The Finer Points of Driving a Diesel Truck
#16
Registered User
I am new to diesel trucks. Bought my 2000 Ram 2500 in December and have been loving every mile in it. There are a few things I've been thinking about and would like to know some opinions, facts etc.
Engine Braking:
-Is any fuel being burned while engine braking? No
-Does fuel still circulate through the VP44? Yes
-Does the engine cool down more going down a hill in gear or in neutral? In gear. And down hill in neutral is dangerous in a stick and bad for an auto.
Idling:
-Is there considerably more wear and tear from starting and stopping a diesel engine? No but starting an engine does creates the most initial wear during those first few seconds.....but no more than any other engine. In saying that, there are con's to extended idling too. Idling is not the most efficient combustion and without proper cylinder pressures and temperature, you can allow more contaminates to squeeze past the rings. Hands down, engines which run at a constant steady load will last the longest. Thus a good reason why semi's get so many miles out of their engines.
-How long before its worth shutting the engine off rather than keeping it at idle? (I've heard 10 minutes) Depends on what you're doing. I tend to let me truck idle far more than the norm. But I live in a low crime area too so I'm comfortable walking into the gas station mini-mart while the truck idles and fuels. Also, if its really hot out or really cold out then if I'm only going to be 10-15 minutes then I'd rather let it idle just for sake of not having to re-cool or re-heat the cab. Its my pennies..... But if you're asking in regards to "cool down" time frames then that will also depend on how much the engine has been working. Towing in summer weather will mean letting it cool for around 3-5 minutes before shut down. Regular driving in cooler weather means only 30 sec - 1 min before shut down. Optimal EGT's before shut down is 300*.
Warm-up:
-From 40 *F how long should I idle before driving? Idling a cold diesel engine in cold weather does very little to warm the engine and will take around 10-15 minutes to even start raising the needle. In sub zero temps that needle probably wont move at all while idling. The best for a cold engine is to only idle long enough for the oil to fully circulate which is about 1-5 minutes depending on how cold it is out, and then drive at a low load until the needle starts moving, then its OK to drive normal. If you live next to a freeway then that may pose a problem and during cold weather it would be best to plug in the block heater to assure immediate engine warmth.
-Do higher or lower RPMs produce more heat? High RPM generates more heat but are you referring to "high idling" or driving down the freeway? Idling at around 1200 RPM in cold weather will raise EGT's to about 325*.
Fuel Efficiency:
-What is the best RPM to shift at to maximize fuel economy? Always as low as you can without lugging the engine. That RPM will be dictated by load and driving conditions too. There is no black and white answer.
-Best RPM to cruise highway at for max MPG? Drive the speed limit of the road you're on is the best answer. Going faster then necessary will use more fuel than necessary because doubling the speed requires four times the HP.
-Start in 1st gear or 2nd gear (unloaded, on level ground with 4.10's) You could easily start in 2nd gear unloaded with 4.10's. I have 3.55's and I could also start in 2nd gear as well but I choose 1st gear simply because the more a clutch slips.....the more wear is taking place. That said, if the trucks facing down hill or if the tires are rolling at all then I take off in 2nd, unloaded.
I know, a lot of questions, I appreciate any shared knowledge!
Engine Braking:
-Is any fuel being burned while engine braking? No
-Does fuel still circulate through the VP44? Yes
-Does the engine cool down more going down a hill in gear or in neutral? In gear. And down hill in neutral is dangerous in a stick and bad for an auto.
Idling:
-Is there considerably more wear and tear from starting and stopping a diesel engine? No but starting an engine does creates the most initial wear during those first few seconds.....but no more than any other engine. In saying that, there are con's to extended idling too. Idling is not the most efficient combustion and without proper cylinder pressures and temperature, you can allow more contaminates to squeeze past the rings. Hands down, engines which run at a constant steady load will last the longest. Thus a good reason why semi's get so many miles out of their engines.
