892 or 871 and what about ethanol in diesel?

[post42]

I have been looking at many hatteras' as well as other types boats lately and I want to buy one soon. My question is which is a better engine in general, the 871 or the 892? Also should I be concerned with ethanol in diesel? I don't want to be changing tanks. Any advise would be appreciated. Thanks, Chris.
________
METHADONE REHAB DICUSSION

 

[67hat34c]

Here is my .02 worth.

Ethanol is going to make it to diesel one day, however I suspect it will be mostly in the clean air states, CA, CT, NJ, MI, MN etc. As I stated in other posts, the capacity to produce Ethanol in the US is limited at this time, no way they will be adding it to diesel in near future, however this is merely an opinion based on the web research and the contacts I made to Phillips Petrolium.

I think the best thing any of us can do is to make the politicians aware of this issue, you will have to keep bugging them.

 

[Genesis]

I don't believe it will ever make its way into diesel.

There are far better ways to make biological contributions to diesel fuel - biodiesel from blue-green aigae (one that will actually work in commrercial quantities), biodiesel from soy, biodiesel from waste fryer oil, etc.....

 

[UNIQUE_NAME]

while i agree with you're sentiment, you are using logic to solve a problem.
politics is driving alternate fuel syndrome and as we all know logic and politics
very rarely join forces. . see uncle sam pay ethanol subsidies along with importing ethanol. never saw that market type explained in any economics course i took.


jim

 

[SKYCHENEY]

Marathon is bringing a new big biodiesel plant on-line soon. I think it is in Kentucky or Tennessee. If ethanol ever makes it to on-road diesel, there will still be opportunity to purchase non-ethanol diesel in the same market areas. They will not put it in heating oil, for example. Phase separation would be way to prevalent in that application.

 

[mwinget]

It is possible, but unlikely that you will see ethanol in Diesel in the USA in any immediate time period. The brazilians do already inject small levels of ethanol in some diesel streams, but they also export massive volumes of it and have more incentive. US ethanol production will be primarily for gasoline.
Further the flash point of Ethanol is basicaly ambient and the flash for diesel is usualy around 140f. Even small levels of ethanol kill the flash point rapidly. It would take very little to drop the flash to 110f as example which is bad news.
As in everything related to the EPA/USA I would not put it past them with all the ethanol lobby's etc, but I honestly think it will a long time forward before you run any risk of ethanol in diesel in the US and you should have many many other pure diesel supply point to chose from before you get stuck. I certainly would not worry about it re the original question on buying a boat.

Mike

 

[Passages]

Just to make sure everyone is on the same page - ethanol blending and biodiesel are not the same.

Bio-d is akin to refined vegetable oil (soy, peanut, ect) vs. ethanol which is an alcohol distillate of corn, switchgrass, sugar beets or cane.

Bio-D is a good diesel supplement - in fact it may be superior to petroleum diesel. The only caveat being the increase solvency. This may be problematic in older tanks with years of accumulated crud. This crud will be re-suspended and lodge itself in your filters. Tank polishing may be a prudent precaution prior to taking on your first load of Bio-d. (Carry extra filters too)

Ethanol on the other hand, will not provide any benefit to diesel applications. Ethanol provides no cylinder lubrication, absorbs injector damaging water, and if present in sufficiant proportion with water in your tank, may phase separate. Feeding a straight water/alcohol mix to your engine would be very bad. Oh yes, ethanol seems to eat fiberglass tanks too.

 

[Passages]

I see your original question was a 2 parter.

8-71 or 8-92 which is better? Well, It depends.

The 8-71 was a 435 hp unit, not all that popular and discontinued in 1979. Reliability was spotty in the turbo versions.

The 8-92 was produced from 1978-2000 and has good reliability if kept under 650 hp.

You did not ask about the 6-92 but that is the engine of choice for a mid 40' Hatt. Keep hp below 500 and they are very reliable.

 

[SKYCHENEY]

Back to the original question about 71 vs 92. There are pros and cons to both engines. Back when we ran them in trucks I would have said stay with the 71's, but there have been many updates to the 92's since then and they are actually still in production. In a marine application, the real question is how much hp are they trying to get out of the engine. I would not own either of these engines if the hp to displacement ratio it at the high end.

