Running uphill in 6th gear == bad for oil?

[Lyman]

Originally Posted By: blackman777
Jetta. I filled the tank with 91 last time so knocking shouldn't be a problem. The engine sounded nice and smooth. I don't shift down & up in order to avoid clutch wear/replacement. I just ride 6th gear all the way to work (unless there's a jam on the highway).

IMHO it would be easier on your car to down shift. Keep it in the peak torque range for going up hills. It is NOT going to wear your clutch out shifting your car. Clutch wear comes from slipping it on take off and riding it like a lot of new drivers will tend to do. I am a truck driver and have yet to wear out a clutch without having over a few hundred thousand miles on it. And in the work trucks that I have driven they sometimes will last 500,000 miles or better.

 

[blackman777]

I followed your suggestion of backing off the throttle until the MPG gauge increased from 20 to 22.5. The car held a steady 72mph up the mountain.

 

[Eddie]

Gotch:This is the first time I have heard of "Lugging" explained like this. Do you have a reference paper we can review? I also have read that an engines maximum efficiency (lbs of fuel per HP)occurs at the max BMEP. I do know that maximum BMEP is the maximum stress on the rotating engine parts, but, engines are designed for this. Ed

 

[Clevy]

Originally Posted By: blackman777
I've heard that turbos can "rev too high" if you push them too hard (while below 2000) but maybe that's just a flaw with VW's TDI engines?




Rev too high. Is this for real?
Carnoobie....or ght's close cousin maybe.

 

[blackman777]

TDIclub posters claim it is. "Don't rev below 2000 as the turbo will try to produce boost and spin too high. Downshift to bring the rpms above 2000 and save your turbo." (shrug)

 

[ueberooo]

Originally Posted By: Eddie
I also have read that an engines maximum efficiency (lbs of fuel per HP)occurs at the max BMEP. I do know that maximum BMEP is the maximum stress on the rotating engine parts, but, engines are designed for this. Ed


Again, this is not true. In most engines, maximum efficiency occurs near WOT (i.e. not too far from max BMEP), but not at WOT.

(If you could reprogram the computer into not burning overly rich, then perhaps you could get max efficiency at WOT. )

 

[KitaCam]

Efficience is not the same as effectiveness...running WOT uphill in top gear allows for little room to accelerate quickly if needed...just not a SAFE way to drive...

Dropping down a gear increases available RPMS with more throttle, leaving WOT available if you need it in an emergency.

 

[aussiek2000]

Best economy at WOT? Do you guys know anything about cars?


WOT kicks the PCM into open loop. Turns off the EGR, quits using oxygen sensor input, and widens injector pulse width, spark timing is retarded to reduce knock. Lugging a gas engine at WOT is the worst economy short of not moving at at.

 

[Boatowner]

"Best economy at WOT? Do you guys know anything about cars?"

Quick answer is NO.

The basic assumption seems to be that running your car hard is best for economy, both fuel and engine life. Wow, just wow.

WOT might get the most out of an engine but it is hardly efficient. Refusing to downshift might spare the clutch, but it sure doesn't do the engine any good.

As far as throttles go, a diesel engine is always at full throttle. This means all the air it can get is going in and the fuel is metered. You increase the air with the turbo, which means more fuel can be burned. A gasoline engine meters both air and fuel for the optimum mixture. Sometimes this is lean, sometimes rich. Basically though, the more open the throttle, the more fuel is pulled in. This changes somewhat with electronic fuel injection.

I am far from expert on this and I really wish someone with the expertise would chime in to end all this nonsense about engines being most efficient when they are wasting the most gas.

 

[Vikas]

Well you do minimize the pumping losses by having the throttle wide open but I bet those small gains are obliterated with the rich mixture commanded by the ECM during the WOT operation.

Once again, get a scan gauge type of device and then watch your mpg dropping in to single digit every time you punch it. Anybody who is telling to go WOT for best fuel economy has no real world experience at all.

 

[TFB1]

Originally Posted By: aussiek2000
Best economy at WOT? Do you guys know anything about cars?


WOT kicks the PCM into open loop. Turns off the EGR, quits using oxygen sensor input, and widens injector pulse width, spark timing is retarded to reduce knock. Lugging a gas engine at WOT is the worst economy short of not moving at at.

Advice on engine theory of operation, mechanical, etc is the last thing I'll look for on BITOG...

 

[Gotch]

Originally Posted By: Eddie
Gotch:This is the first time I have heard of "Lugging" explained like this. Do you have a reference paper we can review? I also have read that an engines maximum efficiency (lbs of fuel per HP)occurs at the max BMEP. I do know that maximum BMEP is the maximum stress on the rotating engine parts, but, engines are designed for this. Ed


It is an SAE paper I wrote what seems a life time ago... I finished top of my class way back in 1989...Seems a lifetime ago...

We had an amazing engine professor... Imagine lugging as lagging and I think you will get the jest of it. Anytime you lose engine rpm with increased throttle, is considered lugging. Gas, diesel, nat, gas... I've seen a few guyz post about industrial engines, which are governed to a certain rpm. It's just that, they are governed to lets say 3600rpm. If those engines can't maintain that rpm they they are lugging. Bad? maybe But for effiency sake they have been overloaded and there is a couple of things that can happen. Overheating is probably at the top. Over stress...for sure. Get into the lower rpm ranges and then comes boundary lubrication, which is very bad and excessive wear. Better to shift up a gear or two and save the extremes.

