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Discussion Starter · #1 ·
You were right letting the bike idle to charge the battery is bad MOJO! :banghead

As I was waiting to get my battery tender for Christmas, I let my GT run on the center stand while I shoveled snow in early Dec. All of a sudden I saw steam coming from it after about 10 minutes. I shut it down right away. Coolant started running on the floor. I took the seat off, and found the cap of the expansion chamber blown off and the expansion chamber empty. I bought some prestone 50/50 premix and replaced the lost fluid. I have not seen any sign of fluid leakage since.

The last few days, I have finally been able to get the bike out for the first time this year. Right after start up the temp warning light comes on. It will go out after you ride it a little, but will come on and go off intermittently. The temp gauge show below the mid mark when the light first comes on. Also, after riding a while the bike is running hotter than before according to temp gauge. But, never in the red. Expansion tank is full and no sign of any fluid leaking.

I plan on taking it back into the dealer, but he is 90 miles away and I must wait for a break in weather to get it there. Just, wondering how sick to the stomach I should be. For being an idiot.
 

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Where did you add fluid?

Did you add to the coolant system and the expansion tank or just the tank?

You could have air in the system.
 

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A water cooled bike should be able to idle all day without overheating.

As mentioned above it is probably the thermostat.

Check both fans to be sure they are running.
 

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Could possibly be a vapor lock (or air in the system) recheck your fluid levels after you run it for a period of time that should allow the thermostat to open. I don't think you'll be too bad off though.
 

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As suggested above make sure your fans are coming on, then check for air in the coolant system.
 

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Discussion Starter · #7 ·
Thanks for the suggestions, guys. I can hear the fans running. My first thought was an air bubble also, or a collapsed hose. I rode it for for a couple of hours yesterday. And no difference to the level in the expansion tank. I added fluid to just the tank. How does one check the radiators themselves? Or get the air bubble out? The manual does not say much about adding fluid, other than the expansion tank.

I never had an overheating problem on my 89 K100RS. Even, if it did over heat. It should have not ruined the thermostat. I am sure that at some point I am going to be stuck in traffic and it is going to be hot.
 

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Check the radiator cap. I had a similar problem and found out there were some bad radiator caps in the field. Dealer replaced mine for free.
 

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You said you shovelled snow the day you ran on idle?

When you get steam in those conditions it's usually a sign of coolant freeze up and bad news. There should be no problem idling these bikes for 10 minutes OCCASIONALLY - the dealers do it all the time for diagnostics and to test the fans! However the fans will be running after about 5 minutes and usually when the temperature guage hits 2/3rds. Were both your fans running at all? Fans should come on, before any warning is given, Can you turn the blades easy with your fingers through the grills? If you've been to scared to idle the bike on the stand, you risk having fan failure without knowing it until you are far away in city traffic in Summer.

The temperature guage, light and fans seem inconsistent, which suggests not all parts of the cooling system are at the same temperature - which they should be if the system is thermally stable.

Assuming your fans are ok or you know they are working (do an electrical check first if you are not sure. Also check for any blown fuses: siezed fans usually blow a fuse) You have probably got air in the system and it can be difficult to get out (check the archive forum) but keep in the back of your mind if you had fan failure that's good news and probably responsible for the air lock. If it was a coolant freeze up, - something else you won't wish to contemplate and may have nightmares about. Often you may ride miles not needing fans, then the first time you idle and need them, discover they are siezed and not working.

There are posts in the archives which recommend 'burping' the hoses at the front to get air out. On these bikes the reservoir tank is only just above the pressure cap level. I read some bikes had caps on both radiators which makes the air purge job easier, my K has a cap on 1 rad only. If your cooling system is stable on idle, you should feel the same temperature evenly across the surfaces of BOTH rads. As the bike warms up (slowly on the stand) The bottom hoses will get warmer as water circulates. If the rad tops get really hot and the bottoms are stone cold, look for a thermostat or pump problem.

You need to be careful because your temperature guages and warnings may not tell the truth in a fault/vapour lock situation. Experienced hands can usually guess an overheat motor without a thermometer or guage. The bike sensors only measure when coolant is in contact and may show a low reading if there is an air/vapour lock around them.

Assuming a good thermostat, you can usually remove air and check if the sytem is stable by removing the header cap, which drains the reservoir, and running the motor at idle a few minutes whilst 'burping the coolant pipes. If the temperature guage climbs slowly until fans comes on and the rads are both evenly warm with no other warnings you have a potentially stable sytem that might be ok under pressure. If you get erratic temperature readings or coolant shooting out of the open radiator after 'burping'- you have a more serious problem. If everything seems stable and ok, replace the pressure cap. There are suggestions in the archives to fill the reservoir, allow the motor to cool (which pulls coolant back into the system) then top off reservoir to mark, run bike and check system temperatures stay stable running on the stand until both fans come on - don't push more than 2500 rpm though.

Most pressurised engine cooling systems can be run without caps in emergency or for short test periods unless you're pushing lost of power through a motor on a hot day. If you ever get a hose leak or a small hole in a rad, depressurising is the best get you home method.

Don't run the bike on the road with an unstable cooling system and remember in this unstable state you cannot be sure the guages are telling you the truth about engine core temperature. Hope some of this is helful.



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What he said!!! Radiator cap went bad on mine

dmiyasaki said:
Check the radiator cap. I had a similar problem and found out there were some bad radiator caps in the field. Dealer replaced mine for free.
I agree. Had a little gieser from the expansion tank cover (under seat on right side). Took it in and dealer replaced the radiator cap (defective one a known issue). Quality control issue again at BMW. WTF? Maybe the'll move to Detroit and build bikes here in the US?
 
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