overheat

[b0mbtrack]

mercruiser, inline 4 cylinder 140. engine number B404271. overheats at full throttle. already replaced thermostat and pump impeller, pulled hose off of where it goes into the engine and there is water flow. Like i said, it only overheats at full throttle and takes a while to actually overheat, any ideas?

 

[erikgreen]

Re: overheat

Backflush the engine to clear out any junk stuck in the block, and if you don't find anything check your circulating pump.

Erik

 

[b0mbtrack]

Re: overheat

to backflush, do you go before or after the thermostat?

 

[Limited-Time]

Re: overheat

Both..................also could be manifolds and risers....................as for the circulating pump...................not likely...............and not the first place I'd look.

 

[hard-3]

Re: overheat

My bet is in manifold and risers I once read that 1/8th inch of corrosion has the same heat transfer rate as 1 inch of cast iron

 

[chiefalen]

Re: overheat

What year is the motor?

5 years tops on a riser in saltwater. And thats with flushing it every time you trailer the boat.

You ever pull the engine mounted water pump to see if the vanes are still there?

You have a flapper come loose thats clogging your exhaust?

When you pull your riser look down the pipe see it there?

You might not have one go online and pull up a view of your year and model # engine and outdrive.

Now a word about w. o .t. You got a ole girl there i'm betting cause you wrote 140 hp. Newer boats have 3.0l motors.

What is w.o.t for your engine, do you know?

I'm betting it's 4200-4600 rpm just a guess.

That boat should cruise around 3500 rpm. You run it at w.o.t day in and day out your gonna be posting on how to rebuild the motor.

Good luck hope you find out what your problem is.

 

[b0mbtrack]

Re: overheat

yeah i got the engine number up there but am not sure the year, it is an old one though and i don't do wide open all the time but it does get up to about 4200.
now about the manifold and riser, it is an in-line engine with one of those one piece manifolds (I think, i'll double check tomorrow). i've never done one of those before but do they have the same rule at 5 years to change them? If so i'm sure that would be the problem because i don't think it was ever done. So is it the same rule with those type of manifolds?

 

[chiefalen]

Re: overheat

I flush every time i come off the water. Pulled the engine yesterday, i cant believe what my almost 3 year old riser looks like.

I'm in saltwater, if i get another year or 2 i'll be lucky.

If it were me i would pull the riser. Or wait. If the overheating condition goes over 185 do it now. If not wait till the winter.

Good luck

 

[b0mbtrack]

Re: overheat

thank you, i don't think it has ever been done. boat is a 1980 : )

 

[b0mbtrack]

Re: overheat

took off the manifold and riser, found riser had some build up so i am just going to replace both. i looked in the manual under the troubleshoot section and it says a blown headgasket can cause a situation like this, i was just wondering how a blown head gasket would do that?