Diesels vs Gas Engine - Pros and Cons

Soul Mate II

Member
Jun 28, 2015
193
New York
Boat Info
99 340 Sundancer
Engines
7.4 Mercruiser w V drives
Good morning. Still on the hunt for a boat. I have always had gas engines before. I know them and the maintenance they require.

What are the pro's and con's to having Diesel engines? I was looking at winterizing costs at it appears that marina's charge more money to winterize them.

How about finding a diesel mechanic? I have spoken to a few folks and they say they are hard to find someone to fix.

I am looking at a boat with 800 hours on the diesel engines. I am looking at the same boat with gas engines with 300 hours. Which would your rather and why?

Thanks for the help - trying to make the right decision on which direction to go...
 
What boat & what engines?? Whats you mission Cruising long distance or Lake? Diesels make sense in 40+ ft and if your cruising longer distances. I find my CAT's pretty easy to maintain as far as fluids and filters. Are you a DIY guy or not?

Lots of variables.
 
Agree with above 100%. As a DIY type I want gas as I can fix anything that can go wrong. Not so with diesel. If I had diesels and blew an engine I'd be declaring bankruptcy. Also if you are financing the boat and pay 30k more for it then at 5% the interest on that extra 30k is $1500 per year as well. Plus I don't like the smell of diesel when underway in the cockpit.
 
Pros that I’ve found with diesels so far are more torque, much better fuel economy, very easy to maintain and so far they’ve been very reliable.
On my third season of ownership and maintenance has consisted of oil changes, filter cleaning, zincs and changing the Racor and engine mounted fuel filters.
My Cats have no noticeable smell of diesel when underway. Neither does my diesel generator when I run it on the hook.
While I haven’t experienced any cons yet, I can see where needing to have a diesel mechanic come out for a significant repair would take some time. There just aren’t as many of them around.
It’s true that a diesel engine replacement would be a significant cost, but big blocks aren’t cheap either.
FWIW: I don’t have any empirical data, but just based on boaters I know it seems that gas engine repowers are more common than diesel repowers.
If you want to keep possible repower costs down as low as possible on a boat then your best bet is to stick with gasser small blocks. New replacements are significantly less money than diesels or big blocks.
It’s true that you’re going to pay more for a diesel boat, but once you get to a certain size most people want diesel boats and the gas versions are usually cheaper because they are a harder sell.

Regarding the higher cost of winterization you mention: the process of adding antifreeze itself is the same for diesels and gas motors. The diesels take more of it because they’re bigger, but that shouldn’t raise the price by a whole lot. Especially if you consider that the gas motors need to be fogged and the diesels don’t so there is less labor.
Most will also do oil changes and fuel filters as part of their winterization process. That will add more to the price of the diesels because they take more oil and the filters are generally more expensive. But again, the process itself and the time to complete should be the same for gas and Diesel engines.
The added cost to oil and filters is more than offset by the increased fuel economy.
Service and winterization costs for all other systems should be the same between diesel and gas boats.
 
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If money were no object I think we'd all have diesels.

Last year I moved from a 99 340 with 7.4's to a 97 400 with 7.4's. Overall I feel my 400 performs better than my 340 with the same engines. More balanced, better planning, similar fuel economy. The only con for me has been handling around the docks. A 400 gasser is a bit more of a handful with the smaller props.

What I give up in dockside handling I make up for in engine room luxury. I could sleep two kids down there with room to spare. Gassers are downright dainty compared to their diesel big brothers.

If budget is not one of your top two concerns get the diesels. I don't think anyone has regretted the move when money is taken out of the consideration.
 
This is our first season with our diesels and we love them. Can't speak with any authority yet but thus far the pros are fuel economy, torque etc. Same as most will post however what we like thus far is the cruise speeds at lower rpms. The comfort of not worrying about gas fumes when fueling up. No worries of CO when running the gen or the mains for that matter. Only vessels of a certain size will come with diesels so there is gain of much more space over the smaller vessels. I found last years winterization much easier than on our previous 320 since there was no need to fog the motors. From what i've seen thus far these motors are easy to care for without breaking the bank. So absolutely no regrets here so far!
 
The best is you can say you have DIESELS...
LOL
I would agree with all the above. I would miss diesels if I went back to gassers. As for maintenance they do cost more. I also know gas moters very well and can do all most any repair that would come up. This is my third season with the diesels and I find them very easy to work on and once you find a good service tech they are very willing to let you pick there brains on repairs.
Because of the location of my boat just to get the service tech there is $800.00 in drive time.
If your looking for torque , safety from CO , reliability, and low engine ware over time go with diesels. if you want to keep cost down go with a gasser.

Overall just go with a very well maintained boat and you should be happy either gas of diesels.
 
IMG_4230.JPG
There are also pros and cons for different diesel brands. Some brands have more expensive parts than others. And the quality of service can vary by brand. Ask around in your area and listen to what people say about local support and pricing. Some areas of the country have more diesel boats than others. Great Lakes tilts toward gas power. Florida offshore boats tilt toward diesel power. The 8.1s and 8.2s kind of changed the game. These are big, high torque engines that blur lines at 40 feet and 20,000 pounds. Lots of boats of this size now come with gas engines because these new blocks are pretty good. Also very easy to work on.
 
