Need HELP on very difficult OVERHEAT issue!!

[dmeals]

This is not your typical overheat issue. I am working on a ?73-74 Mercruiser 225 Ford 302 in houseboat coupled to Merc MCM transmission with TR drive. The port side of motor getting very hot. See below readings taken after 15 mins at 1,000 RPM, just above idle:

Therm hsg 151 degrees

Port side block, 130
Stbd, 130

Port Exh Mfld, 171
Stbd, 130

Port Riser, 174
Stbd, 115

Port Exh Elbow (Y-Pipe equivalent) 219
Stbd, 104

Have performed the following service in attempt to get temp to spec:

- Replaced seawater pump w/new brass pump, new impeller
- Replaced thermostat (142 degree) & ck?d hsg ? OK
- Inspected all hoses to ck for delamination ? OK
- Replaced port exh riser on manifold, 40-50% rust blockage
- Removed & ck?d exh manifold ? Appears OK
- Removed & inspected exhaust elbows at transom to ck for blockage, broken exhaust shutters, etc ? OK
- Ck?d water flow from all hoses (have not measured flow yet) ? OK
- Ck?d seawater pick-up ? OK
- Ck?d seawater hose & inspected for delamination ? OK

This morning, working on carb, Holley 4Bbl . Motor runs very rich. Previous owner had floats set wide open, lots of smoke at idle, extremely rich Am thinking that it may be possible given the intake and the way the Holley feeds from two sides that the carb could be producing enough fuel that is igniting in exhaust manifold and burning in port side of elbow at transom?? Maybe, maybe not. Just pulling my hair out to repair this one. Concern is that the high temp will eventually burn/damage the boot between the riser and elbow.

This is a tough one folks. Any suggestions greatly appreciated!!

 

[anymanusa]

Re: Need HELP on very difficult OVERHEAT issue!!

Sounds like you're burning fuel in the exhaust. Get the carb right and then worry about overheating.

 

[kd7isf]

Re: Need HELP on very difficult OVERHEAT issue!!

If your manifold was that bad, your riser is too. Replace the riser when you replace a manifold...

Replace the power valve -- Holley's are infamous for blowing those -- once that happens, it runs VERY rich... Only takes one backfire....

Then get a carb kit (most will include a replacement power valve), clean the carb well (including all passages) and then set the float level AND drop correctly (no, these are NOT the same thing and both need to be set properly.....)

Hope this helps : o )

 

[dmeals]

Re: Need HELP on very difficult OVERHEAT issue!! UPDATE

Re: Need HELP on very difficult OVERHEAT issue!! UPDATE

Adjusted float level on carb. Confirmed choke is functioing correctly. Still have white smoke but no fuel on water. Motor starts, restarts, runs perfect. Suspect smoke/burn is due to ring/valve wear.

Performed water flow test from therm hsg to manifolds, both sides same. Performed water flow test at exhaust, both same.

Test ran in gear at 1,100 with the following temp readings:

Sender 145-150
Port Riser, 190 Stbd, 134
Port Mnfld, 195 Stbd, 153
Port Exh Pipe, 200 Stbd 105

At this point plan to install a new exhaust manifold. Have been hesitant because they are very pricy ranging from $300-600 for this motor.