Mercruiser Cooling/Overheating Question

[sjajf16]

I have a 5.7 LX Mercruiser and am having a issue with it running hot. Since I have had the boat the gage has always held a solid 175 degrees. Went out for a run this morning and the temp started taking off to almost pegged within 10 minutes. Pulled back on the hoist and raised boat so outlet was just above water line and had good water flow coming out (water was extremely HOT) also verified intake area was not restricted. Opened the hatch and this is where my question is, on the thermostat housing there are two larger hoses fore and two smaller aft. Started the engine back up and went back to the hoses. The forward/starboard one was HOT the other three stone cold. While not getting into where they ran to can someone tell the coolant flow of these hoses and if what I described sounds like a thermostat problem or something more? Found this pic online and is exactly what I have. Thanks for any help/advice.

Steve

 

[Bt Doctur]

the large one on the left wont flow unless the thermostat is open .So if it is getting hot there is no flow .a stuck shut thermostat is a possability.The one on the right and the 2 small ones are flowing cold water that is normal

 

[sjajf16]

Thanks Doctur! Will be swapping it out tomorrow, I'll follow up with what happens.

 

[sjajf16]

Ok, thermostat didn't do much...quick synopsis...got the thermostat replaced, started up on the hoist and temp went to 175 in a pretty short amount of time, temp stayed there give or take a bit of needle movement. Got out on the water under load and temp started climbing pretty steady. Fluctuated between 200-225 but did not peg out (250 on the Gage). Pulled back on hoist and kept motor running, temp never went much below 225. Tried spinning up motor to 1200 rpm no load to see if pulling in more fresh water would bring temp down since the water temp at my place is around 60 degrees, temp stayed where it was. Started getting dark so I gave up for the night....

Anyone have any thoughts or ideas?

Thanks
Steve

 

[sogood]

Is your coolant flowing through freely? Do you have a good flow of warm water through the exhaust. A blockage in the exhaust side can restrict the free flow of water and stray exhaust flapper down in the Y pipe can often be the culprit.

 

[sjajf16]

Thanks sogood, when I lift the boat out of the water enough to see the exhaust discharge, there seems to be good water flow discharging on both sides, not sure if there is a way to ensure good flow through the entire system. As far as exhaust, am I looking at the risers or the manifolds themselves. Is there a possibility of the water pump not meeting demand under load? Also is there the possibility of an issue with the impeller in the drive? Although I did have it replaced last year when I had the drive serviced and bellows replaced.

 

[wellcraft-classic210]

Did you get a chance to run it after the new impeller was installed and drive serviced without overheating?


Was the temp control OK prior to the work last fall ? -- If so something may have gone wrong during the install -- Pinched hose , waterpump and impeller / water pump tube / other ???


Might be good to inspect those Flappers also.

 

[sjajf16]

Yes, the work was done at beginning of last season, ran fine all year, temp was 175 or below all season. Is there a way to check the water feed coming up to thermostat housing? I believe it's through the two smaller aft hoses on the thermostat housing. Going to try pulling risers and elbows tonight and try to get to the two flappers on the Y pipe.

One other question, just to be sure, water exits out through both sides near gimble housing and through prop, correct?

 

[Bondo]

One other question, just to be sure, water exits out through both sides near gimble housing and through prop, correct?

Ayuh,.... That is correct, But,....

If yer liftin' the boat high enough to see the idle relief ports, yer also liftin' the impeller outa the water,.....

I'd rebuild the raw water pump, 1st,..... then see if ya got a problem, or not,.......

 

[sjajf16]

Thought about that, but lifting to the relief ports shouldn't be any different than idleing with the muffs sitting on the trailer, correct? I had never run it on anything but idle and the intake ports stayed completely submerged

 

[sjajf16]

One question, is there a way to check the raw water pump before I pull boat off the hoist, trailer it and pull lower unit?

 

[wellcraft-classic210]

You could Disconnect the inlet hose to the engine & see how water flows --You will not have a way to measure flow so its not an all inclusive test -- But flow it should be significant as in steady & strong-

 

[sjajf16]

Sounds good. Anyone familiar which hose? I believe it's the smaller aft ones on the thermostat housing

 

[Lou C]

Thought about that, but lifting to the relief ports shouldn't be any different than idleing with the muffs sitting on the trailer, correct? I had never run it on anything but idle and the intake ports stayed completely submerged

The muffs push water in under pressure, but just dipping the water intakes into the water does not do the same thing. In order for it to prime without a pressurized flow, the impeller housing must be under water.

 

[Bondo]

Sounds good. Anyone familiar which hose? I believe it's the smaller aft ones on the thermostat housing

Ayuh,..... The small hose, Aft, Port-side, lower on the t-stat housin',.....

Pointed straight up into the air, at idle, the water should bubble up 5" or 6", before it tumbles over onto itself,....

Rubber veined water pumps are Flooded Entry pumps, they don't suck,.....
The raw water pump sits, just Above, the water inlet ports,.....

I'm thinkin' ya want a full Kit, not just a new impeller,....

 

[Bt Doctur]

Rubber veined water pumps are Flooded Entry pumps, they don't suck,.....
The raw water pump sits, just Above, the water inlet ports,.....
Red are the reliefe ports, Blue is the impeller housing.

image search

 

[Bt Doctur]

Green is inlet from outdrive, Red is engine water circulating, Blue is water exiting the motor going into the manifolds and out the elbow

 

[Bondo]

Port-side forward then,....?...

 

[sjajf16]

Port side forward is what I'm getting out of it, thanks again doctur, the illustration was awesome! And it leads to another question...if the two smaller ones are exiting the motor, shouldn't they be pretty warm once thermostat opens? The only one that is hot is the one from the circulation pump on the front of the engine, those two aft are stone cold when it's running

 

[Bt Doctur]

The 2 small hoses aft contain the water leaving the engine. If your temp is 170 then the water leaving the engine should be close to that. Saying the hoses are cold leads me to believe the water is coming in and going right out to the manifolds. So either the therm is staying shut, defective, remaining closed installed wrong or the plastic sleeve (if used) is installed wrong or the therm housing is shot from corrosion