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Classic K, Coolant Change...
Coolant types, including water-less; heat
insulation under the tank;  changes
when installing 700 watt alternator.

Copyright, 2014, R. Fleischer

K bike section, #K13

BMW began manufacture of the 1993 K bikes in early 1992, which was unusual for BMW, as normally BMW begins the next calendar year production right after the annual holiday of August. Through Summer, the 1992 production of 1993 model year K bikes had the Bosch 400 watt alternator.  Late in 1992, BMW began shipping the 1993 models with 700 watt Bosch alternators.  

If you are planning on installing the larger 700 watt alternator, which became a stock item from approximately the end of 1992, a good time to do that is at coolant change as you MAY WELL want to install the later overflow tank and new longer hose to it.  The later overflow tank has the hose nipple to the rear compared to the original...which gives more room for your overflow hose & wiring that passes by a close frame area.   There was a factory service bulletin (SI) on SOME of this, including the longer hose, 1 meter of which is 17-11-1-152-866.

If you have not already closed off the system that vents fuel tank fumes to the crankcase; & installed the overflow cup for the tank at the frame backbone, you SHOULD consider those modifications at the same time.

The earliest coolant radiators were not as efficient as the later ones. BMW INcreased the number of cooling fins on its K bike radiators, but this did not happen until the K1100 was in production for quite awhile...I think the change was in late 80 fins.

Consider doing some insulating to reduce engine & radiator heat getting to the fuel, & also reducing the amount of heat thrown back at you, the rider.   This means improving the insulating/sealing areas done by BMW under the fuel tank (the K1100 was better than earlier models, but certainly can also do with improvements).  Information on doing insulation work, & alternator conversions, etc., is located at various places on the Internet, including the website.

I suggest you install, if missing or badly damaged, aluminized insulation material on the underside of the fuel tank.  This is NOT the big thick super-soft fiberglass insulation that is used in home walls & attics.  BMW sells an insulation kit for the underside of the fuel tank.  You do not have to use BMW's insulating item.   You can, at such places as Lowe's, Home Depot, etc., get a roll of Duct Insulation; MUCH CHEAPER than BMW stuff.  Get the type that has a self-adhesive foil/foam.  This product is used on heating & air conditioning ducts, & the type I purchased is 12" wide, 1/8" thick. It has a reflective layer.  If you can find this stuff thicker than 1/8", use it.  The roll I purchased was 15 feet long....plenty for lots of K bike jobs, & other things around your vehicles & home.  There is another product you might be interested in, for areas that need heat reflective tape, but not an insulating tape.  This is HVAC industrial aluminum tape, a foil tape.  Whatever product(s) you get, be sure the glue/adhesive backing is strong.  Otherwise, get a strong adhesive to use, such as SUPERweatherstrip Adhesive, made by 3M and probably Permatex now, this is the yellow stuff mechanics often call Gorilla Snot, but Gorilla Snot is NOT a name on the tube. It is also available in black.

It is beyond the purpose of this article for an in-depth discussion of various insulating schemes, installation of the larger alternator, overflow cup, etc.

Why coolant selection can be important, and other details:

The subject of which coolant to use has become much more complicated... and often QUITE confusing... due to later model cars using a variety of coolants, & coolant colors; and most owners seem to just purchase coolant from autoparts stores...without knowing enough about the coolants. Some these coolants (Like GM specified EX-Cool in the USA) are NOT COMPATIBLE with each other, & mixing them (by mistake, or, perhaps by not thoroughly cleaning out the old stuff) can result in a gooey clogging gel in the system. For the BMW Classic K bikes, in MY estimation, one of the most important coolant ingredients to NOT HAVE, is mineralized mixing water. You will be much better off by going to the SuperMarket or WalMart & buying some DISTILLED water (I suggest you avoid Purified water).

