merc 140 pontoon
Petty Officer 2nd Class
- Joined
- Aug 23, 2003
- Messages
- 129
Merc 140 - Problem 1 - Engine Overheats at High RPM<br /> <br />Hello. Thank you in advance for any input.<br /> <br />My 1974 Mercruiser 140 holds 137 degF steady at idle, about 145-150 degF at 2500 rpm, but above 3500 rpm the water temp slowly climbs. I throttle back when it reaches 180-190 degF, and over 5-10 minutes it drops down to 145-150 degF.<br /> <br />I have pulled the water feed hose from the thermostat housing, and have strong flow from the stern drive water pump (just replaced that pump and housings). I have pulled and flushed the hose from the engine circulating pump to the thermostat housing, and the hose from the thermostat housing to the exhaust manifold. Both are fairly new and weren't very dirty. I have confirmed that my 140 deg thermostat is working correctly.<br /> <br />At this point, I assume I have (1) a water blockage within the block or within the manifold/elbow water passages, or (2) an exhaust blockage. Here are my questions:<br /> <br />How do I look for a water blockage? I have never removed a manifold before, but am willing to do so. I tried taking the upper elbow off the manifold, but it won't budge, and I was hesitant to pry it. I assume I also need to order all of the gaskets prior to removing anything.<br /> <br />How do I look for an exhaust blockage? I have read about the exhaust shutter dropping and causing overheating. How do I check this? I'd prefer not to pull the entire stern drive if possible.<br /> <br />Thanks.<br /> <br />Steve
<br />good luck,<br />M.Y.