2004 Mercruiser 8.1 motor advise

[lisatim3640]

Good afternoon everyone! Looking at a 2004 420 w/ Mercruisers 8.1 with 1100 hrs on each motor. We initially were looking at diesel motors but was curious if these gas 8.1 motors are reliable or not. Thanks in advance for any positive or negative info

 

[Stee6043]

They are very reliable. I've got 1300 hours on my 7.4's and...knock on wood...with proper care they will last another 1300 before any major work. I believe the 8.1 and 7.4 share many design features, if not the same block? It's all about how well you take care of them. Have a compression test done, maybe check oil samples, buy with confidence.

I went on a charter fishing trip last year on a Tiara with 7.4's. I forget the exact number but I believe he was over 5,000 hours. He was taking them in this winter to get them rebuilt as "preventative action only". Still ran like a champ.

In the "for what it's worth" category, anyone that tells you gas motors are only good to 1,000 hours are generally meth addicts . My 2019 GMC pickup truck has 24,000 miles, practically brand new, and I just pushed past 700 hours. Not directly relevant to how marine engines run but still...

 

[scoflaw]

No the 8.1 is not the same as a 7.4, way more complex with the sensor system, basically more stuff to fail.
I prefer the old style 7.4/8.2 setup. Just bought me an 8.1 and learning the hard way although the 8.1 in my truck has been super reliable.

 

[sbw1]

The 8.1s are excellent engines. They proved to be absolutely reliable in our 3200. Also very torquey and got great mileage. Crusader set them up differently than Merc did. Crusader impellers can be changed in 30 minutes; oil filters, fuel filters are easily accessible and the fresh water pump has a bronze or stainless impeller and does not wear out. Merc 8.1s are much more challenging to provide routine service on. The one concern I had about the 8.1 design is the cylinder walls are on the thin side unlike the 7.4. This difference will present challenges when it comes time to rebuild them as boring them is not really a good option. It would lead to overheating. There might be some work arounds for that issue, although I do not know for sure. May a sleeve can be used. Well cared for 8.1s should last 2,500 to 3,000 hours or more.

 

[mrsrobinson]

Well, DIESELS are sooooooo much better...

I wanted 8.1s in my "next" boat, did a lot of research on them, sea trialed 2 boats that had them. From what I read here and online they are solid/reliable engines. Both of the ones I sea trialed had fuel issues. Had I found a nice 380 with 8.1s I would not have hesitated to make an offer.

Your biggest concern IMHO is going to be resale because of the "1000 hour" perception prospective buyers will have, so get a great price.

 

[lisatim3640]

Thanks everyone for the great advise!!!!