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Merc170 4cyl gets hot at higher speed ok at lower

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bshaw

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My 1986 SEARAY SUNDANCER 270 H

My 1986 SEARAY SUNDANCER 270 HAS TWIN MERC 170 4CYL ENGINES WITH SEALED COOLING SYS AND ALPHA 1 DRIVES. THE PORT SIDE ENGINE TEMP STEADILY CLIMBS WHEN ON PLANE OR HIGHER SPEEDS. IT'S FINE AT SLOWER SPEEDS. THE ENGINE IS NEW AND THE SAME PROBLEM OCCURED WITH THE OLD ENG. THE HEAT EXCHANGER WAS CHECKED AND CLEANED BY A RADIATOR SHOP. THE WATER PUMP IMPELLER WAS REPLACED WITH IN THE LAST COUPLE SEASONS AND SEEMS TO HAVE FLOW. I HAVE LOOKED FOR RESTRICTIONS BUT HAVE FOUND NONE AND MUST BE MISSING IT. HOW CAN I VERIFY GOOD WATER FLOW AT HIGH SPEED? ANY IDEAS?
FRUSTRATED
BRIAN
 
""WATER PUMP IMPELLER WAS

""WATER PUMP IMPELLER WAS REPLACED WITH IN THE LAST COUPLE SEASONS"

It would be the first item I would inspect and change. Backflush the cooling water inlet hose from the heat exc. to the OD after dropping the lower unit.

If the problem persists then get a $40 laser temp. gun and compare temp readings between engines at key locations; exhaust mans. and risers, heat exchanger inlets and outlets. If the hot engine has higher manifold or riser temps, suspect a blocked manifold and/or the exhaust riser. If both are ok then check the exhaust shutter."
 
"Impellers are good for 2 year

"Impellers are good for 2 years max ,then change. riser flow cant really be checked unless you remove it to test. most likely causes:
impeller is tired, or riser is clogged up some."
 
"I have a mercruiser 170 and I

"I have a mercruiser 170 and I blew a nice hole in the motor and I have been looking for a replacement motor, I have found online a used 3.7L 165HP Motor that looks exactly like the one I have so I want to know if I could use that motor and take mine out. If this motor will not work I am open to suggestions. Thanks"
 
The power steering cooler is o

The power steering cooler is on the other engine. So thats not it. I have procured the infared thermometer and will try testing that way. Also will try to look through the system if pos with a boroscope I have access to. However I feel that I will probably be pulling the boat back out and going after that impeller and making sure that passages are free. Come to think of it this problem has existed since the first time I replaced that impeller. Thanks to all for the info and I'll post back with my findings
Brian
 
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