-How long before its worth shutting the engine off rather than keeping it at idle? (I've heard 10 minutes) Depends on what you're doing. I tend to let me truck idle far more than the norm. But I live in a low crime area too so I'm comfortable walking into the gas station mini-mart while the truck idles and fuels. Also, if its really hot out or really cold out then if I'm only going to be 10-15 minutes then I'd rather let it idle just for sake of not having to re-cool or re-heat the cab. Its my pennies..... But if you're asking in regards to "cool down" time frames then that will also depend on how much the engine has been working. Towing in summer weather will mean letting it cool for around 3-5 minutes before shut down. Regular driving in cooler weather means only 30 sec - 1 min before shut down. Optimal EGT's before shut down is 300*.
Warm-up:
-From 40 *F how long should I idle before driving? Idling a cold diesel engine in cold weather does very little to warm the engine and will take around 10-15 minutes to even start raising the needle. In sub zero temps that needle probably wont move at all while idling. The best for a cold engine is to only idle long enough for the oil to fully circulate which is about 1-5 minutes depending on how cold it is out, and then drive at a low load until the needle starts moving, then its OK to drive normal. If you live next to a freeway then that may pose a problem and during cold weather it would be best to plug in the block heater to assure immediate engine warmth.
-Do higher or lower RPMs produce more heat? High RPM generates more heat but are you referring to "high idling" or driving down the freeway? Idling at around 1200 RPM in cold weather will raise EGT's to about 325*.
Fuel Efficiency:
-What is the best RPM to shift at to maximize fuel economy? Always as low as you can without lugging the engine. That RPM will be dictated by load and driving conditions too. There is no black and white answer.
-Best RPM to cruise highway at for max MPG? Drive the speed limit of the road you're on is the best answer. Going faster then necessary will use more fuel than necessary because doubling the speed requires four times the HP.
-Start in 1st gear or 2nd gear (unloaded, on level ground with 4.10's) You could easily start in 2nd gear unloaded with 4.10's. I have 3.55's and I could also start in 2nd gear as well but I choose 1st gear simply because the more a clutch slips.....the more wear is taking place. That said, if the trucks facing down hill or if the tires are rolling at all then I take off in 2nd, unloaded.
I know, a lot of questions, I appreciate any shared knowledge!
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Now that I think about it my grandpa always refers to them with female anatomy
#21
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One objection:
SIX says fuel IS being burned while engine braking. You said it is not.
I was pretty sure no fuel, not even the idle amount, is used when engine braking, 2 reasons I came to believe this:
- Real time MPG's on the overhead jump when you put the truck in gear to roll to a stop (i.e. MPG will be around 50 when coasting in neutral but will be at 99 when rolling in gear at the same speed)
-Engine braking is actually quieter, I dont hear any combustion, just the pistons running up and down, crank rotating, etc.
#22
Registered User
That was great, very informative, thank you.
One objection:
SIX says fuel IS being burned while engine braking. You said it is not.
I was pretty sure no fuel, not even the idle amount, is used when engine braking, 2 reasons I came to believe this:
- Real time MPG's on the overhead jump when you put the truck in gear to roll to a stop (i.e. MPG will be around 50 when coasting in neutral but will be at 99 when rolling in gear at the same speed)
-Engine braking is actually quieter, I dont hear any combustion, just the pistons running up and down, crank rotating, etc.
One objection:
SIX says fuel IS being burned while engine braking. You said it is not.
I was pretty sure no fuel, not even the idle amount, is used when engine braking, 2 reasons I came to believe this:
- Real time MPG's on the overhead jump when you put the truck in gear to roll to a stop (i.e. MPG will be around 50 when coasting in neutral but will be at 99 when rolling in gear at the same speed)
-Engine braking is actually quieter, I dont hear any combustion, just the pistons running up and down, crank rotating, etc.
#23
Administrator
Does the no fuel when engine braking hold true on a 1st. Gen with a VE pump?
Foot off the pedal and the engine still idles.
I workers on transit coaches in the 70's with Detroit engines and V-drive transmissions where the engine shut down during shifts then restarts.
Jim
Foot off the pedal and the engine still idles.
I workers on transit coaches in the 70's with Detroit engines and V-drive transmissions where the engine shut down during shifts then restarts.
