58' Evinrude Big Twin overheating.

It has water flow. Get that out of the way first.

The thing ran like a champ when I put it in the water.

After fishing for a while, I played around a bit with the boat.

I was adjusting the trim to see which one was right and I would run at WOT between adjustments. It appeared to be getting gradually slower. I thought it was just the adjustments. I forgot my GPS so I don't know for sure if it was or not. Just seemed to be.

I noticed the exhaust housing felt a bit warm and so I checked the head. HOT.

So I tried richening the mixture to see if it was a lean issue, no improvement. I only moved the mixture knobs within their movement and returned them to their original settings after I realized it wasn't helping.

Then, the motor started running without power. It would not run to full RPM and would sit there and rev up and down intermittently.

I tried choking the motor to see if it was a lean issue. The motor just instantly died.

There is oil under the powerhead that appears to be leaking at the gasket between the power head and the exhaust housing. Lot's of oil.

I noticed that the handle that is on the back of the outboard was almost falling off. The bolts had vibrated loose.

The plugs are both black and oily.

What model number do you have?
Does it have a thermostat, is it working properly?

No thermostat on this model. Model number 25034

1958 35 hp, "There is oil under the powerhead that appears to be leaking at the gasket between the power head and the exhaust housing"

first you need to fix the exhaust leak if that is what you have,

next you need to pull your head off and check the water passages make sure they are not full of junk.

than let us know and we can go from there.

Alright, I'll do that first.

When you say you have water flow was that while the motor was running on the lake or while you were using the muffs? Bad thing about muffs is they force water thru the motor and can cover up a water pump that is not working. Hard to miss the tattletale on the Bigtwin while the pump is working on its own.

Tell tale? Where? I was under the impression the 58' big twin had no tell tale.

There was water spraying from the exhaust hole.

That would be the tell tale, at least what I consider it to be, and should be steady and strong. Maybe not quite this but not a mist either.

That's what I was talking about as well.

It definitely was not that strong.

I have a new impeller for it now, gonna put it in and re-seal the lower unit so long as I still have compression.

If I don't, I'll put the lower stuff off in favor of a rebuild.

I just came to realize that I have a substantial fuel leak at the fitting on the out board.

Is it possible that this leak would starve the motor for fuel and oil and cause it to overheat?