Mercruiser 165 Inline 6 Overheating

[parisite]

I have a 1981 Merc. 165. Took it out today, first time in two years. Have run it with a water hose feed a few times however. Anyway it overheats now but it seems to have normal/high pressure in the thermo housing when running as I have the thermostat out and checked it. Is the impeller bad even though I have high water pressure in the engine?
Thanks..........

 

[HT32BSX115]

Re: Mercruiser 165 Inline 6 Overheating

Howdy,


If you haven't checked the impeller, you probably should. If it's been a few years, it should be replaced anyway.


If you have high "pressure" in the engine, you may have a clogged (with rust) exhaust manifold and/or riser.

The cooling water must have no obstructions to getting out (just like it must get in!!)

 

[parisite]

Re: Mercruiser 165 Inline 6 Overheating

I'm a pretty fair mechanic but a green horn boat mechanic.

That never occured to me but the riser may be clogged. I know there is a LOT of rust in the manifold. I took out the petcock just below the elbow while it was running and nothing came out.
The riser you mentioned is the big cast iron elbow in back of the exhaust manifold, right?
Never taken one off before. Is it that big of a deal to do?

 

[parisite]

Re: Mercruiser 165 Inline 6 Overheating

I have what I think is the riser, off now. It looks like it is where the exhaust and water join on their way out?

 

[HT32BSX115]

Re: Mercruiser 165 Inline 6 Overheating

I have what I think is the riser, off now. It looks like it is where the exhaust and water join on their way out?

Yup,

That's it! It's designed such that the water cannot get back into the exhaust.

It must be clear enough for the water to exit with the exhaust.

If it's really rusty, enough to be clogged, it MUST be replaced. You cannot effectively "clean" it.

Also, if it's rusty enough to be clogged, your manifold is probably at least as clogged.

If you operate in salt water, the engine block and head might not be far behind too......well....maybe not! Paris Tx is a bit far from salt water!

 

[parisite]

Re: Mercruiser 165 Inline 6 Overheating

I have the riser off, turned it upside down, filled the inlet water ports full of water then gradually turned the riser so the water can flow out the ports to join the exhaust and water just comes out one place about twice the size of a pin hole. I don't think this is normal. How many out flow ports is it supposed to have where water joins the exhaust?

I think my water outflow ports in my riser have corroded shut.

 

[dubs283]

Re: Mercruiser 165 Inline 6 Overheating

the water should just pour right out where it joins the exhaust

most likely the "sleeve" inside the riser/elbow assy has corroded away thus blocking the output

time for a new one - check here on iboats, under mercruiser i/o parts, cooling

 

[parisite]

Re: Mercruiser 165 Inline 6 Overheating

If I take off the two end cap plates off my 6 cyl. log manifold can I blow out the loose rust in the manifold with a water hose?
I've never had the plates off and was wondering?

 

[dubs283]

Re: Mercruiser 165 Inline 6 Overheating

If I take off the two end cap plates off my 6 cyl. log manifold can I blow out the loose rust in the manifold with a water hose?

yep, but if there is that much rust in there, i would be suspect of the manifold needing replacement too

 

[HT32BSX115]

Re: Mercruiser 165 Inline 6 Overheating

If your manifold and/or riser is clogged (with rust) enough to cause cooling problems, they MUST be replaced.

Understand, the "rust" in there is the actual metal that has corroded and flaked off the inside walls of the manifold/or riser.

As they corrode, the walls get thinner and thinner until they "break" though.

If they start leaking when your boat is sitting for long periods of time, (like winter) the water in there can run back into cyls through open exhaust valves and cause destructive corrosion.

 

[parisite]

Re: Mercruiser 165 Inline 6 Overheating

I just bought a new riser on ebay as I "think" that may be the culprit to my overheating because of corrosion not letting water back out. I will go that route first.

Yes, when I drain my exhaust manifold there are some rust particles that come out but I'm not going to spend $500 for a new manifold because of some loose rust particles......would you?

Thanks for all the help guys.