Oil “flowing fast enough”

[doublebase]

Can someone explain to me how a 20wt oil would flow compared to a 40wt oil in an engine sepc’d for 20wt? I guess the question I’m asking is...would it damage the engine to use a 40wt oil in a severe oil burner that is spec’d for a 20wt (in a warm climate with no worry of cold starts).

I’d love it to be as technical as possible. With evidence leaning towards that it is no issue to use the 40wt. I believe it’s been discussed. I’ll search, but any fresh insight would be appreciated, because someone just told me the “engine would blow up if a 40wt was put into a particular V8 that is spec’d for a 20, because it wouldn’t flow fast enough”.

 

[RDY4WAR]

The 40 grade will have reduced flow at bearing exit. Exactly how much is difficult to say. You likely wouldn't have an issue.

Addressing the real issue here of the oil burning, note that a higher viscosity may not solve the problem. In fact, it can make it worse in cases of stuck rings where the greater film thickness allows more oil transport past the rings into the chambers.

I would recommend looking for ways to address the source of the oil consumption instead of just jumping to a higher viscosity. Something like a quart of High Performance Lubricants Engine Cleaner SAE 30 in Mobil 1 0W-40 would clean very well, help condition old seals, and possibly improve ring seal if coked rings are causing the consumption. That's the route I would go.

 

[doublebase]

The 40 grade will have reduced flow at bearing exit. Exactly how much is difficult to say. You likely wouldn't have an issue.

Addressing the real issue here of the oil burning, note that a higher viscosity may not solve the problem. In fact, it can make it worse in cases of stuck rings where the greater film thickness allows more oil transport past the rings into the chambers.

I would recommend looking for ways to address the source of the oil consumption instead of just jumping to a higher viscosity. Something like a quart of High Performance Lubricants Engine Cleaner SAE 30 in Mobil 1 0W-40 would clean very well, help condition old seals, and possibly improve ring seal if coked rings are causing the consumption. That's the route I would go.

The engine has been described as burning 2.5 quarts every 1,000 miles and was told his engine is cooked.

Guy is looking to squeeze out another 100,000 miles and will not do an engine replacement. Think it has 180,000 miles or so. Aside from a cleaner to free up rings, in a warm climate, I can’t imagine a 40wt would blow up an engine (at least from what I’ve read around here). I tried searching, went through a ton of posts. Best I could come up with is at operating temperature in a closed system, the difference between a 20wt and a 40wt is not all that much and that an oil pump controls flow and pressure. That about right?

 

[RDY4WAR]

The engine has been described as burning 2.5 quarts every 1,000 miles and was told his engine is cooked.

Guy is looking to squeeze out another 100,000 miles and will not do an engine replacement. Think it has 180,000 miles or so. Aside from a cleaner to free up rings, in a warm climate, I can’t imagine a 40wt would blow up an engine (at least from what I’ve read around here). I tried searching, went through a ton of posts. Best I could come up with is at operating temperature in a closed system, the difference between a 20wt and a 40wt is not all that much and that an oil pump controls flow and pressure. That about right?

When consumption reaches a rate of 1 quart every 400 miles, the likelihood of reviving the engine with chemical cleaning and conditioning is slim. That high of consumption leads me to think the rings are toast with a lot of metal fatigue, loss of tension, and opened gaps. Such a case would make it more likely that something like a 40 grade would actually increase consumption.

What engine specifically are we talking about? Some engines with VVT may notice some changes in engagement due to the higher viscosity, particularly when the engine's cold, but the 40 grade itself won't otherwise cause a problem in an engine meant for a 20 grade. At least, not in the sense of street driven commuter vehicle. If we were talking high end racing engines with 300°F oil temps and 8000+ rpm, then the increased hydrodynamic friction from the 40 grade with 20 grade clearances could increase bearing fatigue. For a commuter engine though, aside from a possible 0.5-1% mpg drop, there wouldn't be an issue.

Whoever said “engine would blow up if a 40wt was put into a particular V8 that is spec’d for a 20, because it wouldn’t flow fast enough” is vastly overestimating the impact of flow. Most oil pumps are positive displacement so you're going to get the same "flow" from the pump regardless of viscosity, minus some minor viscous losses. The pump only controls the max pressure by way of a relief spring and valve. Pressure is a function of resistance to flow so a more viscous oil, that will have reduced flow at the end of the system, will create more pressure. It's not going to harm anything though. The most it'll do is put a little extra stress on the pump drive. This is especially true living in a warmer climate where the oil doesn't get cold enough to matter much. It's cold starts where flow at bearing exit is most important. Once warmed up, the difference between a 20 grade and 50 grade isn't (relative) all that much. A 0W-20 cranking up in 100°F is 2-3x more viscous than a 20W-50 at 212°F operating temp.

 

[atikovi]

Can someone explain to me how a 20wt oil would flow compared to a 40wt oil in an engine sepc’d for 20wt?

What 20wt? 5W20? 0W20? What 40wt? 20W40? 15W40? 10W40? 5W40? 0W40? Lot info you're leaving out. I've used 5W50 in engines spec'd for 5W30 with no issues.

 

[wpod]

We certainly have this flow thing on the brain. What most matters is the flow when the engine and oil is cold and is the oil being drawn to the oil pump . There are charts for the temps oils are good for. Thicker oil has a "thicker" oil film or wedge, thinner oil leaks from the bearings faster than thicker oil.

