K75s - worried about low coolant reservoir...

[superwesman]

Hi everyone-

I purchased a 1990 k75s last weekend with about 22k miles on it. Drove it home (maybe 40 miles) with no trouble. I took it out today for about maybe 20 miles and when I got home I noticed that there was almost no coolant at all in the reservoir by the battery!

The coolant temperature light never went on, so I'm assuming that there was enough in the system to keep things under control but I'm really not sure. One thing I noticed while riding was that it seemed hot near the top of my legs on the side of the seat. Where the coolant reservoir is, there are two frame tubes (on each side). The ones near the front of the bike were hot to the touch. Not so hot that I couldn't touch them, but hot enough to cause me to check the coolant level.

The little bit of coolant that's in there is greenish in color. I've never owned a liquid cooled bike, so I don't know anything about coolant other than what I've read in the last few hours. I'm planning to pick up the BMW brand this week (unless you convince me otherwise). My guess is that the safest thing to do at this point is to flush the system and refill.

Is there annoying else I should keep in mind? I have no idea how much coolant was in it last week. There was no puddle under the bike, so I assume there is no leak. Did I catch this just in the nick of time? Is it a bad idea to simply fill the reservoir? Have I likely done damage to the engine? Where else should I check for potential issues based on what I've seen? I tried to check oil levels in the gear box and rear wheel, but couldn't get the bolts out. I'm going to try some liquid wrench tomorrow. Engine oil level looks fine but I'm probably going to change it just to be safe.

Any advice us greatly appreciated. Thanks in advance

-soup

[Chaos]

if the bike was running ok and the light didn't come on you are probably good.  Was the fan coming on?  They are known to burn out, that may have something to do with your low coolant.  I use Prestone, don't think the bike cares but BMW brand is good if you don't mind the price.  You need to lift the tank off to get to the radiator cap, level should be flush up to the top there.  Then fill the reservoir about halfway.  Not a bad idea to flush and refill, I do mine every 2 years. 

[johnny]

greetings superwesman...

welcome to motobrick.com... and for heavens sake... bring the red guitar...

i use the 50 / 50 peak premix... filler it up...radiator and overflow... letts it seek its own level by purging out what it doesent want...

some will say bmw brand coolant and distilled water by the book... and measure it in by the book... those are generally folks who fuss with their bricks more than they ride them...

the hard part is getting the coolant in the bung... gotts to take it slow and squeeze the bottom hose to getts the air bubbles out... it takes a while to gett it all in... butts when you do guess what... yawl... its a motobrick... its supposed be hot...

so... like chaos said... if your fan is coming on and you gotts a full radiator... you are good to go...

you will be able to hear the fan come on... i would put it on the center stand and start it up and wait and wait and wait to see if the overheat lights comes on hear if the fan come on... then you will know for sure...

id change all the fluids and be done with it for now... do you have a oem tool kit... i use the oem allen with the spark plug extension for leverage to getts the gearbox and final drive fill plugs lose...

j o

[Scott_]

You don't absolutely have to use BMW branded coolant. You can use anything that is rated for use with aluminum engine components.
You can mix it 50/50, up to 60/40, but absolutely use distilled water(read not tap water) for mixing it.

I'm also with Johnny on this one, go ahead and replace all your fluids now to start fresh. Unless of course you have service records that tell you when it was done last.

I do coolant every 2 yrs and all other fluids every year. Especially the brake fluid, keep it clean and fresh.
Standard motor oil is fine for the engine as these bikes run a dry clutch just like cars/trucks.

The coolant fans are known to seize up on these bikes as they age. Some have been able to open up the assy and free it, others have just replaced them. There are many options out on "the net" when it comes to replacements.
You can go used which would be "plug and go" installation, or you can just replace only the motor, but that involves a little more work. Then there is the total different style fan that requires an re-designed mounting plate that mjydrafter(on this forum) created.

A good mod to consider is a manual fan switch. There are write ups in the lieberry.

Post up your questions and welcome.

[wmax351]

For what it's worth, the bmw brand coolant (from the car dealer) is essentially the same price as any other coolant that seems to fulfil the "Nitrate, phosphate, etc free" that is spec'd for the bike. Last time I bought it, I think it was $17 for a gallon of undiluted stuff, which makes enough for 2 fills of the system on a K75.


Do a coolant flush with some radiator flush from autozone, etc. Pull the thermostat out, put the cover back in, and fill with the little bottle of flushing compound and tap or distilled water. Run it till it's hot. Maybe go for a short ride. Let it sit for a bit, then warm it up again. Then drain it, flush with tap water and no flushing compound, then fill with distilled, run till hot, drain. Then put the thermostat back in (a new one can be bought for a 1500cc corolla, if yours is dead). Fill with distilled, take it for a ride, then drain and fill with 40:60 BMW coolant:distilled.


A little OCD, but with that few miles and green coolant, it probably is worthwhile.



I'd change all the fluids now. Mobil 1 is on sale, at least in CA. At 22k miles, it's broken in enough to switch to synthetic. Change it yearly with Synthetic. Good dino oil is fine too, might make more sense since you will have to winter it down and change the oil twice a year. Final drive and Transmission, good gear oil is fine. Redline makes some special stuff that works really well, there are details elsewhere.

[superwesman]

thanks for all the tips. in the end, I decided just to take it into a local shop and have them check all the fluids and get a nice fresh set of tires put on.

beep beep, beep beep, yeah!