Jim
#24
Registered User
Does the no fuel when engine braking hold true on a 1st. Gen with a VE pump?
Foot off the pedal and the engine still idles.
I workers on transit coaches in the 70's with Detroit engines and V-drive transmissions where the engine shut down during shifts then restarts.
Jim
Foot off the pedal and the engine still idles.
I workers on transit coaches in the 70's with Detroit engines and V-drive transmissions where the engine shut down during shifts then restarts.
Jim
#25
Registered User
If the engine is turning then there is fuel going to it. If you doubt it (at least on the electric pumps) pay up your life insurance and turn off the key while you're going down the road. The reason the milage meter jumps when you are idling down a hill is that it backs of the feuling to an absolute minnimum but you aree still doing highway speed.
I could be wrong but I can't find anywhere in the VA laws that say going down the road in neutral/ out of gear is illegal...not the smartest because you are relying 100% on brakes that can overheat, but not illegal. At least on mine I notice if I take my foot off the pedal the TC unlocks and the clutches disengage, like being in neutral. If i put just 1% of pedal to it though I can feel the tranny connect and hear the engine rev as it brakes. Truthfully I can't remember if it was like that before I had it rebuilt and upgraded.
I could be wrong but I can't find anywhere in the VA laws that say going down the road in neutral/ out of gear is illegal...not the smartest because you are relying 100% on brakes that can overheat, but not illegal. At least on mine I notice if I take my foot off the pedal the TC unlocks and the clutches disengage, like being in neutral. If i put just 1% of pedal to it though I can feel the tranny connect and hear the engine rev as it brakes. Truthfully I can't remember if it was like that before I had it rebuilt and upgraded.
#26
Administrator
If the engine is turning then there is fuel going to it. If you doubt it (at least on the electric pumps) pay up your life insurance and turn off the key while you're going down the road. The reason the milage meter jumps when you are idling down a hill is that it backs of the feuling to an absolute minnimum but you aree still doing highway speed.
I could be wrong but I can't find anywhere in the VA laws that say going down the road in neutral/ out of gear is illegal...not the smartest because you are relying 100% on brakes that can overheat, but not illegal. At least on mine I notice if I take my foot off the pedal the TC unlocks and the clutches disengage, like being in neutral. If i put just 1% of pedal to it though I can feel the tranny connect and hear the engine rev as it brakes. Truthfully I can't remember if it was like that before I had it rebuilt and upgraded.
I could be wrong but I can't find anywhere in the VA laws that say going down the road in neutral/ out of gear is illegal...not the smartest because you are relying 100% on brakes that can overheat, but not illegal. At least on mine I notice if I take my foot off the pedal the TC unlocks and the clutches disengage, like being in neutral. If i put just 1% of pedal to it though I can feel the tranny connect and hear the engine rev as it brakes. Truthfully I can't remember if it was like that before I had it rebuilt and upgraded.
Idling you also have minimal steering assist and low vacuum supply for braking boost.
It is in your vehicle code.
http://leg1.state.va.us/cgi-bin/legp...0+cod+46.2-811
Jim
#28
Registered User
I didn't mean to contradict SIX since he's a smart fellow but no, no fuel is being injected while your Cummins is decelerating. This is not the same as a carburetor engine whereby during deceleration the "idle" amount of fuel is still being sucked into the engine through the idle circuit. Fuel injection systems shut the fuel off while the engine is decelerating.
#29
Registered User
Idling you also have minimal steering assist and low vacuum supply for braking boost.
It is in your vehicle code.
http://leg1.state.va.us/cgi-bin/legp...0+cod+46.2-811
Jim
It is in your vehicle code.
http://leg1.state.va.us/cgi-bin/legp...0+cod+46.2-811
Jim
I'm not sure how enforcable it is though, specially in the towns that post no jake braking signs. But it wouldn't be the first time virginia towns use drivers to make money
Like I said in my post when I let my foot off the pedal my engine goes to idle (high at ~1k) and the lockup and clutches disengage. If I want to use the engine brake I need to step on the throttle just a little.
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