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Discussion Starter #1
Last weekend I serviced my bike including changing the coolant. Now the coolant temp gauge registers different and fluctuates.

The gauge, before the change, would normally display at mid way; and the fan would come on when it displayed 3/4 on the scale. Now is displays most of the time at 1/4 of the scale and the fan will come on at 1/2 on the scale. But it will fluctuate at times. It will jump very quickly from 1/4 on the scale to 1/2 on the scale, and then return to 1/4 after a brief time. Oddly it will sometimes jump this way when you increase the rpms rapidly as in a downshift in a corner.

What do you think is the problem? Did I somehow damage the temp sensor taking it out and reinstalling? I torqued it to book specs of 9 NM and it wasn't dropped.

I believe I got as much coolant back in the system as I took out. Both radiators and all hoses feel hot. I don't believe I have an air lock, but maybe a possibility?

Any thoughts?
 

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My bet is you've got some air in the system. Try taking the radiator cap off and massaging the hoses. You may also want to replace the cap - it is a standard $5.00 (or so) automotive cap - not something you need to buy at a BMW dealer. I've chased many coolant problems back to what looked like a perfectly good cap, only to find that it had a tiny leak.

A tip: You can easily refill through the radiator neck by snaking a section of clear vinyl hose between the frame and fairing. Attach a small funnel to the other end and you're good to go.
 

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My bet is you've got some air in the system. Try taking the radiator cap off and massaging the hoses. You may also want to replace the cap - it is a standard $5.00 (or so) automotive cap - not something you need to buy at a BMW dealer. I've chased many coolant problems back to what looked like a perfectly good cap, only to find that it had a tiny leak.

+1 You may need the engine at operating temperature. Hoses will probably be hot so wear hand protection. Also, make sure the plastic radiator overflow reservoir is at the proper level prior to starting procedure. And I'm sure you know but, use caution when removing the cap from a hot radiator.
 

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Another vote for air in the system. It is important you fix this before you ride again. I recently had this happen to my Speed Triple. After a short ride with the temp rising faster than normal I returned home and after shutting it off there was a load banging noise. So far I haven't seen any oil in the water or water in the oil and it's running good but having cracked a head on my diesel truck when a hose burst resulting in a similar noise I am concerned. Don't take a chance.
 

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When I filled mine I loosened the top hose on the right radiator to get all the air out.
 

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jzeiler said:
When I filled mine I loosened the top hose on the right radiator to get all the air out.
The air doesn't work it's way out as the coolant circulates?
 

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alstrickland55 said:
The air doesn't work it's way out as the coolant circulates?
Nope. The hose connecting the top of the two radiators dips down, effectively trapping air in the top of one side. That is why you need to "massage" the hose, to work the air out and refill through the radiator cap.
 

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As you fill, you have to massage the hoses. Crank the engine (without starting), massage, and repeat maybe 3 or 4 times to ensure all the air is out.
 

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alstrickland55 said:
The air doesn't work it's way out as the coolant circulates?
I was thinking the same thing.
 

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ibbones said:
I was thinking the same thing.
It seems like a logical assumption that it would clear itself but it doesn't.
For the Triumph Speed Triple I mentioned there is an elaborate procedure involving massaging the hose and a plug to remove described in the manual to overcome the problem. As I said, I didn't get all the air out and came close to destroying the engine.
 

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Discussion Starter #11
Thanks for all the replies.

The problem was not the cap or air in the system. I'm thinking now that it is the thermostat. The bike seems to warm up slower now and the gauge level seems to vary based on air temperature. Seems odd that the problem occurred after I changed the coolant. But, maybe the problem already was there, and I had just not noticed it.

I'll order a thermostat tomorrow.

Any tricks in taking out the thermostat? Looks like it is held in by a clip.
 

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mjordans2000 said:
It seems like a logical assumption that it would clear itself but it doesn't.
For the Triumph Speed Triple I mentioned there is an elaborate procedure involving massaging the hose and a plug to remove described in the manual to overcome the problem. As I said, I didn't get all the air out and came close to destroying the engine.
I didn't do any of the hose massaging, but I did crank the engine several times while filling it through the radiator cap. I've ridden the bike about 1000 miles and it hasn't run hot. Is it safe to assume there's no air in it?
 

