gurgling sound when cooling down, K75RT

[DavidATL]

The bike does not appear to have any known cooling issues. It has 21k miles, 2.5k with me.

Earlier today, I rode 150 miles at a fairly brisk pace and did not notice anything usual after pulling into the garage. No problems on the ride.
After that, we went on a 40 min slow ride (mostly between 35 and 40, 55 deg f outside, 20 miles total) two up. After I parked the bike in the garage, I noticed a gurgling sound coming from under the tank. I assume this was coming from the cool filler cap. I've never heard this before. As the second ride was slower, the engine may have gotten warmer but I don't know for sure. The coolant fan spins free but I have not confirmed that it comes on.


Is this sound the normal operation of the expansion tank and pressure valves in the radiator filler neck?

[alexg]

I would not worry much. It could be that after you parked the bike, the temp of the coolant got higher, as the fresh air (55F) circulation stopped. This caused the cap to open and overflow to the expansion tank.
Your bike has a temp gauge, how was it?

[DavidATL]

I would not worry much. It could be that after you parked the bike, the temp of the coolant got higher, as the fresh air (55F) circulation stopped. This caused the cap to open and overflow to the expansion tank.
Your bike has a temp gauge, how was it?

Thanks for the comments.


BTW, the gurgling went on for at least 3 minutes.


My bike does not have a temp gauge.

[Laitch]

. . . I noticed a gurgling sound coming from under the tank.

I haven't heard gurgling coming from the cooling system of my bike during the 40K miles I've ridden it in hot and cold weather. What is the level in your coolant reservoir when the bike is cold? Do you have a oem reservoir? It might be time for you to flush the system, replace the cap or its gasket, and refill the radiator and the coolant reservoir with long-life coolant.

[stokester]

I haven't heard gurgling coming from the cooling system of my bike during the 40K miles I've ridden it in hot and cold weather. What is the level in your coolant reservoir when the bike is cold? Do you have a oem reservoir? It might be time for you to flush the system, replace the cap or its gasket, and refill the radiator and the coolant reservoir with long-life coolant.

Same for me, no noises ever.


As Laitch suggested, I would first look at the level in the reservoir and follow up with a flush and fresh coolant if you don't know the last time it was done.


I follow Bob Fleischer's procedure and recommendations -> http://bmwmotorcycletech.info/k-coolant.htm -<

[The Mighty Gryphon]

Unlike the previous posters, my K100 had that gurgling problem and it was accompanied by antifreeze dribbling from the expansion tank when riding and immediately after stopping along with the temperature gauge running perilously close to the red nearly all the time.

In order to correct the problem, I had to flush the system a couple of times with flush and distilled water.  I also had to remove the radiator to clean a couple pounds of dirt and dead bugs from the fins.  While I had it off, I took the opportunity to soak it a couple hours with distilled white vinegar to make sure there were absolutely no mineral deposits inside. 

No problems with gurgling, dribbling or overheating since.

[alexg]

So the gurgling sound is boiling!!! Then the proper functioning of the idiot temp light should be checked. It should have come up while driving.


To check that coolant to and fro the expansion tank is circulating, you have to take the tank out, and open the fill cap when cold. It should be up to the top.

[The Mighty Gryphon]

Not necessarily boiling.  Small pockets of air can expand pushing antifreeze back toward the expansion tank.  This is usually caused by blocked radiator cores or fins reducing the heat transfer to the air.   

These engines are designed to run hot for efficiency.  Plus, the layout of the bike restricts the size of the radiator.  This means that the cooling has to be at maximum efficiency to handle the heat, especially in warm weather.  That means that the coolant needs to be at the recommended 60/40 ratio, the thermostat has to be working properly, and most important, the radiator and the passages need to be scrupulously clean both inside and out in the case of the radiator.

With bikes as old as ours there is the chance that at some point in the past someone may have put hard water, possibly well water in the cooling system.  This will coat everything with calcium, insulating the water from the engine components it needs to cool.  Also, with a lot of miles on the clock, the radiator has passed through a lot of bugs and dirt.  Air flow can be drastically reduced by blocked fins.  It is always a good idea to remove the radiator on a "new" bike to clean out the fins as part of establishing a maintenance baseline.  This is especially true with K100's because of the higher output of heat from four cylinders.

[Laitch]

To check that coolant to and fro the expansion tank is circulating, you have to take the tank out, and open the fill cap when cold. It should be up to the top.

None of that procedure seems necessary to me.

If coolant is visible between the Min and Max lines on the reservoir tank's coolant level tube when the bike is cold, that's one indicator of correct function. It certainly should not be up to the top of the tank. If the cap is not sealing that will also affect function, along with everything else that Gryph has indicated.

