TomInOregon said:
Anyway, it appears that the leak is somewhere in the back of the engine, but since it butts up against the frame, I can't see exactly where it's leaking. I'm kind of stumped on how to proceed at this point since I can't see much less reach any leaks back there.
There aren't any coolant lines on the back of the engine. The most rearward are the two hoses which come from the thermostat housing under the carburetors and go into the heads. I strongly suspect that's where the leak is. In my reading about the ST1100, more than a few people have had their under-carb coolant hoses blow. Lots of people (me included) change out the hoses even before something bad happens.
I think what has happened is one of the under-carb hoses has split or otherwise developped a leak. The coolant drips down on the top of the engine and flows backward until you can see it. Even a small leak can cause lots of steam. When the engine is hot, the cooling system is under pressure. Just a small leak can compromise that pressure, which allows the liquid to boil, and water vapor can escape a small leak much faster than liquid water.
If you've got the plastic off, removing the carbs really isn't a big deal. It's a major bonus if another ST owner near you can drop by for some advice. That's what I did, and after the guy showed me how to do it, I almost felt silly that I'd asked for his help, but it was very helpful.
Do you have a shop manual of some sort? Many people don't like the Haynes, but I like it for it's down-to-earth style suited for non-professionals. My Honda manual is thorough, but I'm often left wondering how to go about procedures. The Haynes does a good job of explaining how to remove stuff. I've not had any experience with the Clymer, but many recommend it.
As long as the plastic is off, removing the carbs is about a 1 to 2 hour job for someone who hasn't done it. Take out the fuel tank (four bolts and 4 wires), remove the air cleaner housing (six bolts and a fuel line), and you'll be staring at the carbs. to get them out is only a couple of cables and four screw clamps.
With the carbs off, you can look directly at the coolant hoses which have most likely failed. Those links provided by #9 will give you all the part numbers you need to do a full coolant system R&R.
Jamie