For the COOLANT, use only one whose formula is without nitrites, silicates, phosphates, and borates.  The proper coolant will not tend to plate-out, nor otherwise damage your cooling system. Plating-out is BAD, and it means that the above named no-no additives form a very thin blanket or plating on the metal parts of the system.  You want maximum heat transfer, NOT an internal insulating blanket.   Another problem with plating-out, is that those additives are no longer properly doing their original purpose...which includes anti-foaming, anti-corrosion, etc.   When water with a lot of mineral content is used with phosphate additives, the additive reacts with those minerals, which are primarily calcium and magnesium, and make nasty deposits, typically looking and being what is called 'scale'.    This is BAD, hard to remove, and is the reason you SHOULD use only distilled water.  If not available, use purified water.  TRY to find and use DISTILLED water!

BMW says in some publications, and in K owner's manuals, that you must not use coolants containing certain ingredients.  BMW has not used the same coolants in its cars over the years, as in the I suggest you not delve into BMW car coolants.

BMW sells a coolant for MOTORCYCLES.   If you are worried about what coolant to use, you can certainly purchase BMW's MOTORCYCLE coolant, BUT YOU DO NOT HAVE TO.  More information later in this article.

Understanding all the various available coolants is not so easy.    I used to have a much longer treatise on it here.  Then I found an older article that was quite good. With a quite modest amount of reading and comprehension, you will have the needed facts. Below, I will leave some of my original comments on coolants:

If you have previously mixed coolants of various types for your motorcycle, and have found gelling, or other problems, my suggestion is to do a very thorough CHEMICAL treatment/flushing of the cooling system, BEFORE installing the proper new coolant.  A chemical treatment and flushing will REQUIRE you to run the engine enough to have the thermostat open and then run the engine a bit longer.  Because of that, I suggest, depending on outside temperature, conditions, etc., that you may want to cover the radiator, and go for a ride (a lengthy garage warm-up CAN overheat the exhaust system, etc.). This will ensure that the water gets hot enough to open the thermostat more than briefly.   Let the chemicals and water heat up to the point the fan comes on...then continue on a bit.  If any overheating, simply uncover the radiator.   This is easier to accomplish if your bike has the factory temperature gauge, but it is not a must.  I recommend this same FULL process for each of at least TWO water flushings after the chemical treatment. Use de-mineralized or distilled water, even for the flushings, since you will be heating the system between treatment and flushings.  Yes, this process takes time and effort such as lifting the fuel tank upwards for access, and draining the system, each time.  Do not forget to clean the overflow tank chemically, and flush it too.

If you do this chemical treatment and flushing correctly, and use the correct coolant AND use distilled water to create the proper mixture, you will NEVER have to do it again, and your cooling system should work almost like brand-new, assuming you use the proper coolant mixture from then on.  Coolant mixture, here, means the proper concentrated coolant diluted with distilled water.  It is OK to purchase the proper coolant PRE-diluted, as they do use distilled or purified water.

FAILURE to do it fully & properly, on a bike that has not been previously serviced correctly, will result in less cooling ability, more wear on the fan motor, etc.  Whether...or not....your bike has had cooling problems ...I advise you to use my full procedure, at least ONCE.

There are reasons to NOT to want silicates.   Silicates (and/or borates)... while they have worthwhile anti-corrosion benefits....are abrasive when deposited or plated-out.  The primary abrasiveness is not from them IN SOLUTION, but when they plate-out onto sealing surfaces. This was/is particularly important for such as Honda's Gold Wing, with ALUMINUM sealing parts in the water pump...the silicates plated-out, the plating IS an abrasive coating, and the sealing was injured, eventually badly.  Silicates in themselves also tend to gel and settle in the coolest parts of the cooling system. This can cause radiator plugging and overheating. This is above and beyond the plating and abrasive effects. One of the other problems with silicates (remember, their primary purpose is anti-corrosion) is that they are not stabilized very well, so coolant life is rather limited..... one of the reasons that long life coolants have no silicates.  Some coolants contain borates....these can cause pitting corrosion in hot areas like some parts of the cylinder head.  BMW does NOT want you to have silicates nor borates in your cooling system.

The wrong coolant PLATES the inside of the cooling system, and, in effect, puts a very thin blanket on the internal metal, making the cooling system less efficient.  For BMW, the plating makes the fan motor come on more often, can even let hot spots develop in the valves area (and maybe around the upper areas of the cylinders....).  If bad enough, the entire system, including the radiator of course, does not cool nearly as well as it did originally.  You really need all the cooling you can get for many riding situations.   BMW was having cooling problems with the early K bikes, and now you know why.

