ST1100 Anti-Freeze Leak

Uncle Phil

Uncle Phil

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Joined
Feb 26, 2007
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11,215
Age
72
Location
In The Holler West Of Nashville, Tennessee
Bike
4 ST1100(s)
2025 Miles
006132
Before I start removing carbs, etc. take a look at these pictures and tell me where you think the leak is located.

From the left side with the 'inspection' side cover -
ST1100 Looking From Side.jpg

Looking straight on from the front -
ST1100 Looking Straght On Front.jpg
Looking up from the front -
ST1100 Looking Up From Front Bottom.jpg
The leak appears to me to be 'above' the water pump (I'm thinking one of the water necks under the carbs).
What say ye?
 
by "necks" do you mean the elbows? Those typically leak to the rear, but I don't know if they always do.

My first thought was maybe that vertical pipe that has the small hose that goes to the T-stat housing, but I can't recall its name.
 

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The only time I had access to it was when I had the carbs off to do the hoses/elbows so the water pipe and bypass hose was right out in the open in that case. I'm not sure how easy it would be to access it by going in from the front, but it seems like the radiator would have to come off to be able to get in there at all.

Just to throw out some random guesses on the source of the leak, there are two O-rings in the picture I posted. The larger one (#9) seals the housing (#5) where it mounts onto the engine block. The smaller one (#10) goes around the water pipe (#4), which fits inside the hole on the side of the housing. Its possible that either of those O-rings are the source of the leak, or as John mentioned it could be the bypass hose that goes from the water pipe over to the T-stat that's leaking.

The green residue in your photos suggests this leak has been around a while, perhaps after you tear into it you'll find more residue at the source of the leak. If not, then you'll probably have to pressurize the coolant system to see where its leaking from.
 
ST1100Y said:
I'd go from the top by removing air-box and carbs...
Click to expand...
Already there and still not 'clear' to see it - I guess I'll have to take a better look at it.
Since I've gone this deep I figure I'll replace the water necks and the hoses under the carbs while I have it apart.
 
Uncle Phil said:
Since I've gone this deep I figure I'll replace the water necks and the hoses under the carbs while I have it apart.
Click to expand...
If by 'water necks' you mean the cast spigots onto which the hose slides, these often corrode during a long term leak. Replacing them might not be a choice.
 
dwalby said:
The only time I had access to it was when I had the carbs off to do the hoses/elbows so the water pipe and bypass hose was right out in the open in that case. I'm not sure how easy it would be to access it by going in from the front, but it seems like the radiator would have to come off to be able to get in there at all.

Just to throw out some random guesses on the source of the leak, there are two O-rings in the picture I posted. The larger one (#9) seals the housing (#5) where it mounts onto the engine block. The smaller one (#10) goes around the water pipe (#4), which fits inside the hole on the side of the housing. Its possible that either of those O-rings are the source of the leak, or as John mentioned it could be the bypass hose that goes from the water pipe over to the T-stat that's leaking.

The green residue in your photos suggests this leak has been around a while, perhaps after you tear into it you'll find more residue at the source of the leak. If not, then you'll probably have to pressurize the coolant system to see where its leaking from.
Click to expand...
@dwalby - Do you remember if you also had the upper fairings removed when you did that?
 
Uncle Phil said:
@dwalby - Do you remember if you also had the upper fairings removed when you did that?
Click to expand...
I did not take either upper fairing off. I didn't even take the carbs off the bike, I swung them around to one side and let them hang from the cables, over the top of the fairing.
 
SMSW said:
If by 'water necks' you mean the cast spigots onto which the hose slides, these often corrode during a long term leak. Replacing them might not be a choice.
Click to expand...
1729507524351.jpeg
1729507725766.jpeg

This is what I found on my water hose connections back when I refurbished my 1991. These on the thermostat housing assembly were both leaking, with the aux hose connection leaking badly. Sprayed them silver so the damage would show up better. New parts and hoses all 'round. the filler cap looked near new but its gasket didn't.
 
I've replaced the two water joints, all the hoses, trimming the hose to the overflow bottle and installed new carb boots while I was in there.
All that work needed to be done but I was hoping that would resolve the issue as some were leaking.
Unfortunately, I still have a leak and now it appears to be on the left side right where the front case splits so I presume it is coming from the water pump.
Not really something I wanted to do at this point but I don't see any other option. :eek:
If I am missing something or you think the leak could be something else, please jump in.
And any advice/things to avoid in changing a water pump, let me know.

Final Leak.jpg
 
More questions for someone who has replaced a ST1100 water pump (since the Honda Service Manual is pretty cryptic) -
Do you have to remove the exhaust headers?
Do you have to drop the oil pan (IIRC no courtesy of @wjbertrand)?
Do the valve covers have to be removed or just the front section of them?

I know the radiator and the clutch cover has to be removed.
Anything else I am missing?
 
Uncle Phil said:
More questions for someone who has replaced a ST1100 water pump (since the Honda Service Manual is pretty cryptic) -
Do you have to remove the exhaust headers?
Do you have to drop the oil pan (IIRC no courtesy of @wjbertrand)?
Do the valve covers have to be removed or just the front section of them?
Click to expand...
IIRC will you have to remove one cam pulley + housing to gain the clearance...
Oil pan and headers have no business there; front wheel, mudguard, radiator, t-belt covers, pulleys...

Out of interest: what coolant did you use? Evans or some regular, silicate free stuff?

edit:
found some informative pics: http://www.st-riders.net/index.php?topic=7695.0
 
ST1100Y said:
IIRC will you have to remove one cam pulley + housing to gain the clearance...
Oil pan and headers have no business there; front wheel, mudguard, radiator, t-belt covers, pulleys...

Out of interest: what coolant did you use? Evans or some regular, silicate free stuff?

edit:
found some informative pics: http://www.st-riders.net/index.php?topic=7695.0
Click to expand...
Yeah I looked at that thread already but I was more after the 'removal' sequence.
Does the front wheel and mud guard really have to come off or does it just make it easier?
Coolant was good old Honda HP(?) motorcycle coolant in the blue jug. ;)
Evans will be what goes back in it.
 
ST1100Y said:
It does make it a LOT easier, especially when you're not working on a lift...
Click to expand...
Thanks!
Before I tear into that part, I'm going to check one more thing - the metal tube (19510-MAJ-G20) that runs from the valley to the lower radiator hose.
It just seems strange to me that the water pump would be leaking 'from the top' instead of the 'bottom'.
The 'challenge' is you can't get a good view of it very easily.
I didn't see anything in that area when I had the carbs pulled though but it wasn't under 'pressure'.
 
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