My 1985 K100RS has developed a leak in the radiator.  I attempted to replace it, but I cannot work out how to removed it.  There appears to be a single fastener on the top of the radiator that, once removed, would allow the radiator to tilt forward and be removed from the ever-so-snug nest that it occupies.  The problem I face is accessing the fastener. There's a rubber molding around the top of the radiator that prevents access to the fastener.  It is held fast between the radiator and the fairing or frame.  I cannot move it at all, so tight is it secured in there, yet it's removal seems to be the key to removing the radiator.  What am I missing here?  How do wise and experienced owners remove the radiator on this model?
Last year I replaced the fan.  I thought I had removed the radiator at that time, but I can't recall if I did or how I managed that trick.

My rubber "dam" pulled straight out, I don't think there is any way to really secure it in place. You could possibly try pushing it out if you move the tank out of the way?

The bolt at the top of the radiator is a total ***** to put back in, expect lots of fun with it! Also 16v and 1100 radiators fit fine, and seem to be cheaper because they haven't had time to split and be thrown away yet. I had to replace mine with an 1100 item a few months ago, it was quite cheap from Germany and came with the later radiator cap which doesn't gum up and stop working. All good stuff.

I'm puzzled that the rubber bit on your bike put up no fight.  I returned to my task after things had cooled off and drowned the area is aerosol silicon which allowed me to wrestle the bugger off and out.  I'd previously purchased a used radiator and had it renewed by a local shop; I completed the refurbishment with a new thermostat and worked until it became too dark to continue.  That top center fastener did provoke some choice words, but the wife came to the rescue for me.  I gipped both sides of the radiator and pulled in back until she was able to catch some threads on the offending fastener.  Tomorrow I'll complete the job - early in the morning, I hope.  It's predicted to be another day of 100+ degrees f.  here.
I continue to be amazed at riders who say they enjoy wrenching on the K-bikes.  Personally, I hate it!

Today I was to complete the last tasks for installing the rebuilt radiator in my K100RS. I snugged up the clamps on the hoses, topped up the radiator and -- watched as the antifreeze dripped to the ground.  It wasn't even water tight with the engine off and no pressure in the system!  So much for the "rebuilt/cored" radiator.  6-7 hours invested and I'm back where I started.
Is there something peculiar about the K-bike radiators that makes it impossible to rebuild them?  Must I buy new?
BMW wants $726US for a radiator.  Maybe I own a parts bike, but never really realized that until now.

brickrider2 wrote:I continue to be amazed at riders who say they enjoy wrenching on the K-bikes.  Personally, I hate it!

You and me both, I find it a horrible thing to work on. I am so sick of taking all the little bolts out to get the fairing off..

I bought my used K1100 radiator from Germany for about £30 posted, works a treat and certainly better than spending huge amounts on new stuff. I'd be taking that radiator back to them though, clearly they didn't pressure test it?

I don't ever recall anyone repairing these radiators, the cores and headers plates are made from aluminium with plastic tanks which are sealed off using a castellated gripper.
If it leaks from a tube you could try to plug the leak with an epoxy or other, but, leaks from around the tank might be successfully repaired with silicone, a few prayers or swear words.

The radiator leaks on the left side where the tank is crimped, about 8 cm from the bottom.  It's dripping about once ever 4-5 seconds.  When I went to retrieve it from the radiator shop the guy insisted it was pressure tested.  But what can a customer know?  It was painted a shiny black, that was clear.  But beyond that, all I was certain of was paying a substantial bill for services.
If I were to buy another used OEM radiator, there's no guarantee I won't soon be in this situation again-- after all, these are old machines. 
A quick search on fleabay turned up an alternative:   http://www.ebay.com/itm/272244539012?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I like the thought of an aluminum radatior without the plastic bits that one sees everywhere today.  But Chinese?  Would it fit?  Can I use the OEM thermostat?  Big questions and considerable money (for me anyway) are at stake. 

I'd hate to part this bike out, as I've made a considerable investment to make it a reliable machine.  At 42K miles, it should have a lot of life left in it, but I'm at a crossroads here.

Snod Blatter wrote: I am so sick of taking all the little bolts out to get the fairing off..

Electric screwdriver...

[quote defaultattr=""]If I were to buy another used OEM radiator, there's no guarantee I won't soon be in this situation again-- after all, these are old machines. 
A quick search on fleabay turned up an alternative:   http://www.ebay.com/itm/272244539012?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I like the thought of an aluminum radatior without the plastic bits that one sees everywhere today.  But Chinese?  Would it fit?  Can I use the OEM thermostat?  Big questions and considerable money (for me anyway) are at stake. 

[/quote]
That rad on eBay looks the business, expensive though but will give you peace of mind, ensure you fit the mesh cover to protect it from debris.

