Foam in coolant

[Capital]

So I just bought an ST1100 for fairly cheap. The story of it - that is was sitting for a year at least (previous owner made 200km in a year, and I don't know how long it sat before). It is 1991 model with almost 150k km on it. I bought it as a 2nd bike for upcoming long autumn/winter evenings, to work on.

But it could be the evenings will get even longer, as I may've overlooked a big deal. Looking at the coolant reservoir, there is foam on on top of fluid (the coolant level is a little above High mark). I tried to snap a picture of it (blue coolant, white foam).
The oil through the inspection window looks dark, but not mixed. Opening up the Oil cover - there doesn't seem to be any traces of coolant.

Anyways, am I looking into buying new head gaskets? Or water pump? Not sure how common is this to blow a gasket on ST, but I guess pretty rare.

I'm yet to drain the oil and coolant, and maybe do a compression test if that could help showing the head gasket issue.

Thanks for any input, and I am sure there will be more to come from my end

 

[WobblyG]

That foam may not be a sign of a serious problem, it could just be something the previous owner contaminated the coolant with while topping up. A friend of mine once topped up his coolant using an old brake fluid bottle that he thought he'd washed out. He got a greasy foam in his overflow bottle. He flushed the coolant system a couple of times and the foam went away. Could be that the system just needs a good flush. Given that there seems to be no signs of coolant in the oil. I'd certainly try that before I started taking anything to pieces. (other than the plastics you need to remove to get to the radiator cap). Good luck.

 

[The Cheese]

Let's slow down. No reason yet to jump to any major issues.

What does the radiator look like? You said it's been sitting, also you just got it. Who knows what that liquid is. Dump all that, flush out and refill with coolant.

 

[dwalby]

Agreed that there could be more than one explanation for foam in the coolant, but oil is the most likely. Put your finger in it and see if it feels oily. The possible reason there's no coolant in the oil is because the oil pressure is typically 40-60psi while the coolant pressure is 15psi, so the oil usually wins. Fingers crossed for you. As was suggested, flush the radiator and start over with a known, foam free liquid, and go from there. I'd maybe be inclined to use just water for the initial test, if you get more oil in it at least you didn't waste a bunch of coolant while doing the test, and if the foam doesn't return you just did a radiator flush with the plain water.

 

[SMSW]

Sounds to me like the bike needs a thorough going over, and its not only the coolant that should be changed. I'd go for all fluids, pull the calipers and clean and lube them (the pins), check the front forks, battery, etc. Since the bike is pushing 30 yrs old, when you pull the tupperware, look over all the electrical connectors/connections you can find for signs of corrosion and heat. Check all the hoses for cracking and deterioration.

You are one of the younger owners of an 1100 on this website! You will have plenty of time to tinker with the bike.

 

[TerryS]

A 1991 ST has an oil/water intercooler at the oil filter mount; this might have a little pinhole in it. But wait till you've flushed it out and run for a bit before jumping to a conclusion.

 

[Capital]

Thank you all! A lot of good input. I’ll post an update once progress is made. I may not be that fast, but will do my best

 

[Al st1100]

Agreed that there could be more than one explanation for foam in the coolant, but oil is the most likely. Put your finger in it and see if it feels oily. The possible reason there's no coolant in the oil is because the oil pressure is typically 40-60psi while the coolant pressure is 15psi, so the oil usually wins. Fingers crossed for you. As was suggested, flush the radiator and start over with a known, foam free liquid, and go from there. I'd maybe be inclined to use just water for the initial test, if you get more oil in it at least you didn't waste a bunch of coolant while doing the test, and if the foam doesn't return you just did a radiator flush with the plain water.

but there is zero oil pressure when the bike is shut off and the cooling system will hold pressure till it cools down. At that point coolant wins. The head gasket could fail around the piston and compressed exhaust gas would get into the coolant. A blue water test would confirm that. I would be more interested in what the radiator coolant and cap looks like. Oil would come to the top and the radiator cap rubber would be swollen form oil If the rad cap is good I would just flush and and keep it under observation

 

[ChriSTian_64]

hum... is it possible.... that what you are looking at, look like foam.... but it is just the curvy inside of the reservoir..
Same thing happend to me 2 months ago. Looking into my reservoir, I saw that strange white stuff... it took me a second look, a few days later, and a different viewing angle, to realise that what I was seeing, was in fact the white plastic of the reservoir’s fold.

