Engine Warm-Up Discussion.

[serversurfer]

Originally Posted By: demarpaint
Interesting topic. My question is how does leaving the transmission in neutral load the engine?

Oh, sorry, I meant that leaving the transmission in neutral avoids loading the engine. I suspect this is preferable to loading the engine by engaging the transmission and actually driving around, because Shannow was saying that "load" moves us away from hydrodynamic lubrication — where we want to be — towards boundary lubrication — where we don't want to be.

So my method of speed-without-load should keep us towards the rightmost/happiest side of the graph until the system reaches nominal operating parameters. (e.g. temperature, viscosity, etc.) But all of this assumes I understood what Shannow actually meant by "load."

 

[Jetronic]

over half the load on the bearings comes from the engine's own inertia, the higher the rpm the more load you get.

 

[demarpaint]

Originally Posted By: serversurfer
Originally Posted By: demarpaint
Interesting topic. My question is how does leaving the transmission in neutral load the engine?

Oh, sorry, I meant that leaving the transmission in neutral avoids loading the engine. I suspect this is preferable to loading the engine by engaging the transmission and actually driving around, because Shannow was saying that "load" moves us away from hydrodynamic lubrication — where we want to be — towards boundary lubrication — where we don't want to be.

So my method of speed-without-load should keep us towards the rightmost/happiest side of the graph until the system reaches nominal operating parameters. (e.g. temperature, viscosity, etc.) But all of this assumes I understood what Shannow actually meant by "load."

I got it now, thanks!

 

[serversurfer]

Originally Posted By: Jetronic
over half the load on the bearings comes from the engine's own inertia, the higher the rpm the more load you get.

Sorry, but I'm not really sure what point you're making here. I had assumed that nearly all of the load on the bearings would be the result of arresting the inertia of the pistons, and that the more force being applied to the pistons, the more load there would be for the bearings to resist. Are you saying that when I'm turning 3k in the driveway and making less than 10 HP, the loads on the pistons and bearings are roughly the same as when I'm turning 3k up the hill and making better than 40 HP? That's very counterintuitive to me, so can you explain why this is the case?

I'm not sure if you're arguing that I'm not making a significant improvement by leaving the car in neutral, or that Shannow is simply wrong about speed improving things because the increased loads generated by revving the engine higher — even in neutral — always pull you more to the left than the right, meaning we should all be idling up to NOT instead, or what you're really getting at.

 

[Jetronic]

The load rises quicker than the oil film thickness, so in a constant speed environment like the bearings you could be going left in the stribeck curve, especially at very high rpm. for the pistons, you'll generally be moving right with higher speed. Valve train also could use some more speed but that's because they turn half rpm and very small diameters.

But yes, 3k rpm at 10 hp or 3k rpm at 40 hp is roughly the same for the bearings. I'd wager no more than 25% difference, which is very short of the implied 300% difference.

 

[serversurfer]

Originally Posted By: Jetronic
The load rises quicker than the oil film thickness, so in a constant speed environment like the bearings you could be going left in the stribeck curve, especially at very high rpm. for the pistons, you'll generally be moving right with higher speed. Valve train also could use some more speed but that's because they turn half rpm and very small diameters.

But yes, 3k rpm at 10 hp or 3k rpm at 40 hp is roughly the same for the bearings. I'd wager no more than 25% difference, which is very short of the implied 300% difference.

Okay, so by leaving the car in neutral, I'm only reducing the load on the bearings by ~25%. That strikes me as somewhat significant, but you're arguing that it isn't? To what end though? Are you saying that I'm mostly just wasting my time with my minimal reduction in load, and I should immediately drive away like Shannow does, or that we're both fools, and we should be letting our cars idle up to NOT?

Also, what makes the bearings a "constant speed environment"? They don't spin faster as the rest of the engine does? I'd assumed they'd spin at the same speed as the shaft to which they were affixed.

 

[Jetronic]

bearings spin at the rpm of the engine, for the wole of the revolution. Pistons don't spin, and go from standing still to max speed to standing still, to max speed in the opposite direction and back to standing still in 1 revolution of the engine.

Cams have slower surface speeds when the valve is closed, higher speeds when they are pushing the valve open, although their rpm is also constant.

No cooment on the heating up of the engine. You should do what makes you feel better.