 

[wpod]

What 20wt? 5W20? 0W20? What 40wt? 20W40? 15W40? 10W40? 5W40? 0W40? Lot info you're leaving out. I've used 5W50 in engines spec'd for 5W30 with no issues.

The W part is the important factor for oil flow during start up and warm up. Once the oil is at operating temps, the oils will be fine. We can get into the inefficiencies of too thick of an oil and or the protection the oil provides. It is wonderful that a 0, 5, 10, 15, 20 w oil can be used year round depending on the coldest startup temps year round .

 

[BigShug681]

The W part is the important factor for oil flow during start up and warm up. Once the oil is at operating temps, the oils will be fine. We can get into the inefficiencies of too thick of an oil and or the protection the oil provides. It is wonderful that a 0, 5, 10, 15, 20 w oil can be used year round depending on the coldest startup temps year round .

So would a 5w20 and a 5w40 behave the same at cold temps since both share the 5W part?

 

[kschachn]

So would a 5w20 and a 5w40 behave the same at cold temps since both share the 5W part?

It is completely dependent on the temperature. “Cold temps” isn’t an absolute. But they would both pass the cranking and pumpability performance requirements for an oil with a 5W winter rating.

 

[BigShug681]

It is completely dependent on the temperature. “Cold temps” isn’t an absolute. But they would both pass the cranking and pumpability performance requirements for an oil with a 5W winter rating.

Ok thank you

 

[doublebase]

What 20wt? 5W20? 0W20? What 40wt? 20W40? 15W40? 10W40? 5W40? 0W40? Lot info you're leaving out. I've used 5W50 in engines spec'd for 5W30 with no issues.

Let’s say a 5w40 or 0w40 for Southern California temps.

So, going from a 5w20 or 0w20 in an engine that is consuming 2.5 quarts every 1,000 miles - and was told the engine needs reacment because it is “worn out” - taking a chance on heavier weight oil.

 

[c502cid]

There is zero to lose here. Try it.

 

[kschachn]

Let’s say a 5w40 or 0w40 for Southern California temps.

So, going from a 5w20 or 0w20 in an engine that is consuming 2.5 quarts every 1,000 miles - and was told the engine needs reacment because it is “worn out” - taking a chance on heavier weight oil.

Both those are 20-grade oils. And exactly what kind of “chance” are you taking with a higher grade? No engine is threatened nor damaged from an oil with a higher HT/HS.

Consuming 2.5 quarts in 1000 miles is catastrophic consumption. No oil will fix that. None. You’re dreaming if you think so.

 

[OVERKILL]

Does it smoke?

A solvent Hail Mary pass by doing a B12 piston soak, if it is ring coking, this MIGHT yield some improvement, and if it does, then a cleaner might improve it further, like what @RDY4WAR noted.

 

[atikovi]

If it ain't smoking to the point where cops pull you over regularly, just add the oil and keep driving it. Never worth the money replacing or rebuilding the engine on a beater unless you can diy.

 

[OVERKILL]

If it ain't smoking to the point where cops pull you over regularly, just add the oil and keep driving it. Never worth the money replacing or rebuilding the engine on a beater unless you can diy.

My buddy did exactly that (DIY) with his beater Saturn. He was working in an auto parts store with a machine shop in the back. Pulled the pistons, cleaned out the ring lands, and put it back together as it was, lol. Fixed the consumption problem. Can't remember what he ran in it after that, might have been M1 0W-40? As I was probably pushing it even that far back, lol.

 

[DuckRyder]

I’d give “so we are all buying Toyotas” a read.

What particular v8 is this?

 

[doublebase]

Both those are 20-grade oils. And exactly what kind of “chance” are you taking with a higher grade? No engine is threatened nor damaged from an oil with a higher HT/HS.

Consuming 2.5 quarts in 1000 miles is catastrophic consumption. No oil will fix that. None. You’re dreaming if you think so.

It’s not my car, but the topic was that the engine would “blow up” if a 40 weight was used. You say it won’t, I say it won’t either. The engine, for all purposes is toast. The guy is trying to get another 70,000 out of it without repair. I suggested going to a 40 weight. Was told the engine would blow up because of “flow”.
I guess what I’m asking is, what is the difference in viscosity at operating temp and will that cause an engine to blow up?

 

[CentAmDL650]

Let's say a 5W40 or 0W40 for Southern California temps.

It won't blow up under normal circumstances, but it's likely so worn that a few trips up to redline just might do it. But that would likely happen no matter which oil got used.

But if it's burning 2.5 quarts per 1000 miles there is zero way that vehicle can pass an annual California state emissions test. Way too much hydrocarbons in the exhaust stream. Even if it could be cut in half, it likely still could not come close to passing. The state would label the vehicle as a gross polluter. The guy wants to get another 70k miles out of it without repair? Not if CARB has anything to say about it (and they do). Tell him to keep dreamin.

 

[atikovi]

My buddy did exactly that (DIY) with his beater Saturn. He was working in an auto parts store with a machine shop in the back. Pulled the pistons, cleaned out the ring lands, and put it back together as it was, lol. Fixed the consumption problem. Can't remember what he ran in it after that, might have been M1 0W-40? As I was probably pushing it even that far back, lol.

Yep, bought a nice looking $200 86 Camry that was smoking like a mosquito fogger. Had some cracked rings or piston grooves, so replaced them all in the driveway. Sold and delivered 800 miles afterwards so I know I did a good job.