10W40

[A10WartHog]

I recedntly passed on 1991 S15 Jimmy to my son. It has the 4.3Lv6with which has 180000 miles on it. I have always used a 10w30 oil during oil changes. Owners manual specially states not to use a 40 weight oil. However, he put in QS Defy 10w40 during the last oil change. Will that weight be okay until the next oil change or do should I go ahead and change it now? Did not know if the flow characteristics of todays 40 weight oils vs yesterdays have improved enough so as a 40W could be used.

Thanks

 

[addyguy]

The 10W-40 will be just fine for that engine, especially in a warmer southern climate. Run it as you normally would.

I've read more than once that one of the reasons GM banned 10W-40 and 20W-50 from their engines is that they needed their fuel economy scores to go up in the early 1980's, so they started spec'ing 5w30 oils.

However, lots of people still used 10W-40 in their engines, and got lower mileage than they should have. So GM banned thicker oils from use so people would be forced to use 30-weights and get the mileage they should have.

A second reason I have read is that 10W-40's from the 1970's used a lot of poor-quality VII's to make the spread, and these broke down and made sludge and ring sticking a problem. So GM banned them from engines to stop this problem.

Modern 10W-40's of any kind aren't a problem any more, so you are fine.

 

[A_Harman]

40 weight viscosity specs haven't changed since 1991.
But if the engine runs good with the 40-weight, I don't see a need to change it immediately. Go back to 10w30 on the next change.

What addyguy said is true: VII's have improved a lot since the 1970's.

 

[ARCOgraphite]

I don't recall if this year engine has the roller cam with GM's version of "rhoades-style" fast bleed down lifter. If so the bleed down rate will be wrong with sae40 and you'll loose some low end torque and fuel economy.

 

[OVERKILL]

Originally Posted By: ARCOgraphite
I don't recall if this year engine has the roller cam with GM's version of "rhoades-style" fast bleed down lifter. If so the bleed down rate will be wrong with sae40 and you'll loose some low end torque and fuel economy.


If that was the case you'd lose significant power just running it in the winter. Viscosity change with temperature on a given grade is more than the difference between an xX-30 and an xW-40 at 100C.

 

[KCJeep]

Won't hurt a thing but it is mighty thick, have him use a 30 grade Defy next time around.

 

[danthaman1980]

Defy is known to be thick for grade; Defy 10W-40 is right in between your normal 10W-40s and 20W-50s.

It certainly won't hurt anything, but won't help you much in the cold start and fuel economy arenas. If it were mine, I'd use a 'thick thirty' next time; Defy xW-30 or Rotella T5.

 

[TFB1]

Originally Posted By: OVERKILL
Originally Posted By: ARCOgraphite
I don't recall if this year engine has the roller cam with GM's version of "rhoades-style" fast bleed down lifter. If so the bleed down rate will be wrong with sae40 and you'll loose some low end torque and fuel economy.


If that was the case you'd lose significant power just running it in the winter. Viscosity change with temperature on a given grade is more than the difference between an xX-30 and an xW-40 at 100C.


Bingo, so many old wives tales here on BITOG it's sometimes like walking through a minefield...

 

[Chris142]

Meh. The 10w40 will break down into a 10w30 pretty soon anyway. Plus i have several cases of it in my garage.

 

[cknight49090]

some lifters are sensitive to what viscosity you use especially vvt engines the newer ford engines come to mind even if using 5w30 instead of 5w20.But on that 4.3 I doubt it makes much difference I would use 5w30 myself.

 

[OVERKILL]

Originally Posted By: cknight49090
some lifters are sensitive to what viscosity you use especially vvt engines the newer ford engines come to mind even if using 5w30 instead of 5w20.But on that 4.3 I doubt it makes much difference I would use 5w30 myself.


No they aren't, or they wouldn't work in places like Canada, lol

VVT systems are often controlled by oil pressure, certainly. But oil temperature has a far greater effect on viscosity than what is written on the bottle.

 

[Shannow]

I'm interested how the Ford lifters/cam phasers were retroed onto OP's Jimmy truck...that's some engineering.

 

[benjy]

older worn engines can benefit from heavier oils depending on its oil pressure. todays 5-20 waters are for MPG's not for best protection IMO

 

[Zaedock]

Originally Posted By: benjy
todays 5-20 waters are for MPG's not for best protection IMO


That would be your opinion. Millions of engines running 20wts would disagree.

 

[Shannow]

No, the OEMs say it's for economy and greenhouse while "still offering adequate protection", not just opinion, their mission statement.

 

[ARCOgraphite]

Originally Posted By: TFB1
Originally Posted By: OVERKILL
Originally Posted By: ARCOgraphite
I don't recall if this year engine has the roller cam with GM's version of "rhoades-style" fast bleed down lifter. If so the bleed down rate will be wrong with sae40 and you'll loose some low end torque and fuel economy.


If that was the case you'd lose significant power just running it in the winter. Viscosity change with temperature on a given grade is more than the difference between an xX-30 and an xW-40 at 100C.


Bingo, so many old wives tales here on BITOG it's sometimes like walking through a minefield...
Its about performance when at OP temp . All FE will suffer during cold/warmup. This illogical argument would make all multigrades KV100 spec essentially meaningless then.

 

[OVERKILL]

Originally Posted By: ARCOgraphite
Originally Posted By: TFB1
Originally Posted By: OVERKILL
Originally Posted By: ARCOgraphite
I don't recall if this year engine has the roller cam with GM's version of "rhoades-style" fast bleed down lifter. If so the bleed down rate will be wrong with sae40 and you'll loose some low end torque and fuel economy.


If that was the case you'd lose significant power just running it in the winter. Viscosity change with temperature on a given grade is more than the difference between an xX-30 and an xW-40 at 100C.


Bingo, so many old wives tales here on BITOG it's sometimes like walking through a minefield...
Its about performance when at OP temp . All FE will suffer during cold/warmup. This illogical argument would make all multigrades KV100 spec essentially meaningless then.


You don't get what I'm saying, I'm not talking about warm-up or cold starts. My argument isn't illogical at all, you positing that GM uses some funky style viscosity sensitive lifter is what is illogical here.

Ambient temperature has an effect on oil temperature on an exposed pan application without a coolant/oil heat exchanger. And even with a heat exchanger, based on my experience with the M5, that effect is still present, just not as significant.

On a 30C day, let us say that oil temperature gets up to 100C.

M1 5w30: 11.0 cSt
M1 10w-40: 14.71 cSt

On a 25C day, let us say that the oil temperature gets up to 95C.

M1 5w30: 12.23 cSt

On a 20C day, let us say that the oil temperature gets up to 90C.

M1 5w30: 13.68 cSt

On a 15C day, let us say that the oil temperature gets up to 85C.

M1 5w30: 15.38 cSt

You following yet?

So, on our 15C day, the 5w30 actually has a higher KV than the 10w-40 does on the 30C day. Why? Because viscosity correlates with temperature! And since oil temperature has a relationship with ambient, that engine spends much of its time operating with an oil that is heavier than a 10w-40 at 100C. So for many months of the year, when the ambient temperature is cooler, that engine is in effect, running a heavier lubricant due to lower oil temperatures.

If what you posit is true, those lifters would be "malfunctioning due to improper bleed down rates" for half the bloody year! Do you honestly expect anybody to believe that GM is so inept that they'd design something like that? I know I don't.

 

[Rand]

arco man. oil isnt thermostat controlled. It can take upto 30min of driving for the oil temp to stabilize and even then it can vary widely between city and highway driving(and engine load)


just another post of meaningless turds wrapped up in technical language . Did your butt dyno detect this like it did the sticktion?