Taking guesswork out of coolant temperature

[watercooled]

This is a tip on how to measure the temperature  of your coolant I have found preferable to letting the bike idle which relies on the bike to activate the fan which may not be working.  Below is a multimeter equipped with a temp measuring probe wire.

The wire is very thin. You can feed it into the radiator and tighten the cap over it, it will seal. It displays the temperature on its LED screen in Farenheight or centigrade. Its accurate to +/- 1 degree.

The meter shown below is for HVAC and a little pricey. However I picked up a meter at HD hardware store that had a temperature circuit for about 35 bucks. Works great.
tempMeter.jpg (31.55 kB . 318x576 - viewed 511 times)

[Laitch]

What were your results?

[KCinSB]

+ 1
 And…. Does anyone happen to know what temp is supposed to trigger the fan? I’d guess that fan check is the reason to be doing this most the time.

[Laitch]

Does anyone happen to know  . . .

Anyone? It's all in the Radiator section of the BMW K1100 RS/LT service manual downloadable from the Service Manual section at the World Famous MOTOBRICK.COM.
Another check beside the fan cut-in temperature could be the thermostat opening temperature of the coolant but the whole gizmo application seems a trifle obsessive to me. 

[frankenduck]

Fan kicks in at 103C on K75/K100 models, 105C on 4V Ks.

[KCinSB]

Would an IR heat sensor gun work well enough to be a valid check?  We could just aim at the K forehead and check !!

[Chaos]

Even if the wire is thin feeding it through the radiator cap just seems wrong.  Interesting but it might be the answer to a question nobody asked.

[frankenduck]

Even if the wire is thin feeding it through the radiator cap just seems wrong.  Interesting but it might be the answer to a question nobody asked.

It may be a little off. The temp sensors that feed the L-Jetronic or Motronic measure the temp right where the coolant exits the engine to get the most accurate reading of approximate engine temp.

[watercooled]

What were your results?

The first time I employed it the fan came on at 98 centigrade. verifying that particular function was doing its job.

The most recent attempt to investigate the cooling system was derailed by the electrical system which had what i would describe as a catastrophic epic fail.

when the ignition key is turned on the headlights come on and the blinkers will work.  That's it.

 motobrick has been the source of enough information for me to work my way down to the cause and repair it, I'm pretty sure. So far I detached all the ground wires up by the Ignition control module and polished them up. That's it so far. My health is raggedy and I can't work out in the garage when its cold but Im getting underway.I don't want to report on anything i haven't looked into here or elsewhere for information.

I have an r1200r that's running so it's not an emergency but kbikes have always been mu first love. It took me awile to track this one down so I'm itchy to get it rolling.

i will panic after March if it's still not running because I have terminal cancer and this summer will be my last season of road tripping. But I'm very optomistic about the project now that I'm not limited to my knowledge and experience on motorcycle repair, which isn't bad  considering I've owned more than 20. But the only previous k bike i had was only a year old.   

It had been wrecked at 80mph on the right hand side so it needed some work but mechanically all it lacked was the lower radiator hose to put it bck on the street . Everything else was fine. and stayed reliable for the couple years I rode it. so basically i don't know shit about these bikes except for periodic maintenance. 

[watercooled]

+ 1
 And…. Does anyone happen to know what temp is supposed to trigger the fan? I’d guess that fan check is the reason to be doing this most the time.

98 degrees centigrade as I recall. just short of boiling point

[watercooled]

Anyone? It's all in the Radiator section of the BMW K1100 RS/LT service manual downloadable from the Service Manual section at the World Famous MOTOBRICK.COM.
Another check beside the fan cut-in temperature could be the thermostat opening temperature of the coolant but the whole gizmo application seems a trifle obsessive to me. 

guilty as charged , but my interest in monitoring the coolant temperature was right after it overheated and blew the cap off the overflow tank which  emptied half the boiling anti-freeze mix onto my leg and really got my attention. So I doubted in advance that the warning light or fan relay would kick in. I was concerned with the possibility of having to cope with boiling coolant escaping the system and breaking into the wild again because I was pretty freaked out about the last time which left an annoying but sizable burn that was still healing. and especially to avoid the humilliation of suffering another  burn injury in  a motorcycle incident which is some embarrassing loser shit to endure,  too  lame to bring up in harrowing tales of motorcycle horrors immortalized on the road rash pages recalling the damaging results of questionable decisions or inaccurate readings of important data under the existing speed conditions preceding a crunching incident of some gravitas as opposed to whining about getting sprayed by hot water on the leg.

[Laitch]

guilty as charged . . .

You weren't charged; that was a response to KC, who wasn't charged either, just redirected. 
What did you determine from monitoring it, watercooled, except that it can get pretty darn hot? What was the root cause of the attention-getting geyser?

[frankenduck]

If the radiator cap blows before the temperature warning lamp in the instrument cluster illuminates then the cap has probably gone bad and needs to be replaced. Part 17111464720. (That part includes both new gaskets so they do not need to be purchased separately.)

I've had that happen on a K75. Replaced the cap and it's worked fine ever since.

https://shop.maxbmw.com/fiche/PartsSearch.aspx?&searchtype=undefined&parts=17111464720

[watercooled]

You weren't charged; that was a response to KC, who wasn't charged either, just redirected. 
What did you determine from monitoring it, watercooled, except that it can get pretty darn hot? What was the root cause of the attention-getting geyser?

