intermittent overheating of 200hp mercury

This spring the temperature gauge on my Whaler read hot intermittently. I took it in and the marine mechanic diagnosed the water impellor as the likely problem and replaced the part for about $120. We launched the next day and first time out had the same problem (intermittent hot reading at low speeds on temperature gauge with normal water coming from pee hole and with return to normal temperature at higher speeds). At this point I think one of the thermostats are to blame. Is that likely my problem? If so, how difficult are they to replace and can I do it with the boat in the water?

Re: intermittent overheating of 200hp mercury

Very easy to replace, maybe a little more tricky in the water as the t-stats are to the back of the motor. Do you have a manual? If you don't, we are certainly going to need more information on your motor, year, model, HP etc.<br /><br />The impeller change is not too terribly difficult either; it would be a good thing for you to learn to do yourself. I change mine every season just for good measure. Cheap insurance compared to a powerhead rebuild.

Re: intermittent overheating of 200hp mercury

hey your stats are easy to change, the stat housings are held in by i believe a 13mm bolt, use a six point wrench as not to strip a 12. tilt the engine all the way up and now you should be looking down at the tops of the cylinder heads, carefully loosen the bolts,remove and stick them in your pocket, tap on the stat housings, the wil pop off but not go anywhere because the hoses are still attached right. with that wrench you put in your pocket also right, pull out the old stats and insert new ones paying attention to how you pulled the seal off the old stats the narrow inner lip faces the engine.you may need a toothpick to help you get the ols seals off if you didnt buy new ones.. boom, reverse the order and check you temp problem, you may also want to consider the pressure relief system it has a poppet valve and spring and gaskets in there that blister over time and fail causing overheat...that system is under your ignition plate and you need to split the pans to get to it..repost with your results