ST1100 Anti-Freeze Leak

[Uncle Phil]

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 -


Looking straight on from the front -

Looking up from the front -

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?

 

[dwalby]

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.

 

[ST1100Y]

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.

bypass...
Or the w/pump shaft seal...

 

[Uncle Phil]

It appears to be coming from above the water pump from what I can tell.
That's why I was thinking the 'water necks' under the carbs.

 

[John OoSTerhuis]

Bypass hose. #13 in Doug’s schematic. Where it connects to the nipple on the ‘water pipe,’ #4.

 

[Uncle Phil]

Do you have to remove the radiator to get to it?

 

[dwalby]

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]

Do you have to remove the radiator to get to it?

I'd go from the top by removing air-box and carbs...

 

[Uncle Phil]

I'd go from the top by removing air-box and carbs...

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.

 

[SMSW]

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.

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.

 

[Uncle Phil]

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.

@dwalby - Do you remember if you also had the upper fairings removed when you did that?

 

[dwalby]

@dwalby - Do you remember if you also had the upper fairings removed when you did that?

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.

 

[John OoSTerhuis]

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.

BTDT. Popped’m, swung’m to the side onto a clean towel. YMMV

 

[Oldbikefixr]

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.

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.