1987 Searay 268 with twin merc 470"s

[modems]

I have a 1987 searay 268 with twin 470"s. The starboard engine runs fine at apx. 148 degrees. My port motor overheats. I have just put in a new impeller and complete housing kit (Gaskets and housings) It still over heats, but not as fast as before. I have been doing a LOT of reading here over the past 3-4 weeks. I have also changed the thermostat. Ran it w/o the thermostat to no avail. I am pretty much mechaiclly inclined. Need to know whats the next step(s) to take to cure this issue. I do know about the 470"s and the issues with them. I have not let the motor go past 200 degrees, as I am aware of the issues that may arise with this motor. Any/All help will be appreciated. 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.
Regards

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

I also have checked the front of the heat exchanger for impeller pieces. The old impeller was NOT in pieces when I changed it out. No telling about prior to buying the boat, if the impeller was changed and if it was in pieces at that time.

 

[MarkSee]

Re: 1987 Searay 268 with twin merc 470"s

Welcome to IBOATS.

Seems like you may have a blockage going on somewhere.

Could still be a partially clogged heat exchanger; do you have the larger 4 inch exchanger?
Maybe a blockage in the exhaust manifold/elbow/gaskets? Remove and inspect.
Water circulation pump?

It is recommended to run with a thermostat and test it in a pan of water to make sure it's operating properly.

Should be getting some additional ideas or order of testing by a seasoned pro here pretty soon.

Mark

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Hello Mark,
Yes, it is the 4 inch heat exchanger. I have not taken off the exhaust manifold or elbow to look yet. The Water circulation pump you are referring to is the one that works the anti-freeze thru the motor, at the front of the engine?
Thank-You for the help.

 

[Eric 3.7LX Alpha 1]

Re: 1987 Searay 268 with twin merc 470"s

Have you checked the flow from the outdrive into a container.... timing it at the correct RPM yet? Here's the service bulletin on the procedure to check it:

View attachment 82_04.pdf


Here's what Service Manual 8 has for possibilities of over heating:

 

[stonyloam]

Re: 1987 Searay 268 with twin merc 470"s

As Eric suggests check the flow from the exchanger through the elbow. If there is a restriction in the elbow it can reduce the water flow through the exchanger. Remove the aft hose from the exchanger (or from the elbow) and attach a garden hose. Water should flow freely through the elbow and out of the outdrive with little or no backpressure

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Thank-You Eric,Terry,
Will try removing the hose from the aft exchanger (No hose connected at elbow) and see what I get and will report back.
Regards,

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

I do have one more question now. When I put in new impeller and reinstalled lower unit, The new water tube slid over another smaller tube during aligment and installation. Does this sound correct? Thank-You.
Regards,

 

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

There has to be a hose, thats where the outflow from the heat exchanger goes out of the motor.they should be running in the 165-175 range ,there fresh water cooled .

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

No, They are intercooled. Have the anti freeze running thru the motors.

 

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

you dont understand, sea water enters the heat exchanger to cool the A/F then exists the heat exchanger thru the riser/elbow.

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Hello,
Yes, I do understand that. I was thinking that you thought that this boat was fresh water cooled ONLY. (no anti-freeze) Thank-You.

 

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

Raw Water Cooled= uses whatever water the boat is running in
Fresh Water Cooled= (full kit)engine block, manifolds contain AF
Half kit= only engine has AF
470 aka 3.7 is a full system. block and manifolds have AF
"Will try removing the hose from the aft exchanger (No hose connected at elbow) and "
Explain this then.

 

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

"I do have one more question now. When I put in new impeller and reinstalled lower unit, The new water tube slid over another smaller tube during aligment and installation. Does this sound correct"

not really, the guide tube fits IN the upper pump cap to guide the copper tube inth the rubber bushing in the upper cap.

 

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Fresh Water Cooled= (full kit)engine block, manifolds contain AF. Thank-You for the clarification. Am new to iboats.
There is no small hose connection at the elbow except at both ends where the are large hoses connected.(4 inch or so) That I could see. Not a lot of room to work in the engine compartment on this boat. Also, I am here to get help to repair my overheating issue. I never claimed to be an expert. Al thou I am very much mechanically inclined. Thank-You.

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Ok, I do see it more clearly now. The elbow is also a part of the reservoir...Aft side of reservoir.

 

[Bt Doctur]

Re: 1987 Searay 268 with twin merc 470"s

on your motor there is a 1 inch or so hose on the port side of the riser. the water coming out of the heat exchanger goes out that hose, out the riser.The hose between H and F. Your runnig temp is 165 Deg.
go here Boatinfo - The library, containing manuals, brochures and other technical documents from the last hundred years! and look at manual 8. manual 6 for the drive http://www.boatfix.com/merc/Servmanl/6/6covr3.pdf

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Thank-You Bt Doctur,
Looks like I have some work to do here. Do you suggest that I start a "I" and do a back flush to look for any possible restrictions? Thank-You

 

[modems]

Re: 1987 Searay 268 with twin merc 470"s

Should of said, back flush the fwd hose at H/E and watch for free water flow out the back of the outdrive?