'99 K1200RS Temperature Light

I live roughly 15 miles from work and ride daily. For the past week or so, on my way home, the temp is climbing. So much so, that a few times, right after turning onto my street, the needle would cross over into the red zone and my temp light would come on.

Within the past 12 months, I have flushed the entire cooling system, replaced a hose or two, replaced the thermostat and the right side radiator. I can't seem to find any leaks, there doesn't seem to be any smoke in the exhaust and the coolant level is good. Oil and filter were also changed within the last month or so... Level is good.

Any ideas of what could be causing this?

Do you hear the fan operating? They will exhibit that behavior if not, and it is not unknown for fans to seize or the wiring to fail preventing the fan from receiving power when commanded by the Motronic.

By all means, check the fans! And don't run the bike, except for testing, until you sort out why the engine's overheating. I ran into overheating in a boat in the Bahamas, had to keep running the engine, and ultimately had to scrap the engine as the head and/or block upper deck warped past the point of economically acceptable repair.

mneblett said:

Do you hear the fan operating? They will exhibit that behavior if not, and it is not unknown for fans to seize or the wiring to fail preventing the fan from receiving power when commanded by the Motronic.

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The fans seem to be working fine. If I just let the bike sit and idle from cold, they normally kick on shortly after the needle passes the halfway point on the gauge. Also, I periodically check them as I'm sitting at a light, just to be certain they're on.

I meant to mention the fans in my original post.

RBEmerson said:

By all means, check the fans! And don't run the bike, except for testing, until you sort out why the engine's overheating. I ran into overheating in a boat in the Bahamas, had to keep running the engine, and ultimately had to scrap the engine as the head and/or block upper deck warped past the point of economically acceptable repair.

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I would love to park the bike until this issue is squared away... But, it is my only transportation. Thankfully, the light has only come on as I turned onto my street... So, the most I have to ride it at that point is a few houses down.

bmwryder666 said:

I would love to park the bike until this issue is squared away... But, it is my only transportation. Thankfully, the light has only come on as I turned onto my street... So, the most I have to ride it at that point is a few houses down.

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Next thought is a partially clogged left radiator (you said the right was recently replaced) -- just like cars, corrosion build-up can block the coolant flow channels -- or a partially-blocked hose. I'd test by removing the left radiator and putting a hose to the inlet to see what the outlet flow is like.

BTW, I'm assuming that your coolant pump is working properly, i.e., there's no indication that the pump impeller or the oil pump impeller on the opposite side of the common shaft have a problem.

Rad cap. Just replace it.

May sound simple but I have stories about how many water pumps, thermostats, radiators have been changed all due to the rad cap, even when they test fine.

Very carefully verify that the system is actually, really, full of coolant. Then change out the cap as suggested.

dieselyoda said:

Rad cap. Just replace it.

May sound simple but I have stories about how many water pumps, thermostats, radiators have been changed all due to the rad cap, even when they test fine.

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I changed the radiator cap within the last year, also. When I first had an overheating issue, I found quite a few mentions of the cap... So, just to weed that out, I replaced it.

Rules of thumb can be awesome or really bad!

The rule of thumb I have used for almost forty years is; Overheats in the city=coolant flow. Overheats on the highway=air flow.

Almost all the equipment we repair has a highway speed of about 12 MPH and that would be a fast one. In those cases, we look at the temp difference between the upper rad hose and the lower one. If the lower rad hose and the upper has a marked difference, we go with coolant flow. If they are both pretty even, we look at airflow.

Oddly, and you may find this odd, every overheat complaint is immediately met with a cap change, even if we changed it a few weeks ago. Then, we verify the complaint. Even more odd, I don't recall the last water pump we changed due to leaking. Every one in the last 5 years or so we changed has been due to worn out impellers.

As well, you may find my implication a bit insulting, I certainly don't mean it that way but the specific gravity, or percentage of antifreeze to water can't be any greater than 55% antifreeze. The higher the concentration, the more heat the glycol will absorb and refuse to transfer. It's conversely true with too much water, the water can't hold the heat and transfers too fast. We shoot for 50% +/-5%. We also no longer use hydrometers, the $5.00 gadgets with the rubber bulbs. We use refractometers exclusively. We have cooked engines because of antifreeze specific gravity and cooling system problems still account for over 90% of premature engine failures.

Lastly, take my information for what it's worth. I deal almost exclusively with diesel engines and dumb, I mean dumb, bag of hammers smart, one goose short of a flock operators that love to complain.

After eliminating the mechanical suggestions mentioned, you may want to verify the temp sensor/sender is working properly.

Thanks for the info, folks. All good ideas. I'll verify coolant temp between the upper and lower hoses... As well as left and right radiators. For the money, I may go ahead and replace the cap, again. I may also do another drain and fill, if the temps seem fairly even, to verify I have the appropriate mixture of coolant to water. I tried to be pretty careful when I did my repairs... But, you never know. Lastly, I'll verify the temp sender function.

There's a little more info in this thread that may help.
http://www.i-bmw.com/showthread.php?t=53356