F650 Overheating FAQ

compiled & edited by Kristian #562
Please read the
Disclaimer before attempting any work in this FAQ.
Last Updated: 9 September 2006, by Winter #1935

Other related FAQs:


This FAQ should help you identify problems with your cooling system, and direct you to an appropriate FAQ on fixing the problem. While the cooling system on the F650 classic models is fairly good, the cooling system on the Fuel Injected models is marginal (at best). Even small changes to the Fuel Injected models can result in greater stress on the cooling system. In March 2003, BMW NA released two service bulletins (17 001 03-012 and 31 001 03-013) for the GS/Dakar/CS models about voiding your warranty by installing radiator guards and fork boots/gaiters. You can find these bulletins in the Service Bulletins FAQ.

Temperature Classic Fuel Injected
Cold Engine    
Thermostat opens  
85°C (185°F)   Thermostat starts opening
87°C (189°F) Thermostat fully open Thermostat fully open
90°C (194°F) Fan turns off  
95°C (203°F) Fan comes on  
102°C (225°F)   Fan comes on
115°C (293°F) Idiot light comes on  
118°C (245°F)   Idiot light comes on
? Engine starts melting
Warning: Do not overfill oil on a GS/Dakar!
Be careful not to overfill the oil on your GS/Dakar. This can cause overheating problems, and may not be detected by the coolant temperature sensor. The reason why this is such a problem is the F650 is a dry sump motor. If you overfill the oil tank, the "extra" oil will flow into the oil return line. This could lead to hot oil sitting at the bottom of your engine - and thus lead to damage to engine components. Please see Service Bulletin 11 002 05 (015) from Feb 2005.

Cooling System Diagnostics

The following steps are ordered from simple and easy things to check, through to the hardest / expensive things to check.

Diagnostic Comments Classic FAQs FI FAQs
Is your bike clean?
(including radiator and oil tank)
A clean bikes makes the transfer of heat from the engine and
other cooling surfaces to the air more efficient. So make sure you
clean your engine, radiator and any surfaces where oil / coolant reside.
Any bent / damaged radiator fins? Bent radiator fins will reduce the flow of air through your
radiator. Carefully straighten any fins.
  GS Radiator
Check your oil level The cooling of your engine is performed through heat transfer
to both the coolant, and heat transfer to the oil. Thus if you are low
on oil, the average temperature of the oil will be higher. Top up your
oil as required. Note: Do not overfill your oil!
Oil Change GS Oil Change
Check coolant resevior level This can be tricky on the fuel injected bikes, because it
can be hard to see the coolant level. Top your coolant level as
required on all models (not just the fuel injected!)
Coolant Change GS Coolant Change
Is radiator cap installed correctly? That cap is a little tricky to get installed and locked on the
radiator. You need to press down and rotate it and make sure that both
tangs of the cap are locked in the slots of the radiator top. When
pressure builds up, the cap blows off and the fluid starts boiling.
Refill the system as needed and be careful about installing the cap.
Check coolant level in radiator
(When bike is cold)
Let the bike cool down (approximately two to three hours).
Carefully open the radiator cap, and check the coolant level. Top up
as required.
Remove obstructions from front of radiator
(aftermarket guards and fork boots)
If you have an aftermarket / custom radiator guard, remove it.
If you have fork boots, remove them. On the classic this is not such a
problem. See Overheating and Gaitors
Aftermarket Forks
Change coolant every 2 years! Coolant looses certain qualities over time. You should replace
your coolant every two years at a minimum. If you have no idea when
your coolant was last changed, change it anyway.
Coolant Change GS Coolant Change
Check coolant:water ratio The coolant:water ratio will affect the performance
of your cooling system. Water has excelent heat transfer properties
but boils at 100°C. Coolant helps reduce the freezing point and
increase the boiling point.
Check for general air bubbles Squeeze your coolant tubes carefully. There may be some air
bubbles in the cooling tubes - these will sometimes work their way
out, but a little encouragement will sometimes help.
Bleed air from engine cooling system Air trapped in the cooling system will reduce its effectiveness.
Check waterpump weephole for drips The seals on your waterpump may be beginning to fail.
This is a fairly common thing - so check the detailed FAQ.
Water Pump Seal Repair
Check bleed nipple for leaks The cooling circuit has a bleed nipple on the RHS of the
engine. Is the nipple torqued correctly. The bleed nipple may have
been damaged somehow.
Coolant Change GS Coolant Change
Is the fan operating?
(Tests - check free spinning blades)
(Tests - run bike till it comes on)
(Tests - apply power to fan)
Turn the bike off, and check the blades of the fan spin
freely. Next run the bike until the fan comes on. If the fan does
not come on before the idiot light comes on, your fan is broken.
You could also try applying power to the fan.
Cooling Fan Radiator FAQ
Measure coolant volume drained If there is not enough coolant in the system, and
bleeding the air from the system did not work, you may have a
blockage somewhere.
Coolant Change GS Coolant Change
Is the waterpump spinning freely? With the coolant drained, remove the waterpump cover only
(not the full clutch cover). If the waterpump spins freely with the
engine off, the waterpump pinions are not engaged with the engine.
Remove the clutch cover and check the pinions.
Water Pump Seal Repair
Does waterpump have white impeller? Earlier model bikes had a white impeller on the water
pump. You should probably replace this.
Broken fins on the water pump impeller? If you have any broken fins on the water pump impeller
the coolant will not be flowing effectively through your engine.
Check thermostat operation Remove the thermostat and check it opens and closes as
per specifications. If not, replace the thermostat.
Check temperature sensor ???    
Check coolant tubes and radiator for obstructions If the coolant flow is obstructed, the engine will overheat
very quickly. Remove coolant hoses and check for obstructions.
Identify source of obstruction and fix that too.
Check coolant tubes and radiator for leaks Pin-hole leaks or damage to coolant tubes will either
leak coolant, or allow air into the cooling system.
Check coolant circuit through engine??? ???    
Pressure test Perform pressure test of cooling system (including
radiator cap).