There is probably very little—if any—coolant in the reservoir and the radiator coolant level probably is low also. I agree though that checking both the temperature light and fan for function is necessary. There are procedures for both checks on the site.

[Martin]

Get your radiator cap tested, a faulty cap that is not holding pressure can cause the fluid to over heat early.
Regards Martin.

[DavidATL]

Right now, the level in the expansion tank is at approximately 63% of the range between the min and max lines on the expansion tank (~ 22mm of the 35mm range, eyeballed). I have never noticed the level to be different but I have not watched it. 


The coolant is blue which I understand to be BMW long life coolant.


I am planning on pulling the most of the lower fair off and doing a flush fill, filler cap gasket replacement (both?), blow the line to the expansion tank clear, and inspect the hoses and thermostat. While I am at it, I will probably also inspect or change the air filter, replace the fuel lines from the tank to the fuel rail, and inspect the spark plugs all to set a base line.


Any other "while you are in there" suggestions are welcome.

[Martin]

A good time to check and clean the temperature sensor connector with Deoxit. Due to the fact it can be subjected to a lot of road spray, I also smear dielectric or heavy silicone grease around the connector. A lot of inmates suggest not doing this as it can insulate the connection causing problems. I work on the theory that the grease will stop air and water getting in that will lead to the connectivity problems. Your call on that.
Regards Martin.

[The Mighty Gryphon]

Take the caps off the filler and the expansion tank and take a good look inside.  Do you see any chalky white coating inside?  That is the sign that someone has been using hard water in the system and that you have mineral coatings in the engine and radiator.   Even if you don't see anything, it's still a good idea to run a gallon or two of distilled water through the engine with radiator flush just to be sure. 

Soak the radiator in hot soapy water or white vinegar to soften the bugs and other crap and then pour water from a bucket through the fins to flush them out.  Don't use a high pressure spray to avoid bending the fins.  Pour from the back to the front.

While the radiator is out, look at the fan motor.  If the engine is getting overheated, the odds are pretty good that if you look you will find that the brush holders on the motor are showing signs of melting.  I know that on my K100RS the brush holders totally melted preventing the motor from running.   If that is your situation, it's a great time to retrofit a Spal replacement fan.  There is a good thread on the forum with some posts from late 2014 that explain a nice way to install the Spal fan.

[DavidATL]

Here's what I've found so far. The radiator passages ways look perfectly clear. The thermostat and it's housing looked clear. The line to the expansion tank was clear. Inside the water pump at the lower hose was clear.


But I did find a slimy coating inside the filler hose to there it connects with the upper right side of the radiator. Nothing inside the radiator at least that I could see. I wiped the hose inside completely clear.


The coolant appears pretty dark blue and I am wondering if it is not diluted to 50/50. I haven't tested it yet and I have not seen this coolant before so I am just guessing.


I am starting to think that some of the slime caused the inner gasket on the filler hose cap to not seal as normal. The cap was stuck in place as is normal for something that has not moved for a while. The inner gasket has a groove in it characteristic of a seal that has taken a set from being in place for a while.


At minimum, I am replacing the two gaskets if not the entire radiator cap.

[DavidATL]

Who thinks this is the issue?


This gasket surface should be flat and it appears to have taken a set over the years.


The BWM part number is 17-11-1-460-759. Retail is $3.77 and probably costs about 15 cent to produce. Replacing proactively when the bike was 20 years old would have been a good idea.

[DavidATL]

In addition to the cleaning up the gunk in the filler neck, I replaced the radiator cap to renew the gasket materials. One of them had taken a shape set (see above). I believe that my gurgling noise was caused by either that or a misplaced chunk of gunk from the filler neck. Everything seems to be running well now. Tests fine sitting still warmed to the point of the cooling fan starting to cycle. Rode 100 miles - no issues.


The prior cap was of the new design but there has since been an even newer design. The attached images shows them side by side. The newest one is dry, the older but 'new design' is wet. The newest design has a collar around the inner gasket material which I supposed helps the seal not squish out. This makes for a more robust seal.

[DavidATL]

and for future reference: in the interim, I flipped the inner gasket and reinstalled the cap and everything worked fine for 300 miles. The gasket's shape has a retention feature which, when installed correctly, revents it from falling off the cap as you are handling it. I wouldn't recommend this as a long term fix but it worked fine for the week + that I waited for the new part to arrive.


Gotta get every good weather day in!!!!!

[stokester]

and for future reference: in the interim, I flipped the inner gasket and reinstalled the cap and everything worked fine for 300 miles. The gasket's shape has a retention feature which, when installed correctly, revents it from falling off the cap as you are handling it. I wouldn't recommend this as a long term fix but it worked fine for the week + that I waited for the new part to arrive.


Gotta get every good weather day in!!!!!

I'll be checking mine this spring when I do a coolant change. :2thumbup: