Coolant Leak While not Running

tpasco1995

tpasco1995

Joined
Jan 29, 2024
Messages
97
Age
30
Location
Columbus, OH
Bike
2003 ST1300A
Hey everybody! It's been a while. Life turned hectic.

I'm servicing my '03 ST1300 to get it ready for riding season, and in jostling it back and forth trying to jiggle out the last few drops of old oil, I seemingly started a small coolant leak.

It's barely anything, maybe 4 drops a minute, but that's without the bike running. I've left it overnight and the pace hasn't changed. The drip is from the bottom front Tupperware right behind the front wheel, where it comes to a point at the bottom of the bike, so obviously it's leaking downward.

If I can avoid a tear-down I'd like to, and if anyone has some sort of really useful knowledge like "it can splash out sometimes and this isn't anything to worry about" I'd love that, but I'm also okay with the bad news. Just hoping for insight.
 
Unfortunately, leaking down the front of the engine block can be caused by issues almost anywhere in the coolant system. This is because the hoses tucked under the throttle body in the "V" of the engine and the water pump drain out through two holes in the right-hand side of the engine (one circle one square hole). See this article. I would recommend cleaning up the engine of any oil, road grime, and coolant and then re-check to see if you can tell where the leak is coming from. If the bike is leaking consistently when the engine is off I don't see how the issue will go away on its own so sadly you will probably need to pull off the side fairing and start inspecting the weep holes, hoses, water pump cover, and clamps. Removing the airbox and side fairings can give you access to most but not all of the hoses.
 
What’s the temperature in your garage?
Small coolant leaks from the engine valley hoses are common in winter since the rubber contracts in the cold. You might notice the leak lessens or stops after warming up or running the engine for a while.
Most leaks stem from loose clamps around the alternator area - or in the front of the engine were the thermostat is located. Retightening them can offer a temporary fix, but replacing them with constant-pressure clamps is the best long-term solution—I did the same in my case.
If you spot oil mixed in with the coolant, the issue could be more than just the clamps—potentially a failing water pump seal.
 
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It is either the thermostat housing which is right up behind the radiator at the top the seals go on it.
Or it's a hose in the engine v.

I remember on my old pan i started to see the oil light on the dashboard flicker and it was due to a long time slow coolant leak in the v that eventually corroded the wire to the oil pressure switch causing the flickering oil light who knew.
I replaced the sub harness the wires were a mess to the oil light.

it's the place i would start, I know its a pain to get to but sometimes its worth going in there just to check over these things for me it effected the wires on the sub harness due to leaking for so long without detection the oil light made me suspicious plus that oil switch is right in v passage where coolant leaks flow.

You will find it, how many miles on the bike my water pump started weeping at 80k from the rubber hose and it continued to do this until I finally gave in and did the pump at 100,000 miles.
 
easy rider said:
It is either the thermostat housing which is right up behind the radiator at the top the seals go on it.
Or it's a hose in the engine v.

I remember on my old pan i started to see the oil light on the dashboard flicker and it was due to a long time slow coolant leak in the v that eventually corroded the wire to the oil pressure switch causing the flickering oil light who knew.
I replaced the sub harness the wires were a mess to the oil light.

it's the place i would start, I know its a pain to get to but sometimes its worth going in there just to check over these things for me it effected the wires on the sub harness due to leaking for so long without detection the oil light made me suspicious plus that oil switch is right in v passage where coolant leaks flow.

You will find it, how many miles on the bike my water pump started weeping at 80k from the rubber hose and it continued to do this until I finally gave in and did the pump at 100,000 miles.
Click to expand...
If the drain canal in the engine valley of the ST1300 is clear, a minor leak may not be a major concern. However, if the canal is clogged, coolant can accumulate around the alternator, potentially leading to failure. I use compressed air regularly to keep it unobstructed, the alternator is $$$$ and it is a big job to replace it!
 
Taking the fairing off really isn't a "teardown". If you want to track the leak down you'll have to take most of the fairing off which might seem worse than it actually is.
 
Sidekick said:
What’s the temperature in your garage?
Small coolant leaks from the engine valley hoses are common in winter since the rubber contracts in the cold. You might notice the leak lessens or stops after warming up or running the engine for a while.
Most leaks stem from loose clamps around the alternator area - or in the front of the engine were the thermostat is located. Retightening them can offer a temporary fix, but replacing them with constant-pressure clamps is the best long-term solution—I did the same in my case.
If you spot oil mixed in with the coolant, the issue could be more than just the clamps—potentially a failing water pump seal.
Click to expand...
The garage is ambient to the Ohio weather, so while the leak has been happening it's been about 45-55°F.

No oil mixed in. Thankfully it's just translucent blue as can be.

I've got a snap case filled with various constant pressure spring clamps and another full of worm screw hose clamps, so I'm hoping it's just a loose clamp. Sounds like worst case might be a hose which I can replace easily enough.

Appreciate the help so far and I'll update
 
tpasco1995 said:
The garage is ambient to the Ohio weather, so while the leak has been happening it's been about 45-55°F.

No oil mixed in. Thankfully it's just translucent blue as can be.

I've got a snap case filled with various constant pressure spring clamps and another full of worm screw hose clamps, so I'm hoping it's just a loose clamp. Sounds like worst case might be a hose which I can replace easily enough.

Appreciate the help so far and I'll update
Click to expand...
FYI, don't overtight the radiator clamps as they will deform the pipes and leak badly.
 
So the saga has come to an end.

The radiator cap was loose. When I shook the bike it sloshed a puddle of coolant into the fairings and that was the drip.

I can see where the coolant ran down from the loose cap, and there's still a good bit of coolant in the rad. I topped it off several hours ago and no leaking since.

For good measure I have a new radiator cap on the way.
 
tpasco1995 said:
Hey everybody! It's been a while. Life turned hectic.

I'm servicing my '03 ST1300 to get it ready for riding season, and in jostling it back and forth trying to jiggle out the last few drops of old oil, I seemingly started a small coolant leak.

It's barely anything, maybe 4 drops a minute, but that's without the bike running. I've left it overnight and the pace hasn't changed. The drip is from the bottom front Tupperware right behind the front wheel, where it comes to a point at the bottom of the bike, so obviously it's leaking downward.

If I can avoid a tear-down I'd like to, and if anyone has some sort of really useful knowledge like "it can splash out sometimes and this isn't anything to worry about" I'd love that, but I'm also okay with the bad news. Just hoping for insight.
Click to expand...
My 2009 ST1300 is showing the same type of small coolant leak after starting during winter storage in an Ontario garage (above freezing, but probably 40 F). I'm reading this after pulling the fairing off and removing the water pump. The gasket (O-ring) actually looked OK after removal, so now I think my leak was coming from the V hole. Wish I had read this first and not spent all that time removing parts. Now I need to chase potential leaks above that might be coming out that pathway. Add yes, it was clean coolant with no oil in it, after sitting for winter months so there may have just been some hose shrinkage somewhere above....
 

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A month and a half on, no more leaking. Apparently didn't fudge up the oil change or shaft fluid change either, because they're both fine.

I need to do clutch juice and I'm scared.
 
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