Mercruiser 260 3000 rpm wot and drop in oil pressure

[chris0061]

I had bought a 1980 Cobalt Condesa over the winter and we took it out for the first time this weekend. First I'm suspicious of the engine in it. The previous owner swore its a Mercruiser engine, after looking closely I think its a car engine. When we took it out I put the same prop on it that pushed my 24 foot mark twain since this is 23 foot and roughly the same style boat. The prop is a 19 pitch stainless the engine is supposed to be mercruiser 260. First I could only get it to 3000 rpm at wot. Second I noticed the oil pressure fall a little after running wot for about a minute or so. I let it idle around and the pressure came back to about 45. It had dropped to about 30. We came home I changed oil and out-drive lube and will take it out today to see if that helps and I've got a 17 and 15 pitch prop I'm going to try. Any thoughts on this situation?

 

[Don S]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

If it only goes to 3000 rpm, the prop is not your problem.
You can go up to the Adults Only Sticky and go to item #13, it's a list of possible things that can cause rpms to be that low. You can also find manuals there along with some other information that will help you find your problem.

 

[chris0061]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

ok thanks Don

 

[chris0061]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

I checked the dwell, was under 26 so adjusted it to 30 degrees, rang is from 26-31. Checked the timing it was way off so set it to 8 seems to run smoother, had to adjust the idle after timing. The rotor was oily residue on it so cleaned everything with elec cleaner. Will test this afternoon and see if it all made a difference.

 

[QC]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

Did she plane? Are you sure the tach is right?

 

[chris0061]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

yeah she planed good. I forgot my gps so I'll bring it today and do the math on it. I'm not sure about the tach, It reads right with the dwell meeter at idle but beyond that I don't know. Its not the tach that cam in the boat and I have another on the way so I'll keep that in mind.

 

[QC]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

If she planed easily, I am pretty confident the tach is wrong. If either low power or the prop was limiting you to 3000 RPM I believe she would struggle to plane . . .

 

[chris0061]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

Went out yesterday with the 15 pitch prop and could get a little over 4000 rpm wot. It's almost got me wondering about the upper if its the wrong ratio. The engine runs smooth as can be it just doesnt seem to have the power of a 350. The boat is 23 feet and I would think a 15 pitch prop would make it hit its wot range about 1./2 to 3/4 throttle. The speed was 35 mph at 4000. Will check carb cable tonight.

 

[Bondo]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

Ayuh,... A 350 should be running 1.50:1, which is the tallest standard gears...

I'd think a Compression Test is in order,... It sounds Sick..

 

[chris0061]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

I did a compression test when I put new plugs in. They were all around 145-152.

 

[chris0061]

Re: Mercruiser 260 3000 rpm wot and drop in oil pressure

However I think your right, The man sold me a sick engine. When I ran it the first time when I tryed to wot it you could smell that old sick smell but after I changed the oil after running it again wot for a while the smell went away.