 

[dwalby]

but there is zero oil pressure when the bike is shut off and the cooling system will hold pressure till it cools down. At that point coolant wins.

good point, thanks for pointing that out. So I guess if there's a gasket breach between oil and coolant you typically get mixing in both directions?

I know its also possible to have an internal coolant leak drain into the oil pan, but that's not applicable to this scenario.

Is there another scenario where oil would get into the coolant, but not vice/versa? Is it possible that the pressure differential is enough to leak a small amount of oil into the coolant, but the lower pressure of the coolant after the engine is off doesn't put much coolant (if any) into the oil so the oil looks fairly normal at first glance?

 

[Al st1100]

good point, thanks for pointing that out. So I guess if there's a gasket breach between oil and coolant you typically get mixing in both directions?

I know its also possible to have an internal coolant leak drain into the oil pan, but that's not applicable to this scenario.

Is there another scenario where oil would get into the coolant, but not vice/versa? Is it possible that the pressure differential is enough to leak a small amount of oil into the coolant, but the lower pressure of the coolant after the engine is off doesn't put much coolant (if any) into the oil so the oil looks fairly normal at first glance?

every car I came across it went both ways. Now a head gasket failure around the piston will cause air pocket in the cooling system, a/f to blow out into the over flow tank and overheating. The cooling system builds pressure quickly. Oil will not get into the system, the piston are surrounded by coolant. That cylinder will misfire as the coolant seep into that cylinder. It may only be slight leak and the symptoms my be intermittent at first.

 

[Al st1100]

good point, thanks for pointing that out. So I guess if there's a gasket breach between oil and coolant you typically get mixing in both directions?

I know its also possible to have an internal coolant leak drain into the oil pan, but that's not applicable to this scenario.

Is there another scenario where oil would get into the coolant, but not vice/versa? Is it possible that the pressure differential is enough to leak a small amount of oil into the coolant, but the lower pressure of the coolant after the engine is off doesn't put much coolant (if any) into the oil so the oil looks fairly normal at first glance?

not every car I came across went both ways. Now a head gasket failure around the piston will cause air pocket in the cooling system, a/f to blow out into the over flow tank and overheating. The cooling system builds pressure quickly. Oil will not get into the system, the pistons are surrounded by coolant. That cylinder will misfire as the coolant seep into that cylinder. It may only be slight leak and the symptoms my be intermittent at first

 

[Capital]

Did i just win the lottery? (Except all the rust...)

 

[OkieRider]

I have had oil leak into the coolant, but not the other way around, with an exhaust side head gasket leak.

If you have an exhaust side leak, with the radiator cap off, you'll see the coolant "blooping" up, like a water drop in reverse. That's The exhaust pulse pushing against the coolant. If you're not seeing that, you don't have an exhaust side breach. Exhaust side will sometimes result in oil or carbon soot floating in the radiator.

With a gasket beach on the intake side, you'll typically see coolant in the oil, steam in the exhaust.

 

[ChriSTian_64]

How can your radiator be so low in coolant, while your reservoir is above the high limit ?
The manual ask to add coolant in the reservoir. And from there, it is suppose to go in your radiator, if the radiators needs some.
So, the little hose going from the reservoir to the rad must be clogged.

So... maybe that "foam" doesn't come from the rad, if the hose is clogged.

Now, some coolant type are not compatible.
And, if a previous owner changed of coolant type, all the time, there is a little left from the old coolant type.
Could this be the source of the foam.... a bit of the old coolant type (green)... interacting with the blue one... and creating that green foam ?

