Mercury 496 C.I.D. 8.1-liter H.O. 420 H.p

[Nagaj54]

is 700 hours alot for this engine?
I am told these engines are bullet proof.
Boat is a 38' 2006 Sundancer with 700 hours.

 

[paulswagelock]

700 is less than half the average life expectancy, but it is all in the maintenance and care. Skimp on those and it could be done tomorrow.

 

[blaster]

Hours are only one clue of the engines potential longevity.

Maintenance records, cleanliness, and compression test results should also factor into the decision.

My opinion, 700 hours is not a lot of hours. The type of use and maintenance during that time is what matters.

 

[Nagaj54]

Hours are only one clue of the engines potential longevity.

Maintenance records, cleanliness, and compression test results should also factor into the decision.

My opinion, 700 hours is not a lot of hours. The type of use and maintenance during that time is what matters.

Thanks, are these engines good performance engines for the 38?

 

[blaster]

Not a clue, I have not piloted this boat with this propulsion. 38’ is getting close to diesel territory. Are these stern drives, v-drives, or straight inboards? I’m sure someone with this model will chime in.

 

[Nagaj54]

These are inboards 8.1 HO 420 HP.

 

[dtfeld]

Thanks, are these engines good performance engines for the 38?

There are several 8.1 powered 38 Sundancers on my dock. All are very happy with them. Good speed and hole shot. Extremely reliable. Great boat/power combination.

One consideration is they are thirsty engines. I think they are burning 30-32 gal/hr at cruise, but average about 20 gal/hr combined cocktail speed/cruising. On our lake, not a big deal.

If you going long distances on a regular basis, Diesels might be an option, but pretty rare in a 38.

 

[Nagaj54]

Looking at 2 boats
1 with 8.1 s with 370 HP
1 with 8.1 HO with 420 HP

what’s the best bang for the buck and best performance

 

[blaster]

I’m going to go out on a limb and say that the performance difference, if both inboards, will mostly be the top speed. The HO will definitely burn more gas.

 

[paulswagelock]

Theoretical calcs would be about 5 mph faster top end, most of the rest of the performance will be the same.

 

[Gary B]

I had 2006 8.1’s in my last boat.The engines themselves are very good . The first 6 years they were bullet proof then we had multiple problems. Some of which are due to the components Mercury used on the engines. They were not designed to last even though I was very proactive with the Maintenance.

Mercury painted the inside of the fuel coolers and the ethanol in the gasoline ate the paint off of them which caused problems. The coolers are not cheap nor is fixing the paint issues if paint travels down past the fuel coolers to the injectors. There are threads on this site that cover this issue. Mercury would not take responsibility for the poor design of putting paint inside the fuel coolers.

multiple sensors failed - IAC, exhaust temperature & crankshaft position sensors. When these go it puts the engine into safety mode and you have to limp back to the dock. Ours failed on multiple occasions. We used to carry a jumbo zip lock bag with replacement sensors in case one failed on a trip.

The water pumps are also quite expensive to replace and do need to be replaced ( totally expected maintenance). The pump housings are bullet proof however Mercury puts a cheaply made metal clip on the the inside of the pump that holds the pulley shaft in place. The clip should have been brass or stainless so it would not corrode in salt water. When the clip starts to corrode the shaft wobbles and water starts to spray out like a squeezing a hose nozzle. The throttle body & air cleaner mesh is right next to that pulley. The engine can easily ingest the spraying water right into the fuel injection system. If a better clip were used by Mercury the pumps would last much longer.

You may want to look for a diesel 38 DA. The 38 DA is a great boat. The diesel boats are less common, harder to find and more expensive to purchase however the engines should be more reliable and more fuel efficient.

 

[Nagaj54]

Great reply thanks so much.
This is a fresh water boat, will these issues still arise with fresh water?

 

[blaster]

Great reply thanks so much.
This is a fresh water boat, will these issues still arise with fresh water?

I would highly recommend a mechanical and hull survey to root out these potential issues and leverage them in negotiating a purchase price. The money spent on this will potentially save you ten fold in the long run.

I would make a list of concerns based on other users experience to present to the surveyor to check. Of course, an experienced surveyor will be well aware but knowledge is power.

 

[juggernaut1]

I have this boat with the 8.1s motors and also circa 700 hours all in salt.

In my nearly 6 years of ownership, only things that have failed on these motors are:

1 chaffed spark plug lead arcing out against the exhaust manifold;
On ignition, the ECU on one motor not shutting down the fuel pump once pressurised (sent it to Whipple Superchargers in the US to have fixed);
Raw water pump seal (which I now understand has a 3-4 year service life); and just recently
Water pressure sensor on the transmission heat exchanger (which does not send the motor into limp mode).

I haven't had the cool fuel module problems regarding paint chips as we don't have ethanol fuel at the docks where I live, just 95 or 98 RON fuel, and diesel.

At my survey, the things that were identified as needing attention was one cool fuel module replaced (due to obvious corrosion), the exhaust manifolds, and a couple of hose clamps.

I do undertake preventative maintenance and do replace things each year before they fail, and this may account for the reliability I've had from these motors throughout my ownership.

In short check:
When ex manifolds were last replaced;
If the ss elbows have ever been replaced;
When spark plugs and ignition wires were last replaced;
On ignition that the fuel pumps pressurise and then shut down;
When raw water pumps were last kitted with impellers, shaft, seals, bearings, or otherwise replaced in their entirety - their latest design has ss end plates to reduce housing wear;
Last time all heat exchangers were last serviced/cleaned/flushed;
Whether raw water hoses and clamps have all been replaced, including for the generator and aircon (they would be near on 15 years old now).

Check all maintenance has also been done on the generator.

In other, check the fridges and freezer work fine on 12 volts.

The 8.1HO will cruise faster as it has a 3800rpm cruise rating compared to 3600rpm for the 8.1S. The should give you an extra 2 knots of speed which should put it in the 23 to 24+ knot cruise speed zone assuming clean bottom and props in check.
The HO will use more fuel as it has a bigger cam to achieve the extra 50hp plus it is rated to turn higher revs. So the decision on the two motors essentially comes down to how fast you desire to cruise at, if your typical local conditions will allow that cruise speed and whether the extra fuel is worth it.

Good luck - great boat.

 

[Gary B]

Great reply thanks so much.
This is a fresh water boat, will these issues still arise with fresh water?

The corrosion issues with the water pump metal clips will likely not be an issue in fresh water. The fuel coolers are an issue only if you use gas with ethanol. The sensor problems we lived through would not be different if we had our boat in fresh water vs. salt