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alstrickland55 said:
I didn't do any of the hose massaging, but I did crank the engine several times while filling it through the radiator cap. I've ridden the bike about 1000 miles and it hasn't run hot. Is it safe to assume there's no air in it?
Each bike is different and it's not even consistent with the same bike. I haven't had problems with my LT or K100RS and the first time with the Speed Triple there were no problems even though I didn't know the correct purging procedure at the time but once the air pocket forms it can be a hassle to get rid of it. The important point is it can happen, if the cooling seems different after draining and refilling the system it's worth checking for trapped air.
 

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Discussion Starter #14
Here's an update on my problem.

I have now tried a new thermostat and a new water temp sensor. There is no change in the gauge reading.

To rehash what has changed: the temp gauge before the coolant change would normally read at 1/2 of the scale, now it is normally at 1/4 of the scale. I can stop and let the bike idle for 1 minute and it will climb to 1/2 the scale and stop. If I then travel 1/2 a mile the gauge will return to 1/4 of the scale. I can run the snot out of it and it stays right at 1/4 on the scale.

This is what I have tried:

burping the system for air
new radiator cap
new thermostat
new water temp sensor

This has bugged the heck out of me! I am inclined to just say this is normal and not worry anymore about it. The only thing that concerns me is whether or not the engine is heating up enough.

The only other thing that has occurred to be is that maybe the Spectro coolant I used is more efficient than the coolant that came out. I don't have any idea how much the difference in degrees the water temp is at 1/4 of the gauge and 1/2. Maybe not as much as you might think. I need to find someone who has a heat sensor I could borrow.
 

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slmorley said:
The only other thing that has occurred to be is that maybe the Spectro coolant I used is more efficient than the coolant that came out. I don't have any idea how much the difference in degrees the water temp is at 1/4 of the gauge and 1/2. Maybe not as much as you might think. I need to find someone who has a heat sensor I could borrow.
You did mix 50/50 with water, didn't you...? I had to ask...
 

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Discussion Starter #16
zippy_gg said:
You did mix 50/50 with water, didn't you...? I had to ask...
No I didn't add any water; Spectro coolant is pre-diluted. But thanks for the suggestion, I'm glad at this point to listen to anyone's ideas.
 

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I agree that would bug me too!

I have two suggestions. Trace the wire all the way from the temp sensor to the gauge (display). I realize this may involve a lot of work. If there is a wiring problem any change in resistance will make the gauge read higher or lower than it should. If that’s not it, it seems the only thing left is the gauge (display) itself. I know it seems unlikely that it would fail at the same instant you changed the coolant, but what else could it be? Stranger things have happened. Perhaps someone else with an LT would let you swap out the gauge unit and see if that’s it.
 

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slmorley said:
No I didn't add any water; Spectro coolant is pre-diluted. But thanks for the suggestion, I'm glad at this point to listen to anyone's ideas.

This might be redundant,,, I had a similar issue on the other end of scale. Normal read at 1/2 then jumping to 3/4 but not red. Also notice the fan going on far more frequently than usual, you can clearly hear it at a stop. Earlier had just flushed the radiator, replaced the coolant, hoses, and checked everything out. A local BMW mechanic told me that is a K bike 4 cylinder 4 stroke. A monster of an engine and should be run on the highway not around town on a hot or cold day. Once I got her back on the freeway for a couple days everything went back to normal. That baby is meant to run over the road. Makes sense.. Now in your case could it also apply, or not.. Seems like if its at 1/4 temp reading that would be a good thing. Just .02 cents for what its worth. Hope you can resolve the issue
 

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Discussion Starter #19
update:

I guess I had a lot of concern about a problem that doesn't really exist. I borrowed a lazer heat gun from a friend. I should of done this before I tinkered with everything else!!!

I tested the heat temp on the radiators many times while driving the bike normally with the heat gun. The left radiator would usually average 10 degrees warmer than the right. What I discovered was that the difference between 1/4 on the temp gauge and about one bar below the 1/2 mark (where it had normally stayed before the coolant change) was only 7 degrees. It would appear that the Spectro coolant is just a little more efficient than the factory coolant.

I sure wasted a lot of time tinkering with everything, but did learn a lot. The biggest thing I learned was not to mess with the thermostat unless needed; it was a real pain to install.

It's sure nice to have the proper tools! I may add a lazer heat gun to my tool box, I can see how it could be useful for other things. The're not really that expensive.
 

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did the lower temp affect the way your bike runs either good or bad? if not it sounds like a good thing since our bikes do seem to run a bit hot this time of year especially.
 
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