1978 85hp fuel consumption

[iwombat]

More boat shopping questions:

I'll be looking at a boat with a '78 v-4 85hp that the owner claims is a "gas hog" (I don't have numbers to work with yet). What can I expect for fuel consumption out of this motor?

If it really is consuming an undue amount of fuel I'm suspecting either stuck rings, or a head gasket leak could be the culprit. Any other thoughts?

I plan on doing a full compression check, spark test, etc. But going in with a few theories never hurts.

 

[iwombat]

Re: 1978 85hp fuel consumption

More detail: It runs smooth and idles well.

 

[F_R]

Re: 1978 85hp fuel consumption

Oh, I don't know, I guess it's how you look at it. They were not bad really. A heckova lot better than say an old V4-75. I had a similar 100hp and thought it was OK at the time but then gas wasn't $3 a gallon + oil back then either. They were pretty much state of the art for their day. Are there any better? Maybe. How about a nice new 4-stroke?

More important is whether it is well suited for the boat. A motor that has to run flat out to push the boat will burn a lot more gas in an outing than a motor that can give satisfactory performance at part throttle.

 

[OBJ]

Re: 1978 85hp fuel consumption

Welllllllllll......my 86' 90hp Johnny runs very well and idles smooth. I have installed Boyesen Reeds and keep it tuned to a gnats tooth all the time. Still likes its gas though. If I cruise at around 3600rpms, not bad. When I pull the rug rats on tubes and such.......I use a lot of fuel. Don't expect the same economy of modern DFI engines or new 4 strokes. Just won't happen. Still, the block is a proven performer and is fairly easy to work on.

And as FR posted, make sure the boat can handle the hp. Check the hp rating on the rig.

 

[emdsapmgr]

Re: 1978 85hp fuel consumption

Not sure why you think the 85 burns a lot of fuel. It really does not have the jetting for high fuel consumption. The 78 85 hp uses .045 high speed jets and a low speed jet. The 84 90 hp uses .056 high speed jets along with low and mid jet. Believe some of this difference is that the older v4 85 hp (your 78 engine included) may be a 92.6 cubic inch block rather that the 115, 135, 140 standard 99 cubic inch blocks. When you compare the 78 85 with the 140 of that year with .065 jets, it is not a high fuel-flow engine. It is always possible that a prior owner put the larger carbs on the engine to increase hp..that would explain high fuel consumption. Check the front flange of the carbs for size, or pull a high speed jet to check it's size.

 

[Texasmark]

Re: 1978 85hp fuel consumption

Beins I grew up with the old cross flows, the largest was the '72 125, they were all gas hogs if you compare them to the Loopers or the Merc Direct Charge, all the way back to my '58 or '59 18 hp Rude cross.

I hear a lot on here about figuring 10% of your hp for consumption in gallons per hour. I don't know about that; never put a stopwatch to it. I do however, remember when 35 hp was the biggest beast out there (on a 14' plywood boat) and we would go out for a Sunday afternoons water skiing caper and those 2 ea 6 gallon tanks would be sucked dry before you could bat an eye. The 125 had an 18 gallon tank and there was no problem drying it out.

My first looper was a '75 70 hp Rude and then came a 115 Merc Direct Charge. Don't remember the tank(s) with the Rude (1 or 2 ea 6 gallon portables) but the Merc had a 10 gallon built in and only on one long distance fishing occasion did I bring along an extra 5 gallons.

I don't know if the boat's design made all the difference, or I changed my aquatic habits, or what, but fuel consumption was definitely, significantly, noticeably, lower. When they came out in '68 with the Rude Triumph 55, 3 cyl, they were the talk of the town........including their new lower unit design (was an OMC fan at the time).

The Rude was on an early BB like the Ranger early design (16' stepped glass flat bottom, long and narrow, straight sides...Kingfisher brand) and the Merc was on a 17 1/2' heavy, Ranger glass Padded hull.

