Gas verses Diesel Tow Vehicle

[pteck]

Thanks for the detailed explanation jcl.

[pteck]

Originally Posted by franklyfrank

The day gasoline engines will be replacing diesel engines in Construction Equipment, Marine and Locomotive use, I will agree with you and your son.
We would run our Mack and Cat diesel engines to 750,000 miles rebuild them and run them another 750k.
When it comes to long term durability and power diesel rules. Knocking Diesel engines makes no sense at all considering their wide use and important contribution to our lives.
Ford and International built a line of diesel engines haphazardly without much testing for pick up trucks and now all diesel engines are judged by that.
Does everyone need one or like one absolutely not. I love mine and am not interested in gas . Does one need a $ 130 k Airstream Classic to go camping at the local State park ? A Lamborghini a Yacht ?

You know what is more similar to the HD diesels installed in pickups?

Passenger car based diesels.

Yes, the wimpy ones that cannot even be made to pass smog such that engineers have to cheat to make enough power and efficiency. With questionably reliability. Not all roses.

[Tuco]

Originally Posted by jcl

The piston is working against a throttle point, a restriction caused by the throttle body and throttle plate. The work the engine has to do is overcoming the pumping losses through the intake tract. That is what provides engine braking on a gasoline engine. It isn't compression braking, it is engine braking. The incoming air goes through the engine, and out the exhaust, but restrictions along the way means the engine does work, which we utilize to slow vehicles on descents.

Unfortunately this is an incomplete and ultimately an incorrect answer. When dealing with vacuum systems you need to look at the differential pressure. At peak manifold vacuum the piston is acting against a lower initial pressure. Thus the delta from the top of the stroke to the bottom nets only about .5 psi (~25"-27"). And when the compression stroke finishes you have given back most of that energy with the exception of heat losses. Fortunately you are still compressing the smaller charge at a ratio of ~10-1 on the compression stroke. This is the work done and there is a lot more energy converted to heat and is not fully recovered. The proof is in the the fact that my truck will slow down as well as any gas vehicle I have ever owned (without using the exhaust brake). If what you say is correct then it wouldn't slow down much at all, and that is not the case.

[GettinAway]

Originally Posted by Countryboy59

Any good truck will go 250k easy, all of mine have gone way past that. However, routine maintenance at that point could include anything that wears out, like several sets of brake rotors, ball joints, and control arms, and hopefully it’s had a couple sets of shocks by then. Suspension work ain’t cheap and if those parts haven’t been touched on that Toyota I’d hate to be next to it on a freeway.

I replace shocks and brakes as needed. My original point was the large expense I keep hearing about with diesels on $2500 repairs to Diesel engine specific problems. Way more stories going around on the diesels than on gassers. I’m glad you’ve had good luck with yours. I wouldn’t own one out of warranty.

[GettinAway]

Originally Posted by gypsydad

Not sure anyone is saying a diesel is safer....but, to your point about coming down a mountain pass...Sure you can pull an AS with just about any TV and if your happy, that's great!

But, as I said earlier, if you are pulling a bigger, heavier AS up/down/around in the Rockies or some mountainous area, like many of us do, the bigger TV 3/4 and 1T with diesel engine, offer obvious advantages. Not saying you can't get it done with a gasser....just saying, if you have not towed in these types of conditions with a newer diesel TV you may never understand what we are talking about.

It was a few pages back, about safety etc,, I said it was certainly easier to go down a steep slope with an exhaust brake. I just don’t think it’s worth it to go diesel for that one situation. It’s a clear advantage for diesel. It’s just that it’s a small percentage of my total time pulling my AS. (And we almost always camp out west in the summers to escape the Midwest heat and humidity.)

[GettinAway]

Originally Posted by franklyfrank

The day gasoline engines will be replacing diesel engines in Construction Equipment, Marine and Locomotive use, I will agree with you and your son.
We would run our Mack and Cat diesel engines to 750,000 miles rebuild them and run them another 750k.
When it comes to long term durability and power diesel rules. Knocking Diesel engines makes no sense at all considering their wide use and important contribution to our lives.
Ford and International built a line of diesel engines haphazardly without much testing for pick up trucks and now all diesel engines are judged by that.
Does everyone need one or like one absolutely not. I love mine and am not interested in gas . Does one need a $ 130 k Airstream Classic to go camping at the local State park ? A Lamborghini a Yacht ?

I’m glad you haven’t had any troubles with your diesel. I wouldn’t mind owning one. My point was I wouldn’t own one out of warranty. I don’t see what heavy truck and construction diesels have to do with what’s in your pickup, except the fuel. I’ve heard way too many horror stories about the modern pickup diesels. I don’t think it’s a super high failure rate, but too high for my comfort level.

