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motor overheating

3124 Views 32 Replies 9 Participants Last post by  newbie
new boat has an 89' merc 470, with a FWC system. while running today, engine overheated since i wasent paying attention to my guages
boat overheated pretty **** bad, smoking to holy **** and spewing anti0freeze to the bilge. if you were in jones this morning, i was the idiot with the smoke pouring from my engine, and doing the tow-of-shame back home.

ive ran the boat 4x prior to this, and quite hard in thursdays weather with no issue. only difference is today, since i left on dead low tide, i only have about 3.3ft in my canal, and i got a bit too close to the edge and was kicking up some nasty black muck. (had no choice, was a bulk-head barge parked in canal)

im assuming i have some sort of restriction of water flow somewhere now? but where do i start looking, and could me kicking up muck have caused it?? i would think so since i had no issues prior to this running the engine in water, or out with ears.
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Toasty Merkruzer / Fish Smoker

I go through a lot of engines!!!

I think yours is a 6 cylinder I/O ?

I would take off the outdrive and clean out the cooling passages and replace the water pump or at least the impeller, I am not sure if you have a replaceable plastic impeller housing. $50 kit?

I would clean out all parts of where salt water goes through. I think you said you are fresh water cooled, so your block should not be affected by the uptake of crud. Disconnect all the hoses and drain plugs and maybe replace any pencil zincs (just because everything will be apart). Basically chase all the passages where salt water goes and make sure the sediment is gone.

Manifolds? I don't think they will be a problem unless the boat always overheated under a load at speed.

Now that your salt water stuff is clean, probably a good time to flush the motor and put new water/antifreeze miture.

So much for the cooling system pennance.

Now for the motor - note the stuff that comes out of the salt water passages, is garbage even coming out?

Note the coolant that you change in the motor ... is there any oil in there? Let's hope not. Bad head gasket.

Change your spark plugs. Run the motor, go for a ride. Take them out if stuff feels wierd, do any of the plugs look different? Is one really clean? Let's hope not, Bad head gasket.

Probably better to do up front... do a compression test.
I was wondering how come one of my motors was running badly... I 'did everything' ... then I did a compression test, one cylinder, no compression at all. Dang!! Motor number one!

If you have oil in the coolant, or coolant in the oil, a really different looking spark plug from the others and or low or no compression in a cylinder or two, a head gasket needs replacing, and possibly a head needs to be machined straight. Just exchange the head(s) at that point for a rebuilt one ($150 plus gaskets?).

I am doing motor number two this year (the other side), why not, I now know where all the bodies are buried with the job!

A good source for hard engine parts (heads, blocks, etc) is Rapid O Marine in Florida.

Good Luck,

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Don't know til you go

Those are good signs. Clean out the saltwater passageways, do the impeller and see how it goes.

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