I prefer to wait (in winter) until I get enough heat from the HVAC to keep the windows clear rather than driving blind. In summer, I start the engine, put on my seatbelt, check the mirrors and for warning lights on the dash, then I'm off with a light load on the engine.

My car has a turbo, and I prefer to keep turbo pressure (and thus turbo shaft speed) low until the engine is fully warm. I also prefer that the head (aluminium) and block (cast iron) get up to temp gradually and equally, considering the difference in thermal expansion. Changing the head gasket is a big thing on these modern DOHC turbo engines, can certainly ruin my weekend!

 

[serversurfer]

Originally Posted By: Jetronic
bearings spin at the rpm of the engine, for the wole of the revolution. Pistons don't spin, and go from standing still to max speed to standing still, to max speed in the opposite direction and back to standing still in 1 revolution of the engine.

Cams have slower surface speeds when the valve is closed, higher speeds when they are pushing the valve open, although their rpm is also constant.

Ah, I see what you mean. Thanks for clarifying.
But while the bearing speed is constant at a given RPM, what we're discussing here is the possibility of increasing the RPMs to facilitate lubrication. So while a given bearing will flow a given amount of oil at 3k RPM, that'll still be more than was flowing through it at 1k RPM, right? And if, as you say, the loads on the bearing are fairly stable whether the engine is doing work or not, then spinning the bearing faster should move us firmly rightward on the Stribeck curve, since the load doesn't increase much in proportion? So it sounds to me like spinning the bearings faster is a net win, even if you load the engine in the process.

Also, per Shannow's graph, it looks like the bearings are actually the least of our concerns here, as they mostly hang out in the HD zone, barely dipping in to EHD during low-speed/high-load conditions. Meanwhile, the rings and liners barely make it out of EHD, and the cam barely makes it in from Mixed. With the cam and cylinders spending so much time in Mixed or even Boundary lubrication, I figured that's where most of our wear was actually occurring, and that's where we'd mostly be concerned with our relative position on the curve. (Even under the worst conditions, the bearings barely slip in to EHD, so our primary concern is actually getting the pistons and cams even that well lubed. Right?)

Quote:
No cooment on the heating up of the engine. You should do what makes you feel better.

Well, I was trying to do what makes my engine feel better, and science usually points me in the right direction!

Quote:
I prefer to wait (in winter) until I get enough heat from the HVAC to keep the windows clear rather than driving blind. In summer, I start the engine, put on my seatbelt, check the mirrors and for warning lights on the dash, then I'm off with a light load on the engine.

My car has a turbo, and I prefer to keep turbo pressure (and thus turbo shaft speed) low until the engine is fully warm. I also prefer that the head (aluminium) and block (cast iron) get up to temp gradually and equally, considering the difference in thermal expansion. Changing the head gasket is a big thing on these modern DOHC turbo engines, can certainly ruin my weekend!

Wouldn't the increased flow of coolant and oil at higher RPM help to better equalize the temperature of disparate components like the head and the block by ferrying that much more heat between them?

 

[wemay]

Originally Posted By: MolaKule
Quote:
If so, why doesn't the ECU just do this on its own?


My Nissan Frontier does just that, idles the engine at about 1800 RPM until the engine warms up and then drops the idle to about 700 RPM.


I always wondered why my start-up RPMs were higher.

 

[Shannow]

wemay, it's nominally to get the cats firing quicker, but there's also some papers to suggest that it's to get the oil thinner quicker.

 

[wemay]

 

[Jetronic]

Originally Posted By: Shannow
wemay, it's nominally to get the cats firing quicker, but there's also some papers to suggest that it's to get the oil thinner quicker.


Isn't that counter productive? You want the oil thinner so consumption drops, and to do that you increase fuel consumption at a time the engine efficiency is 0%...

 

[FCD]

Atleast from my experience my cars warm up way slower idling than driving, that is why i never warm up regardless of temperature.
Not even when i go to Finland in winter, my aunt's Corolla 1.6 VVTi starts right up regarrless of temperature and i drive off after 15 seconds, the engine is warmed up completely by 10 or 15 minutes even on -30C morning starts.

 

[SatinSilver]

The Matrix which is basically a Corolla starts up LOUD. So the rpms drop when I put it into drive. So the quicker I do that the better as far as noise goes. I get heat pretty quick. Used every day even in sub zero temps. Burrrrr.

Glad summer is finally here!