My ST1100 just started puking out all it's coolant from the overflow tank - why?

On a tour with some family members in SW Colorado and surrounding area, my 88,000 miles 94 ST1100 started vomiting coolant out of the expansion tank.

Bike and weather were not particularly hot, coolant level was checked about 2 weeks prior to the trip, bike was running fine.

Let it cool for 20 mins, refilled the expansion tank, let it idle for 10 mins, same thing happened.

About 20 mins later rode the bike over to a place where I could store it, no coolant came out.

Put it on the center stand, disconnected the fan, revved the knackers off it for about 3 mins until it got real hot, nothing came out.

I have 2 theories - let me hear yours, I will pick the bike up soon and get it home for either:-

1. Easy fix
2. Open heart surgery.

Thanks

Ian

Check the hose that goes from the rad filler neck to the overflow tank. Very common for that hose to split at the filler neck, allowing coolant to flow in one direction only - into the overflow bottle.

Also, your rad will be very low now and "revved the knackers off it" was probably not a good idea. Cut an inch off the split end of the hose and re-attach and refill both the rad and bottle. Obviously, a bit of plastic removal is necessary to get at the rad filler neck.

Bush said:

Check the hose that goes from the rad filler neck to the overflow tank. Very common for that hose to split at the filler neck, allowing coolant to flow in one direction only - into the overflow bottle.

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I fixed the hose for that very reason when I checked coolant level, I omitted to say that when I refilled the expansion tank and the bike cooled a little, it sucked the coolant back into the radiator and the level in the expansion tank went to nothing.

When the expansion tank started filling again, there were no bubbles.

What is the temp gauge saying during all of this?

Temp gauge was right where it should be when it was puking, when I got it hot (revving knackers off) it was almost into the red with nothing coming out and the expansion tank not filling.

How well has the cooling system been maintained over the years, if you know? Any chance you could have a plugged, or partially plugged rad?

Could also be a bad rad cap. not holding any pressure at all.

Bush said:

Could also be a bad rad cap. not holding any pressure at all.

Click to expand...

That's my hope. Can't diagnose until I get the bike back which will be a few weeks.

linny999 said:

That's my hope. Can't diagnose until I get the bike back which will be a few weeks.

Click to expand...

OK, please come back to let us all know the outcome.

I will as there is nothing more frustrating than a thread that 'dies on the vine'.

However, I am still open to suggestion, the other more costly repair is a head gasket

linny999 said:

I will as there is nothing more frustrating than a thread that 'dies on the vine'.

However, I am still open to suggestion, the other more costly repair is a head gasket

Click to expand...

Head gasket would be the avenue of last resort. And, from my experience w/ older cars, with the radiator cap off, and the engine running, you can sometimes see bubbles coming up in the radiator. Since the ST's cap is so small and space is tight, this might not be a good way to verify what the problem is.

I'm told head gaskets going are rare, having said that, running the knackers out of it could be questionable. The hoses that go under the carbs are prone to failure especially the narrow one from the rad cap to under the carbs becomes brittle. I ended up changing all coolant hoses and flushing the system a number of times. Given the age of our bikes this is strongly recommended. Check your oil for antifreeze contamination, that could indicate leaking head gassket

I would think if the head gasket was blown, allowing the volume of coolant pushed out the overflow that the OP seems to be reporting, the engine would be running very poorly.

I think the most likely cause for steam to blow coolant out of the expansion tank will be the radiator cap failing. The cap is designed to hold 16-20 psi pressure in the cooling system and that elevates the boiling point of a water-glycol mixture from 107C to 130C. For reference, redline on the temperature gauge is usually around 120C, fan start is usually at 100C and thermostat opening is around 80C. So if your radiator cap is faulty, the coolant will start to boil at about 3/4 on the gauge, and because steam takes up a much bigger volume than liquid, the expansion forces coolant out of the reservoir.

It is possible that in opening and closing the cap to check the coolant, you may have caused the cap to seal again, but odds are that it will fail again at an inconvenient moment. The ST11 takes a common automotive cap which will be pretty cheap to buy:

Radiator cap:
1990-96 Honda Accord 2.2L 16psi
Stant 11233 or 11242
Gates 31336

^ I concur with Terry. I'd put money on the radiator cap. What altitude where you at when it happened?

I've had two episodes of coolant puking, both occurring at higher altitudes (6-8000 ft ASL). At sea level my cooling system behaves normally. I suspect the reduced atmospheric pressure in combination with a marginal radiator cap is allowing the coolant to boil at a reduced enough temperature that the fan can't' keep up.

I would also suggest be systematic in your approach. One gets over zealous and changes a whole bunch of things and if the problem gets solved you really don't know what the solution was. You will get good at taking off the tupperware. As suggested above the automotive radiator cap is cheap, though you have to make sure the locking mechanism is properly locked on the cap or it will leak a bit. If you replace the hoses, most of the coolant hoses are available through honda except the overflow hose and the 5/16" hose that goes into the "V" under the carbs, those you can purchase by length at an automotive store. You can test the sensor by the thermostat with an ohm meter. I made an adapter so that I could plug a wire onto the sensor and the other wire from the meter I attached to ground. the thermostat opened when the meter read about 37 ohms and the fan would cycle on at 28 ohms and shut off at 31 ohms.
Good luck on finding the issue

MV_Dave said:

^ I concur with Terry. I'd put money on the radiator cap. What altitude where you at when it happened?

I've had two episodes of coolant puking, both occurring at higher altitudes (6-8000 ft ASL). At sea level my cooling system behaves normally. I suspect the reduced atmospheric pressure in combination with a marginal radiator cap is allowing the coolant to boil at a reduced enough temperature that the fan can't' keep up.

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Dave, very good, we were at 7,100 after coming down from 10,500 so I like the sound of your theory.

Kiltman, I am being systemic, I don't shotgun things, 15 years in field service, first time you see a problem you've not seen before you call your colleagues and ask them, or check the knowledge database, that's why I posted here. The last thing I want to do is make a load of work for myself - my wife already does that for me!

TerryS said:

I think the most likely cause for steam to blow coolant out of the expansion tank will be the radiator cap failing. The cap is designed to hold 16-20 psi pressure in the cooling system and that elevates the boiling point of a water-glycol mixture from 107C to 130C. For reference, redline on the temperature gauge is usually around 120C, fan start is usually at 100C and thermostat opening is around 80C. So if your radiator cap is faulty, the coolant will start to boil at about 3/4 on the gauge, and because steam takes up a much bigger volume than liquid, the expansion forces coolant out of the reservoir.

It is possible that in opening and closing the cap to check the coolant, you may have caused the cap to seal again, but odds are that it will fail again at an inconvenient moment. The ST11 takes a common automotive cap which will be pretty cheap to buy:

Radiator cap:
1990-96 Honda Accord 2.2L 16psi
Stant 11233 or 11242
Gates 31336

Click to expand...

+1, I concur with your assessment. Just ordered one for my coolant system overhaul. Thanks for part numbers.

So I picked the ST up after about 5 weeks, started first time as you would expect.

I have fitted a new radiator cap, there was nothing to see on the old one.

Unfortunately due to some pretty hefty surgery I had 3 weeks ago, it's doubtful I will be riding again this year but as soon as I have put some miles on the ST, I will give an update - but don't hold your breath.