Mercury 1150 running hot? (updated, with pics)

fishdog4449

Chief Petty Officer
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Jul 16, 2007
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462
Hey guys,
Took the '76 115 out on the lake today for the first time. it ran great, started on the first try had plenty of power. However, after running for a while the telltale water and water spitting out of relief ports was hot. Not scalding hot, but quite a bit hotter than lukewarm. Impeller is brand new and the motor has great water pressure, fast stream even at idle. However, we were pulling two tubes so I was driving slow...mostly around 3000 and nowwhere near wot.Is this cooling water temperature normal...? (My Merc80 never got the telltale above lukewarm even at wot)

Lake Water temperature was 84 degrees.


Running a 19P stainless Quicksilver on 18' Glassmaster runabout. I know I should have a tach and will get one before my next trip so I can prop it perfectly.

Thanks in advance guys!!
 

rightcoastrob

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Jun 18, 2008
Messages
101
Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

I have 2 1979 115 one runs luke warm at 5000 rpm and the other one runs hot as you say both mine have new impellers
 

emckelvy

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Messages
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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

Well, 84 deg is pretty warm for cooling water! Maybe that has something to do with it. Never seen that but of course the lakes up here in the PNW don't usually get that warm.

Try feeling the exhaust cover and see if that's getting real hot. As long as it's not much more than 130 deg you're probably OK.

If your water flow is strong thru telltale and exhaust reliefs and stays that way at speed, I'd say you're pumping as much water as you'd expect for an Inline.

It'd be interesting if you were to run in a colder body of water to see how hot things get.

About the only time I can recall having an Inline with a quite warm (or even steaming) telltale, it was on an old 100HP and I think it had a lot of silt buildup in the water jackets. Had to remove the cyl block water jacket cover (the one over the spark plugs) and clean things out.

If you decide there's something fishy going on, you can pull the cover off without removing the powerhead. Just watch out for stuck bolts, use a combination of penetrant and heat to release any bolt that won't come out with normal force on a wrench. Any Merc dlr should have the cover gasket in stock.

BTW the Fours are known for running quite cool, I reckon Six in a Stack generates a bit more heat!

Let us know if you find anything strange..........ed
 

fishdog4449

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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

Thanks!
Well, I just replaced all the exhaust gaskets and it looked very clean inside there. (its a very low hour Lake Erie motor, no rust or corrosion)

exhaust ports have a very large spray coming out of them (like putting your thumb over the garden hose) and tell tale is good. I did feel the exhaust cover and it wasn't very hot, but not cool either. When I run it on the hose I did notice it ran cooler, but that was at idle so can't really compare the two.

The lake is Lake Anna in VA, it's a man-made lake used to cool the north Anna Nuclear power plant. It has two sides separated by dikes and the water from the plant travels up the 'hot' side (bout 15 miles long), then down the cool side (another 15 miles) and back to the plant. The hot side reaches 90 degrees during the summer and the cool side hovers around 80-85. I was on the cool side.
'
Fishing is actually much better on the 'hot' side believe it or not the fish love it!
 

fishdog4449

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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

Well I ran it today on the hose for about five minutes and the water was hot out of both telltale and cavitation plate exits. It ran at idle speed only.
I know this motor has fixed high speed jets and the idle mixture is set at 1-3/4 turn out, is there anything else that could contribute to it running hotter?
Thanks guys,
 

emckelvy

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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

I'm assuming the water coming out of your garden hose is plenty cold.

Fuel mix at idle with no load on the motor will have such slight effect on engine temperature as to be insignificant.

IMHO you've got a water circulation problem somewhere. No way the telltale should be hot, on a flusher at idle speed.

One particulary pesky problem a poster had here lately was with a 50HP Merc that was running warm like yours. Eventually he pinned the problem down to a chunk of impeller blade that had lodged part of the way up the water tube!

Talk about a tough one to diagnose, especially long distance!

At this point, you may have to start tearing into it more just to narrow down the problem.

I'd recommend pulling the back cover (over the spark plugs) and checking for silt/debris in there. Even though the exhaust manifold side was clean, there's no guarantee that there is no debris in the block.

With the back cover removed, you can blow compressed air up the water tube and see what happens. You can also hook up water and check for free-flow. It should literally gush out of the block and if it doesn't, you've got problems between the water tube and the block itself.

I still find it strange that you seem to have strong flow but it gets so warm.
Something very fishy going on.

