Merc 110 9.8 hp intermittant telltale and overheat

[dajohnson53]

Hi: Serviced the water pump in my 1974 Merc 110 this spring. It seemed to work fine - motor ran fine, steady coolish-luke warm stream from telltale, engine block warm but not hot to touch. Everything fine, right?

The old impeller was not broken or damaged in any way, just routine change.

But sometimes the engine will run same as above, but sometimes the tell tale stream sputters and steams, very low flow, hot water (caught some in a jar, measured it with meat thermometer and it was around 140 F), engine block is hot to touch - can't keep my hand on it for more than a few seconds.

This will come and go, it seems.

Just yesterday, I was running it and it did the hot water thing described above. I shut down the engine, then restarted - the tell tale was immediately full flow, warm (not hot), and the engine quickly cooled down.

Obviously, there is something in there that intermittently blocks the water passage somewhere. First thing I'll check is the intake - but after that, All I know how to do is drop the LU and check the main water tube.

Can someone give me some advice how to trouble shoot this? I do have a factory service manual.

 

[Laddies]

Re: Merck 110 9.8 hp intermittent telltale and overheat

Re: Merck 110 9.8 hp intermittent telltale and overheat

While you have the unit down seal the grommets on the pickup tube and if that don't help you will have to remove the exhaust cover and look for junk and if theres nothing there you will have to remove the water jacket cover and ck the passage from the exhaust water jacket

 

[dajohnson53]

Re: Merck 110 9.8 hp intermittent telltale and overheat

Re: Merck 110 9.8 hp intermittent telltale and overheat

While you have the unit down seal the grommets on the pickup tube and if that don't help you will have to remove the exhaust cover and look for junk and if theres nothing there you will have to remove the water jacket cover and ck the passage from the exhaust water jacket

Thanks for the pointers. Sounds pretty straight forward and do-able for me.

I don't have the manual in front of me (but will when I do the work). Will there be torque specs and gaskets that are needed if/when I remove the exhaust or water jacket covers? Maybe I can get the gaskets ahead of time.

I'm a semi-competent mechanic, know enough to get into trouble sometimes. I don't like to get into things too far... although I do have a mechanic who would put it back together if I get in over my head (he will give me grief, but in a good natured way).

 

[Laddies]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Both are 70 in.lbs

 

[dajohnson53]

Re: Merc 110 9.8 hp intermittant telltale and overheat

I dropped the lower unit and checked out the screen, pickup tube, the water pump and the water tube - everything is OK (impeller changed this spring, just a couple hours use on it).

I made an adapter for my bicycle pump so I could blow air through the system. When I pumped air through the water tube, I could hear the air passing out somewhere, but could feel nothing coming out of the telltale. Although I didn't check at the time, I think it was coming out the exhaust that is on the back of the leg, just below the cowling.

Put it back together and ran it in the barrel and again, it usually worked just fine, but occassionally would get hot.

With it still in the barrel, I pumped air backwards through the telltale tube. No bubbles from the lower unit, and this time it was obvious that all the air was coming out the exhaust port on the back of the leg.

Does this seem normal? I don't know anything about how water is supposed to circulate and there's no schematic of water flow (that I can find) in the OEM service manual. In fact, I can't find anyting about the cooling system in the manual except water pump service.

Should my next step continue to be removing the exhaust cover? I plan to do that (seems simple) but want to get gasket first.

Thanks again for your advice.

 

[CharlieB]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Does the lack of water flow from the tale-tale coincide with the throttle position in gear?

That is, idle in gear OK but part throttle the stream slows a little, more throttle and a little less TT stream, and so on, til WOT and NO stream and the engine starts to heat up fast?

Sounds almost like a head gasket, no leak at idle, leak begins to show under load as cylinders pressure begins to raise, coresponding with more throttle.

Moore cylinder pressure leaking and less water flow, more heating, slow down to an idle and it cools off, not so much cyl head gasket leak and the water flow from the impeller can cool the engine again.

Try a cyll leak down test, remove the t-stat and listen carefully for cyl pressure bleeding into the cooling system.

