Rising Temperature

[OJ_Simpson]

Went out this evening and while coming back in (running about 4200rpms) I noticed the temp gauge was wandering up to around 200. I backed off the throttle to around 3000rpms and the temp returned to 170?ish, but would still move back and forth towards to 200 (but would mostly stay around 170).

I?ve had the boat (2005 merc 3.0) a year, and haven?t changed the impeller. Obviously the impeller needs to be changed, and I plan on taking care of it this weekend and will probably replace the thermostat as well. My concern is that this might be related to riser & manifold. It did seem hotter than normal under the hood/dog house when I checked after getting back in, but that could have just been me and the hotter than normal outside air temperature. I didn?t have an IR therm to check.

The boat is run in salt water. I?ve put about 50 hours on it, and it is always flushed and garage stored. I?m not sure how many hours the previous owner may have put on it, but my guess would have been around 40-50 (so I figure100 total in salt), and they also had it dry docked. Any advice is ppreciated before I get started.

 

[bruceb58]

Re: Rising Temperature

Definitely change the impeller and pull the riser to have a look at what its condition is.

 

[karatejoe]

Re: Rising Temperature

Replace the lower impellar. Once you take it apart , by its design you will understand why it needs replaced every 2 years.

 

[OJ_Simpson]

Re: Rising Temperature

Trust me, I totally understand the need to change the impeller! My main concern was that the temp would rise, and then drop back to normal (or just above normal) after lowering rpms. I ran it for quite a while at 4-4k rpms. I was planning on doing the manifold and riser at the end of this year, and not in the middle of summer!

 

[bruceb58]

Re: Rising Temperature

I was planning on doing the manifold and riser at the end of this year, and not in the middle of summer!

Why wait if that is your problem?

 

[OJ_Simpson]

Re: Rising Temperature

Why wait if that is your problem?

I'm not certain if the manifold or riser is the problem. I'll start with the impeller, and then thermostat. I'm not into tearing apart the engine for the fun of it. Not to mention that I'd much rather change out a $50 part, versus a couple $500 parts. Another year should be about normal for the manifold/riser. Hopefully, the impeller change takes care of the fluctuating temp. It's also hot as hell working in the garage this time of year, and I'd prefer to do the larger job next winter.

 

[bruceb58]

Re: Rising Temperature

Pulling the riser to look at its condition costs you the price of a gasket. We are talking an hour or two worth of work here.

 

[cr2k]

Re: Rising Temperature

I would check the riser as well. A marine temp gauge is the most inaccurate thing in the world.