Overheating and Gaitors (GS Only)

BMW released a service bulletin in March 2003 (17 001 03-012) that stated: The installation of [radiator guards] significantly reduces the engine's ability to cope with high ambient temperatures.... Essentially the installation of radiator guards would compromise your warranty. A second bulletin released in March 2003 (31 001 03-013) stated: Installing front fork gaiters reduces the engine's ability to cope with outdoor temperatures by more than 20%... Please notify customers who have installed front fork gaiters that engine damage due to overheating will not be covered under the terms of BMW's New Motorcycle Limited Warranty.

You can find copies of the two service bulletins on the Service Bulletins. Also see the Aftermarket Forks FAQ for further information on Fork Protectors and Warranty.

Installing an Oil Cooler

Thanks to dlearl, #476, 13 July 2006

First the facts: I've posted several times on different threads that I've been concerned about the oil temperatures that rise upwards of 250F in continued crusising above 5,000 rpm. Seeking a remedy, I decided to install an oil cooler on the F and see how that affected it.

Before: Oil temp would cliimb to ~ 200F and pretty much stay there in normal commuting or highway cruising as long as I stayed under 5K rpm. If I went above that, oil temperature would rise up towards 250, getting there in under 5 minutes if I continued at those rpms. Once it was above 200, it would cool very slowly after I dropped the rpms back under 5K.

After: I did a 25 mile ride this morning once I finished everything and although ambient temps weren't what they are mid-day, it was above 90F. Normal commuting the temps rose a little slower than normal, and stayed at 180F (the operating temperature of the thermostat) for quite a while. I was a little nervous at this point thinking perhaps I'd overdone it, and my oil wasn't going to hit the magic 200F to evaporate the moisture. Once I hit the freeway, it slowly rose to 200F (wheew) and STAYED THERE. I ran more than 15 minutes at 6k and the hottest it ever got was 205F. Once I backed off, it cooled right down to 195. Even a long sustained hill with a significant headwind at 5500 rpm in 5th gear didn't get it above 200. Once I pulled into the RedRock Recreation area and did a nice leisure cruise at 4K it cooled to, and stayed at, 195F.

So I'm judging the project a success. I MAY continue and install a different (more trick) cooler with stainless steel lines and Aeroquip fittings It will make it cleaner, but lot's more expensive. As it is, I think this could be duplicated for around $150.

Here's the thermostat and the hose routing. The normal hose from engine sump to tank was cut and put into thermostat in and out. Lines were then run across the front of the frame behind my Jesse sump guard to the cooler.
Here's the routing across the front. I used the OEM oil line, as I knew it would fit. On any subsequent kits I put together, I'm going to use Aeroquip hose. It's cheaper and at least as good, if not better. (Sorry it's out of focus, I guess my camera decided that the shock on my SherpaT was a more interesting subject).
The oil cooler installed on the right side OEM engine protection bar with a cable clamp. It's actually a differential cooler made for racing cars. I like it because unlike most oil coolers, it's not delicate. Most oil coolers are like a radiator and in that position would require a significant guard to avoid catastrophe. This one has heavy aluminum grating away from the cooling passages so it looks pretty durable. I wish I could fit it INSIDE the protection bar like I had originally planned, but the hose routing wouldn't allow it. (One reason I'm thinking of going an alternative route, one that mounts the cooler in front of the sump guard).

General Questions

Is it possible to use some kind of thermal insulation covering the inner side of your legs and the bike? Could this overheat the bike?

Can a slipping clutch cause overheating (on a GS)?

Coolant Squirting from Coolant Overflow Tank?

Can a dead battery cause overheating?