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.
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).
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 motorcycles....so I suggest you not delve into BMW car coolants.
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 someplace...so 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.
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!...so the thermostat is positively OPEN.
After draining, and a thorough flushing with hot
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. DOING IT; what follows after the burping & filling:
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 +20°F. 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 runand 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.
What about water-less coolants?
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.