I have owned my 97 40 DB with CAT 3116s for 1 year. Love the Diesels, the big cats contently purr along in slow cruise, 4.5 to 6 knots. I was beginning to think the fuel gauges didn't work because they weren't moving. My ski boat with a 350 Gasser will constantly prove the fuel gauge is working. I was running the 40 DB almost WOT next to a buddy in a Tri-toon when he took the picture on the left, still the fuel burn was not really that noticeable. Decided early when looking at big boats that the diesel was the only way. Had a small fuel leak bringing the boat home on the second day of my first trip and ended up with some diesel in the bilge. I was alarmed but could only imagine the risk had it been gas. That was enough reason for me. I keep the oil absorb pads down there just in case of another leak but no more issues. I recommend diesels. Having a diesel mechanic for a son might help some day but haven't needed him yet.
 
Steve, I feel you will get better feed back on this if you state where you boat. Salty side of NY or fresh side.
 
Lot's have been written on this subject - both on this site and externally.

I have "read" in published articles opinions that the break over point for gas vs diesel is around 35ft.

Personally - the improved safety of CO emissions is a big deal, along with the torque. I prefer Diesel.
 
It has also been my understanding that the overall use time vs cost formula. If you plan on traveling more than 75 hours a season the cost of diesel maintenance is justified over gassers. If you are going to use it as more of a dockaminium, the maintenance cost annually may not seem worth it.
 
12 years ago I had zero diesel experience... I thought the learning curve would be pretty steep, I was a little intimidated. I have had the mechanic in there for valve adjustments, replace a thermostat and maybe a couple other things. All fluids, filters, zincs, impellers and a bunch of other smaller stuff has been all me. I don’t leave the dock until I have done an engine room inspection and with my first hand experience in there it’s really easy to spot something that is not right. Do not let lack of experience be a factor...
 
Ordinary maintenance cost difference between gas and diesel shouldn't scare a guy off. There's always money to be saved in either case doing the routine stuff yourself. You don't have to be a mechanic to pour in fuel additives, to change oil, filters, impellers, any one can learn to do it.

Sure comparable diesels boats are higher priced than gas, they'll be that way when you go to sell also.

Hard to say which would be better for someone else without knowing how they'll use the boat. How many hours, how many miles, up running on plane or being a trawler, how many gallons you going to burn?

FWIW, a friend with a boat the size as mine but an aft cabin gasser recently compared fuel costs with me. On a little over 200 mile 4th of July trip his fuel costs were almost 1,000 bucks more than mine. On top of that he runs slower and is always the guy that comes in a couple hours after everyone else. He's been using his boat more and more, is thinking about some runs down in Lake Michigan and Huron, he'll be burning some fuel and now he sees why some of us were pushing him to get diesel(he didn't listen). To be fair...he just didn't understand.

On his last trip he left his boat at the destination, put it up for sale, and called someone to come pick him up via car.

He's shopping for a diesel boat now.
 
Lot's have been written on this subject - both on this site and externally.

I have "read" in published articles opinions that the break over point for gas vs diesel is around 35ft.

Personally - the improved safety of CO emissions is a big deal, along with the torque. I prefer Diesel.

The improved safety over gas due to reduced CO emission has always been a big deal for me. I don't think this is mentioned as much as it should.

Overall in most situations... go for the diesel. More info on your situation will help everyone on the site give you better guidance.
 
Diesel all the way. Much more economical, more reliable, more torque, safer no CO worries, cheaper fuel. Rock steady power, just set it and forget it. No RPM variations in rough water. Easy to maintain, just take care of them preventatively.
 
Good morning. Still on the hunt for a boat. I have always had gas engines before. I know them and the maintenance they require.

What are the pro's and con's to having Diesel engines? I was looking at winterizing costs at it appears that marina's charge more money to winterize them.

How about finding a diesel mechanic? I have spoken to a few folks and they say they are hard to find someone to fix.

I am looking at a boat with 800 hours on the diesel engines. I am looking at the same boat with gas engines with 300 hours. Which would your rather and why?

Thanks for the help - trying to make the right decision on which direction to go...

I was exactly in your shoes when I bought my current boat. I have rebuilt several gas auto/motorcycle engines from flatheads to dual overhead cammed motors and feel very comfortable with a wrench in my hand.

My thought process was this: I am confident in my abilities to work on gas motors and when the repairs would be my expertise I would be able to decipher and BS being laid down by any hired mechanic. Since I purchased my boat, I've had to pull a head (broke spark plug)and replaced both raw water pumps, both alternators, both oil coolers and all four manifolds and risers. Not to mention a whole bunch of standard maintenance (i.e. oils, filters, belts, etc.).

I had the exact same fears as you. If I blow up a gas motor around 20-25K for replacement. Diesel, 50-60K and up depending on manufacturer.

If you are that confident with your gas motor skills, you can easily adapt to the standard maintenance of Diesels.

My 360DA does seem to suffer a little while docking in contrary winds or currents due to smaller props and lower torque of the gas motors at idle. I can compensate by adding throttle while docking, but it can add to confusion operating four levers instead of just the two shifters.

In your case, we have to guess on what model boat we are talking about, but if they offered it with both gas and diesel options, it would probably be a larger boat, which would also benefit from Diesels.

If I had to make the decision again with the knowledge I have now, I would 100% go diesel. My next boat will be diesel. Marina diesel prices are always cheaper than gas at every fuel dock I've stopped at for the last three years.


A final thought based only on anecdotal information and only my opinion: I believe if the proper maintenance has been done and continues to be done, you will never have to open up or pull your diesel engine out of your boat. There may be some pricey repairs (after-coolers and the like), but good maintenance will prevent a lot of issues.
 
Diesel all the way. Much more economical, more reliable, more torque, safer no CO worries, cheaper fuel. Rock steady power, just set it and forget it. No RPM variations in rough water. Easy to maintain, just take care of them preventatively.

This (above, bolded by me) I should have pointed out as well. If the seas come up a bit to where you are climbing then surfing, then the gas motors suffer due to lack of torque.
 

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