[Isuzusweet]

Originally Posted by franklyfrank

The day gasoline engines will be replacing diesel engines in Construction Equipment, Marine and Locomotive use, I will agree with you and your son.
We would run our Mack and Cat diesel engines to 750,000 miles rebuild them and run them another 750k.
When it comes to long term durability and power diesel rules.

Agree wholeheartedly.....except for one thing.....the only comparison you can draw between your old MACK engines, or old industrial Cummins diesel engines, to modern day automotive diesel engines, is that they all have cylinders and pistons; that's about it! They sometimes didn't even use the same grade diesel fuel.

To compare my Isuzu 6BD1a to a Cummins 6BT isn't even fair. The Isuzu is an industrial diesel engine that can be endlessly rebuildable, with removable sleeves. It was designed to go 500,000 miles before needing any work at all. Built to power everything from generators on trawlers to mining, it is a workhorse; but no comparison to a modern day automotive deiesel engine.

Cheers
Sidekick Tony

[Countryboy59]

Originally Posted by GettinAway

I replace shocks and brakes as needed. My original point was the large expense I keep hearing about with diesels on $2500 repairs to Diesel engine specific problems. Way more stories going around on the diesels than on gassers. I’m glad you’ve had good luck with yours. I wouldn’t own one out of warranty.

Good point about the warranty. I haven’t needed a single warranty repair on any vehicle except a used Duramax I bought needed a wheel bearing.

I would gladly do the $2500 repair on a Diesel after the first owner took the $15,000 depreciation hit. I’ll take out of warranty any day.

[GettinAway]

To each is own. Just waiting for it to have a problem. I just wouldn’t want to be that situation.

[Countryboy59]

Originally Posted by tjdonahoe

..I never had any problems leaving them stock.....and I have always got a long life out of them....the manufacturer spent 25 million dollars on designing a good engine.....I don’t think by spending a couple thousand is going to make it better.....whether it is the engine in my truck or my pickup...I do like the dealer life time oil changes....they use synthetic t6 shell 5- 40.. this is not a garbage oil...and the stock filters are not cheap...

I cut the dealer service interval in half. The stock EGR puts a lot of crap in the oil. Have you disassembled your EGR and cleaned it yet? I’ll post pics next time. It’s a two hour job. After looking at that I understand why some guys delete these engines.

[gypsydad]

Originally Posted by GettinAway

It was a few pages back, about safety etc,, I said it was certainly easier to go down a steep slope with an exhaust brake. I just don’t think it’s worth it to go diesel for that one situation. It’s a clear advantage for diesel. It’s just that it’s a small percentage of my total time pulling my AS. (And we almost always camp out west in the summers to escape the Midwest heat and humidity.)

And I understand that...no argument. My point to Ptek and others who "dis da diesels" is not meant to be an argument against their choice of Lexas or other TV's. I pose the question asking "have you ever driven a newer diesel pulling a larger AS??" I get all kinds of "yea, but's" which tells me likely not. The airbrakes are only one benefit I like with my 6.7l. As I cruise the steep grades at highway speeds 60-65mph while on cruise, the engine is loping along at 1500rpms getting 13.0-13.4 mpg; I have kayaks on top, generator in back with 2 BBQ grill's, charcoal and propane bottle, firewood, camp gear, and 1100lbs tongue weight...that's all I am using to compare...not sure Ptek has pulled his AS with a newer diesel like many of us do, to give a actual comparison of his opinion? I respect the daily driver need...I didn't buy my F250 for daily driver. I do love driving it on the highway; just don't like filling it, parking it, nor servicing it; it's expensive, but when I am on the road pulling the 28' in MT and Northern states...it is night and day more pleasurable over my F150 in many ways; and I loved my F150 for my 25's when I owned them.

[pteck]

Originally Posted by Tuco

Unfortunately this is an incomplete and ultimately an incorrect answer. When dealing with vacuum systems you need to look at the differential pressure. At peak manifold vacuum the piston is acting against a lower initial pressure. Thus the delta from the top of the stroke to the bottom nets only about .5 psi (~25"-27"). And when the compression stroke finishes you have given back most of that energy with the exception of heat losses. Fortunately you are still compressing the smaller charge at a ratio of ~10-1 on the compression stroke. This is the work done and there is a lot more energy converted to heat and is not fully recovered. The proof is in the the fact that my truck will slow down as well as any gas vehicle I have ever owned (without using the exhaust brake). If what you say is correct then it wouldn't slow down much at all, and that is not the case.

You sound like you’re savvy, so please don’t take this as criticism.

You’re focused on the wrong thing and need to look at the bigger picture. The significant work done is not taking the vacuum from ~25” to ~27”. But moving the piston against the pressure delta that exists between vacuum in the combustion chamber and atmospheric pressure on the other side. Just like in an actual combustion event, we’re not necessarily concerned about the pressure differential between TDC and BDC…unless the discussion is about efficiency.

