NorEast Fishing Forum banner

Running Hot

1071 Views 6 Replies 5 Participants Last post by  CaptRon
I have a mercruiser 1997 5.7 liter I/O set-up; I have been using it since 1997.
Early this spring after haul-out I noticed that the starboard manifold and riser were running much hotter than the port. However the engine operates at normal operating temps and doesn't overheat. The marina replaced the thermostat which was cracked and needed replacing. The problem did not go away. I took it back and asked them to examine the risers etc.; when they took the risers apart they were badly coroded after 5 yrs of use- they suggested replacement and I agreed. After replacing the risers ,manifold and elbows the problem still persists. I would say that the temperature differential between starboard(hotter) and port (cooler) manifold and risers is at least 30 deg. I don't know if this is even a problem. But it doesn't seem right. After prolonged operating (or even after a short operating period) the port riser is warm, but it is cool enough so that I can keep my hand on it indefinately- the starboard riser gets so hot that I can barely touch it for a second. But engine temps are normal. Any suggestions would be greatly appreciated.
1 - 1 of 7 Posts
running hot.

When you say engine temps I assume you are talking about "water temp" ??

What about the heat exchanger and coolant ?? Any work done there ??
Also what manifold did they replace ??

Assuming all of your intake (raw water) hoses are good, your water intake is not clogged and your raw water pump is good, (new impeller) you may need to look at your FW pump for better circulation through the heat exchanger, or check the port/hose that feeds the hot side to be sure there is good water movement.

If the riser is too hot to touch this is not good, (assuming they are new and the e.m.'s are new too ??) this would indicate that there is not enough water dumping into it, or another problem.

Sometimes a worn impeller will push enough water to keep the engine from overheating, but not enough to cure your problem. I do not see you mention that it was replaced. When was the last time you did your impeller, or checked your fw pump ??
Somtimes too it's just a matter of how long the hose is.
In other words the cooler water from the heat exchanger is hitting the port side exhaust manifold first, and with more pressure, and thus keeping it cooler. 30 deg is not too bad. If it was 100 then I would say you are likely buring up a cylinder in that bank, from too much fuel or a bad valve, or something.
Do your impeller, and check to be sure the hoses carrying the cool water from exchanger are feeding well to the em, and make sure you have enough water dumping into the riser, and see if that takes care of it, if not I cannot help without looking at it myself.
See less See more
1 - 1 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.