Why drive gentle if hydrodynamic lubrication achieved?

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Omahaug

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Often the internet is full of people saying things along the lines of:
1. Is it true most wear occurs during start up?
2. How much oil is left on parts after the car is shut off for X hours?
3. Drive gentle after the car is started.

After the car is started, assuming wear does occur from corrosive byproducts of combustion, missing lubrication, whatever, why drive gently? I've literally seen someone say it takes up to ten minutes for oil to "warm up" to fully reach all parts of the engine (which to me is utter hogwash). I'm under the impression that with a good 5W or 0W full synthetic, the oil will be fully circulating in single digit seconds even on a single digit frigid day. If we already have hydrodynamic lubrication, why bother driving gentle?

My guesses:
* The tolerances are looser from the shrunken metal. Okay but does the oil not cover those spaces and how much could the metal shrink between critical wear parts to change the wearing characteristics? It's not like the piston is going to start rocking sideways in its cylinder right?
* There are parts where oil is not as thick or pressurized as it is between bearings? Anything splash lubricated or even between the piston and cylinder walls?

I'm fine with not hitting redline within three minutes of starting a car. I'm just wondering why people are saying we can't just drive normally, that we have to drive extra gentle. Seems to me that normal driving should be just fine. By "normal" I mean 2000-3000 RPM? I admit all of the talk has me mentally conditioned to drive around 1500-2000 RPM.
 
Originally Posted by PimTac
Some additives do not function until the oil is up to a certain temperature.


Right, I think that is the key during warmup.
 
It would take my GTI 10 minutes to reach 180F oil temp...during the summer. 20 minutes in freezing temps.

No WOT until that temp, just like the Porsche museum.
 
I drive gentle until the coolant is up to temp. Reason being... Have you ever heard of cold seizing in two strokes? This happens when the piston gets too hot too quick and gets tight in the still comparatively cold cylinder. Granted, we're talking about 4 strokes here that are naturally less susceptible due to their extra strokes between power strokes, but still this is why I take it easy until the coolant is up to temp at least.
 
Last edited:
Originally Posted by NoNameJoe

If we already have hydrodynamic lubrication, why bother driving gentle?


High thermal ramp rates are not good for other equipment that comprises the engine/transmission configuration. Nothing to do with the lubrication system or lubricant used, but rather, other components.

Of course this has to be contrasted with the cost of time simply spent idling, and additional fuel burned.
 
Allowing thermal expansion of the engine components to stabilize. A nice steady acceleration form startup to cruising speed works fine. Some parts warmup faster than others and this can cause issues with alignment and clearance issues if high rpms or boost is used to soon on a cold engine.
 
I plug in a "Scan Gauge 2" into my vehicles every now and then and drive around and see what sort of data the sensors pick up. What really gets me is the amount of time the Automatic Transmission Fluid takes to get to operating temperature. I definitely have made changes to my driving style; going a little slower in the winter months at first start up, not gunning the engine right a way. I think that helps the engine operate a little better.

Nuff said,

xtell
 
Originally Posted by xtell
I plug in a "Scan Gauge 2" into my vehicles every now and then and drive around and see what sort of data the sensors pick up. What really gets me is the amount of time the Automatic Transmission Fluid takes to get to operating temperature. I definitely have made changes to my driving style; going a little slower in the winter months at first start up, not gunning the engine right a way. I think that helps the engine operate a little better.

Nuff said,

xtell


Exactly

People don't realize that the transmission needs time to get up to temp before you can really start operating a vehicle in a stop-go environment.

I learned this when I took auto mechanics classes in high school and have never had a transmission problem nor engine failure.
 
Higher pressures system wide even with the 5W20 and more mild temps of my climate. I prefer to not go over 3k rpm for a least a few miles. In my head at least it keeps the filter out of bypass and is less stressful for any seals that would be under pressure.

Plus many of the things mentioned here before, metal expansion and all that. I do hardly ever crank the car and let it sit for a while. Always just crank and go..the wife however, she's been driving my 2003 Accord since her car got totalled and I think she idles that thing for about 20 min in the recent cold mornings we've been having. Ohh well, I'll get my daily driver back just as soon as we get her something else.
 
Drive gently for 8-10 min in summer and 15-17 min in winter. That is don't immediately get on freeway going 60-70 mph.
Some automatic cars, don't shift to overdrive or higher gear when cold.

stay away from used cars used for short trips to grocery store or work or mostly city driving or if driven by young males
lol.gif
 
Only the bearings rely solely on hydrodynamic lubrication. The pistons, rings, cam lobes, lifters/buckets, rockers, pushrods, valve guides, timing chain, etc... all rely on mixed and boundary lubrication where the additive package, most notably the extreme pressure, anti-wear and anti-friction additives, are far more important than the base oil. Those additives require heat and pressure to activate. In the cylinders, this isn't an issue as you have plenty of combustion heat to get things going early. The cylinders also account for about half of the engine's total friction so it's good the additives start working quickly there. This can be an issue with the valvetrain if not loaded as they are relying on sump temperature, which is near ambient, and not allowing for reactivity. That said, the high pressure points such as pushrod ends (in an OHV V-engine) rocker tips, lifter/lobe interface, etc... will create lots of pressure, and therefore heat, to get activation early on in those areas.