There are certain ingredients that are needed in a coolant, and the important ones are anti-corrosives or corrosion suppressors, and anti-foaming/aeration types. Corrosion does more than just eat away at metals....those particles have to go corrosion, while liberating particles, lets such become abrasive EVERYPLACE in the system. There are three types of corrosion: cavitation caused by tiny air bubbles (which have MONSTROUS forces when they implode); pitting caused by aeration; and galvanic/electrolysis from dissimilar metals.

I suggest you drain and flush the old system rather well.  Use a commercial (autoparts stores) system cleaner if you think there is any chance of plating or other deposits or filth. Clean the system really REALLY well after any cleaner is used. Use only distilled water (de-mineralized water if you absolutely have to) when mixing from concentrate, if you intend to purchase a concentrate (it is often CHEAPER, and BETTER to purchase a concentrated coolant).

Be sure the cap and its rubber gaskets are OK. Hoses usually last a very long time, as does the thermostat, but DO A GOOD INSPECTION.  You really do NOT want to have hose problems while riding....and any leaking of the cap gaskets WILL cause problems.

The equivalent OR BETTER coolant than BMW's, at a much better price (especially when on sale!), is specified in this article, as Prestone LL. 
Once you clean and flush your system with chemical treatments, NEVER EVER use anything afterwards but a quality coolant, and distilled water (ONLY!!), and the coolant should be the long life type with NO nitrates nor silicates.  Prestone LL coolant is fine for this.  Use 40% coolant, balance is distilled water.  DO NOT USE TAP WATER, even if you have a 'water softener' at your house.  I suggest you do NOT use "purified" water.  DO NOT USE any other coolant but the Prestone LL, or, BMW's.   I have not tested but half a dozen coolants, and those two are the only ones I approve of.  The Prestone LL coolant MAY now be available in pre-mix, you want 40%.  Best to mix the concentrated coolant and distilled water, yourself.

***BMW has had bulletins out on problems with using the wrong antifreeze.  This is not just Snowbum's ideas.   One very pertinent bulletin about the gelling and heat blanket coating is here:   SI  00 055 88   (2333).

Use only a long life coolant, either BMW's, or the Prestone LL I recommend!

Coolant change and flushing:
I suggest you have on hand 1 gallon of Prestone LL coolant, of the concentrated version.  The Radiator cap has a small gasket I have had to sometimes replace, it is 17-11-1-460-759.  The larger radiator cap gasket was usually OK, but if you need one, it is 17-11-1-460-316.   It is a good idea to have these on hand before you start work on the cooling system. You want to be sure the rubber gaskets are OK...not deformed or broken, so that those cap valves work properly...and, that the cap does not leak. The radiator cap has both a pressure valve and a vacuum valve built into it. Cap releases at 1. BAR at 120C; and the vacuum releases at -0.1BAR.    I don't keep the hoses in stock, but you could consider having a set, particularly if the hoses are quite old.

There are minor variations between models, most of what follows is for K1100LT.  An example of one of these minor variations is that the K1100RS is drained at a screw plug on the water pump, while the K1100LT is drained via the water temperature sensor removal.  There are more differences with earlier models.   When I did the coolant RR job to a K1100 I kept detailed notes on what & where parts were used.  The RS & LT were different, as the LT has its water temperature sender up front below the oil sender as noted above.  The oil sender has a 15/16" hex, the water sender is a 14 mm hex.  Don't mix them up.   The RS has a PLUG in place of the water sender.  Don't unfasten the oil sender by mistake.  No harm will be done, but you won't see water draining, because it won't!  I think BMW made size changes to sensor & plugs in late 1993 or into, CHECK YOURS.

You will need a new water temperature sensor gasket (crush ring, washer) if you have the model that uses its removal, such as the K1100LT.  On a K1100LT I did recently, the sender was the small one, it had a COPPER washer #07-11-9-996-072.   There is an aluminum washer -073 used on the Airheads.   I suggest you use the proper -072 copper version.

