K1100LT Radiator cap

[pat7762]

Hey everyone, im having trouble locating a new Radiator cap. i don't want to go to the dealer, what website do you guys use for new parts? My bike(96) is having trouble staying cool, fan comes on, system doesn't seem pressurized so i was going to start with the cap. it wouldnt heat up to high if im ridding but if i get stuck in traffic alittle to long it climbs to high. Thanks

[The Mighty Gryphon]

My favorite source of parts is eBay, with MaxBMW for the stuff I cant find there.  You should have pretty good luck searching eBay; when I can't find a K100 part that is interchangeable with the 1100 it seems the k1100 part is always there.

MaxBMW's parts fiches are great for cross referencing parts as well as diy ordering.  Pretty disappointing that they no longer enclose a bag of M&M's with my orders.   :musicboohoo:

[Laitch]

Checking to determine if the coolant is topped up, that there are no air bubbles in the system and that the coolant reservoir is at the right level is a cheaper way to start diagnosis. Removing the thermostat and testing it to determine if it opens at the correct temperature is also helpful. What is the condition of the radiator cap gaskets? Are they pliable or cracked?

[wally.fisher]

Hey everyone, im having trouble locating a new Radiator cap. i don't want to go to the dealer, what website do you guys use for new parts? My bike(96) is having trouble staying cool, fan comes on, system doesn't seem pressurized so i was going to start with the cap. it wouldnt heat up to high if im ridding but if i get stuck in traffic alittle to long it climbs to high. Thanks

Radiator caps are serviceable, parts readily available from motobins, these bikes will run hot , bleed  all air.


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[pat7762]

thanks guys for the replys, i have checked to make sure its topped off and also the reservoir is at proper level. seals are good on the cap but i suspect the 1 bar valve may not be sealing to the spec pressure. as for the thermostat being faulty thats possible but the actual evidence of the system not being pressurize would suggest cap. thanks for your input guys! :2thumbup:

[wally.fisher]

thanks guys for the replys, i have checked to make sure its topped off and also the reservoir is at proper level. seals are good on the cap but i suspect the 1 bar valve may not be sealing to the spec pressure. as for the thermostat being faulty thats possible but the actual evidence of the system not being pressurize would suggest cap. thanks for your input guys! :2thumbup:

I move the tank back to remove the rad cap, then start the bike with the cap off to allow the system to burp itself of air.

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[Laitch]

but the actual evidence of the system not being pressurize would suggest cap. thanks for your input guys!

I haven't read of any alternative radiator caps, yet. If you find a source, please publish it here and let us know how you finally resolve the overheating.

[pat7762]

I move the tank back to remove the rad cap, then start the bike with the cap off to allow the system to burp itself of air.

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Thanks for the Tip. i did find a new cap on ebay, part name Radcap720 bmw part number 17 11 1 464 720. i will update

[pat7762]

i replaced the cap, system is now under pressure but the temp still climbs. next(when i find time) i will clean the radiator. i read that the oil from leaking fork seals with dirty up the radiator(rebuilt the forks 200 miles ago) and sure enough its dirty. not super bad but worth a try before dropping coolant and checking T-stat.

[pat7762]

UPDATE


so i cleaned the fins of the radiator, replaced coolant cap, flushed cooling system, installed new t-stat, bleed the system several times and still no change. i believe i have flow from the water pump because when the fan turns on( comes on at 3/4) the system does cool down. i believe now that the radiator must be clogged, i cant find my laser thermometer to check the inlet to outlet temp difference but i don't think it could be anything else. oh and i removed the t-stat all together. next i will pull the radiator and try to flush better or replace.

[The Mighty Gryphon]

Pulling the thermostat is not a good idea.  There is a bypass around the radiator that is blocked when the thermostat opens.  With no thermostat, a lot of the circulating coolant will not be going through the radiator and thus cooled.  You are losing over half of the bike's cooling capacity.

[Laitch]

installed new t-stat,

OEM or what, exactly? Did you test the t-stat that was in there?