Gas engine braking is a well understood and accepted concept among engineering circles. I’d reference material for you, but I’m sure you can find it on your own.

[pteck]

Originally Posted by gypsydad

And I understand that...no argument. My point to Ptek and others who "dis da diesels" is not meant to be an argument against their choice of Lexas or other TV's. I pose the question asking "have you ever driven a newer diesel pulling a larger AS??" I get all kinds of "yea, but's" which tells me likely not. The airbrakes are only one benefit I like with my 6.7l. As I cruise the steep grades at highway speeds 60-65mph while on cruise, the engine is loping along at 1500rpms getting 13.0-13.4 mpg; I have kayaks on top, generator in back with 2 BBQ grill's, charcoal and propane bottle, firewood, camp gear, and 1100lbs tongue weight...that's all I am using to compare...not sure Ptek has pulled his AS with a newer diesel like many of us do, to give a actual comparison of his opinion? I respect the daily driver need...I didn't buy my F250 for daily driver. I do love driving it on the highway; just don't like filling it, parking it, nor servicing it; it's expensive, but when I am on the road pulling the 28' in MT and Northern states...it is night and day more pleasurable over my F150 in many ways; and I loved my F150 for my 25's when I owned them.

I’m not here to dis diesels. I’m only interested in fair and factual statements in the differentiation between diesel and gas. So the next person doesn’t mistake to understand that diesels have engine brakes (some do not, all gassers do), diesels are safer (not necessarily in significant ways), diesels climb mountains faster (not always true, weight), diesels are longer lasting (at a cost), etc.

Why do I need to drive your burly diesel? It’s like saying you haven’t driven my Porsche. It’s just unnecessary. You’re diesel won’t do what I want or need like seat 8, daily drive, technical off-roading, etc. Just like my Porsche doesn’t fit your use, even though it’s surely many many more things…that you don’t need. You weren't happy with your older F150 and upgraded. That talks to your old F150 vs new F250. Yet F150s have also come a long way. I'm very happy with my gas Lexus towing the same size trailer you are.

At the same token. Enjoy your diesel. I’m sure it suits you and many other well. Please do share your great experiences with it. Just don’t assume and overstate what it offers over other modern vehicles, with whatever engine type. Just like grade logic. It is a modern vehicle control function, that doesn’t really depend on what type of engine is utilized. EV’s will have it too.

[Tuco]

Originally Posted by pteck

You sound like you’re savvy, so please don’t take this as criticism.

You’re focused on the wrong thing and need to look at the bigger picture. The significant work done is not taking the vacuum from ~25” to ~27”. But moving the piston against the pressure delta that exists between vacuum in the combustion chamber and atmospheric pressure on the other side. Just like in an actual combustion event, we’re not necessarily concerned about the pressure differential between TDC and BDC…unless the discussion is about efficiency.

Gas engine braking is a well understood and accepted concept among engineering circles. I’d reference material for you, but I’m sure you can find it on your own.

What you fight on the intake stroke you gain back on the compression stroke. No work is being done there. The only work is the heat loss during the delta phase which is negligible.

[pteck]

Originally Posted by Tuco

What you fight on the intake stroke you gain back on the compression stroke. No work is being done there. The only work is the heat loss during the delta phase which is negligible.

True. Yet there's 4-strokes.

Compression vs Combustion strokes - negligible/wash.

Intake vs. Exhaust stroke - that's where the magic happens.

[Tuco]

Originally Posted by pteck

True. Yet there's 4-strokes.

Compression vs Combustion strokes - negligible/wash.

Intake vs. Exhaust stroke - that's where the magic happens.

We have covered the intake and compression side as far as vacuum is concerned. There is no vacuum on the power and exhaust stroke. Besides how do you explain that a diesel engine provides this mythical engine braking? Anyone on here will tell you that a diesel performs the same way as a gas engine when you let off the throttle (without using the exhaust brake). If they didn't act the same then everyone on here would say so wouldn't they?

[jcl]

Originally Posted by Tuco

We have covered the intake and compression side as far as vacuum is concerned. There is no vacuum on the power and exhaust stroke. Besides how do you explain that a diesel engine provides this mythical engine braking? Anyone on here will tell you that a diesel performs the same way as a gas engine when you let off the throttle (without using the exhaust brake). If they didn't act the same then everyone on here would say so wouldn't they?

At one time I drove a Passat diesel for several years and had access to a gas version as well. The gas version had engine braking while the diesel had none. It might as well have been in neutral when descending.

The difference to your experience comes down to engine size and drivetrain losses. With a smaller and more efficient VW engine the lack of inherent engine braking with the diesel was very obvious. On the other hand, your larger engine experience is based on having much more friction. You don’t have inherent engine braking but you still have engine friction. You are confusing engine friction with the engine braking associated with a gasoline engine working against pumping losses.