When re-installing the water temperature sender, tighten to about 9 Nm.

The below procedure can be modified, and the engine run with the fuel tank slightly elevated, especially on the right side. If you have a 2-valve K100 or a K75, modify appropriately.

Drain your K bike's coolant system when it is still a bit warm from the engine having been run.  Unfasten the front of engine located water temperature sensor and drain from there for the LT; for RS it is the PLUG.  Your bike may be different. Remove the radiator cap to help the draining.  Inspect the rubber gaskets at the cap carefully...and if at all doubtful, replace them.  The earliest caps were not as good, and the rubber gasket didn't stay in position very well, could be squeezed out.  These gaskets MUST SEAL or the system will give you problems!

Flush the now mostly empty system at the radiator cap neck, with a considerable amount of quite hot water.  I use a teakettle and near boiling water for this.  If your system is very badly gunked-up, obtain a commercial cleaner used for this purpose, and follow the instructions.  Be SURE to flush VERY well after using such a cleaner (that includes the engine being HOT!).   If you use such a cleaner, take your time to use the product properly.  The more 'plated' hard insulating 'stuff' you can remove from the system, the better your system will cool.....and the less your fan motor will come on, and the longer the fan motor will last!

When flushing, you will have to put the fluid in slowly.   It is also important to put the fresh antifreeze fluid in VERY SLOWLY.

Remove the contents of the overflow tank using something like a turkey baster, not the one in the kitchen!  I also like to clean and flush that tank if it is grungy.  You can do it all with the baster; tank remaining in place.   Purchase a baster just for this job, and keep it in the garage...not the kitchen!  Flush the baster when you are ready to store it.  If the baster barrel tip is too large, add a piece of small hose to the tip.

Inspect both ends and middle of the large hose from the radiator; & check the small hose to the overflow tank.  

If you have a grungy system with built-up deposits, you will have to use a commercial cleaner product in order to obtain the best cooling.    You need only do this once, as you WILL be using a long-life coolant, forever, as recommended; ..... riiiight?   Flush the system truly thoroughly after using such a product!   Flush also at least once with the engine quite HOT! the thermostat is positively OPEN.

After draining, and a thorough flushing with hot
water, using a cleaning solution if required, then repeatedly flushing with hot water, replacing the sender (or plug) with a new crush gasket, torque properly... & you are ready to refill the system. 

Use an antifreeze mixture, NEVER just plain water, even if you live all the time in hot weather.  
Use 40% or 50% concentration of coolant, mixed with DISTILLED (best)  OR, at a minimum, purified water.   The % of coolant in the mixture you make up depends on conditions you store/ride in.  I recommend the 40% coolant mixture that BMW recommends, which will be OK to  -28C.  (-18.4F). Increasing the concentration to 50% could be done if you store your motorcycle where it can experience extremely cold temperatures.  For storage in arctic conditions, below those temperatures, consult the coolant container.

Do NOT use a stronger % of coolant if the motorcycle is not exposed to temperatures nearly at or below those temperatures .....more coolant does not mean better cooling.  You DO need ENOUGH coolant. 
Coolants RAISE the boiling point, not just LOWER the freezing point.  You need BOTH these effects, and your K bike system is PRESSURIZED by the radiator cap sealing and pressure valve (and vacuum valve to keep the system filled from the overflow tank) to enable an even higher operating temperature, when needed.   This means that use of an 'antifreeze' mixture is helpful for both hot weather riding as well as cold weather riding/storage.  You should NEVER run plain (or even just purified or just distilled) water in your K-bike, NO MATTER THE WEATHER CONDITIONS.  COOLANTS of the PROPER type also lubricate moving parts in the cooling system.

I do NOT usually purchase 'pre-mixed' coolants, they often cost much more, and you cannot 100% depend on the total formula with SOME brands....but, Prestone is supposed to eventually, maybe now, sell the LL coolant, properly mixed.

