OK, sounds like it's time for BMW Radiators 101.
There is an existing plastic radiator Protecting Grill (part #2 below) that blocks most small rocks. There is also a center Mud Flap section (part #3 below) that blocks crud thrown up from the tire when running in a straight line.
This same basic setup is used on all the Slant/4 K1200/K1300 bikes, as well as the Slant/6 K1600 bikes. In fact, the Protecting Grill and Mud Flap are the exact same parts.
The basic concerns are small or large rocks causing direct damage to the radiator, or crud embedding in the fins and reducing cooling efficiency over time. We've seen these things happen on many different bikes, although it's usually not critical and doesn't generally cause any direct damage to the bike. Although we have seen a few cases where the blockage has gotten bad enough that the overheating was serious enough to stop riding the bike, and at least one case where the radiator was unable to be cleaned and needed to be replaced (thanks to Texas chip-seal roads).
It has been shown that giving the radiator a good cleaning and inspection at the 18K service intervals (when it comes off for the valve check) is usually a good idea. Scratch that - it's a great
idea, and really should be part of the normal BMW Maintenance Schedule. Most good mechanics know to do this, but still, it's definitely something I would specifically ask about when the bike goes in for the valve check.
Even so, folks are looking at ways to minimise the damage and keep the radiator cleaner betwen services.
There are several options here:
1) Leave it alone, and trust the BMW factory guards. That's OK for most riders, but some will still have trouble with rocks or road tar or other crud thrown up from shitty road surfaces.
2) Add some simple aluminum window screen material sandwiched between the factory guard and the radiator like I did on my K16GTL. Mine came from the local hardware store and was cheap. This will block bugs and crud, while the factory plastic guard still blocks small rocks. Mine still looked fine at 60K miles, and I had no overheating issues at all, even when dead-stopped in NYC traffic, or running across the desert at speeds at well over 100°F. Other riders have used fiberglass window screen, but stay away from the cheapest plastic stuff as it quite literally can't take the heat.
3) Add some filter foam material between the factory guard and the radiator like some K16 riders have done. This is also pretty cheap, and should help block road tar and other sticky crud that can get into the radiator and harden, causing a noticeable loss of cooling efficiency in extreme cases.
4) Add a much stiffer metal mesh screen material, the same as some riders have used for an oil cooler guard. This should help with rocks, but the larger openings would still let sticky crud through.
5) Add a Fenda Extenda to help minimise crud and small rocks thrown up from the front tire. This is probably a good idea no matter what else you may do here.
6) Replace the factory plastic guard with a metal guard like the RadGuard
. This will help with rocks, but would still let some crud through, much like option #4 above. Plus it's expensive . . .
7) Use some combination of the above to get rock protection plus crud abatement.
8) Sell the bike and buy something air cooled.
Those options are listed roughly in the order of cost. Which way an individual rider may go depends on their experience, their concerns, and their pocketbook.
For more information, see this thread
and this thread
over at the K1600 forum. Warning: there are some pretty ugly pics in those threads . . .
This ends BMW Radiators 101.
Be sure to tune in next week for Oil: Facts and Fallacies, and the week after for Which Tires Should I Buy?
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