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1985 K100RS coolant boiling over?

Richard is correct. Coolant coming out at the cap indicates that the OUTER cap gasket is not sealing.

In your middle picture, it shows a nick in the outer sealing surface of the filler neck between 10 and 11 o'clock. That would cause a leak of coolant along the threads as the bike heats up. It would also suck air into the radiator as it cools down. Do yourself a favor and follow Greg's suggestion and buy a new filler neck. It will probably solve all your coolant problems. The cap has to have a good seal at BOTH the inner and outer gaskets.

Make SURE that there are no cracks in the hose from the filler neck to the expansion tank!




:dance:dance:dance

Hi Lee,

That nick that you believe you are seeing is an illusion created by the ring of dried coolant around the sealing surface of the filler neck. When wiped off there is nothing there. I can see no issues with the filler neck whatsoever, and I did inspect them a few weeks ago as posted farther back in this thread. All new Samco coolant hoses (just because) and new hose from filler neck to expansion tank too.

Cheers,
Tom
 
So I had some time this morning and decided to squeeze hoses again. Nothing to lose, right? Put the bike on the side stand and continually squeezed the hose that runs across the top of the engine block. It still bubbled up air and some large ones that spit coolant out the top, and the coolant level, while visible, was down in the upper hose. I also squeezed the lower hose, but in using both hands I could not look into the filler neck. I went back and forth between the two. Guys, can these systems really be this difficult to remove trapped air? I took my time filling it.

I put the bike on the center stand and started it up. The coolant rose up in the filler neck to the point where I had to shut the bike off or it would have spilled over. This shouldn't happen. If I have understood the procedure for these bikes after replacing coolant, I should be able to run the bike with the cap off to watch for trapped air being released. As Paul mentioned, and it was a thought I had, this indicates trapped air being heated, expanding and raising the coolant level.

Tom
 
So I had some time this morning and decided to squeeze hoses again. Nothing to lose, right? Put the bike on the side stand and continually squeezed the hose that runs across the top of the engine block. It still bubbled up air and some large ones that spit coolant out the top, and the coolant level, while visible, was down in the upper hose. I also squeezed the lower hose, but in using both hands I could not look into the filler neck. I went back and forth between the two. Guys, can these systems really be this difficult to remove trapped air? I took my time filling it.

I put the bike on the center stand and started it up. The coolant rose up in the filler neck to the point where I had to shut the bike off or it would have spilled over. This shouldn't happen. If I have understood the procedure for these bikes after replacing coolant, I should be able to run the bike with the cap off to watch for trapped air being released. As Paul mentioned, and it was a thought I had, this indicates trapped air being heated, expanding and raising the coolant level.

Tom

1. Obtain a good turkey baster syringe and a two quart pan.
2. Start bike.
3. As coolant rises in filler neck use baster to draw out coolant and squirt it into the pan.
4. When all of a sudden you get a big burp of air clean up the mess.
5. Slowly refill the system while the engine is running.
 
1. Obtain a good turkey baster syringe and a two quart pan.
2. Start bike.
3. As coolant rises in filler neck use baster to draw out coolant and squirt it into the pan.
4. When all of a sudden you get a big burp of air clean up the mess.
5. Slowly refill the system while the engine is running.


I think you're right, Paul. My current, repeated approach is not yielding different results. A project for Thursday morning.

Tom
 
There is no way that coolant will come out around the cap threads IF the outer gasket of the cap is sealing. Any expansion of the coolant will go into the exansion tank (hence the name). If the outer gasket leaks, it will also suck air into the radiator when the coolant cools.

Fix the leak and you will probably fix the rest of the problems. There are only three components involved with a leak at the cap; the cap, the outer gasket, and the filler neck. Your problem is with one (or more) of those.:dunno

Actually, another possibility; if the hose to the expansion tank is plugged and the hose is loose or cracked at the cap end, it could blow coolant toward the cap threads making it look like it is coming from the threads.




:dance:dance:dance
 
Okay, so here is where I am at everyone. Fired up the bike on Thursday morning. As it was warming up, I had to extract 180ml of coolant with my BMW turkey baster so it wouldn't come out the filler neck - not much, really. I did see some bubbles. I let the cooling fan cycle a couple of times and then shut it off as I had no more time.

