Replace or not? Intake Manifolds on Merc (2x) 5.7L MIE after several years storage

I'm recommissioning a boat with two 5.7L MIE, 1995 inboards after several years of layup. The engines (named Burt and Ernie--port and starboard--by my 4 year old son) have been turned consistently over the years just not started. Raw water cooled. Ran in saltwater, then fresh.

I'm trying to decide whether or not to replace the intake manifold, after finding some loose rust debris (scale) when inspecting inside the thermostat port, and through the holes that fit to the circulating pump. I have a strong industrial vac that will get some of it out, but should I go ahead and replace it? If so, is this a big job? At this point I'm going by the "if it ain't broke" principle, but I'd hate for some other rust derbis to clog up some port once underway and have to replace it later. There's no evidence of any seal or gasket failure. The outside appearance of both engines is quite clean in fact.

Thoughts?

Re: Replace or not? Intake Manifolds on Merc (2x) 5.7L MIE after several years storag

Howdy,

If you use the same logic considering the blocks and heads.....you might be inclined to replace the engines since they probably have the same amount rusty scale throughout.


The intake manifolds are probably usable. This is quite common in all raw water engines. If you're worried that there might be too much rust that could break loose, you could try flushing out the engines as best as you can. You could probably remove the soft plugs from both sides to enhance your ability to flush the loose rust and debris out the blocks.

I also removed the water pump and flushed the block using a hose and got a lot of rust and sand that was sitting in the bottom of the water jackets.

It was easy for me since the engine was out and sitting on an engine stand.

It won't be as easy for you with the engines in the boat.


If you do nothing and just run them you'll also probably find that as long as they don't get hot you probably won't be able to tell much difference.


I believe that Mercruiser has a procedure described in a service bulletin for starting an engine that has been sitting for a long time. It involves either getting an adapter or making one for turning the oil pump using a drill to pre-oil the engine prior to starting.


You should also look VERY closely at the exhaust manifolds, riser/elbows and gaskets. The risers (gaskets) could leak and allow water to enter the engine via an open exhaust valve after shutdown.



These are just a few areas to think about.

I'm sure others will jump right in here!



Regards,


Rick

Re: Replace or not? Intake Manifolds on Merc (2x) 5.7L MIE after several years storag

Thanks HT, I appreciate the insight. Actually, both engines are out of the boat and in the garage. Manifolds and risers are off, wires, electric and pumps are removed. And the engines are roller stands. So your advice is good. I'll try running a hose throughout every (water) hole possible and see if I can get rid of some, or most of the debris. Should I be concerned about getting any moisture in the exhaust openings, where I've removed the exhaust manifolds?

Second, where do I find the service bulletin regarding restarting long layed up engines?