 

[blackman777]

When I listened to others advice and backed off the throttle (about 75% WOT) the MPG gauage did increase from 20 to 22.5. Still fifth gear.
.

 

[Garak]

Originally Posted By: aussiek2000
Best economy at WOT? Do you guys know anything about cars?


A lot of the posters here are, I suspect, speaking from a rather theoretical standpoint that ignores modern fuel injection and electronic engine controls, not to mention parasitic losses, particularly, but limited to, air drag.

 

[blackman777]

Correction: 6th gear. My car's most-efficient is just above 1700 which yields a speed of 45-50. It has very little torque though and can't climb hills. I would have to shift to 3rd at ~30 to maintain that ideal rpm.

 

[aussiek2000]

Originally Posted By: Boatowner
"Best economy at WOT? Do you guys know anything about cars?"

Quick answer is NO.

The basic assumption seems to be that running your car hard is best for economy, both fuel and engine life. Wow, just wow.

WOT might get the most out of an engine but it is hardly efficient. Refusing to downshift might spare the clutch, but it sure doesn't do the engine any good.

As far as throttles go, a diesel engine is always at full throttle. This means all the air it can get is going in and the fuel is metered. You increase the air with the turbo, which means more fuel can be burned. A gasoline engine meters both air and fuel for the optimum mixture. Sometimes this is lean, sometimes rich. Basically though, the more open the throttle, the more fuel is pulled in. This changes somewhat with electronic fuel injection.

I am far from expert on this and I really wish someone with the expertise would chime in to end all this nonsense about engines being most efficient when they are wasting the most gas.


Not on light duty truck diesels made in the last few years. They both meter fuel AND air. They have a throttle body just like a gas engine. Specifically to control NOx emissions.

 

[rvt]

One thing I'd like to see and it is relevant to this topic, is a simple light on the dash indicating whether the engine is in closed loop or open loop.

Generally speaking, at least to my knowledge, most cars /light duty trucks will go to significant enrichment at full throttle (richer than 14.7 to 1). I'd like to know where that point is when driving and just be able to avoid it. Scanguage has this feature I believe.

 

[ueberooo]

Originally Posted By: rvt
One thing I'd like to see and it is relevant to this topic, is a simple light on the dash indicating whether the engine is in closed loop or open loop.


That's a good idea, one simple LED; how expensive would that be to the Ford motor company? 20 cents! Or, if you want to get fancier, a gauge or computer text output that tells you the air:fuel ratio.

I'm finding a lot of good use for the manifold air pressure gauge, that I installed the other year. Cars back in the day used to come with this. It was much too useful of an instrument, so of course it was gradually removed decades ago.

Very useful in knowing when to shift and how to hypermile. It basically gives me a good idea of the air pressure at the intake manifold. Due to the ideal gas law (p proportional to rho*T, p being pressure, rho density, and T temp), this is equivalent to very approximately telling me the air density relatively to the density of the air at atmospheric pressure. Because air fuel mix is approximately constant, this is also roughly equivalent to telling me how much fuel is injected in one cycle of the engine.

Idle intake density is about 1/3 density of normal air (at about STP).

Light throttle is about 1/2 density of normal air.

Medium throttle is about 2/3 density.

Near WOT (where the engine is near peak efficiency) around the economy&reasonable sweet spot rpm band of about 1800-2700 rpm, I am speculating is about 80% density.

And finally, WOT is almost 100% density, by definition.

 

[DragRace]

Originally Posted By: TFB1
Originally Posted By: aussiek2000
Best economy at WOT? Do you guys know anything about cars?


WOT kicks the PCM into open loop. Turns off the EGR, quits using oxygen sensor input, and widens injector pulse width, spark timing is retarded to reduce knock. Lugging a gas engine at WOT is the worst economy short of not moving at at.

Advice on engine theory of operation, mechanical, etc is the last thing I'll look for on BITOG...


Agree 100%

 

[Gotch]

Originally Posted By: ueberooo

Again, this is not true. In most engines, maximum efficiency occurs near WOT (i.e. not too far from max BMEP), but not at WOT.

(If you could reprogram the computer into not burning overly rich, then perhaps you could get max efficiency at WOT. )


maximum efficiency = maximum volumetric efficiency, which occurs at the engines torque peak. This is where naturally aspirated engines are filling with most of their displacement. As rpm rises, efficiency goes down... Yes, horsepower goes up (it is a function of torque and rpm) but volumetric efficiency goes down. You can see this happen on an engine dyno equiped with an airflow meter. A calculation is made to canel rpm out and that determines the volumetric efficiency.

Turbo engines are a little different (they can obtain great than 100% volumetric efficiency, but the same rules apply. They are less efficiency at high rpm.

Throttle reduction reduces volumetric efficiency so maximum efficiency occurs at WOT. Note, this does not mean it is most FUEL efficient in this senario.