Merc 7.4 Questions

[gkehoe]

I am looking at buying a 1993 Sea Ray 270 Sundancer with a Merc 7.4L. No idea on total hours or if it has been rebuilt. Before investing time and money in a motor survey, I was hoping someone might be able to share some general comments on this motor. Really interested in approx Hours Per Gallon stats, overall reliability of engine, ease of maintenance, approx # of Hrs to rebuild on average, or "run away quick" suggestions. Thanks in advance for taking the time to reply.

 

[Scott Danforth]

Re: Merc 7.4 Questions

the 7.4 is a nice engine, extremely reliable. it will suck a bit of fuel, then again, your pushing a 270. the hours to rebuild depend solely on maintenance. with proper maintenance, the motor will last a long time.

Fuel consumption will rely on load, water conditions, wind speed and direction, engine speed, prop, etc. expect anywhere between .2 and 2.5 miles per gallon depending on the parameters.

 

[HT32BSX115]

Re: Merc 7.4 Questions

the 7.4 is a nice engine, extremely reliable. it will suck a bit of fuel, then again, your pushing a 270. the hours to rebuild depend solely on maintenance. with proper maintenance, the motor will last a long time.

Fuel consumption will rely on load, water conditions, wind speed and direction, engine speed, prop, etc. expect anywhere between .2 and 2.5 miles per gallon depending on the parameters.

Yeah, I'll agree with the above. Probably one of the best engines made by GM.

I installed a 1997 7.4 In my Four Winns 21' boat. At 3000 RPM ( 30mph) it burns 10gal/hr. In a heavier boat it's going to use more fuel to get the same speed.

There's no "set" time for rebuild. rebuild or replace when it starts using a LOT of oil or the compression drops below recommended limits etc....

 

[Bondo]

Re: Merc 7.4 Questions

There's no "set" time for rebuild. rebuild or replace when it starts using a LOT of oil or the compression drops below recommended limits etc....

Ayuh,... 'n it might be 500 hours for a Hot Rod boat,...

Or,... 5000 hours for a Cruiser type boat...

Depends on Maintenance, 'n Abuse... 'n how much of each...

 

[tpenfield]

Re: Merc 7.4 Questions

Ditto on the good comments about the 7.4L (a.k.a. GM 454). It is one of the more bullet-proof engines on the water. There are no real trends to follow in terms of maintenance that I am aware of . . . except, if your engine is based on the GM 454 "Mark IV" then it has nylon teeth on the timing chain. As the engine ages they *may* become brittle . . . so something to keep in mind with an older engine.

I have a 1991 boat/engine and it is 24 feet . . . gets about 6-7 gph overall fuel consumption and maybe 2 mpg during cruising speeds. Your boat is a bit bigger, so maybe a bit less than those numbers. I have 500 original hours and did a valve job last Fall, because the joint between the exhaust manifold and the elbow failed and allowed water to get in/around the valves. The 'bottom' end of the engine looked fine at 500 hours. Very little sign of wear.