5w-20 In A '92 4.3L Chevy?

No, 5W-30 is the preferred oil for you engine. You can use a 0W-30 or a 10W-30 but a 5W-20 is not on the GM recommmended oil list.

I don't know of any GM model that uses it. IMO 5W-20 is for fuel economy.

Mike,

Good afternoon. Yes, I realize 5w-30 is the preferred year-round viscosity for my "light-duty" 4.3L.

Outside of individual opinion though, and disregarding GM's broad stroke recommendation, what reasoning could one use to evaluate whether 5w-20 would be an acceptable viscosity for my particular engine?

Question for AEHaas

http://members.rennlist.com/oil/Motor%20Oil%20101.htm

The current "ultimate" oil is Redline 5W20 with HTHS of 3.3 which will cure all known problems!

However your psi is low.

It is interesting that this type of oil is used in F1, although long life is not a high priority, it is a weekend of being near the limit.

quote:

Originally posted by Leojle:
Just something I was thinking about...

According to GM, the oil pressure specification for my 4.3L V6 is as follows:

Minimums:
6psi @ 1000rpms
18psi @ 2000rpms
24psi @ 4000rpms

Now, I have no tachometer in my truck, but running Castrol HM 5w-30, it's at about 31psi doing seventy miles per hour and 16 at idle (both when engine is fully hot).

With this in mind, wouldn't it be plausible for me to consider using a 5w-20?

Well there goes the 10 psi per 1000 rpm thumb rule.

These specified pressures do seem a bit on the low side to me. I don't think you have a thing to worry about, but if you wanted to thin out a bit, I think the HM oils are on the thick end of 30 wt. Mobil 1 and Havoline Synthetic 10w30s both list around 10 cst, whereas the HM might be closer to 12 (look it up on the Castrol site). Maxlife HM is listed at 10.5 cSt.

quote:

Originally posted by TallPaul:
These specified pressures do seem a bit on the low side to me.

Ditto here Paul, as it goes against the aforementioned adage of 10psi per 1000rpm's, but who am I to argue against GM's minimum pressure specification?

Deviating from the recommended viscosity is another story though...

I'd like to add that, at this point, usage of a 5w-20 in my 4.3L is more of an exercise in probability at the moment as it suffers from faulty valve seals, which is a common issue with this particular engine.

For this reason, I'm currently using Castrol HM 5w-30 and it's treated me exceptionally well in comparison to the various other oils I've used.

If anything, I may consider experimenting with a GF-4 high-mileage product (Mobil Clean High Mileage, for example) in the immediate future to optimize efficiency as much as possible.

I'm still void of any reason though as to why I shouldn't run a 5w-20 in this engine once I undertake the valve seal replacement...

quote:

Deviating from the recommended viscosity is another story though...

You may change the word "recommended" by "released" to understand your owners manual. This is what the guys from GM Powertrain mean when they say "recommend".

quote:

Originally posted by Callisa:

quote:

Deviating from the recommended viscosity is another story though...

You may change the word "recommended" by "released" to understand your owners manual. This is what the guys from GM Powertrain mean when they say "recommend".

I suspect what you are getting at is that the "released" publication on what oil to use is not strictly what the engineers would put in the engine, but a compromise to also satisfy the GM legal team and public relations team. Have to make sure they avoid lawsuits and must dumb down the recommendation so the least intellegent element of the public can understand it. A single viscosity grade recommentation removes all doubt for those who couldn't care less about oil, but that the car runs, but raises many doubts for those of us who think about these things too much.

@Leojle
Nice picture. But it is somehow wrong. One should use 0W-w oils below -25°C. See SAE J300 Spec.

quote:

Originally posted by Callisa:
@Leojle
Nice picture. But it is somehow wrong. One should use 0W-w oils below -25°C. See SAE J300 Spec.

Callisa,

Good evening.

While SAE J300 dictates the five viscosity parameters an oil must meet to be labeled with the correct grade designation, it has absolutely nothing to do with proper application. These decisions are left to the O.E.M.

While I do agree with you that a 0w synthetic engine oil will have significantly improved ambient temperature flow properties relative a 5w conventional lube, GM, back in '92, made no differentiation between the two, solely staying with the two most common grades.

In regards to your post, J300 states that a 5w must have a low temperature cranking viscosity mPa-s max of 6600 at -30°C and a low temperature pumping viscosity max of 60000 at -35°C. Combine this with the pour points of modern mineral-based 5w's, and while not the most ideal, I'd have no qualms with using a 5w-30 at -25°C.