You sure you don't have a miniature nuclear reactor in there or a problem with surplus fissile material in the water jackets!!!! If you plan on running near the Nuke power plant again, might be a good idea to scrap the water pressure gage and install a Geiger counter!! arr arr!

Keep us posted..........ed
 

fishdog4449

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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

Thanks ed I will pull the cover tomorrow if I have time!
Is there any point on the engine where i could hook compressed air up to back flush the whole system and that could maybe force any stuck objects free?

...heres a pic of the old impeller...
I assumed that the old blades had melted away but pieces of them may very well be lodged up in there!!
imepllerjk2.jpg
 

emckelvy

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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

...heres a pic of the old impeller...
I assumed that the old blades had melted away but pieces of them may very well be lodged up in there!!

DUDE! Not thinkin' that air is gonna get rid of all them chunks of rubber lodged who knows where in your cooling system!!!!!!! :0

Most of them are probably stuck in the water tube and unfortunately I don't think you can just pull it down from the rubber grommet, I believe it's captured in place, in the exhaust adapter plate.

Best case, chunks in the water tube are removable from below by running a stiff wire or small 'grabber' up the tube; 2nd best, pull the back cover and flush things out from there; worst case, pull powerhead and start fishin' (no, not Fission!!!!!). I'm sure glad we finally Nuked this one out!

I sense some Heavy-Duty Wrenching about to occur!

Let us know where you find the rubber chunks............ed
 

fishdog4449

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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

EDITEd (double post)
 

fishdog4449

Chief Petty Officer
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Messages
462
Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

EDITED (double post)
 

fishdog4449

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Re: Mercury 1150 running hot?

Re: Mercury 1150 running hot?

Well I dropped the lu and back flushed through the teltale and it seemed clear, nice stream of water coming out the water tube.
When I was flushing it, i noticed a small amount of water leaking out around the #6 spark plug. The cover gasket probably needs replaced and while I'm replacing it I will inspect that area for blockage.
Also, I noticed that near the top of the driveshaft it looks like it has been exposed to exhaust gases...is this supposed to be like so?
Heres a pic...
(theres another section about the exhaust cover below)

p1040064mediumsn7.jpg



OK well i pulled the cylinder cover and it looked clean inside, as does the rest of the motor. I have to replace the gasket because of the previously mentioned leak. I hooked the hose up to the water pump line running up to the powerhead, and LOTS of water gushed out of the block through a slot under the number 6 cylinder. I'm guessing thats good...Judging by the amount of water coming out I doubt there is anything blocking there.
However, I would like to know a little more about the cooling system. Could someone explain how the water gets from that slot up around the cylinders and where it goes from there?



p1040067mediumcm6.jpg


p1040066mediumhb2.jpg
 

fishdog4449

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Re: Mercury 1150 running hot? (updated, with pics)

*bump* in case anyone missed the last post
 

jimmbo

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May 24, 2004
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12,944
Re: Mercury 1150 running hot? (updated, with pics)

It fills the block, then at the top it spills over and runs down between the exhaust covers on the port side. Then it exits the block filling the space between the exhaust tube and the driveshaft housing. Some exhaust gets into the drivshaft housing at low speeds as it finds its way out thru the idle reliefs, That's why there is soot on the driveshaft.
 

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emckelvy

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Re: Mercury 1150 running hot? (updated, with pics)

Well, it appears water can at least get into the powerhead, but perhaps it's not getting out where it should.

Think you're gonna have to pull the powerhead and inspect every passage.
 

fishdog4449

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Re: Mercury 1150 running hot? (updated, with pics)

What I might do when I get the new gaskets, is run the motor with the lower unit off with the hose connected to the water tube, and see how it runs water temperature wise. Can I damage anything doing that?


I seem to have good flow and may turn out that this motor simply runs at that temperature, however I would like to be sure.
At the lake, I could hold my hand on the powerhead for a few seconds all around and we were most likely lugging the motor too because I had the wrong prop on.
 

emckelvy

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Re: Mercury 1150 running hot? (updated, with pics)

What I might do when I get the new gaskets, is run the motor with the lower unit off with the hose connected to the water tube, and see how it runs water temperature wise. Can I damage anything doing that?

As long as you follow the precautions I laid out earlier, it should be safe to run it that way.
 

redjmp

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Mar 16, 2005
Messages
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Re: Mercury 1150 running hot? (updated, with pics)

Running a 19p on an 18' is way too much and then you are lugging it even more when you pull tubers.
Your 115 is really only about 90 at the prop.
I would say you need a 15 or 16 p.
 
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