a small stream of bubbles within the coolant in the overflow tank...

Timothy1959 · May 18, 2016

I have a recently purchased 1996 Honda ST1100 (standard) with only 45,000 miles.
After a long hard test ride tonight that included a mixture of high & low speed, I shut of the engine & inspected the bike with a flash light.
I then noticed a small stream of bubbles within the coolant in the overflow tank.
Also, the level of coolant in the reserve tank does not increase & decrease with thermal cycling of the engine like it should.
Also, there is a mysterious loss of coolant (only about 2 cups) over 3 days of riding. There are no visible coolant leaks anywhere.
Is this ALWAYS an indicator of a leaking head gasket, or is there a less expensive & simpler solution?
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I discovered a pin hole leak in the radiator today (5/31/16). This explains the bubbles and mysterious loss of coolant!

The system couldn't drink from the overflow tank because it was sucking in air through the pin hole. The pin hole was near the TOP of the rad so the leak was hard to notice. It was an intermittent leak. Live & learn!
Thank GOD no head gasket leaks!!

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I thought about solder, but there was SO MUCH internal corrosion (due to neglect from the PO), I didn't think solder would work.
I tried epoxy (which would adhere to the uncorroded outside surface of the tank). This didn't work. As soon as the cooling system developed pressure during initial engine warm up, the hot pressurized coolant spewed right past THREE LAYERS of cured epoxy.
To avoid buying a new radiator (at $425) I bought a used one on eBay for $75. I will see how this works.
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Update: I just installed the used radiator (6/7/16). Good news - The rad is LEAK FREE!

I warmed up the engine (electric fan turn on), the coolant level in the reserve tank increased (by like 1/2") , the engine warmed up fast, there are no visible leaks anywhere. NOW this engine can run at normal operating temperature & cooling system pressure!

Slydynbye · May 18, 2016

Just a guess but, it could simply be the radiator overflow working as it should spilling some of the radiator fluid to overflow.
If it works correctly (no split in the overflow tube) it should be sucked back into the radiator when it cools.
Hopefully someone will concur or tell you the real reason.

Jim Van · May 18, 2016

I would also first check to see if the small tubing that runs from the overflow/reservoir tank to the thermostat housing is split at the thermostat housing end.

Bush · May 18, 2016

Sounds like normal operation of the overflow to me. Once you shut down a hot engine, without coolant flowing through the system, it will heat up more and expand, the thermostat will be open and coolant will be "burped" out through the rad cap seal into the overflow hose. What you are seeing is air trapped in the hose being expelled into the overflow tank as the coolant enters. When the engine cools, the coolant "shrinks" again (for lack of a better word) and coolant that had been forced out of the engine during expansion, is drawn back via that overflow hose, but DO check that hose at the rad cap connection to ensure no splits, otherwise your engine will drawn in air, leaving the rad level low.

Timothy1959 · May 18, 2016

Jim Van said:
I would also first check to see if the small tubing that runs from the overflow/reservoir tank to the thermostat housing is split at the thermostat housing end.

This tube is new and has no leaks.

Jim Van · May 19, 2016

Is there a hose clamp installed ??

scout · May 20, 2016

Jim Van said:
I would also first check to see if the small tubing that runs from the overflow/reservoir tank to the thermostat housing is split at the thermostat housing end.

+1

If you notice the overflow keeps getting fuller and not sucking the coolant back into the radiator, then you most likely have a cracked overflow house near the thermostat. Common issue. I would certainly check the hose before I started messing with the head gasket. In most cases you can trim a bit off the affected end and re-attach. There is usually enough slack. I however would then order a hose.

Timothy1959 · May 20, 2016

Jim Van said:
Is there a hose clamp installed ??

The overflow hose is new and there are worm clamps on both ends.

Timothy1959 · May 20, 2016

scout said:
+1

If you notice the overflow keeps getting fuller and not sucking the coolant back into the radiator, then you most likely have a cracked overflow house near the thermostat. Common issue. I would certainly check the hose before I started messing with the head gasket. In most cases you can trim a bit off the affected end and re-attach. There is usually enough slack. I however would then order a hose.

The overflow hose is new and there are worm clamps on both ends.

Timothy1959 · May 20, 2016

Jim Van said:
Is there a hose clamp installed ??

The overflow hose is new and there are worm clamps on both ends.

Bush · May 20, 2016

So tell us, what shape is the overflow tube in?

Timothy1959 · May 21, 2016

Bush said:
So tell us, what shape is the overflow tube in?

Antagonism is a good example of troll behavior. YOU HAVE NOW BEEN EXPOSED!

Timothy1959 · May 31, 2016

Bush said:
Sounds like normal operation of the overflow to me. Once you shut down a hot engine, without coolant flowing through the system, it will heat up more and expand, the thermostat will be open and coolant will be "burped" out through the rad cap seal into the overflow hose. What you are seeing is air trapped in the hose being expelled into the overflow tank as the coolant enters. When the engine cools, the coolant "shrinks" again (for lack of a better word) and coolant that had been forced out of the engine during expansion, is drawn back via that overflow hose, but DO check that hose at the rad cap connection to ensure no splits, otherwise your engine will drawn in air, leaving the rad level low.

I discovered a pin hole leak in the radiator today. This explains the bubbles and everything else.
It is NEVER "normal operation" to have bubbles in a liquid cooling system on an ST1100.
I must be careful with anything you write on this forum now that I know you are a troll attempting a smear campaign against me.

You will continue to be frustrated with me though, because I have built up an immunity to troll behavior on the Web!

Jim Van · Jun 5, 2016

Congrats on finding that. What are your plans for the pin hole ?? Maybe it can be soldered shut.

Timothy1959 · Jun 6, 2016

Jim Van said:
Congrats on finding that. What are your plans for the pin hole ?? Maybe it can be soldered shut.

Thanks Jim!

I thought about solder, but there was SO MUCH internal corrosion (due to neglect from the PO), I didn't think solder would work.
I tried epoxy (which would adhere to the uncorroded outside surface of the tank). This didn't work. As soon as the cooling system developed pressure during initial engine warm up, the hot pressurized coolant spewed right past THREE LAYERS of cured epoxy.
To avoid buying a new radiator (at $425) I bought a used one on eBay for $75. I will see how this works.

a small stream of bubbles within the coolant in the overflow tank...

Will ride for Pie