1987 Searay 268 with twin merc 470"s

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

It`s basically water in =water out. verify the impeller work is correct. the pump assembled correctly or it can suck in hot exaust instead of water. from the impeller it goes thru the water pocker cover. this item is prone to destruction by a severe overheat and leaks water coming up from the impeller.from here it goes thru the connecting hose between drive and transom. A kinked hose or internal collapse will cause lack of water flow. from here thru the connector fitting inside the boat. overtightening the clamp crushes the plastic fitting, no /reduced water flow. from there to the heat exchanger, thru the exchanger and out the riser/elbow.clogger riser/elbow prevents water from leaving the cooling system
You cant, dosent work that way, you need to remove the drive first.

 

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

going on the road, pm`d a number if you need something quick

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Thank-You Bt Doctur,
It is easier to work with one person on this issue, all thou 2+ brains are better than one. Thank-You for the PM. I will very possibly be having some questions, as for we can get back on the water. (with 2 motors)
Regards,

 

[MarkSee]

Re: 1987 Searay 268 with twin merc 470"s

The motor does not overheat with ears on it here at home (because of the water pressure pushing the water thru), but at the lake it overheats when the impeller has to push the water thru.

An idea that might shed a little light based upon your statements above.

If you're running the problem engine on the muffs, how does the water flow that you can visually see coming out the idle relief port compare with that of the good engine?

If the problem engine has drastically reduced flow then that might point to a problem on the raw water side.
If they seem about the same then, to me, that says the raw water side might be ok and really is pushing enough water through and the issue may be on the fwc side.

Regarding the 2nd sentence of water pressure on the hose vs. lake: by what I've observed with my engine flushing on the muffs:
when I turn on the garden hose, the muffs are not making a water tight connection and most of the water is just hitting the water pickup opening and just spilling out; nothing really going into the drive. When the engine is turned on and the impeller starts spinning, the water is then sucked into the drive and the muffs form a better seal around the drive with that pressure.

Maybe someone will correct me on this, but being in the lake with all the water the drive will every need available to it instead of the limited amount of water coming through the muffs, you're not overheating on the muffs for reasons of load, stress or rpm.

Mark

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Hi Marc,
That makes sence to me Mark. I do have a couple of things that I am going to try. (Ideas from Bt Doctur) I am report back after these tests are complete. You could be right thou. It could be on the fwc side of the cooling system. I need to eliminate the raw water side 1st. Thank-You and have a nice evening.
Regards,

 

[stonyloam]

Re: 1987 Searay 268 with twin merc 470"s

There are really only a few things that can go wrong with the 470 cooling system, as far as overheating goes. 1) poor circulation of the antifreeze through the exchanger and engine. Since the engine pump impeller is bolted directly to the cam it is not going to fail, so as far as antifreeze circulation goes the main reason for reduction of flow would be a bad thermostat. The antifreeze flows around the tubes carrying the cooling seawater in the exchanger so a restriction there is unlikely. 2) Impeller failing to circulate enough cooling water through the tubes in the exchanger. Either worn impeller or housing. 3) blocked tubes in the exchanger from debris or impeller pieces. They would show up as blocking the first set of tubes on the starboard side of the front of the exchanger. Tubes could also need cleaning. 4) Restriction of the water exiting the exchanger at the exhaust elbow. The warm raw water exits the exchanger through the aft tube and travels through a tube to the water inlet on the exhaust elbow. The water enters the inlet, circulates around through a channel in the elbow and exits into the exhaust (thereby cooling the hot gasses) and goes out through the outdrive. If the water channel through the elbow is partly blocked it can restrict the flow of water through the exchanger causing an overheat.

One thing different about the 470 is the terminology used. The 470 does not have a "riser", it has an exhaust manifold and an exhaust elbow (the reservoir being part of the elbow assembly) shown here: http://www.mercruiserparts.com/Show...=EXHAUST+MANIFOLD+AND+EXHAUST+ELBOW(ALUMINUM)

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Thank-You ALL for the help & advice. I do have to get to work on this issue, I am armed with information now!