Odd 650 Dakar overheating issue

[mat_brook]

My 03 650 Dakar seems to overheat.

The issues are:

The engine runs for a short period, maybe 5 minutes, before the water is being pushed up into the expansion tank and then squirts out of the top.

In this time the fan does not come on neither does the overheating light. Once it gets seriously hot i turn the engine off.

Now i know what you are all thinking, check the usual things. Have done all that. I have:

1. checked coolant mix
2. checked fan with 12v supply - it works
3. changed fan temp switch
4. removed thermostat - it justs seams the take longer to do exactly the same thing.
5. flushed through whole system with a hose
6. checked the water pump is spinning - that seems fine.

I have discovered that when the engine is running, if i unplug the fan temp switch then the fan comes on. It will do this when the engine is cold. Is this normal? Will someone check this with a normally functioning bike. Maybe BMW have supplied a part that is difficent!

I have been told by a BMW mechanic that the thermostats never break? Not sure if that is true or not. Also does anyone know much about the radiator cap? Is this likely to be the problem.

I rebuilt the bike over last winter, not really any major internals though, but have toured around France on it, during that time it only overheated twice, once on really hot day in traffic and once on my way home again.

Does anyone know how to test the fan temp switch - can you just put a multimeter on it and test it cold and hot to see if it allows current to pass?

Not sure if i should get a new Rad cap and a thermostat to make sure.

Cheers

Mat Brook

[Toyark]

p.m'ed you b ut I suspect it's air trapped in the head.
Bleed the system!
green circle is air box drain
red is radiator air bleed screw both on RH side of bike near yoke

[*Touring Ted*]

Originally Posted by mat_brook

My 03 650 Dakar seems to overheat.



Does anyone know how to test the fan temp switch - can you just put a multimeter on it and test it cold and hot to see if it allows current to pass?


Mat Brook

YES !!!!

Is the fan not coming on ???


Still, wouldnt make the bike act up like you said !

Like Bert said, bleed it all out. The cooling system on a bike is a circuit and what you had described seems like a block.

The 650's are very unreliable concerning their waterpumps. Just because it spins doesnt mean it's working. It's the seals which go.

I would pull the whole pump out and check it or have it checked properly. Is it leaking from the drain hole ?

[Threewheelbonnie]

Originally Posted by mat_brook

My 03 650 Dakar seems to overheat.


I have been told by a BMW mechanic that the thermostats never break? Not sure if that is true or not. Also does anyone know much about the radiator cap? Is this likely to be the problem.

Totally untrue (and typical of BMW techs knowledge of all things Rotax), mine ate two of things in 36000 miles. The usual effect of a stuck rotax-bmw thermostat was a bike that could come off the choke in about 100 yards then put the light on, I never had gushing back into the tank but maybe I caught it in time or didn't notice earlier bouts of sticking. There is also the issue of the fan switch using gravity to hold the contacts in place yet being mounted on it's side. This results in the temp warning light coming on in traffic, but no other obvious bad effects (I did 3000 miles through Norway running the fan off the horn switch). Bad design is the culprit IMHO , I don't know if the chain gang etc. have anyone who's used non-BMW components, but that would have been my next train of though if I'd kept the bike.

I would go with the more knowledgable posters above and say you have an air lock or a blockage, but I havn't touched a water cooled bike since my F650 waterpump related walk in the desert, so can't really add much.

The day mine went pop (failed waterpump and warped head, not sure in what order) the thermostat and switch were actually working. The only useful knowledge to be gained there is not to ignore the oil tank mounted temp gauge if you have one.

Andy

[hook]

Same thing happened on my '02 Dakar. Replace the radiator cap, the springs are tired. On the F650 (and some other bikes!) it works like this: When the fluid reaches a specified temperature the cooling fan engages. If the fan fails or the temp reaches another temperature level the bike will emit a coolant overheat red warning light. If you continue to ride, the springs on the radiator cap will allow the fluid to escape into the expansion tank- when the tank is full a tiny hole on the removable black cover will spew coolant. When the springs are tired/old fluid will fill the expansion tank before the fan engages or the warning light is activated due to simple expansion of the coolant as it warms. In the Sudan the bike and I cruised through sand at temps exceeding 56c with no probs. The new radiator cap cost me 12usd. Safe roads.

[mat_brook]

Thanks for that Mr Hook, i was suspecting as much.

I measured just under 1L in earlier after i made sure there wasn't any air, tried it again and it did exactly the same. After i sat and thought through it i came to the same cycle that you described.

Knew it couldn't be anything to do with the oil. It is foaming ever so slightly but no more than i would normally expect for quite newish oil (1000m). Plus it hadn't risen either.

Thanks one and all for your time and help. Always useful to know that there are others who have gone through it before.

Mat. Brook

[tmotten]

Let us know what is was.

If it were me I'd start by trying a different cap as well. They may seem simple, but there are actually a brilliant piece of engineering. Most simple things are.

I'm going to assume you don't know anything about maintenance on this bike for clarity. If you know all this (which is seems you do as you've flushed it) all the better. Other people may not know this though and/or you may have forgotten something.

Than I'd drop the coolant fluid and check if the water pump is turning by turning the motor off by hand with the real wheel. You have to remove the water pump cover off course. While you're there make sure the weep hole is unblocked. BMW fills it up which is the stupidest thing.

Than flush the whole system with a hose (low pressure) and flush it out the RHS of the engine as per the picture. Newer bikes don't have that nipple but a bolt instead. Flush until you get clear fluid and heaps of it. If you're anal you can collect the clear stuff and check it for grit of other crap.

Than re-fill with a nitrate free coolant mix of 50-50. Make sure some passes past the RHS burp bolt and put it back in and tighten when it does. It's at the high end of the system, so it may take some fillings. Rinse off excess coolant off the motor and electrical components when you put the bolt back in.

As you fill the system make sure you squeeze the crap out of the hoses on both sides to push the air our the system. Pour slowly to allow air to escape. Fill it all the way to the neck and put the cap on. Than fill up the burp tank to the max level.

Go through a heat cycle (run till the fan comes on or around the block) and check and fill if required when it's cold.

If there is still an issue, there are other things at play.

[mat_brook]

Sorry this took me so long to get back to the forum.

It was indeed the rad cap...as soon as i saw the replacement it was obvious. On the underside of the cap there is a small cup with a black rubber insert in it. This was missing and contributed to the issue.

These things are always obvious after they are solved.

Thanks one and all for any help.

Mat. Brook

[tmotten]

You reckon it's floating in your system somewhere now?

[darkhelmet]

I had the same problem in Swaziland once.

The light came on, fluids came out of the radiator. I tried to find the problem, I suspected the radiator at first, but starting the bike and revving didnt show any leaks. Removing the radiator cap didnt seem possible.
I then rode until the light came on (every couple minutes or so). I managed to get to a BMW dealership (40KM around the corner considering being in Africa) they had trouble finding the problem. They said it was the thermostat.

The bike went back to Pretoria, and there they changed the radiator because they said it sprung a leak because of a little stonechip. The problem was slved, but what riddles me, is that I rode all the way to the BMW dealership without loosing any fluids. So Im still not sure what the problem was...

Glad you found out!