 

[Laddies]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Charlie, that engine has no head gasket

 

[Motor Boater Bill]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Is it possible the pin that holds the impeller in place on the drive shaft is missing, so the impeller only spins part of the time, only held by friction to the drive shaft? Just a long shot but thought I'd mention it. I think it would have to be pretty tight on the drive shaft to spin at all without the pin/key thing. In other words, instead of an intermittent blockage, you have intermittent pumpage? One other thing--are you running it on muffs, in a barrel, or in the lake/river? If it's in a barrel, is it deep enough? If muffs, is there enough water flow?

By the way, Laddies really knows his stuff, so I'd put a lot of stock in his recommendations

One other thing regarding your last post above, unless I am mistaken, it is normal for air to pass freely from the water tube or the telltale to the exhaust on these motors. The manual observes that water will come out the exhaust if the pump is working and the telltale is blocked.

 

[dajohnson53]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Is it possible the pin that holds the impeller in place on the drive shaft is missing, so the impeller only spins part of the time, only held by friction to the drive shaft? Just a long shot but thought I'd mention it. I think it would have to be pretty tight on the drive shaft to spin at all without the pin/key thing. In other words, instead of an intermittent blockage, you have intermittent pumpage? One other thing--are you running it on muffs, in a barrel, or in the lake/river? If it's in a barrel, is it deep enough? If muffs, is there enough water flow?

By the way, Laddies really knows his stuff, so I'd put a lot of stock in his recommendations

One other thing regarding your last post above, unless I am mistaken, it is normal for air to pass freely from the water tube or the telltale to the exhaust on these motors. The manual observes that water will come out the exhaust if the pump is working and the telltale is blocked.

Thanks for the ideas. I did a cursory look at the impeller and it turned when I turned the drive shaft. I didn't try to hold onto the impeller to see if it would slip. I'll drop the L/U again and try that.

I've run it in a barrel with the water well over the AV plate (the inlet is on the underside of the av plate). I've also run it in the river on my boat, av plate was well under water. Same effect both situations.

If I can pick up the gaskets, I'm going to remove the covers and look in there. I have never done that and am curious. It looks to me like it's pretty straight forward, given the gaskets and a torque wrench.

 

[dajohnson53]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Does the lack of water flow from the tale-tale coincide with the throttle position in gear?

That is, idle in gear OK but part throttle the stream slows a little, more throttle and a little less TT stream, and so on, til WOT and NO stream and the engine starts to heat up fast?

Sounds almost like a head gasket, no leak at idle, leak begins to show under load as cylinders pressure begins to raise, coresponding with more throttle.

Moore cylinder pressure leaking and less water flow, more heating, slow down to an idle and it cools off, not so much cyl head gasket leak and the water flow from the impeller can cool the engine again.

Try a cyll leak down test, remove the t-stat and listen carefully for cyl pressure bleeding into the cooling system.

Doesn't seem to be related to in gear, out of gear, idle or WOT. I've had cool water and hot water in all of these situations.

 

[Motor Boater Bill]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Be careful removing the cover bolts, they can break off if they're corroded into the block, then you have to drill and tap to get them out.

It's also possible for the brass hub to break loose and spin within the impeller--I know it's new, but sometimes you can get bad new parts.

 

[Harker]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Not sure what year they went with a rubber tube telltale but my 67 tell tale is a small hole in the lower cover. It plugs pretty easy. Mine runs almost cold all the time. I popped the powerhead and there is a series of channels cast into the bottom where they flow to the hole and they were pretty dirty and corroded so I cleaned it all out (this is a freshwater engine) and it pee'd twice as hard as before. Water and exaust comes out of the holes in the back of the lower unit too. Do you notice any water in the housing like a gasket is leaking? Are you sure you got the little key in the prop? Those are a real B sometimes..make sure the plate with the slot in it is on correctly too. Get the gaskets ahead of time and clean the old ones off completely if you remove the exaust cover.

 

[dajohnson53]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Update and further questions:

I've removed the exhaust cover and water jacket cover (the one surrounding the spark plugs).

I cleaned everything up, but really there wasn't any significant build up of anything in there. All passages appear clear - I can probe them with wire and blow air through them.