The 92's are wet liner engines. This can be a problem, but with proper maintenance to keep from overheating them, they should be fine. I think it is probably best to find a boat that you like and then see what it has for power. I would not let the 71 vs 92 thing be the deal-breaker.

 

[Genesis]

The biggest issue with 71s is that if rebuilt and ALL the liner measurements are not taken properly you WILL have a premature failure.

IOW, they're harder to rebuild properly.

Both are excellent engines when not overstressed...... but if they've been overhauled, my nod goes to the 92s as the odds of it being done wrong are lower.

 

[Boss Lady]

8v71 Naturals last and last, the turbo versions can and do go bang, and have much shorter lives, the minimal HP gains provided by the turbo versions are not really worth the shorter lifespan, greatly increased maintenance costs and complexity. The 8v92TA gets my vote, with one caveat, if you overheat one, even just slightly, you will have major problems on your hands due to the wetliners. Preventative maintenance on all cooling system components are a must. The 8v92TAs I just put in my boat were new in 1988, rebuilt in 1996, again in 2005 and averaged 2800 hours between rebuilds in a 54 Bertram, fished heavily, mostly marling tournaments and run hard. These are 735 HP engines, which puts them in the high risk catagory, based upon the more than a HP per cubic inch rule of thumb, I think this is a pretty good track record for hot rodded engines. It also says volumes for preventative maintenance. I have seen owners of these engine that can make them go bang at 1500 hours or less. My 8v71 naturals (330 HP) had 3700 hours on them and only the port engine was showing a little blue smoke under load. On a turbo engine, 2000 hours is good, and 3000 hours is lucky from my experience, how you use them and how you take care of them will determine how long the will last. 200 hours per year=10 years

 

[Genesis]

An overheat on ANY Detroit is likely to crack a cylinder head. Once that happens you may as well major the engine.

Dry liner engines (71s) are immune to liner SEAL problems but NOT due to liner WARPING. The latter is really, really, really bad, as sometimes that can result in a liner that won't come out of the block when you want to rebuild the motor! This can lead to all sorts of interesting words being used when you're attempting an overhaul on it, and in really severe cases can leave you with a lunched block (if you manage to damage the block's bore while extracting the liner, you're screwed.)

One of the first things I did on Gigabite was to replace the overheat alarm switches in the water elbows with 195F ones (the usual "stock" setting is 205.) My reason for this is that in my experience anything over 200 is flirting in the danger zone.

What most people don't realize is that the internal block temperature is higher than the elbow temperature. If you get localized boiling of the coolant THAT's what usually cracks the head - you have hot and cold spots right next to each other, and bang - you're done. This is almost always "silent" - in that it doesn't produce a recognizable "boilover" in the engine - but the damage happens anyway.

The liner seal deformation temperature is close to 250F (by the numbers on the material used for the seals) but again, the internal temperature is higher than that registered on the gauge. As a result its not uncommon to "cook" a seal with coolant temperatures in the 200-205F range. That results in an oil/coolant leak. Glycol in the oil will trash a main bearing very, very quickly, and if you spin it and/or damage the crank then the engine has to come out of the boat - at minimum.

The first rule of owning Detroits is that you never let them run hot. If you start to see problems with that - temperatures over 185F - you do not run the boat until you figure out what's going on and take care of it. If you're going somewhere and it starts creeping on you the idiot at the throttle backs off until things stabilize - if this ultimately means you come in at displacement speeds, then so be it.

Detroits have VERY LITTLE excess cooling system capacity. This is due to their original design being set up for FAR LESS output than they are rated for in your boat. The original "Detroit" design for a 6V92, for example, was in a transit bus in the high 200/low 300HP range! At that horsepower they had lots of excess cooling capacity. The same engine at 500HP has almost none; at 625HP they add a "boost cooler" because there is literally not enough!

 

[Boss Lady]

Karl,

I like your strategy for the early warning system, I will be changing my sensors before Boss Lady splashes.

thanks!