I use Prestone Extended Life; also called Long Life or Prestone LL , because it is a trustworthy brand.  I know what the ingredients are; and have had new and used coolant TESTED for the various additives, AND aluminum from the engine, ETC.  I change the coolant every 3 to 7 years on my own K1100LT, depending on my usage. That coolant does NOT contain silicates NOR nitrates nor borates.   YOUR change interval should depend on how many short trips, how much total mileage, & TIME since last change.  I drive my K sidecar rig in the Winter, & the 40% has always worked fine for ME, since my garage is lightly heated, & I do not ride below +20F. I use the BMW recommended 40% concentration, & 60% DISTILLED water.  I do not use common tap water, I believe it simply ages the coolant faster & increases carbonate deposits, which also act like an insulating blanket.  

The trick to refilling & proper operation is to be as sure as you can that the system is refilled as much as possible without air bubbles.   This means dribbling the coolant mixture into the neck VERY slowly;  'burping' the system a number of times by squeezing the hose as you very slowly refill.  I have found that it helps for the final burping's if the neck is filled to the ledge & the cap FULLY tightened, before the squeezing.  I then remove the cap & continue refilling until I can't do more filling without the coolant mixture going into the overflow hose.

DOING IT; what follows after the burping & filling:

Fill the cleaned overflow tank at this point to not quite half-full.  Do not fill it too high.  The overflow tank level will shrink some after the engine is run and cooled.   Just how much the overflow tank level will go down, after a full heating-cooling cycling of the engine, depends on how well you did your job of filling the engine. Even if you were careful, there may be air bubbles someplace in the engine.  Install the radiator cap, inspecting the rubber seals carefully first.   

Using a dowel, or other long tool, rotate the cooling fan blades a turn or two, to be sure the fan motor is free to rotate. BTW, this should be done after any lengthy storage period. Ride the bike enough to get the coolant hot enough so the fan comes on for a short while.   I typically block the radiator ...using a piece of cardboard, to be sure the fan will energize. Depending on weather, and road/traffic conditions, etc., you may want to block off a considerable portion of the radiator at the front.   The temperature gauge must be high at the time the fan comes on, because what you are after is to be SURE the thermostat opens and therefore the water pump ensures circulation throughout the engine and radiator, etc.   If you have a problem with the fan or thermostat or sensor driving the fan circuit, you want to be very careful.   After the engine heats enough that the fan comes on, you can remove the cardboard, or partially, and ride home, and park the bike on the center-stand, to cool-off.  

I do not recommend running the engine (until the fan comes on) be done in a garage setting unless you have a big squirrel-cage fan, as the exhaust system, including header and exhaust ports can get considerably hotter than I think is OK for them, could crack, etc.  If you DO use such a fan, DO put cardboard in front of the radiator to block the air flow; which will reduce the amount of time the engine must run.  Try to direct the fan output to the underside of the engine, meaning the left side exhaust header area.   Squirrel cage fans are very handy....and often available free from heating and cooling companies, who have old worthless house heaters you can remove a fan unit from.

After the bike is completely cooled, recheck the overflow tank.   Its level will usually have gone down some as the system sucks the fluid back. If it did not suck back anything, remove the radiator cap, & see if the system is full.  If not, you may have a bad cap, or bad cap gasket (there are two gaskets at the cap).   This is why I said to check the cap gaskets first. If the overflow tank level is quite low or near empty, then refill to nearly half-full, and repeat the ride and cooling.

Recheck the coolant tank after this second ride and full cooling-off.   Adjust the coolant level in the overflow tank to a bit above the minimum mark...& not as low as the minimum mark. THIS ALSO MEANS DO NOT FILL IT TO HALF WAY AND HIGHER!   You MUST have it at or slightly above the minimum when the engine is cold.

It is a lot easier to add a small amount of coolant to the overflow tank, than to lift the fuel tank, unfasten the fuel lines, and lift the tank more in order to refill at the radiator cap.  If you followed my instructions carefully, you won't have to add very much coolant mixture to the overflow tank after the first ride, and you likely will not need a second ride test.

