mpg/mp$ gas/diesel

[BobH]

In another thread we agreed that mpg for diesel was higher than mpg for gas. Haven't been to a fuel dock in ages but the street price of diesel is higher than the gas price. So instead of focusing on mpg what would the result be if we use mp$?
Just a thought,
Bob

 

[rslifkin]

The diesels will still be cheaper to run in most cases. But they'll be more expensive to buy, so it'll take some amount of usage before you hit the break-even point and then the diesels start to become cheaper.

Price spread for gas vs diesel at fuel docks varies depending on where you are too. Right now, where I am, ethanol free gas is more expensive than diesel at most fuel docks. Some areas that sell ethanol containing gas are cheaper for gas than diesel, but not always. Last year, diesel was consistently higher than gas locally, but as prices have settled back down, diesel has come down faster than ethanol free gas has.

 

[Lepke]

In general diesel engines run much longer before needing a rebuild. Diesels don't have ignition problems and less affected by damp conditions. Better diesels don't have electronics at all.

 

[rslifkin]

In general diesel engines run much longer before needing a rebuild. Diesels don't have ignition problems and less affected by damp conditions. Better diesels don't have electronics at all.

There's a good point in there. A good, reliable ignition system is the #1 important thing with gas engines in my mind. That alone makes 99% of the difference between engines that are fussy / finicky and engines that "just work". And with any engine (gas or diesel, electronics or not), it's important to know the systems well, how to diagnose them, etc.

 

[Nomad Willy]

rslifkin,
Air and/or water in fuel is much easier to deal w in gasoline engines.

Lepke,
Can you break it down? What causes gas engines to have less life other than how they are used?
It would seem to me that the lower forces in gas engines would tip the longevity scale toward gasoline.

Are combustion pressures of diesels not causing higher piston to cylinder wall wear w their higher compression ratios? And how does the combustion forces different gas to diesel?

What does the diesel rattling noise come from. I had an 82 Nissan Maxima in-line 6 cylinder diesel car and the light load rattle drive me nuts.

 

[rslifkin]

rslifkin,
Air and/or water in fuel is much easier to deal w in gasoline engines.

Lepke,
Can you break it down? What causes gas engines to have less life other than how they are used?
It would seem to me that the lower forces in gas engines would tip the longevity scale toward gasoline.

Are combustion pressures of diesels not causing higher piston to cylinder wall wear w their higher compression ratios? And how does the combustion forces different gas to diesel?

What does the diesel rattling noise come from. I had an 82 Nissan Maxima in-line 6 cylinder diesel car and the light load rattle drive me nuts.

I don't think it's an inherent limitation of gas engines, just of the engines available for us to use. Nobody builds gas engines as heavy duty as many of the diesels that are available (probably because of a limited market for really heavy duty gas engines).

 

[Hippocampus]

Compression in diesels is much higher than in petrol. I think due to that and not size nor HP diesel engines need to be more heavily built.

 

[kthoennes]

Fuels prices have fluctuated so much around here that I don't think I'd venture any conclusions or predictions on comparative cost per gallon. Flipped at least three times that I can remember in the past year, but then I'm in the heart of ethanol country and ag country, which distorts regional markets really badly.

 

[mmullins]

For most of us, a boat is a "want" not a "need." And most of us "want" diesels. You don't have to justify it. Just get what you want or you won't be happy.

 

[Nomad Willy]

For most of us, a boat is a "want" not a "need." And most of us "want" diesels. You don't have to justify it. Just get what you want or you won't be happy.

BINGO,
Really great perception. Spot on mmullins!

Most all want their rec trawlers to sound like a teal trawler or a tugboat.
They don’t wanna be seen on a boat mostly owned by men w clean shoes.
They want to be seen as a manly man .. the smoking a pipe image.

 

[Nomad Willy]

Diesel engines don’t make more power.
But they do have much higher compression ratios. That (like the power stroke) puts heavy loads on the side of the pistons. But does is the downward force from combustion higher w a gas engine, the same or lower? Should be about the same as they both put out about the same amount of power.

Why make the diesel heavy duty? Compression forces is the only “in the face” (sticks right out) reason to make the engine components heavy duty.

Maybe it’s the duration of combustion, heat and force that requires stronger components?

In 1950 there were almost no trawlers because the diesel engines were too heavy. Much too heavy seeing that gas engines were heavy too.

 

[motion30]

Diesel might be more expensive on the street but on my observation at the marina diesel is usually cheaper than gasoline

 

[slowgoesit]

In another thread we agreed that mpg for diesel was higher than mpg for gas. Haven't been to a fuel dock in ages but the street price of diesel is higher than the gas price. So instead of focusing on mpg what would the result be if we use mp$?
Just a thought,
Bob

Back to the OP's post, fuel prices are all over the map, so unless you're comparing performance from two different boats that bought fuel for the same price, any comparisons are meaningless.

