I just went through the same thing with my '00Merc 200 EFI. Here is what I did and learned:
1. Get a manual for your engine!! This is the most important thing. Preferrably one from the manufacturer.
2. If you havent changed your impeller in the last year, you shoud change it. My Merc manual said every 100hrs or every year, whichever comes first.
3. Take a look at this post on another forum
http://www.in-depthangling.com/forum...3/fpart/1/vc/1
It's for a mercury engine, but yours should be similar. The water pump anmd impeller are located in the lower unit. You have to remove the lower unit to change it. It's tricky and probably a two man job, but it's not that difficult.
4. If you're not overheating at idle, your problem may actually be in the poppit valve, but you won't know until you change the impeller. Poppit valve on my engine was on the starbord side toward the bottom of the lower cowling. I had to remove the lower cowling to get to it. Thermostats regulate cooling at lower speeds, the poppit valve takes over at higher rpm's.
Again, if you decide to tackle this yourself, get the manual and study it. Parts for the water pump and impeller are about $45 if you get the impeller repair kit and another $20 if you replace the upper housing of the water pump. I didn't actually replace my poppit valve, I just dissasembled and cleaned it up (nothing was broken), but the parts for this would only be about $25. It took me about 5-6hrs by myself to change both. But I highly recommend an extra set of hands when you go top get the lower unit off and back on.
There are lots of threads in this forum that will also help you. Search around.
Good Luck.
Mariner Impeller
Linear Mode
