Overheating problems

[Skull]

My Merc 150 OB Carb, 6 cyl. is acting up lately. Idle to 5 knts she runs @ around 185 deg. 13-WOT she runs @ 165degs ...but when I'm pushing along 6-12knts with the motor trimmed/tucked under the hull ie receiving as much h2o as possible in the intakes, she overheats ..~210-220degs and the alarm is going off. I monitor the temp gauge , granted its analog but it does respond coinciding with the info I gave above.

Any thoughts?

 

[GradyDiver]

I'd have someone watch the outlet to see that water is coming out at those speeds. If not, there is certainly a problem. The only reason I could guess at for this is a hose getting crimped because of the angle of the motor and boat (my 20 footer's bow started lifting at about 10mph and didn't come to plane until ~18mph).

Good luck, I know what a pain these things can be. I finally got mine fixed, but upgraded to a 25' with dual IOs (different problems I'm sure, but runs great now).

 

[Nemrod]

Water pump, should be a yearly chore or every 100 hours whichever comes first. Your water pump impeller is stiff, needs a new one.

N

 

[dannobee]

I'm with Nemrod, replace the impeller and/or water pump. Probably stiff or missing a couple of fins/teeth.

 

[Skull]

thanks guys I suspected that is the problem ...but wasn't quite sure. Seems odd that it only occured at moderate speeds ...then again that is when the most energy is needed to push the boat not on plane.

 

[Nemrod]

At that "just off plane" speed the engine is under a good bit of load and working hard and yet the water speed is still fairly low limiting water uptake into the inlets on the lower unit. This speed is common to see overheating symptoms manifest themseleves.

I have to tell you that I fin it amazing that in this day and age with all of the miracle materials they (Mercury) cannot come up with an impeller that will last a lifetime. They could alos design an externally acessable cartridge system that would facilitate an easy impeller change without having to drop the d---n lower unit. Would that really be asking to much for a 12,000 to 18,000 dollars product.

BTW, all of your temps seem high, further indicative of a water pump issue, if I were seeing those on my Opti I would be feeling really blue. I never see more than about 152 and at speed much lower.

N

 

[Tom Winters]

Hey - you want to hear about overheating... I broke the ignition collar on one of my engines this morning - simple little delrin part where the key goes in.
The replacement Yamaha stuff came to $353 with Floriduh sales tax. Yeah, I was overheated... almost blew my head gasket.

 

[Skull]

At that "just off plane" speed the engine is under a good bit of load and working hard and yet the water speed is still fairly low limiting water uptake into the inlets on the lower unit. This speed is common to see overheating symptoms manifest themseleves.

I have to tell you that I fin it amazing that in this day and age with all of the miracle materials they (Mercury) cannot come up with an impeller that will last a lifetime. They could alos design an externally acessable cartridge system that would facilitate an easy impeller change without having to drop the d---n lower unit. Would that really be asking to much for a 12,000 to 18,000 dollars product.

BTW, all of your temps seem high, further indicative of a water pump issue, if I were seeing those on my Opti I would be feeling really blue. I never see more than about 152 and at speed much lower.

N

I'm guessing planned obsolescence ...how else are they going to hit you up for replacement parts and ...labor. Though I will change it out myself this week.

As always N ...thanks for the insight.

 

[saltydawg]

while you are at it flush the water jacket on the head also. The tattle tail hole actually comes off the impeller housing not the showing the flow through the jacket. Many times sand and dirt will build up and fill in the jacket reducing the cooling.

 

[Skull]

BTW I also changed out the T-Stats ...one was partially blocked

Seems to have solved the trolling speed overheating problem.

thanks guys