Given that:

• a gallon remains a gallon
• a mile remains a mile (let's just assume nautical miles instead of statute miles, shall we?)
• and an hour remains an hour

so it stands to reason that fuel usage is generally referred to in either gallons/mile, or gallons/hour.
The cost of the fuel is a totally different discussion!

 

[bumpkin]

??

I've read your post a few times and I'm not sure what you are after.

If you are after consensus, I agree with you, at gas stations, on the street diesel is more expensive than gasoline. On the water, at fuel docks, I didn't find that to be necessarily true. Sometimes the prices were the same and sometimes the price of diesel was cheaper, occasionally by a good margin.

The price of 100% gasoline has always been higher than diesel both on the docks and on the street.

I haven't been on the water for a month so relationships may have changed.

Mike

 

[Fish53]

One difference I haven't seen stated in gas vs diesel is tax. Marine diesel doesn't have as high of taxation were I am being off-road. I get my diesel at a commercial dock and pay less than I pay for gas in my car. The fishing trawler I used to own had 22000 hrs. on when I sold it and served the new owner well for quite awhile after, I doubt many gas engines last that long.

 

[rslifkin]

One difference I haven't seen stated in gas vs diesel is tax. Marine diesel doesn't have as high of taxation were I am being off-road. I get my diesel at a commercial dock and pay less than I pay for gas in my car. The fishing trawler I used to own had 22000 hrs. on when I sold it and served the new owner well for quite awhile after, I doubt many gas engines last that long.

Good point, and that can be why the price spread at a fuel dock isn't always the same as you see at a gas station.



As far as lifespan, I doubt there's any common marine gas engine that will run that many hours before overhaul. But very few recreational boaters will ever put anywhere near those hours on a boat regardless.

 

[jgwinks]

Compression in diesels is much higher than in petrol. I think due to that and not size nor HP diesel engines need to be more heavily built.

Right. Back in the 70's when gas prices first started to rise, GM tried converting one of thier gas V8 car engines to diesel. The engines ran well, for a while, then started blowing head gaskets. Not heavily built enough for the pressure. The idea didn't work at all and of course as always they let the public do all the quality control. My brother in law bought one, nothing but trouble.

 

[jgwinks]

One difference I haven't seen stated in gas vs diesel is tax. Marine diesel doesn't have as high of taxation were I am being off-road. I get my diesel at a commercial dock and pay less than I pay for gas in my car. The fishing trawler I used to own had 22000 hrs. on when I sold it and served the new owner well for quite awhile after, I doubt many gas engines last that long.

Buying at a fuel dock neither fuel will have road tax. But you will be paying "marina tax", higher price due to lower volume, higher insurance premiums to cover spills, etc. Back when I had the sailboat and only a 26 gallon tank, I bought my diesel at gas stations in Jerry cans. Was usually cheaper than the marina even with road tax applied. Lately I've noticed diesel in gas stations is less than gas around here, but the price of both is really volatile. Changes 20-30 cents daily. Haven't been to the fuel dock lately.

 

[Fish53]

States vary but here diesel is taxed higher than gas. It's true that marinas charge significantly higher prices for both, that's why I don't buy fuel from them. When I owned my commercial boats at times I'd fuel from a truck as it was frequently the cheapest option, especially when getting 800 to 1000 gallons.

 

[Fish53]

As far as lifespan, I doubt there's any common marine gas engine that will run that many hours before overhaul. But very few recreational boaters will ever put anywhere near those hours on a boat regardless.[/QUOTE]

Very true, I only pointed it out to show the increased reliability of diesel. That said they do cost significantly more to buy and fewer can do their own service or repair on them. They do increase the value of a boat when it's time to sell though. Boils down to personal preference and type of use for each individual.

 

[Iggy]

My current boat is a diesel and and past boats were gas. I will never go back to gas.

With 3800 hours, it starts right up even after being laid up for the winter.

I don't think its been mentioned, as we all know. Gas engines run at a higher RPM. My last boat ran at 3300 RPMs (gas) this boat runs at 2000 RPMs. More wear on the engine?

At 3 times the wight of my last boat, I am getting the same MPG. Gas engines just can't do that.

 

[Barking Sands]

Right. Back in the 70's when gas prices first started to rise, GM tried converting one of thier gas V8 car engines to diesel. The engines ran well, for a while, then started blowing head gaskets. Not heavily built enough for the pressure. The idea didn't work at all and of course as always they let the public do all the quality control. My brother in law bought one, nothing but trouble.

I remember that engine. It was terrible. Had a relative that bought one and was pitching it as the next big thing to anyone that would listed. Everyone got tired of hearing about it.....for the 2 months it ran...:lol:

The caddy 4-6-8 was another one.