Merc 170--wants to overheat.

[nola mike]

But I won't let it. Replaced my outdrive this weekend while i track down a leak on my last "new" one. Ran it at 4k rpms, no real issues. Noticed it running a little hot--160' v. normal 140'. Seemed worse at lower speeds. When i when to pull it out, the temp bumped to 180'. No problems last weekend with the other drive. When i had it on muffs, i thought i noticed exhaust gas coming from the sea water exhaust near the gimble housing, but it didn't register until later. It also ran hot on muffs--140' before i shut it down. again, usually the temp needle doesn't budge from 120'. i split the case, and the impeller looked rough, but i don't know if it's enough to cause my problems (see pics). Water flowed freely through the upper housing and out the seawater exhaust when i put a hose to it, and i didn't see it come from any place else.
so...
i'm going to replace the impeller anyway, but don't know if i have a separate issue causing this. weird that i didn't have the issue last weekend.
during the offseason i replaced the mani and riser gaskets and the shutter after taking everything apart for inspection. i didn't pressure test, but everything looked to be in good shape. the only thing i can think of is a leak either in the riser or at the gasket--could this cause my problems/symptoms?
guess i'll order a new gasket just in case, and see what happens with the new impeller (good news is that the new outdrive didn't have any water in it after my trip)...

 

[Bt Doctur]

Re: Merc 170--wants to overheat.

The 470 motor usually runs at 160-175,also looks like a vane or 2 was reversed. Might add the impeller is trash.

 

[EddiePetty]

Re: Merc 170--wants to overheat.

....it doesn't take but a small remmant of a previous impeller to block the sea water flow in the heat exchanger nor a scrap of a former flapper to block the exhaust water in the lower unit.
Ed in 'ol Virginny

 

[Don S]

Re: Merc 170--wants to overheat.

i split the case, and the impeller looked rough, but i don't know if it's enough to cause my problems (see pics).

That impeller is total junk. No wonder it overheated.

Water flowed freely through the upper housing and out the seawater exhaust when i put a hose to it, and i didn't see it come from any place else.

The water would never make it past the impeller if it was in good shape.


Replace your impeller, new gaskets, and you will most likely not have an overheat anymore.

 

[nola mike]

Re: Merc 170--wants to overheat.

That impeller is total junk. No wonder it overheated.

yeah, it's junk. seemed like it made a good seal in the upper housing though, so i didn't know if it was still functional.

The water would never make it past the impeller if it was in good shape.

it would if the lower half of the drive was laying on the driveway next to the boat

Replace your impeller, new gaskets, and you will most likely not have an overheat anymore.

that's what i wanted to hear...

@bt, this is for sure hotter than the motor usually runs, esp with water temps of 59'. last summer it never bumped from 140 with water temps of upper 70's.
@ed: all the vanes were intact, and it seemed like i had good flow when put the hose on the intake. where in virginny are you?

 

[cr2k]

Re: Merc 170--wants to overheat.

I would also look at the upper and lower housing for any signs of melted plastic, it looks as if it may have been run without water.