There are quite a lot of good radiators for sale on fleabay.
That all alloy is one I would go for or if you do go for a used get one from a late model K1100, 1997 or later. Providing they have had the good quality coolant they will be OK.
I have a 3 row core in my K1100 from a 1984 RT that had well over 200K miles and it always had fresh coolant and is as good as the day it was made.
Salt on the roads in winter will kill then so try to get one from down south.

A two-row radiator in the climate we have here sounds like an invitation for a problem, Rick.  There has been a number of riders who have posted about installing a manual fan switch due to heat concerns.  Overkill?  I don't know....  I have two radiators in the shop now, both are three-row models.  I hope one of them turns out to be serviceable.  If not, then I'll have to go to Plan B (whatever that is....)
There apparently has been no one on this forum who has used that Chinese alloy radiator.  I was hoping someone could comment on their experience with it.  The OEM radiator is crazy expensive.  It makes the Chinese copy look cheap, still....

There are at least six K75/K100 radiators on eBay US right now for less than $60. I simply searched using 'radiator BMW K100'. I'd look closer but you'll likely stumble across a three row. I paid $40 plus postage for mine several years ago and it was in really good nick - the owner didn't really know what he had. I scoped it out by enlarging the pictures. When we discussed it later he wasn't fussed that he'd sold it as a two row or a three row, just happy to have sold it, so no one was taken advantage of. It cools my K100/K12 hybrid well right now.

Yes, there are a bunch of used radiator available.  I've 2 of them myself  . Buying another used one on fleabay is a leap of faith I'm postponing at the moment.  Initially, I thought a cheap, used radiator would be the way to go. Bought one, paid to have the leak repaired and subsequently it turned out that it was not.  
I had an interesting conversation with gentleman in the radiator shop today.  The shop has the original I pulled from the bike, plus the one I'd bought and had "repaired".  Both have now been pressure tested and both failed.  He explained the original was leaking from the hot side (in this case, the left tank); the one that the shop had "repaired" leaked from both right and left tanks.  This raises a question in my mind: can this type radiator be repaired at all? Buying used and then paying for futile repairs will quicky get one to or beyond the cost of the Chinese alloy radiators available on fleabay.

I'm sad to say I'm still trying to fix the cooling system on my K100RS.  I gave up on the radiator shop, the guy is a crook.  I bought another used radiator and installed it.  No leaks on start up and run for about 6-8 minutes.  Next day, there was a pool of coolant on the engine case again.  I determined with some considerable probing that the coolant temp sensor was dripping.  I snugged it up with a really short  and handy wrench and drip stopped --- until I finished putting the plastic back in place on the bike!
Evidently I'm going to have to replace the washer on the temp sensor.  Is there anything else that I should know before I tear into that beast yet again? Is the washer made of some special material? What sort of torque should the sensor have when I replace the washer?

All this sounds so very straightforward, but resolving the coolant leak has morphed into something far more frustrating and time consuming that I ever imagined possible.

Are you talking about the sensor on the underside of the engine on the water/oil pump?

From what I gather it's the temp sensor on the coolant riser stub behind the radiator.
It should be a copper washer (nothing special) make sure the surface of the stub is clean and not corroded and DONT use teflon tape.

Snod Blatter wrote:Are you talking about the sensor on the underside of the engine on the water/oil pump?

I would guess that a leak on that sensor won't drip on the engine case.

Sensor at coolant stub: gasket material, aluminium...torque: 30 Nm.

Managed to get my mitts in there and put some additional torque on the temp sensor this morning.  Between the rain showers I then got a short test ride in.  No leaks evident!  
Thanks Inge, for giving me the confidence to use more muscle when tightening the sensor.  No threads stripped in the process!

I would be putting it on the to do list still

the flange of the sensor usually has an aluminium washer as the seal part, we know that aluminium corrodes and in close proximity of a brass sensor  this will help that process

but good to hear its not leaking at the moment ..

ride well

ALUMINUM ALLOY RADIATOR FOR BMW K100 RT/RS 1985-1990

This is just too cool

I hear what you're saying, Charlie.  That sensor is all of two years old and I generally don't have corrosion-related issues on my bike because I ride in an arid environment; I hope to go some miles more before I have to drain that radiator yet again.  
The radiator repair guy sort of redeemed himself in my eyes today.  He finally repaired his repair.  Now I have a modest collection of K-bike radiators in the shed. When I picked the radiator up I asked about the pressure testing.  He said they test them to 16 psi (I've no clue how that is translated into metric measuring units!).  That got me thinking.  What sort of pressure would a K-bike cooling system see?  The cap on my truck has 11 stamped on it.  Good 'til 11 psi?  I don't recall seeing any number on the K-bike radiator cap, but it could be there somewhere. If the cap doesn't release at some given pressure, the radiator could blow.  Do K-bike caps need to be inspected, replaced somewhere along the way?

It's a good idea to replace the rubber seal in the radiator cap as they do swell with age. The later type of cap is designed to control the seal better.


The rubber sealing ring on the left is an old swollen seal and should be the same size as seal on the right. 

Paul.