The developers of diesels for highway transport understood this very well. That is why they invented the compression release brake, to overcome an inherent design limitation. If you want to understand this better suggest you read The Engine That Could, the history of the Cummins Engine Company.

[jcl]

Originally Posted by Tuco

Unfortunately this is an incomplete and ultimately an incorrect answer. When dealing with vacuum systems you need to look at the differential pressure. At peak manifold vacuum the piston is acting against a lower initial pressure. Thus the delta from the top of the stroke to the bottom nets only about .5 psi (~25"-27"). And when the compression stroke finishes you have given back most of that energy with the exception of heat losses. Fortunately you are still compressing the smaller charge at a ratio of ~10-1 on the compression stroke. This is the work done and there is a lot more energy converted to heat and is not fully recovered. The proof is in the the fact that my truck will slow down as well as any gas vehicle I have ever owned (without using the exhaust brake). If what you say is correct then it wouldn't slow down much at all, and that is not the case.

What is incomplete and thus incorrect is analyzing a portion of the flow and not the complete flow. Before the air filter we are at atmosphere. After the tailpipe we are at atmosphere. Any analysis that focuses on a segment of the flow is incomplete. Through the entire system there are restrictions that cause the engine to do work, what I referred to as pumping losses. Those restrictions can be on the intake with a throttle plate, or if such a device is not part of the design then a restrictor can be added on the exhaust side whether with variable turbine blades or a separate exhaust restrictor (brake). They all accomplish the same thing.

All designs have friction just to turn the engine over. That isn’t a differentiator between gas and diesel. You may have enough friction to have appreciable retarding effect on a hill. That isn’t a good thing, however, since you have the same friction going up a hill.

[Tuco]

Originally Posted by jcl

At one time I drove a Passat diesel for several years and had access to a gas version as well. The gas version had engine braking while the diesel had none. It might as well have been in neutral when descending.

The difference to your experience comes down to engine size and drivetrain losses. With a smaller and more efficient VW engine the lack of inherent engine braking with the diesel was very obvious. On the other hand, your larger engine experience is based on having much more friction. You don’t have inherent engine braking but you still have engine friction. You are confusing engine friction with the engine braking associated with a gasoline engine working against pumping losses.

The developers of diesels for highway transport understood this very well. That is why they invented the compression release brake, to overcome an inherent design limitation. If you want to understand this better suggest you read The Engine That Could, the history of the Cummins Engine Company.

Yes, and I have a Lincoln MK VIII that provides little to no engine braking. My wife complains about it all the time. You have to take it out of OD to get any meaningful engine braking.

As far as friction is concerned are you trying to tell me that a diesel engine has more friction than a gas of the same size? I'm sorry but i'm laughing on that one. Engine internals are the same between the two designs. There is no meaningful added items on the diesel to explain parity in engine braking. You say that its the drive train, but if you compare the same truck one gas the other diesel they will both have engine braking which is similar with comparably sized motors and the EXACT same drive train. Your argument about the vacuum doesn't fly and neither does this.

[jcl]

Originally Posted by franklyfrank

The day gasoline engines will be replacing diesel engines in Construction Equipment, Marine and Locomotive use, I will agree with you and your son.
We would run our Mack and Cat diesel engines to 750,000 miles rebuild them and run them another 750k.
When it comes to long term durability and power diesel rules. Knocking Diesel engines makes no sense at all considering their wide use and important contribution to our lives.
Ford and International built a line of diesel engines haphazardly without much testing for pick up trucks and now all diesel engines are judged by that.
Does everyone need one or like one absolutely not. I love mine and am not interested in gas . Does one need a $ 130 k Airstream Classic to go camping at the local State park ? A Lamborghini a Yacht ?

Who is knocking diesels? I thought posters were knocking misinformation.

I knew those old Cat engines well. 3406B, maybe a C, maybe an E? We enjoyed a market share around 50%, partly due to product longevity, partly due to the product support, partly due to the hp offered in our mountainous territory. Competition was Cummins, Detroit, Mack. Then 2007 emissions rules came into play. Reliability suffered. With the 2010 emissions regulations our supplier withdrew from the highway truck market. Completely. (at least in North America.)

Pre emissions control and post emissions controls were a different world in terms of customer experience. There is a parallel here to light duty diesels in pickups. We don’t read about piston failures, we read about emissions control issues with modern light duty diesels.

Apart from that it is hard to compare pickup diesels with 14 litre engines. Dry liners vs wet. Higher rpm range. Highway use vs short trips. Professional drivers vs recreational drivers. And a focus on total cost of ownership for the heavy duty product vs appealing to consumer tastes with the light duty product. Generally, the only time we sold a heavy duty engine like a 3406 to someone who wanted one regardless of all other issues was in the marine pleasurecraft market. We painted them white, added chrome engine covers and so on. Those were emotionally driven purchases more often than not