2000 mercruser5.0 Looking back at the engine from the front of the the left manifold is running about 20 0r 25 degrees hotter than the right side. Any thought on why this is happening and how to fix it so they both the same. left side 120 or more right side 100. Th
heating
- Thread starter marincicm
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signature27
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do you boat in salt or fresh water? When was the last time you replaced both the manifolds & risers ? If they are at or over 5 years old and the boat is in salt water change them NOW before you cause a larger problem with the motor.
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one side is always hotter than the other. I agree if manifolds and risers are 4 years old or more they're due for replacement. What drive? The Bravo's have issues with the water passage thru the transom assembly corroding closed. Alpha drives impeller should be replaced every two years.
Rob
Rob
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That seems to be normal - I've had Merc 5.0s like you have and now have a 4.3 in my little bowrider. It has to do with how the water flows through the system, but the Port riser / manifold is alwasy cooler. The simple test for water flow on manifolds is if you can lay your hand on the riser you are probably good. So no "fix" that is normal operation.
If this Merc engine is strictly RWC, it likely employs spring-loaded-ball-&-seat poppet-style valves on either side of the t-stat housing .
If one of those balls has different spring pressure than the other side or there is debris buildup holding one semi open or closed, there will be different bypass flow to the ex manifolds and risers and temps will differ. Water flow seeks the path of least resistance .
I'd check those poppets 1st.
Note that if it has been that way for quite a while, the lower-flow side may have more mineral & rust buildup than the other , & that further contributes to temp difference.
Common preventative maintenance replacement schedule of RW cooled cast exhaust parts in SW is around 3 to 5 yrs as Signature suggested above, though many boater take their chances of bigger spendier problems by ignoring that kind of timetable. If you replace them , be sure to "deck" them gasket mating surfaces of the iron. Even if they look and feel flat , they aren't .
If one of those balls has different spring pressure than the other side or there is debris buildup holding one semi open or closed, there will be different bypass flow to the ex manifolds and risers and temps will differ. Water flow seeks the path of least resistance .
I'd check those poppets 1st.
Note that if it has been that way for quite a while, the lower-flow side may have more mineral & rust buildup than the other , & that further contributes to temp difference.
Common preventative maintenance replacement schedule of RW cooled cast exhaust parts in SW is around 3 to 5 yrs as Signature suggested above, though many boater take their chances of bigger spendier problems by ignoring that kind of timetable. If you replace them , be sure to "deck" them gasket mating surfaces of the iron. Even if they look and feel flat , they aren't .
Thanks for the replies. The boat is used in fresh water only. The reason I ask this is because after I have run for 20 or 30 minutes and then s stop for awhile it will boil the fuel out of the filter and I have to remove the filter and fill it up before I can get started again. I checked the temp on the riser.
Marine engines run in a lot hotter environment than auto engines. Some models like the 4.3 are well known for heat continuing to build up after the key is turned off. The general recommendation is to NOT shut down the engine hot but rather do a cool down to let the cooling water lower the engine temps before shut down.
Now, another causes of overheating usually involves insufficient air circulation in the engine room. Try running with the hatch or door open a bit or leaving the exhaust fan running. Sometimes it's a just a matter of the vents are too small.
Now, another causes of overheating usually involves insufficient air circulation in the engine room. Try running with the hatch or door open a bit or leaving the exhaust fan running. Sometimes it's a just a matter of the vents are too small.