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Discussion Starter #1
Hi guys, riding back from work one evening I hit traffic and noticed the temperature needle creeping up to the red. As I managed to leave the motorway the red temp light came on for about 5 seconds and went off as I was moving over 60mph. Got home which was like a 80 mile run and keeping an eye on the needle which was behaving plus was around midnight so air cooler. Next day checked water level in the rad which was low so topped it up with the proper liquid I bought plus reserve tank was empty so filled it between max and min. All OK for a 50km ride non traffic however when I got back to the bike after a coffee break the right hand side had water staines. As the engine heated up with the seat off the resevoire tank started to fill up and overflow and when I turned off the engine but the fan was running it settled. I have however noticed only the left hand side fan was running and not the right hand side one. Tomorrow I will pull off the plastic and test the fan by running 12 volts to see if it spins up. The radiator cap looks OK but should I be looking at replacing it with a new one? Can the activation of only one fan cause this issue

Thanks in advance
 

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Your bike is old enough to warrant a new radiator cap. It does sound like one of your fans has seized. These bikes suffer from insufficient cooling capacity. They tend to over heat going less than 55 mph. Also it would be good to clean your radiators when you do the fan check. Make sure all fins are straight and no junk clogging them. To check each fin passage takes an hour or so but worth it.
 

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The radiator cap looks OK but should I be looking at replacing it with a new one?
I would. Matter of fact, I did when I noticed that there would be a little burping of coolant out of the overflow tube after returning from any kind of jaunt. Cheap insurance.

As an aside, do you have a GS911 tool? It has a fan function test as part of its capability.
 

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Plenty of fans on EBay, Not much money:
I don't remember but if the same fan snaps into both the left and right housing, I'd buy a couple. Nice to have spares of expensive parts on the shelf. Maybe even a set of radiators. I know, I go overboard. I have a set of used but good headers for my K bike hanging from the overhead....Looking for a radiator.
 

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I'm reaching back so slap me if my memory is poor. I have owned three of these bikes. I seem to remember in the beginning some were experiencing fan failures. The ones with one dot of paint on the back are the old ones and the ones with two dots are the new and improved ones. Also something about fan fuse covering one or both fans. Good luck. I remember my yellow checker bike 1998. Boy I liked that bike. Locomotive on rails. BMW would not let their dealers give demo rides with out an escort. Things have changed.
 

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$0.00 unseizing a fan.Did that to my bike 2yrs ago.Been fine for +60,000kms.
 

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Discussion Starter #7
Guys is the left and right fan the same...interchangeable? i see its held on the plastic by 3 small bolts.
I took out the right fan and put 12V across it and it didnt work and when i did it to the working one it worked so suspect fan!
 

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On my 98 both fans failed. Even when they were working the bike constantly seemed on the verge of overheating. It made for some stressful riding... And don't get me started about the charcoal canister!
 

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I had this issue with my 2003 K12GT. The fans stopped running like the other posts here. I had them replaced and it fixed the issue.
 

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Hi guys, riding back from work one evening I hit traffic and noticed <overheating issues> ...
Yep, the K12s' cooling system is running on the ragged edge at the best of times. Yes, you should replace your radiator cap. If you're bored, flush the coolant, pull the radiators, clean out any sludge from inside, and clean and straighten the fins. And, as mentioned, both fans operate from the same fuse, so if one seizes and overloads, both will stop, so fusing them separately isn't a bad idea.

Years ago, somebody on one of the forums outlined his project that eliminated his overheating issues. He attached small, flat, automotive-radiator electric fans to the fronts of his K12 radiators. They ran at low speed all the time that the bike was on. When the standard fans kicked in, the aux fans went to high speed. He described the circuitry he made to do that. It worked.
 