I would start by taking the reservoir out (easy to do), empty it, have a closer look at its content, wash it (scrub the inside by shaking it with crushed ice and a bit of water).
Then : make sure the hose from the reservoir to the radiator is not clogged (simply by trying to blow thru it). If it's clogged, well, fix that.
Finally, flush the old coolant in radiator, rinse it with distilled water (tap water normally contains minerals, wich may create deposit inside your colling system) and refill with fresh coolant.
Well... I say flush the radiator... cause... I am assuming there is some cooloant left in that rad, right ? I hope so.

After that.... if foam reappears after a while... you will know it is not from old coollant sitting there for too long, and something else is causing it.

 

[paulcb]

Did i just win the lottery? (Except all the rust...)

I had a similar concern and posted about it here. Turned out to be just frothy oil, but there are some good comments in that thread. A couple things you can do...

• Drain your coolant and let it sit for several hours, see if you see oil in it.
• Drain your oil and try to boil it. If it has water in it, the water will boil and it will be obvious.

​

 

[SMSW]

I had a similar concern and posted about it here. Turned out to be just frothy oil, but there are some good comments in that thread. A couple things you can do...

• Drain your coolant and let it sit for several hours, see if you see oil in it.
• Drain your oil and try to boil it. If it has water in it, the water will boil and it will be obvious.

​

Would not either contaminant be visible if you simply left the two fluids to sit and settle for say an hour or two?

 

[paulcb]

Would not either contaminant be visible if you simply left the two fluids to sit and settle for say an hour or two?

You're probably right. I did let my oil sit in the drain pan for a while and saw nothing, but I also wanted another confirmation point. Plus I just wanted to see my wife's face when I cooked some engine oil on her stove.

See post #38 of that thread where I did a experiment with oil and coolant sitting in a jar.

 

[The Cheese]

How can your radiator be so low in coolant, while your reservoir is above the high limit ?

So, the little hose going from the reservoir to the rad must be clogged

When the bike heats up enough the coolant expands and is sent to the reservoir. When cooling of it sucks it back into the radiator. If the hose is broken nothing will return. The hose is probably broken enough to break suction but intact enough to send coolant to the reservoir.

A common issue with the 11s is the hose that connects the radiator to the overflow gets damaged. Where it connects to the thermostat housing. Most times there is enough slack to trim it and reuse the hose.

 

[Bmacleod]

How can your radiator be so low in coolant, while your reservoir is above the high limit ?
The manual ask to add coolant in the reservoir. And from there, it is suppose to go in your radiator, if the radiators needs some.
So, the little hose going from the reservoir to the rad must be clogged.

So... maybe that "foam" doesn't come from the rad, if the hose is clogged.

Now, some coolant type are not compatible.
And, if a previous owner changed of coolant type, all the time, there is a little left from the old coolant type.
Could this be the source of the foam.... a bit of the old coolant type (green)... interacting with the blue one... and creating that green foam ?

I would start by taking the reservoir out (easy to do), empty it, have a closer look at its content, wash it (scrub the inside by shaking it with crushed ice and a bit of water).
Then : make sure the hose from the reservoir to the radiator is not clogged (simply by trying to blow thru it). If it's clogged, well, fix that.
Finally, flush the old coolant in radiator, rinse it with distilled water (tap water normally contains minerals, wich may create deposit inside your colling system) and refill with fresh coolant.
Well... I say flush the radiator... cause... I am assuming there is some cooloant left in that rad, right ? I hope so.

After that.... if foam reappears after a while... you will know it is not from old coollant sitting there for too long, and something else is causing it.

When the bike heats up enough the coolant expands and is sent to the reservoir. When cooling of it sucks it back into the radiator. If the hose is broken nothing will return. The hose is probably broken enough to break suction but intact enough to send coolant to the reservoir.

A common issue with the 11s is the hose that connects the radiator to the overflow gets damaged. Where it connects to the thermostat housing. Most times there is enough slack to trim it and reuse the hose.

Good point X2. I would be checking the hose. Also, if you can remove the overflow bottle, it would be worth cleaning it well to get rid of old contaminents. A good way to clean it is to put some soap/degreaser, water and some gravel in the bottle and shake it real well till clean. Rinse well and reinstall.