[pat7762]

understand about the t-stat will, reinstall. as for testing the t-stat and brand, i went with an aftermarket one that was recommended on this site. before installing i tested the old one to verify that it was opening. i did see it open at the appropriate temp. as for the new one i checked it as well. the new one seemed to open farther, i felt that would be a benefit for more flow but like i posted there was no difference.

[pat7762]

so i retested the oem stat and cold its 30mm, same as what was on another post i found on here. after boiling it i remeasured and it measured at almost 39mm. so its doing its job but that's at boiling, shouldn't it close off the by pass a bit earlier like 190? maybe thats the issue. the stat is a little slow? also i notice that you can see the lower inside part of the radiator and mine looked pretty clean.

[wally.fisher]

so i retested the oem stat and cold its 30mm, same as what was on another post i found on here. after boiling it i remeasured and it measured at almost 39mm. so its doing its job but that's at boiling, shouldn't it close off the by pass a bit earlier like 190? maybe thats the issue. the stat is a little slow? also i notice that you can see the lower inside part of the radiator and mine looked pretty clean.

Have you run the bike for some time with the cap off, this helps remove any air trapped in the system, I run mine for at least 10 or 20 mins on the main stand with the cap off and since then the bike runs as intended,also make sure the expansion breather pipe is not being fouled up under the tank.


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[pat7762]

yes i have

[Laitch]

How long have you owned this bike? How many miles have you put on it?

[wally.fisher]

yes i have

Did it purge any air or water? Did you top up.


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[pat7762]

i have own the bike for about 500 miles, bought it from my uncle. it was sitting 3 years. i bleed the system several times because i tried a few different things. im a knewbe too bikes but ive been an autotech for the last 15 years working on BMW and MB, not trying toot my own horn just want to show its not my first time touching something mechanical. i think im going to buy an OEM t-stat and check when it open and closes temp wise. i feel like my original might be opening to late, it was damn near 212 when it was fully open. and like it was previously posted, the back end closes off the by pass and if its not then your not getting the full cool down from the rad. anymore ideas? i see the water pump is metal and shaft driven. the older bmw cars had fiber water pump impeller that would disintegrate and no longer push the water. i will report back
 oh and i was going to block/pinch off the by pass with out a t-stat. if that work then i would now the bike can be cooled down and the t-stat is most likely the problem.

[alexg]

Just an idea: is the check valve of the radiator cap allowing fluid from the expansion tank back into the radiator upon cooling? you might want to read this post: http://www.motobrick.com/index.php/topic,10478.0.html.

[pat7762]

Just an idea: is the check valve of the radiator cap allowing fluid from the expansion tank back into the radiator upon cooling? you might want to read this post: http://www.motobrick.com/index.php/topic,10478.0.html.

replaced it with a new good one, now holds pressure

[Laitch]

not trying toot my own horn . . . anymore ideas? i feel like my original might be opening to late, it was damn near 212

I suggest you add Clymer, Haynes and BMW K-bike workshop manuals to your 15 years of accumulated information and wisdom. The specs are simple and you should know them. The thermostat should open near 185ºF. 212ºF is too hot. Anyway, the thermostat's stroke should be sufficient to direct coolant effectively. The fan starts operating near 220ºF. Which thermostat did you buy? Did you read this thread and then buy one of those non-oem thermostats?

I think your plan to buy and install an OEM will fix your problem if your coolant system is clean and your pump impeller is working, unless the radiator is plugged.

[wally.fisher]

These bikes are "little cars" on two wheels, with your background this overheating shouldn't be a problem to solve.


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[The Mighty Gryphon]

How many bugs are in the radiator fins?  I had overheating issues on a K100 that had enough bugs in the fins to feed a family of four for a week.  Along with a good system flush to remove the well water minerals that coated everything, cleaning them out got the system working very nicely. 

To clean it right, you have to pull the radiator.  Yeah, it's a big job, but while you are in there, it's a good time to clean up the terminals on the engine temperature sensor which can create problems.