Sea Ray

One time when I was replacing my exhaust I also wanted to ensure that the engine internals were good, so I removed the heads, replaced all the valves and reassembled.

All was and is good. It was a good insurance policy.


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Flagshipengine.com on the west coast of Fl has new GM longblocks. I have almost the same problem on my 1998 454 mpiHorizon engines

Thanks Stressbreaker! I will have to check them out. My mechanic cut his teeth at Sea Ray working on Mercruiser so I am confident in his diagnosis.

Hey Wingless. Do you still have your 380? Do you have the same GM 454's that are out of production? My mechanic made a decision to reinstall my manifolds after inspection. This engine has already had head/valve work and so, after some serious discussion, we decided the head removal was a lot of work that won't bear fruit. Although, with long blocks in short supply we may be looking at some other alternative to re-engine this thing.

Any other thoughts? We started looking at a pair 502s if you can believe it...(I am learning what BOAT really stands for)

Yes, my 454 MAG MPI Horizon engines are still in-service on the 380DA that I have owned for 18 years.

On mine, I turn my own wrenches.

This engine has a few design deficiencies that took me a while to discover, then arrive at solutions, either by performing undocumented preventative maintenance, or by engine modifications.

Now, instead of the performance problems associated w/ those design problems, I instead have properly operating engines.

One thing that REALLY bugged me was being forced to discard an obscenely expensive exhaust system every three to four years like clockwork. I would remove the elbows for internal raw water passage inspection annually to determine if I could justify getting another year out of those parts.

At the last replacement, four years ago I had enough!

I redesigned the exhaust system, from impossible to flush and retaining raw water 24/7/365, to now draining after every usage, then flushing w/ fresh water, followed by soapy water, then Salt Away, finally draining bone dry, ready for the next usage.

My most recent disassembly / internal raw water passage inspection revealed the parts still looking brand new after four years of service. IMO, these parts should now last the life of the engine.

Some other changes I made were a custom high-volume high-pressure five-zone oil change system. It sucks my engine sump dry in ten seconds for a five minute oil change cycle. My suggestion is add this if swapping the engines. If not, mine was installed by me w/ full engine sumps w/ very little spilling.

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Another change I made was to design and implement a thermostatically-controlled heat exhaust system. When I started operating in the tropics I discovered that heat soak vapor lock would prevent restarting the engines after sitting for an hour. Now my system kicks on and off to maintain the engine room cool enough to prevent that problem. Problem solved. This was all before Mercruiser introduced that expensive kit to conceal the vapor lock by pushing fuel through to purge the vapor.

Sorry for your problems. For me the 454 MAG MPI Horizon engines are now an acceptable long-term solution. I have no idea on the 502 engines, but they are probably fine.

I have the same boat, same year, same engines. You’re speaking my language as im still limping along (in freshwater) though the boat was originally in saltwater. Kudos to you for your creative mods....wish i had that level of expertise!