2000 MERC 150 xl OVERHEATING

[Matty J]

I have a 2000 Merc 150XL (two stoke carb'd) that is having some overheating problems. I just recently replaced the complete impeller kit, new 143 thermos, replaced the poppet valve and replaced the sparkplugs. When I flush the motor or run at a no wake spped less than 5 knots, the motor runs at about 145- 150 degrees. At speeds of lets say 20+ the temp rises to about 170. So far all is ok. My problem is when I am trying to run at trolling speeds of 5-8 knots the temp rises to 200 degrees in a matter of minutes. If I accelerate the temp will eventually drop back down after a few minutes of open throttle. My concern is temps of 200 degrees when I am 20 miles offshore.

Today I used a laser temp gauge and pointed it at each cylinder while I was flushing the motor. My temp gauge on my consol read 145 degrees, but my reading from each cylinder were very different. The port side degrees read from top to bottom were 150, 155, 170
Starboard side were 150 173 and 155. I also took the temp of the water stream exiting the pee hole and it read 135, so I am assuming that my consol temp gauge is off about ten degrees. Is the varying cylinder temps a concern? Any suggestion as to why my temp is rising so high at trolling speeds?

Thanks!

Matt

 

[Matty J]

Re: 2000 MERC 150 xl OVERHEATING

Concerned that it might be a cracked head, but all the plugs looked ok when I changed them out. There is alos no residue around the head gaskets.

 

[gss036]

Re: 2000 MERC 150 xl OVERHEATING

Go back and check your work since the problem started after you changed things. Easiest to check is the poppet valve, if it is sticking open and allowing water to dump sooner than needed, that could cause a rise in the temp at low speeds. If that doesn't do the trick, drop the lower end and make sure you did eveything correct in the impller install, most critical is the water tube which goes in the bottom of the head. If it is not correct, then the water flow is impaired. make sure the key way is in place holding the impeller in place.
You did not mention water pressure so doubt you have a water pressure guage. That is the best indicator you can have.

 

[Matty J]

Re: 2000 MERC 150 xl OVERHEATING

Thanks for the help! I forgot to be clear, the impeller was done by a certified mechanic. As for the problem, the overheating has been an issue since I bought the motor (used). I replaced the entire impeller assembly after this started to happen at 6-8 knots.

I do not have a pressure gauge, need to put one in. I also called Merc, and they actually told me not to worry about this issue at trolling speeds. If anyone wants to chime in plese do so.

 

[hkeiner]

Re: 2000 MERC 150 xl OVERHEATING

If you do choose to install a water pressure gauge, the below troubleshooting guide may help identify the problem.