I have a 1987 K100, and find that in hot weather the fuel tank can get so hot it starts to boil the fuel (at low levels). Any suggestions?

Thanks

The tank comes originally with 3 pieces of insulating material. This material is glued under the tank.
If your bike has been repainted, there is a good chance that this material has been discarded.
See the picture for part #s

High and thanks for the reply. I've had the tank off several times chasing this problem, its the original paint work and the insulation is still in place. So still scratching my head, but thanks for the reply.

I read about a similar problem on another forum some time ago. In that scenario the fuel return hose at the front corner of the tank was being exposed to too much hot air coming off the radiator and fan. This was causing the tank and the fuel to get very hot. Try insulating the hose and see what happens. Just a thought.
Cheers
Jeff

I have a 87 Motorsport. The K bike fuel system is a closed loop system: the fuel is constantly circulated through the tank by the fuel hoses exposed to all the heat from the radiator. You figure the heat from the radiator is 200+deg. Thats HOT.

Using plumbing pipe insulator(the cheap grey stuf from Home Depot) cover all the fuel line. You need to remove the airbox to get the return line from the regulator and cover the fuel rail too.

Ive done this and the tank never gets hotter than ambient temps. This doesnt solve the hot air coming from the radiator but keeps the tank cool. To solve this I used some firewall insulator(1/4 " fiberglass with aluminum cover) to force the air out of the side vents.

Amazingly....the last year of the stock k11rs('96) has all these mods done...and no insulation under the tank??

as weel dont let the tank get too low
in cars if the pump[which uses fuel for cooling] gets too hot will fail

Hi Folks,
Really important point from red green because heat is merely uncomfortable whereas a dead fuel pump is a major karate chop to the bank balance. You go into the dealer who says "Hold out your wallet and repeat after me - Help Yourself" The points made above are exactly what is recommended in several K related keeping cool comments. To précis the advice on the net get some heat insulating plastic or rubber foam that is designed to insulate and be exposed to the 100 C air coming off the radiator and engine and using that insulation and 3 M glue like their excellent General Trim Adhesive use that to block all points where hot air can leak from the high pressure air zone behind the radiator to the lower pressure zone around your legs. A very large amount of the hot air will then go out the side vents. Insulating under the tank is a good plan as is insulating the fuel hoses. A number of people who live in quite hot parts of the US like Texas have successfully insulated their K Bikes until they have progressively blocked off all the heat they can.

Look up insulation suppliers in the Yellow Pages and ring around for those who sell the heat insulating foam in sheet and pipe insulation, Armaflex is a proprietary brand and is of very high quality. You may well find if you talk to industrial air conditioning installers who put in the big plant they will let you have off-cuts from a job. You don't need much compared to the cubic metres they use on a job.
Regards,
K-BIKE

I am currently working through all the ideas already posted on this and other forums. I have insulated the fuel lines as per abreeze and the next step is to insulate underneath the tank as much as possible with some self adhesive car firewall/ underbonnet insulation which is quite thin but designed to reflect radiant heat so we will see how it goes.

Now a question. A suggestion from another forum (IBMWR?) was to remove the large rubber seals from around the fork legs that join to the fairing which was done before I got the bike but the idea is to fit some small air scoops that will direct air up and also cool the tank. These were supposedly available as a mod from BMW. Any ideas before I try and modify something else.

With luck I will have it all done just in time for the cooler weather

Regards,

Phil

I have the modified scoops installed on my rt and they do help in the hot weather. Also I have insulated everything. The bike runs better in hot weather.

moorefsd wrote:I have the modified scoops installed on my rt and they do help in the hot weather

Any chance of posting a photo and were they available as a spare part or did your bike have them already fitted.

Regards,

Phil

Part 22

http://www.realoem.com/bmw/showparts.do?model=0504&mospid=47867&btnr=46_0118&hg=46&fg=48

Thanks Rene, not quite what I was expecting them to look like but would certainly help.

I have also seen a post regarding fitting a vent in the lower part of the screen which Bert suggested a while back so will be worth doing when things warm up again down here.

Regards,

Phil

Remember those Vetter Windjammers? I have one on my Honda CB750K (1980) and they had vents in the screens, which helped to equal out some of the pressure difference over the screen. That was great to reduce some of the noice around your head.
The 1100 had a vent in the lower part of the fairing, at the sides, which allowed a lot of the heat build up to be reduced. Maybe that's an option?? Cheers, Rene.

