Not sure if this is the right place to post this, but here goes.

My 1992 k100rs 16v seems to be running hot. This is a bike that I have replaced the motor in. The motor I put in has 29,000 miles on it and had probably been sitting for at least 6+ months. The rest of the bike has ~96k miles on it. The bike runs great, the only issue is the heat.

I flushed the cooling system out a long time ago and got a bunch of crystallized coolant and crap out. I also took the pump cover off and scraped out all the build up. I now had a decent flow of water through the system, so I put it back together. Still though, it would run all the way up almost to the red on the temp gauge and the idiot light would come on.

Later, I replaced the thermostat with a new one rated at 82 deg Celsius and flushed the system again. This time, there were no chunks of 'stuff' coming out of the system. The water was just a little rusty. After I did this, it was fine for a few days, but then I noticed it running hot again. It's not as bad as before, but it still seems a little high to me.

I also had to wire the fan to a switch on the dash as the motronic unit is not sending the ground signal for it to turn on when it's supposed to. I am consistent with turning on the fan when the temp gauge hits around the half way point. (and turning it off when I'm at around 40mph)

This is the temp gauge as of now, in about 60deg Fahrenheit night weather. So I'm worried for when summer hits:

http://postimage.org/image/gh5te2hb5/

-Orange Line = On normal acceleration or in stop and go traffic.
-Blue Line = Cruising around town / on freeway
-Green Line = Idling with fan on


-Could there still be crusted parts in the cooling system that are hindering the water flow? If so, any suggestions for products to clean/dissolve that out?
-Could it be possible that the motronic unit thinks the engine is a different temperature thereby making it run lean and hotter?
-The fan squeaks a bit when it's turned on and off due to, I believe, a drying bearing. It still seems to come on nice and strong and gives a good air flow, but could the fan be insufficient?
-any other ideas?


(I am just using regular water in it until I get this all sorted out.)

Those readings are a bit high but not real bad.
Onr thing that happened to me was that I had leaking fork seals and the oil was blowing back onto the radiator then dust and dirt stuck there blocking the air flow and overheating at low speeds. When I held the radiator up to the light I could still see the fins well but the air flow was not at all good. I cleaned it with degreaser then hosed it a few times and blew it with air then sat down with a small piece of high tensile wire (.8mm MIG wire) with a hook at one end and dragged a lot of sand grains out but giving them a hook and a blast of compressed air. All works well now.

looks close to about right to me ....but if your saying those readings are in 60 degree f ....it is a little high

at around 60- 70 f mine hardly gets to the middle of the dial

could some of the crystaline stuff have formed partial blockages in the hot feed side on some of the crossflow portions ? thus restricting just some of the effectiveness ?

would it be an idea to attempt a reverse flush with presure from the thermostat side pushing the crud back out the motor feed end ...?

radiator out might be best ..as its a central feed in a crossflow radiator, you could get some advantage of having the engin feed side at ground level letting the crud drain well ?

just a thought

Alright. Based on both of your posts, it seems it may be best to drain the system and remove the radiator. Clean the radiator up if it needs it, then I'll flush it again.

When I flush it, you're suggesting I flush it by putting the garden hose up to the thermostat hose that leads in to the engine, thereby doing a reverse flush? Should I look in to something like a sink cleaning agent such as "Drain-O" as well?

Draino is very corrosive to Aluminium it may be better to get some of the radiator flush like Wynns and soak it in that at the right concentration and get it hot.

K, I'll do some work on it in the next couple days when I have time and then post results. Thanks guys.

no ...im suggesting that you remoove the thermostat ...just in front of the thermostat are the radiator water feeds that sit between the thermostat cover and the thermostat propper ....this is the only paths that the radiator hot water passes through ....from the radiator core ......the hose that is near your left knee is the feed from the motor .... and this is the area i suggest that may have the partial blockage needing a revese flush from the thermostat side .

is that clearer ? or am i just confusing ? you will see the holes once you pull the thermostat cover off

the hose that feeds around the back of the radiator from the water stub is a bypass till the heat builds up enough for the thermostat to operate

but the hose that comes from the filler could be used for this reverse flush

I see, that makes more sense now. I think I'm clear and can give it a go... as soon as I get some free time! Thanks!