+ rated.


All of the aforementioned oils from Mobil, Chevron, and Valvoline are robust, full-SAPS oils with HTHS over 4 and very good oxidation resistance with reasonable gasoline API Specs. For an older vehicle in Arizona, you’re not going to find a better oil off the shelf for the cheap prices these HD oils go for. The cost effectiveness comes from the massive quantities they produce since they’re used in commercial applications that often have huge oil capacities.

If you value higher HTHS and oxidation resistance, these oils are a great way to get that for reasonable prices. Conversely, it’s almost impossible to find an oil at wal mart with an HTHS over 4 that is NOT one of these diesel-rated oils unless you step up to a 50 grade. Your typical A3/B4 oils even in 40 grade are going to be in the 3.7-3.8 HTHS range.

 

[Hohn]

Maybe if you lived somewhere that it actually got cold you’d have a case to change with the season. Keep running that Rotella.

Where in AZ? Flagstaff is different than Phoenix.

Indeed, it can get plenty cold in the mountains. Probably not cold enough to make a 15w unworkable, but the point remains— not all of AZ is hot desert. And deserts can get super cold at night and FAST after sundown.

 

[84gmcsierra]

I say go for it with an original engine that old

The engine really isn't that old. It's not the original from 84. If I remember correctly it's a 1999. It's a crate motor a friend ule out of his 72 C10, and sold to me

 

[84gmcsierra]

Indeed, it can get plenty cold in the mountains. Probably not cold enough to make a 15w unworkable, but the point remains— not all of AZ is hot desert. And deserts can get super cold at night and FAST after sundown.

Cottonwood, 50 miles south of Flagstaff.w get in the 30's inte winter and up to and above 110 in the summer

 

[Cujet]

As mentioned above, using a 15W-40 diesel oil is a solid choice, and quite budget friendly, for your location and engine. There are some really solid choices, with great additive packages and high HTHS (4.0 is excellent). 2.5 gallons for $36 locally. Hard to beat $14 per gallon price.

Rotella T6 5W-40 is a fav of mine. Great for all temps and works amazingly well in South Florida in air cooled engines that operate at 260ºF oil temps. Price is about $28 per gal locally.

 

[GI_GRIFF]

I have an 84 GMC Sierra and just had another engine put in, and the mechanic said run 30 weight in it all the time. I usually do 40 weight, of 15w40 Rotella since it is a used engine. I live in Arizona so would it hurt to go to a 15w40 all the time, and go up to a 20w50 in the summer or just stay with one weight?

Your ideas are not bad, but why not listen to your mechanic? Do you buy your oil at Walmart? Mobil 1 ESP 0W-30, Pennzoil Ultra Platinum 5W-30, or Castrol Edge 5W-30. The 0W or 5W-30 will protect you fine anywhere in the USA in any season. The highest
oil film strength would come from the Mobil 1 ESP 0W-30 as it is a ACEA C3 European spec. oil that require a >3.5 HTHS film strength. My next choice would be the Pennzoil Ultra Platinum or Platinum 5W-30. Pennzoil has that "Pure Plus" base stock people rave about plus many users say you may notice your engine running quieter using that oil. The 40 or 50 weights will not hurt your engine, but a 30 weight would be more than enough to protect your engine under stress, if you do stress it. If your mechanic put a turbo charged Porsche engine in your GMC pick-up and you have "track days" there may be better choices. LOL! Money and bang for your buck would be the Walmart Mobil 1 ESP 0W-30 usually on the shelf at Walmart, they have good prices on their 5 qt. jugs.

 

[OM617YOTA]

My truck has a similar-ish engine and has much better and steadier oil pressure at hot idle with 40w. I'd at least give that a shot.

 

[84gmcsierra]

Your ideas are not bad, but why not listen to your mechanic? Do you buy your oil at Walmart? Mobil 1 ESP 0W-30, Pennzoil Ultra Platinum 5W-30, or Castrol Edge 5W-30. The 0W or 5W-30 will protect you fine anywhere in the USA in any season. The highest
oil film strength would come from the Mobil 1 ESP 0W-30 as it is a ACEA C3 European spec. oil that require a >3.5 HTHS film strength. My next choice would be the Pennzoil Ultra Platinum or Platinum 5W-30. Pennzoil has that "Pure Plus" base stock people rave about plus many users say you may notice your engine running quieter using that oil. The 40 or 50 weights will not hurt your engine, but a 30 weight would be more than enough to protect your engine under stress, if you do stress it. If your mechanic put a turbo charged Porsche engine in your GMC pick-up and you have "track days" there may be better choices. LOL! Money and bang for your buck would be the Walmart Mobil 1 ESP 0W-30 usually on the shelf at Walmart, they have good prices on their 5 qt. jugs.

I do my own oil changes. I don't trust anyone else to do them as the last time they stripped the oil pan bolt on my old 65 Suburban Carryall. Anyways I was just curious about the oil I should use.

 

[hemitom]

So what is this crate motor ? details may help with a better recommendation

 

[GaryMX5]

I have to assume your mechanic has some reasons for suggesting 30 weight. Before making an arbitrary change I suggest you ask why he suggests that weight of oil. His experience could be that that motor is just fine with 5w or even 10w-30 oil in your climate. Heck, I remember when multi-weight oils first became popular and 10w-30 weight was the magic elixir used in climates across the country with regularity.

 

[ripcord]

A Chevy small block with good bearing clearances and oil pressure doesn't care if it's got 30 or 40 weight oil in it under normal circumstances. A 40 weight does give a little more margin when running on the edge of overheating.