BTW, just bought a set of the scoops with fasteners etc for about £5.00 from MotorWorks (second hand scoops, new fasteners) How's that for a deal!

Good deal indeed but I think I will have to fabricate something as I could not justify the freight.

Do you really need them in Scotland?

I am pretty sure I will be able to do without them here for the next few months at least.

Regards,

Phil

Phil, you're right, but here's me waiting (wishing!!!!) for summer.

Do you realy feel that shipping would be expensive? If you're willing to wait..................maybe by snail mail.

Hi Rene, the "trouble" if you like with Motobins etc is that everything is sent to the colonies as express freight which is excellent service but not cheap (about 30 GBP) so unless I was to buy something else..... it is a tad on the expensive side.

I am sure I can make up some sort of hideous replica that will do the job now I know what they look like.

Regards,

Phil

Hey, I was seriously considering installing some computer fans on the fairing to extract the heat from the engine. This is cheap

Hi Bert I was flirting with the idea of Peltier Effect plates but that would probably have involved some sort of large heatsink out in the airflow but perhaps another challenge for you engineers out there

Regards,

Phil

Spooky
When was the last fuel filter replacement?
A fuel pump working very hard does what? Draws more current to get the job done..It Draws a ton of current under heavy load then some of which gets lost as heat.
The fuel is a natural coolant for the pump and as the level of the tank drops the remaining fuel gets hotter, you know where this is going.
Pop the fuel pump fuse out and insert an amp meter in it's place then start the bike,after things settle into an idle compare your current draw to a friends K bike and that will tell the story.

Pain is the teacher

Helmut118

Helmut,

You get a very good point about a clogged fuel filter.

I personally always try to refill the tank when the 7 liters warning light comes on. This way, I always have enough gas to keep the pump immersed and cooled down.

Bert

Hi All,
The air scoops are available from your friendly BMW sealer and I bought a set recently here in NZ and although I can't for the moment recall what they were I thought the price was OK.
Regards,
K-BIKE

Brisbane Queensland Australia.

4 hour ride up and through the mountains.

The end result - of course this is through my heavy deams jeans, (Inside left thigh).

Thanks for all the above advice I will do everything suggested - unacceptable condition currently.
(I used to see those big rubber pads on the side of the tanks in photos and thought, Ummm, good for down hill breaking - now - I think, Ummmm I'm not going to catch on fire !)



Full tank of petrol - 20Lts of very hot petrol between your legs is not a nice feeling -
and yes, I do understand the physics of the "BANG" factor and what has to be in place...., however, un-cool........

My legs got burnt like a bad sun burn on the K100 but the knee pads made the K1100 better, the biggest improvement was placing a small auto trans cooler in the return line and having it in front of the radiator. I need to get another one for the chookie so can pass on details, from memory it was about $80.
Also if you have a look on fleabay for go kart fuel coolers and put 2 or 3 in series in the return line. I recall someone here using one and claiming success in the war on hot tanks.

Thanks Rick G,

Mate I had to reverse the rheostat in the fuel tank level sensor to make the new fuel gauge work, I had been worried that I had done something, even though it was not logical. I feel better now, I'd like to see some pics of oil cooler, I like the idea.

Mark, check out Charlie's reno thread...around page 12 or 13. He's done the mod with the fuel cooler and it works well.

Thanks blakey, I'm glad its not just me. Charlie is a local so he has obviously had the same problem.

I think rick and I have the same device mark

heres a pic so you might be able to chase up the numbers

note mine has 9mm barbs ....so 8mm line just fits on it ok



I mounted mine up like this using nutserts to the aluminium frame ..and some uchanel aluminium  and 4mm bolts  washers etc all stainless



this is shown on the 2 core radiator for clarity ...but will be retro fitted again to the 3 core radiator once the fuel mixture and running is sorted out a little more ...(think my orginal afm is faulty after a swap over ...measurements to come )

but the result is a much cooler tank .....it wont solve the heat around the inner thighs altogether ...that's just a constant blast from the airflow from the radiator ...but will go a long way to help

more details of some other mods to air cooling into the under tank area are about to happen

hope that helps

Thanks Charlie, I have some down time to do the mod.

Mine is the same as that and is attached to the grill of the fairing with 2 hoses going over the top of the grill to the tank and FPR.

I saw a very nice little oil cooler off an R bike yesterday with its own little fan that I fancy I can install some where within my fuel system.

I will up date with photos when available......