Overheat questions

[bones774]

I have a 1988 merc v-8 350 ci that has been overheating during idling and slow speed, finally removed the lower unit today for impeller inspection and the unit looks brand new, like it was just replaced. I have only had the boat this summer the previous owner told me his mechanic told him that the overheating was caused by sediment /mineral buildup in the block, i was a bit leery until now, could that be?
I also notice that where the shifter fork passes thru the drive unit casing on the inside it looks somewhat corroded and that the lip of the circle it sits in has degraded some, it certainly does not look like a watertight arrangement.
Also the painted surface where the upper and lower come together is missing paint in some areas, will that be a problem when assembling.
Don't know if this means anything but the boat does not reach WOT under load.
Thanks for any help.

 

[NHGuy]

Re: Overheat questions

Do you have very low idle? My engine temp creeps up when my idle gets too low. But when I am at 650 rpm or more, which is correct, it will normally hold at 160.
Is the entire pump and tube in good shape? And how does the hose from the bell housing to the transom look? That hose makes me crazy, it has to be free of kinks.
It is possible that a piece of an old impeller could be stuck in the cooling system.
I think the first thing I would do is run it at high rpms to see if it improves, might clear out mud that could be in there.
The shift fork system is not watertight, that's OK.
If the boat won't go WOT it might need tune up parts or be mistimed. And coincidentally mis-timed motors can run hot.
I'd do cap, rotor, wires, plugs, both fuel filters, and set timing just because I want to be sure it's correct.

 

[bones774]

Re: Overheat questions

I don't think my idle is low.
I'll have to take a look at that bell housing hose, not familiar with it off hand, so need to take a good look.
The impeller and housing look new and unworn. When I looked in the short plastic tube attached to impeller I saw some very little signs of some type of flaking.
I'm gonna do all the plugs,cap, rotor and timing as we get near spring.
Re: that shifter fork, how do i set that in correct position as i re-assemble?
Thanks
That stuff about the water jacket/exhaust manifolds having deposits seems like a bunch of bunk?

 

[wire2]

Re: Overheat questions

If it's established that the block/heads are partially blocked by rust & debris, there's a caustic solution available to dissolve & clear it.

 

[bones774]

Re: Overheat questions

If it's established that the block/heads are partially blocked by rust & debris, there's a caustic solution available to dissolve & clear it.

So do I remove the risers for inspection? Should I just use it anyway and see what happens or is there a downside? (I've actually done something similiar on my home tankless water coil, worked well).

 

[bones774]

Re: Overheat questions

OK while my boat is on the hard with outdrive removed I inspected the hose within the gimbal setup and it appears that it does have somewhat of a kink to it. What are my options? remove the gimbal? special tools needed? cut the hose to take the kink out? anything to be done from inside engine compartment? Thanks

 

[Bondo]

Re: Overheat questions

OK while my boat is on the hard with outdrive removed I inspected the hose within the gimbal setup and it appears that it does have somewhat of a kink to it. What are my options? remove the gimbal? special tools needed? cut the hose to take the kink out? anything to be done from inside engine compartment? Thanks

Ayuh,.... Why not systematically Diagnose the problem, insteada throwin' parts at it...

Pull the In-bound hose off the T-stat housing, 'n Back-flush it out with a garden hose....
Does it flow,..?? any Junk come outa it,..??

Put it together, 'n SEE where the water's gettin' too,..
Or Ain't...

 

[bones774]

Re: Overheat questions

OK, that's what i will do, nobody suggested that previously.
Thanks

 

[bones774]

Re: Overheat questions

I put the hose where the t stat housing connects and the water flowed from the outdrive and no junk came out, not such a super flow though.

 

[Brentathon]

Re: Overheat questions

In your first post, you mentioned "impeller inspection". Did you actually take apart your drive and ONLY "inspect" the impeller, and not replace it???
I agree with Bond-O to try and diagnose problems, EXCEPT for impellers.......ALWAYS REPLACE THEM. They are sooooooo cheap compared to all other time/expenses of owning a boat, especially one that has a temp problem.

So, you now know that you have some (unknown and un-measurable) amount of flow coming from the drive, which doesn't tell you much....it still may be insufficient. That's why impeller should have been eliminated as a culprit.