 

lemme think, seem to have bought the bike with a dead fan. Im in houston so i could really feel the heat rising from the engine at a stoplight on any 100degree summer day. checked fan with 12v and pronounced it dead. got a non BMW  replacement online. the Haynes manual was stuck in the mail so I had to wing it and that is when I used the meter to monitor temp, even though I didn't know what it was supposed to be. It was a bit of a surprise  when it activated so close to boiling point and  the warning light  didn't light. that still seems ass backwards to me. seems like it should warn us that the fan is ganked immediately.

next time was the overheat and third time was aborted due to electrical fail. so i never got back to solving the cooling system mystery because bikey no startee but I have in the meantime learned the relay functions and that there's a temperature module. I already discovered the temp sensor during fan install but haven't tested or traced the wire back yet.

but I will stick to using the meter until the bike is up to snuff on all essentials . the idea of checking the fan, waterpump, sensor  and relays by starting the bike up and letting it idle until it performs all the functions in sequence or overheats activates my internal OCD controller .

[watercooled]

If the radiator cap blows before the temperature warning lamp in the instrument cluster illuminates then the cap has probably gone bad

the radiator cap didn't blow, the soft rubbery cap on the overflow tank popped off and released the water. If the fan runs when getting 12v, but fails to come on when underway resulting in an overheating event and enough pressure to blow most of the coolant out from maybe a secondery pressure release cap in the expansion tank it seems to me thats a failure of temperature sensor circuit since the temperature warning lamp didnt light either despite a generous surplus of  available hotness on hand. I'm guessing.

[Laitch]

the radiator cap didn't blow, the soft rubbery cap on the overflow tank popped off and released the water.

That depends upon how blow is defined. If a Brick radiator cap's pressure valve becomes defective, pressure in the radiator decreases causing the temperature of the coolant to increase. Boiling coolant and hot vapor is then directed into the coolant reservoir where pressure increases until it blows coolant out of the reservoir. It is possible that a defective radiator cap could be one valid cause of your boil-over problem, as frankenduck indicated.

The radiator fan and thermostat work in tandem to keep the engine at an optimal operating temperature. When a radiator fan kicks on, it's just keeping the coolant at the optimal temperature. It isn't a sign of a system defect. If the fan's operation fails to stabilize an increasing engine temperature, the instrument cluster warning light is lit.

Your Brick could have a defective temperature sensing module, but it could just as easily have a blown warning light bulb or a defective coolant temperature sensor. The sensor has two circuits, one is connected to the fuel injection control unit and one feeds the temperature sensing module. Test each possible source.

View the flow chart and the troubleshooting guide found using a link at the bottom of the Service Manual page. The guide explains most of your Brick's systems and how they interact. Also, this BMW manual gives a detailed explanation of the ignition and fuel injection control units' interaction with other engine components. Many other references are available at this site.

[frankenduck]

the radiator cap didn't blow, the soft rubbery cap on the overflow tank popped off and released the water. If the fan runs when getting 12v, but fails to come on when underway resulting in an overheating event and enough pressure to blow most of the coolant out from maybe a secondery pressure release cap in the expansion tank it seems to me thats a failure of temperature sensor circuit since the temperature warning lamp didnt light either despite a generous surplus of  available hotness on hand. I'm guessing.

When the radiator cap blows it sends coolant back to the coolant reservoir via a hose so if the cap pops off of the reservoir then that is because the radiator cap blew. There is only one pressure release from the cooling system - the radiator cap.

[Swampyankee]

Whilst trying to troubleshoot a badly running K100 8V, I've been using an IR thermometer aimed at the bottom radiator hose. It seems to give a good indication of my motor's temp (and verify that my cooling fan is inop.). And  the IR thermometer read about right for when the temp warning light illuminated. 

[VitK]

I’m new to K75 ownership having just bought a 1991 model with 9,000 miles. In the few times I’ve ridden it I do notice quite a bit of heat coming off the engine when stopped at traffic lights. I checked that the fan turns when the engine is off, but I haven’t heard it come on yet. Two questions: is noticeable heat off the motor to be expected and should the coolant be changed on what I believe is a bike that sat for long periods and likely has the original fluid? Thanks much. I’m slowly reading through the posts to learn as much as I can so I hope this was an ok place to ask these questions.

[K1300S]

yes, these bikes give off a LOT of heat.

yes, change the coolant.

[Swampyankee]

Jumping in there without hijacking the thread - When I pulled my rad to replace the cooling fan I had to top the "blue" coolant off with what was at hand and used standard green stuff. I will probably replace coolant completely once I get everything else sorted. How important is it to use the blue stuff?

[The Mighty Gryphon]

In the 30+ years since your bike was made huge advances in coolant chemistry have been made.  Today you can pretty much use any long life coolant.  I use Peak and Prestone long life coolant with distilled water.  The water is the critical ingredient.  Distilled water mixed 60:40 with coolant is what you need.

[VitK]

K1300 and Gryphon - thanks much for your replies. Appreciate it.

[frankenduck]

Yes, it's normal for Ks to put some heat off to the sides.

Fan testing:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/fantest/fantest.htm

[VitK]

Thanks Frankenduck.