I can't see how you can tie it down like that (10% of hp in gallons per hour) with the different technologies including 4 cycle I/O's which were definitely more economical (Had a late '60's 120 Mercruiser in an 18' Starcraft Holiday).

If I were buying, It would be a looper or better; no more crosses for me.

My 2c and it's worth what it cost you. 8)

Mark

 

[Silvertip]

Re: 1978 85hp fuel consumption

10% of horsepower = gallons/hour at wide open throttle. And it doesn't make a lot of difference if you have a 2007 motor or 1987 motor. While the new technology makes great strides in fuel savings at less than wide open throttle, the 10% rule is still fairly accurate. If you don't believe that, check Yamaha's web site (click on performance tests). Depending on the boat, you'll see the four and two strokes pretty close in fuel consumption at wide open throttle. I run a 75 Merc two stroke with a fuel flow monitor. It burns exactly 7.5 gallons/hour at wide open throttle. At 4000 RPM it's in the 5.0 g/hr range. In this case the 10% rule is spot on.

 

[F_R]

Re: 1978 85hp fuel consumption

I would agree with what Texas said about comparing cross flows to some other technologies. However, the crossflow/looper issue is only part of the picture. Back before we became concious of environmental concerns outboards dumped huge amounts of unburned fuel into the water. Then in the late 1960s they started to make them more efficient, partly because of environment and partly because of the horsepower race. Fuel ecomomy benefited by both. Compare the fuel/air flow through the all-time champion gas hog 1958 V4-50 and the 85hp in question. Both are cross flow V-4s, but the similarity ends there. Gone are the huge caverns and dead air spaces that allow gas to rain out of the charge and be wasted. Exhaust tuning conserves fuel that used to just blow out the exhaust. Better shape of lower units and propellers apply energy to pushing the boat instead of beating water. Lighter weight per horsepower makes the load lighter.

 

[iwombat]

Re: 1978 85hp fuel consumption

His number is 1 gal/hr at WOT, which doesn't really seem all that bad to me. Given what everyone has said that seems pretty close to what I should be expecting. (Silvertip, don't you mean 1%? 8.5gal/hr is more on par with my '64 Ford Galaxie. Passes anything on the road except a gas station.)

It's pushing an 18ft aluminum starcraft. If anything I'd say it's probably bigger than it needs to be. Especially since I'll be running it in the chuck where it's more likely to be choppy than not.

I'll be diving into the nuts of it all on Friday.

 

[F_R]

Re: 1978 85hp fuel consumption

I'd say that 1 gal/hr is attained only while going over a waterfall.

 

[ezeke]

Re: 1978 85hp fuel consumption

If the Starcraft is a 18' runabout, the 1978 85hp is a minimum for good performance. I have a 115 on mine and I consider it to be a good balance. If the plate is still on the boat, check the horsepower rating.

If you are running at WOT at 8.5 gallons per hour, I would consider that to be good.

 

[iwombat]

Re: 1978 85hp fuel consumption

Okay good to know.

I'll be taking it out for a spin, and I'll watch the fuel consumption carefully. I'll be especially watching out for waterfalls. It sounds like he's got more of a perception problem than an acutal fuel issue with the whole "gas hog" thing.


Thanks all for the info.

 

[Silvertip]

Re: 1978 85hp fuel consumption

No -- I did not mean 1% of horsepower. I indeed meant 10%. Therefore 115 HP = 11.5 gallons per hour. 200 HP = 20 gallons per hour. 50 HP = 5 gallons per hour. Those figures are all at wide open throttle and will depend on the load, type of hull, wind and water conditions. It nevertheless gets you in the ballpark and is quite accurate with an efficient hull, average load and relatively calm water. As I said, I run a fuel flow monitor and it is spot on with these figures for my engine.

