Mercruiser Overheat

Just a thought, I beleive there is a flip flop valve in the lower exhust cow horn that prevents back wash when slowing down. I have blown them out before but perhaps they can restrict the exhaust---hence the change in note and overheating. Dave.
 
Re: Been there - done that....me to............

On my boat the hoses (2 x 120 hp Mercruisers)just burst open.Filling the engine compartment with impressive amounts of steam and hot water.Even after fitting new riser still had overheating problems afterwards.Suspect that crud and scale breaking loose from within the equally badly corroded engine block caused overheating all the time the boat was in my possesion.Dreadful cheapskate design and what ever happened to the new ceramic or was it plastic risers that were on the verge of being launched.
Raw water cooled engines suck big time.
 
Mercruiser Overheat update

Thanks for all the well informed advice,

I suspect as most that manifolds are required, changed these on a previous boat before they got to this stage & they ran luke warm after.

These on the otherhand would give first degree burns at 10 paces.
The disconcerting thing was our mechanic dismissed this as a problem & concentrated purely on water flow.

We trialed without a stat & with a new stat but she would still overheat!

We left our berth on the day that she overheated, our first run was to an anchorage only 3m from our marina where we stoped for lunch, nothing was apparently wrong at this stage, after restarting after lunch we proceeded at 5 knots to leave the anchorage but imediately overheated on flooring the throttle & it has been like this eversince.

I planed to change the manifolds anyway so this has just brought the change on sooner.

Now for the killer question, where is the best place to pickup a set of 1 piece manifold/risers & what is a reasonable price ?

The last set cost £1000 so it's not exactly back pocket change!

Thanks all
 
Re: Been there - done that....me to............

Yes indeed. My first symptom was one of the fannimold stoppers busting clean open. Then hoses started to pop off the spigots inspite of a severe tightening of the worm clips and finally (and funnily) I was on my way out of Pwllheli and a hose burst, so I turned round and came back in and moored up and the fuel quay.

The engineer fitted a new hose and this was being watched by Shipswoofy, who was peering down into the engine bay. I revved the motor up and BANG!! Poor ol' Shipswoofy. Never seen him move so fast in all my life. /forums/images/graemlins/grin.gif

Those Jabsco pumps are amazing. It was like watching one of those American movies where a car drives over a sidewalk fire hydrant
 
Obviously you are not aware that seawater temp and salinity has a direct bearing on this, and varies greatly from place to place!
 
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