This is where your boutique oils tend to be superior in that they tend to use (more expensive) additives that are more reactive at lower temperature and pressure. ZDDP with secondary alkyl groups, trinuclear MoDTC plus highly reactive moly-sulfur complexes, and so on. Those oils wouldn't pass API specs because they'd exceed the 0.6% sulfur and 800 ppm phosphorus limits.

The reason I wouldn't hammer on an engine with cold (foaming.
 
Last edited:
Originally Posted by NoNameJoe
Often the internet is full of people saying things along the lines of:
1. Is it true most wear occurs during start up?
2. How much oil is left on parts after the car is shut off for X hours?
3. Drive gentle after the car is started.

After the car is started, assuming wear does occur from corrosive byproducts of combustion, missing lubrication, whatever, why drive gently? I've literally seen someone say it takes up to ten minutes for oil to "warm up" to fully reach all parts of the engine (which to me is utter hogwash). I'm under the impression that with a good 5W or 0W full synthetic, the oil will be fully circulating in single digit seconds even on a single digit frigid day. If we already have hydrodynamic lubrication, why bother driving gentle?

My guesses:
* The tolerances are looser from the shrunken metal. Okay but does the oil not cover those spaces and how much could the metal shrink between critical wear parts to change the wearing characteristics? It's not like the piston is going to start rocking sideways in its cylinder right?
* There are parts where oil is not as thick or pressurized as it is between bearings? Anything splash lubricated or even between the piston and cylinder walls?

I'm fine with not hitting redline within three minutes of starting a car. I'm just wondering why people are saying we can't just drive normally, that we have to drive extra gentle. Seems to me that normal driving should be just fine. By "normal" I mean 2000-3000 RPM? I admit all of the talk has me mentally conditioned to drive around 1500-2000 RPM.
 
Last edited:
Originally Posted by RDY4WAR
...
The reason I wouldn't hammer on an engine with cold (foaming.


Good to know. I still have to think about it a little ...
For some reason, I would have guessed the opposite. You know like hot water and laundry detergent additive vs. cold water
grin2.gif
 
Originally Posted by pschnahc
Yeah flogging on cold shrunken pistons is just asking for scuffed up skirts especially before AW adds come online.

Absolutely-that's the one noise, even using Magnatec, that the 4.6 in my sig still has. There's audible slap, either pistons or wrist pin noise, for about the first mile (or less in summer), the aluminum pistons need to expand to fit the bore. When it's warmed up completely, can barely hear it running.
 
Originally Posted by Bryanccfshr
Allowing thermal expansion of the engine components to stabilize. A nice steady acceleration form startup to cruising speed works fine. Some parts warmup faster than others and this can cause issues with alignment and clearance issues if high rpms or boost is used to soon on a cold engine.

It's not talked about much these days but in the olden days piston and cylinder liner clearances where the reason for being easy during warm up.
 
An engine would certainly have pretty uneven heating. Is there data from a fully instrumented engine that shows this ?
Also, how much time does a transmission or differential take to get to a point where it has hydrodynamic lubrication ? I would think it would take considerably longer than the engine, but that's only speculation.
 
Originally Posted by RDY4WAR
Only the bearings rely solely on hydrodynamic lubrication. The pistons, rings, cam lobes, lifters/buckets, rockers, pushrods, valve guides, timing chain, etc... all rely on mixed and boundary lubrication where the additive package, most notably the extreme pressure, anti-wear and anti-friction additives, are far more important than the base oil. Those additives require heat and pressure to activate. In the cylinders, this isn't an issue as you have plenty of combustion heat to get things going early. The cylinders also account for about half of the engine's total friction so it's good the additives start working quickly there. This can be an issue with the valvetrain if not loaded as they are relying on sump temperature, which is near ambient, and not allowing for reactivity. That said, the high pressure points such as pushrod ends (in an OHV V-engine) rocker tips, lifter/lobe interface, etc... will create lots of pressure, and therefore heat, to get activation early on in those areas.

This is where your boutique oils tend to be superior in that they tend to use (more expensive) additives that are more reactive at lower temperature and pressure. ZDDP with secondary alkyl groups, trinuclear MoDTC plus highly reactive moly-sulfur complexes, and so on. Those oils wouldn't pass API specs because they'd exceed the 0.6% sulfur and 800 ppm phosphorus limits.

The reason I wouldn't hammer on an engine with cold (foaming.


Great post.

Although I wouldn't say boutique oils are superior in this area.
 
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