Sometimes, even with care, the engine & radiator are not fully filled; there are large air pockets, during the procedure.  If so, you must repeat the ride/cool process.  After there is no longer a drop below the minimum mark on the overflow tank after the engine has cooled fully, you can then set the final mount for the overflow tank. Filling the overflow tank too much will have the tank spit fluid on a hot day.  Usually half an inch or so above the minimum mark AFTER full engine cooling, is about correct.   That level should hardly change between now and your next coolant fluid change.

BMW said in its literature for this K1100LT bike to use 3.4 L of 40% coolant. They mean that the total mixed coolant amount is that figure.  That is 3.6 U.S. quarts....about what I found necessary.  I made the mixture from 46 ounces of the concentrated Prestone Long Life Coolant, plus 69 ounces of distilled water. I use an old plastic 1 gallon antifreeze jug I had (with a clear side edge area to see liquid level, which had level graduations) when mixing.   I filled the overflow tank to 1/2 before starting the engine, since I knew from past jobs that this was going to reduce its level the next morning down to a bit above the minimum, but not need refilling; or, little.

The Radiator cap has a small gasket I have had to sometimes replace, it is 17-11-1-460-759.  The larger radiator cap gasket is usually OK, but if you need one, it is 17-11-1-460-316.   It is probably a good idea to have these on hand before you start work on the cooling system. You want to be sure the rubber gaskets are OK...not deformed or broken, so that those cap valves work properly...and, that the cap does not leak.

The radiator cap has both a pressure valve and a vacuum valve built into it. Cap releases at 1. BAR at 120C; and the vacuum releases at -0.1BAR.

What about water-less coolants?
Some folks promote using such as Evans water-less coolants.  I am not convinced. I've being curious about the stuff for a long time, so I delved into it more deeply. 

The Evans product is a mixture of a high percentage of ethylene glycol and a lower percentage of propylene glycol.  It is, OVERALL,  a very high percentage mixture of two common long life antifreeze products.

My primary concern, since I knew Evans contains a corrosion inhibitor, was the actual cooling capacity change, if any. 
Those glycols reduce "specific heat capacity" .... which probably means MORE fan motor use, and works best with higher water pump rpm (poorer cooling at low rpm) other words, more air cooling to the radiator and increased liquid flow rate in the engine to enable the SAME cooling as with other coolants.

I THINK that these various coolants, including BMW's own, & the LL Prestone, are likely to slightly reduce over-all cooling capacity, and perform, over-all, very well, considering all other factors..... and have the advantage of long life.  I don't expect wearing of the pump nor plating out, scale formation...and other problems of the conventional antifreeze coolants (that contain nitrates, nitrites, silicons, borates, etc).

I think the Evans coolant, or other 'waterless' types, specifically, will trade off too much cooling ability for their even longer life (assuming a good anti-corrosion package in the Evans, and I have limited information on that).  I can NOT recommend such coolants.  Since I have somewhat limited cooling capacity in my K1100LT for the hottest SouthWest areas, I'm not inclined to reduce the capacity by using waterless coolants....meaning the fan would then come on more motors are a sore point on Classic K bikes.

I will continue to use the LL Prestone, which matches BMW's requirements for its own coolant....and does not have any plating-out problems, abrasiveness, silicates, nitrites, borates, etc.   My testing of that product shows excellent performance.  

I specifically recommend AGAINST any common coolant that contains borates, nitrites, silicons, etc.   Use of them will probably...IMO.... result in short water pump life and WILL result in poorer cooling....and probably shorter fan motor life.


12/23/2009:  Expand entire article, to include specifics on the alternators, and other suggested modifications during the coolant change.  Add information on the insulating products.
06/20/2011:  Clean up a bit.
10/07/2012:  Add QR code; add language button; update Google Ad-Sense code; clean up article more; fix redundancies; but add information too.  Language button and code removed in 2013.
04/05/2013:  Add section discussing details of coolants and move things around a bit.
04/06/2013 & 04/07/2013:  Clarify chemical treatment and flushing; add hyperlink and edit commentary.
01/24/2016:  Add comments on water-less coolants.
03/06/2016:  Metacodes update; layout.
08/14/2016:  Update metacodes, scripts, H.L., fonts, clean up article.

Copyright, 2014, R. Fleischer

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Last check/edit: Monday, January 15, 2018