 

[rickdb1boat]

Re: 1978 85hp fuel consumption

I think a better comparison would be how far you can travel with a particular type of boat in an hour with a given amount of fuel. Sure they may all get 10% GPH of their rated power at WOT, but one boat may be much more efficient than another requiring less time to get to a given point, therefore having less run time and using less fuel. Unless of course, everyone runs around at wide open throttle all day..I know that on my toon, I get about 20 miles per 6 gallons of gas using a 70 HP engine at WOT (Much better if I cut back some). My runabout gets a whole lot more MPG using the same HP...I guess what I'm really saying is that it all depends on the type boat you have and the type of boating you do that really determines fuel efficiency....

 

[iwombat]

Re: 1978 85hp fuel consumption

Sorry Silvertip, I got that from later responses. I suppose if I thought about it long enough I would have arrived there myself. How many times have I spent 1hr at WOT?

um . . .

maybe once - maybe.

So expecting a 6gal tank to go 5mi or so to the fishing hole, time off for trolling with the kicker, a few of short runs to "that point over there", and back to the dock in the evening is just about right. All-in-all that's probably about 45minutes of WOT or so during the course of a day.

 

[iwombat]

Re: 1978 85hp fuel consumption

Really what I'm all about here is trying to determine if the "gas hog" description indicates a problem. Given that the guy comes back with an answer of 1gal/hr indicates he's got no idea what it really uses other than a lot of gas during the course of a day. This could mean something, or nothing - it's indeterminite.

In otherwords, it's junk data that I'm just going to have to toss aside going forward.

 

[BF]

Re: 1978 85hp fuel consumption

yes, sounds like more of a perception problem than anything (to me anyway)... non-boaters often are amazed at how much fuel a big displacement 2 stroke can burn. My merc 150 V6 isn't a particularly bad hog for an outboard, but it'll go through 10 gallons in hurry if you're pulling a couple (or three) tubes around.... or blastin' at WOT. But, given our short season here, that only means a few days in the summer where I purposefully try NOT to add up how much the day's gas cost. Definately the scariest part about tubing. My kids are very used to the saying "we need a gas break". When the weekend is done, there are empty gerry cans spread about like beer bottles after a frat party.

I was filling some gerry can's last summer before heading to the cabin for a weekend, it was >$180.. (gas was ~$120 / litre) even the gas station attendent said "ouch". That didn't include gas for the vehicle.

My other boat (with a 45 hp) burns about 5 gal per hour when tubing (which is almost all at WOT). Even for really mild "real life" use... some cruising, some trolling etc etc. 1 gallon per hour for an 85 hp sounds too low.

 

[iwombat]

Re: 1978 85hp fuel consumption

Almost all my experience with two-stroke outboards is with kickers under 15hp. 8gal/hr sounds like a lot at first until you really stop and think about it.

 

[Silvertip]

Re: 1978 85hp fuel consumption

If the guy told you his 85 HP Johnson burns 1 gallon of fuel per hour he either doesn't have a clue or he's hoping you are clueless and will fall for the statement. Fact is, it takes so much fuel to make so much horsepower. I just gave you an example using my 75 HP. It burns 7.5 gallons per hour at wide open throttle. That 85 HP will burn 8.5 gallons per hour. Yes -- certainly it will burn less at lesser rpm. But you have to run longer to get to your destination so the saving are not as high as you think. Maximum burn rate (gallons per hour) or pounds per hour is used in the aviation industry and it applies to boats as well. It's a far more meaningful and useful measure than miles per gallon which is highly variable. You may get 3 MPG on a nice calm day but only 2 MPG on a windy rough water fouled hull day. Whether you like it or not, that's a 33% drop in MPG. If you bank on the 3 mpg getting you back to port you may have to paddle some of the way. Maximum burn rate is not a variable. It's the absolute worst case. If you know how much fuel you have you know instantly whether you can make your next destination on available fuel. But then if you run small lakes and resevoirs, fuel consumption should not be an issue as you can usually see shore. Again, go to Yamaha's web site and check Performance Tests. You will see the 10% is pretty close regardless of technology.

 

[iwombat]

Re: 1978 85hp fuel consumption

I agree, gal/hr @ rpm is the best way to measure fuel consumption. Miles/gal has a whole lot to do with tides.