I left the bike until Friday morning and poured all of the 180ml back in. After pouring it in, the coolant level was visible in the upper hose at the horizontal point before it transitions to the vertical towards the filler neck. Fired the bike up and let it warm up. I had to extract 110ml so it wouldn't overflow the filler neck and saw some more bubbles. Let the cooling fan cycle a couple of times with no issues. I shut the bike off and left it until this morning.

I poured the 110 ml back in and started up the bike. I had to extract 80ml as the coolant was rising in the filler neck. Saw some more bubbles. Really? Still? What I did see today - and not that it didn't happen on Thursday or Friday as I could have missed it - was the coolant level immediately dropping as soon as the cooling fan switched on. Thermostat opening? If so, isn't that a little late? Clymer states thermostat opens at 85C and cooling fan comes on at 103C.

I am going to let the bike cool down for a few hours and then start it back up again without adding the 80ml of coolant I extracted and see what happens.

Thoughts, suggestions, guys?
 
I'm getting the feeling (I could be wrong) that you aren't understanding how an expansion tank coolant system works.

When cold, the radiator is completely full, the hose between the cap and the expansion tank is full, and the expansion tank is at least to the low mark.

As the coolant heats up and expands, the pressure cap (inner gasket) opens and allows the excess coolant to go through the hose to the expansion tank keeping the radiator full. When the coolant cools in the radiator and contracts, it creats a suction that sucks coolant back into the radiator thereby maintaining a full radiator. All of this is dependent on the outer radiator cap seal maintaining a closed system.

With the cap off, like you are doing, you are sucking off the expansion with your turkey baster and sucking in air when it cools. Then you are topping it back up and trapping air in the radiator. That doesn't show anything. If you look at the expansion tank, the distance between the hot and cold line is about equal to the amount of coolant that you are removing and replacing.

Get the outer cap gasket to seal properly.




:dance:dance:dance
 
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Lee,

All fair comment considering. As I upgraded the filler neck cap to the new style, which had new rubber seals obviously, then I have no choice but to replace the outer rubber seal or revert to the original cap altogether. There aren't ten different ways to hand tighten the cap.
 
Lee,

All fair comment considering. As I upgraded the filler neck cap to the new style, which had new rubber seals obviously, then I have no choice but to replace the outer rubber seal or revert to the original cap altogether. There aren't ten different ways to hand tighten the cap.

But you still haven't found out why the outer cap seal is leaking.:dunno




:dance:dance:dance
 
Lee mentioned earlier to check that the hose between the radiator neck and the expansion tank is not clogged. Is it?
 
mcmlcccvrs

Did you ever determine the problem with coolant escaping from around the cap?

If not there is one more thing (very remote possibility) that I can think of. I'll start with a story about an oil change on a car. Several years ago after changing engine oil and filter the new oil filter started leaking. What happened was when I removed the old filter the gasket stuck to engine. When I put the new filter on there were two gaskets and because they weren't captured by the depression in the filter, one blew out.

Fast forward to today, every time I've removed the radiator cap the gaskets have come off with the cap, that is until today. After removing the cap I noticed the outer gasket had stuck to the filler neck. If you put on a new cap with the gasket already installed you may have two gaskets in there.

Like I said, remote possibility, but easy to check.



Regards,

Richard
 
Here it is a Saturday evening and I just read through every post in this thread. It reads like a mystery novel and I'm excited to see "who done it". What has safe at home done to me?
 
Me too, but all I can tell you at this point is that it isn't the butler! I'm not one to assume that new parts can't be defective, so I have a new rad cap on the way. It won't be any earlier than the end of the coming week, though, as I am also installing a temp gauge and I don't expect to have all the bits until then. Found all of the items I needed for the gauge installation at reasonable prices. For instance, I got the complete gauge with R.H. panel for £29.

I haven't abandoned this thread. I will update when I believe I have it resolved.
 
Since the filler neck 17 11 1 460 313 CONTAINER is only $7.82, it might not be a bad idea to replace that also to eliminate the possiblity of a hairline crack that might be opening up when it gets hot. :dunno






:dance:dance:dance
 
I have been remiss by not updating this. When I installed my coolant temperature gauge last month with all the associated bits, I also installed a complete new rad cap. It seems to have solved the problem. I have put on several hundred miles since and there has been no sign of coolant escaping from underneath the cap.
 
I have been remiss by not updating this. When I installed my coolant temperature gauge last month with all the associated bits, I also installed a complete new rad cap. It seems to have solved the problem. I have put on several hundred miles since and there has been no sign of coolant escaping from underneath the cap.

Thanks for the update.
 
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