Ok thats why they were cheep whats bad with them thanks mike
I've seen many guys come in to the marina with those 3.7s, and they all had the same problem: cooling/overheating issues via coolant mixing into the oil/block. I forget exactly what the cooling issue was specifically, but it basically leads them to think they have a blown head gasket because of the symptoms, when in reality it's something to do with the crappy block design and seals not holding up near the crank area and/or the cam area that separates the coolant and oil. So much of a problem, Mercruiser themselves even put out numerous bulletins to try and head these issues off at the pass when it started having such a common occurrence, but it was far too late in the process after they were already manufactured, in the hands of customers all over the world, when the massive amount of problems started rolling in.
They have had all of the following as being REALLY common issues (when saying 'issues', I'm really saying 'faults that happen far more in this motor, than they ever should, and far more than they ever arise in other likewise motors in the industry under even average to very light use"). So, here it goes:
- The impeller is driven via the end of the camshaft and it has an 'after the fact' bandaid seal to separate out fluids/oil/low-water that ends up going bad from warpage due to even normal engine temps. (This is the head gasket issue many people dig in and "fix", only to find out after all that work, that it was never the head gasket to begin with).
- most of this above stems from the poor choice in what they used to build this engine: cast iron heads with aluminum block... -_- That alone is asking for trouble back then, because the whole era was an engineer's wet dream as it still hadn't really been thoroughly figured out yet like a lot of today's stuff (they still hadn't figured it all the ins/outs and ask the do's/dont's in the weight saving area of engine efficiency yet, and various other specialty areas of the engineering of everything, so they would do wonky things like over engineer things that didn't need touched, and not address issues that really should've never happened to begin with, ie- aluminum block with cast iron heads. Going the other way would've been more acceptable (cast block and aluminum head) but they didn't do that. They were trying to shave some weight, and "aluminum everything" was becoming the new wave trend in the market. So, to stay competitive, they rolled out the 3.7 the way they did, and it just didn't work out.)
- there were Electrical/charging issues out the wazoo. Something to do with the way they set up the wiring on this engine being sub-par and the stator always crapping out nonstop on these things with seemingly no rhyme or reason as to why.
- a few other issues that show up here and there. But, the main ones are the block seals going bad/leaking/mixing coolant with the oil because of faulty 'after the fact' rig jobs they pulled (remember the service bulletin I was talking about earlier? It was for a "fix" for the crappy seal due to all the warping that would go on in the block/crank area) and the mixture of an aluminum block with cast heads being the other huge issue.
Sorry for the long winded reply. I just didn't want to see you get burned like I've seen happen to many people over the years with the Mercruiser 3.7. It was a good idea they had, being semi modular, but it just didn't work out as well as it looked on paper.