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Hi guys, riding back from work one evening I hit traffic and noticed the temperature needle creeping up to the red. As I managed to leave the motorway the red temp light came on for about 5 seconds and went off as I was moving over 60mph. Got home which was like a 80 mile run and keeping an eye on the needle which was behaving plus was around midnight so air cooler. Next day checked water level in the rad which was low so topped it up with the proper liquid I bought plus reserve tank was empty so filled it between max and min. All OK for a 50km ride non traffic however when I got back to the bike after a coffee break the right hand side had water staines. As the engine heated up with the seat off the resevoire tank started to fill up and overflow and when I turned off the engine but the fan was running it settled. I have however noticed only the left hand side fan was running and not the right hand side one. Tomorrow I will pull off the plastic and test the fan by running 12 volts to see if it spins up. The radiator cap looks OK but should I be looking at replacing it with a new one? Can the activation of only one fan cause this issue

Thanks in advance
If your reserve tank was empty AND the radiator itself was low on coolant the upper “leg” of the coolant circuit was probably not full of coolant. This means the coolant pump was likely just sloshing around coolant instead of flowing it through the circuit. If my
Memory isn’t too foggy on this these bikes coolant circuits are not self bleeding so you need to alternately squeeze the coolant hoses to burp the air out of the circuit.
 

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Discussion Starter #14
Left and right are the same. Also, if shopping for used, fans from 96-05 GT or LT are also interchangeable.
If your reserve tank was empty AND the radiator itself was low on coolant the upper “leg” of the coolant circuit was probably not full of coolant. This means the coolant pump was likely just sloshing around coolant instead of flowing it through the circuit. If my
Memory isn’t too foggy on this these bikes coolant circuits are not self bleeding so you need to alternately squeeze the coolant hoses to burp the air out of the circuit.
Brilliant put fan in took it for a long run in and out of traffic fans working. Left fan blowing hotter air than right fan. I take it its normal. Also the temp light comes on faintly at times is this normal?
 

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Not normal to have the over temperature light turn on. You need to be sure that you thoroughly purge the coolant circuit of air. I believe these bikes need to use a vacuum-fill method to minimize the airpockets which remain at the upper end of the cylinder head when filling from the radiator cap.
 

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No, they do not require a vacuum purge method to fill. Just make sure you give all the hoses a good squeeze to force air bubbles to the top. In my 18 years (184,000kms) of ownership I’ve found the best insurance against overheating is to make sure your rads are impeccably clean and all fins are straight. Every two years at service time I remove both rads and thoroughly clean them. I also remove and check all the hoses for wear although to date they are still all original. You can test for fan operation easily by disconnecting the coolant temp sensor at the back of the block. Connector is to the left and behind the battery on the L/H side. Disconnect it and turn the ignition on - the ECU will run the fans automatically as it is in default mode. I also fitted radiator guards that help immensely in preventing bugs damaging fins, and stops stones penetrating the tiny coolant tubes that will stop your ride in its tracks.
 

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Discussion Starter #17
No, they do not require a vacuum purge method to fill. Just make sure you give all the hoses a good squeeze to force air bubbles to the top. In my 18 years (184,000kms) of ownership I’ve found the best insurance against overheating is to make sure your rads are impeccably clean and all fins are straight. Every two years at service time I remove both rads and thoroughly clean them. I also remove and check all the hoses for wear although to date they are still all original. You can test for fan operation easily by disconnecting the coolant temp sensor at the back of the block. Connector is to the left and behind the battery on the L/H side. Disconnect it and turn the ignition on - the ECU will run the fans automatically as it is in default mode. I also fitted radiator guards that help immensely in preventing bugs damaging fins, and stops stones penetrating the tiny coolant tubes that will stop your ride in its tracks.
Thanks for the info, i now have a functional Bike! got all air bubbles out and the fans come on and off as they should and the temperature stays where it should ...woohooo
I was now thinking of adding 2 small LED's one on the left and one on the right somewhere to come on and off for the fans so at a glance i will know if the fans are on or not as with the gear on its difficult to tell unless you are stopped and gloves off to feel the airflow from the fans.
The final question maybe someone can point me in the right direction is the temperature light sometimes comes on instantaneously and goes off while riding i think its like when changing gears so the RPM drops but im not 100% convinced on this. The light dont stay on permanent but at night its definitely visible. The bike however rides perfectly normal no heating issues at all.
 
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