The only thing that was blocked up was the "flush" port. That has always been clogged since I've owned the engine (about 3 years), but this time I got after it and was able to get it totally clear. But my understanding is that this passage really has nothing do do with cooling.

I took the lower unit off again and checked the impeller functioning - it is firmly attached to the drive shaft and does not slip at all when I try to prevent it from spinning as I turn the drive shaft.

The water tube connects with the pump output via a short rubber hose that slips down from the copper tube and seats firmly into the output.

Should I actually seal this - if so, with what?

One thing I'm curious about - and wonder if I can/should do it: I'd like to hook a hose up to the water tube and see if the water comes full force out of the water passages in the engine. I'm uncomfortable because with the exhaust cover off, the pistons are exposed and the water might get in there.

From what I can tell, the water from the water tube goes to a fairly large opening into the water jacket where it circulates around the cylinders (spark plug area) and also goes to the tell tale outlet.

I do not see a passage from the water tube directly into the exhaust cover area. It looks like that it is only after circulating through the water jacket that water goes to the exhaust side through little passages between those areas. If the water jacket is not in place, the water won't go through those little passages, and therefore, that area (and the open cylinders) won't get wet.

Is this correct?

I can "seal" the cylinders on the water jacket area easily by simply putting the spark plugs into the holes. I could then pump water through the water tube, and see if it passes freely out of that main water jacket passage I've identified.

Should I see water flow anywhere else?

To deal with spray/splash, I can stuff a clean rag into the exhaust side cylinder openings.

Thanks again for your guidance. This is the first time I've taken any covers off an engine or checked water flow.

 

[emckelvy]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Yes, flowing water up the supply tube with the covers off is an excellent way of diagnosing circulation problems.

A rag over the exhaust ports and spark plugs in the cyl's will keep water out of the engine's internals just fine.

I suspect that if you don't find you're getting good flow, your problem is the water tube rubber grommet or washer, under the powerhead (or debris such as busted impeller blade in the supply side).

HTH & G'luck..........ed

 

[dajohnson53]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Yes, flowing water up the supply tube with the covers off is an excellent way of diagnosing circulation problems.

A rag over the exhaust ports and spark plugs in the cyl's will keep water out of the engine's internals just fine.

I suspect that if you don't find you're getting good flow, your problem is the water tube rubber grommet or washer, under the powerhead (or debris such as busted impeller blade in the supply side).

HTH & G'luck..........ed

Thanks for the follow up. I'm going to flush up through the water tube later today and see what happens. If there seems to be any impediment at all, I'll try back flushing if I can work out the correct fitting. I've got some ideas.

 

[Motor Boater Bill]

Re: Merc 110 9.8 hp intermittant telltale and overheat

I've been wondering about the supply side of the pump also. Not sure how that's set up on the 1974--my 110 is a 1962!

 

[dajohnson53]

Re: Merc 110 9.8 hp intermittant telltale and overheat

Thanks for the follow up. I'm going to flush up through the water tube later today and see what happens. If there seems to be any impediment at all, I'll try back flushing if I can work out the correct fitting. I've got some ideas.

I flushed everything backwards and forwards and the water is flowing unimpeded as far as I can tell. So, when my gaskets arrive, I'll put everything back together and see how it works. Maybe something fell or flushed out that I didn't see.

I was wrong about the water routing. In case anyone's interested, it appears that this is how the water circulates (it seems to be somewhat of a mystery, i've never seen a diagram or schematic).

The water comes up via the water tube and "T's" with one side going directly to the flush port, the other side going directly to the main passage into the engine which is located in area covered by the exhaust cover and diverter. It circulates through that area in the space between the exhaust cover and the diverter. It then goes through various channels through the cylinder block, ending up filling a space around the cylinders themselves. I believe this area is called the water jacket (its cover is the cover the spark plugs go through - I've seen it called water jacket cover, but others call it cylinder block cover). The tell-tale outlet is in that area. From there, I'm not sure where it goes, exiting the system I guess down through the leg to the prop exhaust??

 

[rsjuhasz]

I have had the same problem and have been stumped as well. Will take off the LU again to be sure that the key way is in place and if it is will check the compression....