A have a German Mate riding an F800GS (??) - clockwise from Perth around Oz. I think he has till Christmas. He started having problems when he got as far North as Mount Magnet - he says he thinks it is the fuel pump and it sounds like it might be heat related.

This prompts me to ask a question I've had in mind for yonks - why is the fuel heating worse on some bikes than on others?

A BMW guru South of Brisbane told me the early K100 introduced in Oz experienced these problems regularly and OME cured it by fitting up-rated fuel pumps....

The logic isn't clear to me - why would circulating more fuel increase the heat loss more than the heat pick-up?

Unless the change to pump volume delivery was linked to return fuel being discharged into the air space in the tank as opposed to being via the old type non return valve which is under liquid most of the time?? I can imagine that this might then have resulted in the non wetted  (upper) part of the tank being able to contribute more to hear loss...

Any interest out there as regards batting this one around a bit?

AFAIK all the bricks were prone to it,my K1100 was so bad that I put a small cooler in the front on the grill in the return line.
Insulation around the lines helps as well as keeping the tank full as possible.
Aluminium foil crumpled around them, lots of layers and as wrinkled as possible for lots of area. Clark Rubber has rubbery insulation that is split for easy application, use white zip ties as they dont absorb the heat as much.

Aren't the white cable ties prone to UV attack?

I do hope other forum members will not be side tracked by cable tie and perhaps 'blinker fluid' issues....

rawdonball wrote:Aren't the white cable ties prone to UV attack?

I do hope other forum members will not be side tracked by cable tie and perhaps 'blinker fluid' issues....

UV will attack white cable ties, but until they fall off, they will reflect heat better than black ones. (Just don't tell Olaf, and especially, photoshop them out of any pictures.)

Given that the blinker fluid ducts pass near the tank for part of their passage, carrying away some heat may be an undocumented benefit. When did you last change yours?

Bill

As a proven 'hook line and sinker' guy, I feel it is already an over documented subject!

The back up fuel pressure relief valve incorporated in the fuel pump, strikes me as a potential source of variation. If one has a unit that relieves at a lower pressure than most - I presume this would mean that one would have to change the fuel filter more frequently but would it have an effect on the heat balance and therefore the equilibrium temperature of the fuel?

perhaps the question should be asked is your mate carrying stuff in a location that might contribute to heat retention around the tank - engine area ...front of tank and below ...maybe extra lights redirecting air flow away from the engine area ... tank bag with overhang etc ?

dave (tackler) has a similar machine ...I wonder if he has experienced similar

I would have thought that as heat affects the fuel that the viscosity would diminish affecting the pumping volume and pressure  .... in addition to the over pressure bypass relief valve never being able to be activated at higher temps  ...the machine might be running slightly leaner with the lower attainable fuel pressure and volume ...causing to run slightly hotter as well ..?? not to mention the absolute crap fuel out there ....89 ron at best I recon and quite possibly 10 % ethanol as well ...not the best

hope he is running slightly higher sae rated oils as well
\
was up in Townsville just a week or so ago ...nice 30 odd c near the coast.... cooking inland during the day .

Good points for me to forward to him thanks Chaz. 
When we were up in the Pilbara last week the two K bikes didn't seem to react to the fuel ever but the DR650 complained on a couple of occasions. 
Are you thinking that temperature related lowering of the fuel viscosity might reduce fuel pump volume to the point at which main FPR valve doesn't have to open at all to control pressure at a particular level of engine air intake. Further throttle opening would then result in leaner mixture and more heat (vicious circle effect)?

This would perhaps explain why BMW may have adopted the option of up-rated pumps as a solution...

the fpr would still be working ...kind of  ...flow will be reduced (and cooling effect as high pressure becomes low pressure, through a valve of sorts ) possibly near boiling on the way back to the tank by proximity and slow flow ...but severe lag in maintaining pressures is what in thinking rawdon ...especially at some kind of throttle opening speeds and delivery to the injectors ...but you got the drift I guess

you never really know what has happened during the assembly process ...could the return line be routed the wrong side of an interference ...had a mate recently with a brand new bike fail completely 16 k s out in the bush deep valleys

the assembler had routed the pump power cables across - close to the exhaust .....didn't take long to burn through the plastic resulting in pump failure ..blown fuse that could not be fixed ...dead $14,000 bike after 18 ks ...no phone works out there  and dickhead left the handheld radio  in the car
in the haste to test it all out

/

do you think that there maybe a possibility of picking up some air con refrigerant insulation pipe stuff  to overlay the fuel lines ...and installing it ...might help a little and cheap as anything to buy

just another thought ...some recent vehicles have an integral fpr in the pump housing ...so just insulating the pressure line may help on its way to the injector ....cant do anything about the accumulated heat if this is the case ...but to free up the cool air feed around the tank ? plastic panel air redirection maybe ????





good luck

My first K was an 85 K100RT.  The fuel would boil with monotonous regularity once it got about half tank on a hot day.  Generally I was glad to get off the bike anyway at the time (I dont like heat).  I'd also heard about the uprated pump being the answer.

Re the blinker fluid issue, how much does the viscosity of the fluid affect the blink rate and do you need a special viscosity fluid if using LED blinkers?

Al

Even the fifth year I spent trying to get through a four year degree is no help to me on the  blinker fluid issue....

Can we not get an electrical boffin somewhere to compare the current draw of fuel pumps with and without the fuel heating problem. The trouble is that there are too many variables like fuel viscosity and ambient temperature

I reckon the fuel lines, being directly behind the radiator and continuously circulating will eventually bring the fuel temperature up to ambient temperature behind the radiator. At 35c outside temperature and coolant at about 90c it has to be between the two, in slow traffic the radiated heat from the engine also increases it. As the level drops fuel is circulated more and the effect of the cooler fuel in the tank is surely lessened. Fuel in tank is cooler but can't fall below the same 35c.

Add a tank bag and there is even less cooling of the fuel in the tank.

A fuel pump in good condition will have less friction and therefore less heating. Other option is the often mentioned fuel cooler.