Well, the summer's almost over here in New England, and it's time now to release the results of an insulation test aimed to reduce fuel tank overheating on the early models.

The RT was the last of three models to be released in 1984, the others being the RS and the K100. The only plan for insulating was to add reflective strips glued to the bottom of the fuel tank, and a foam rubber sleeve on the return fuel line. As the summer of '84 wore on it became apparent this had been inadequate as many an owner reported over-heated fuel tanks.

The only change made to the RT in the '85 model year was to remove the fork boots that sealed the underside of the faring, and attach air scoops to the back of the openings. This approach had been a small improvement, but bikes continued to experience over-heated fuel tanks while operating in heavy traffic, stop-and-go urban riding, or in desert conditions.

On this board, the recommended method of eliminating fuel tank over-heating is through the addition of a fuel cooler, which circulates the fuel return line through a separate radiator attached to the main radiator. This method is the only real solution to desert riding conditions. 

-continued-

My own experience in two years prior was that in normal summer heat the fuel tank gets very hot when riding in stop-and-go traffic. And, once the tank gets hot it does not cool off again even after prolonged riding at speed. The only way to cool it off is to let the bike sit overnight--so much for air scoops.

As a semi-retired aerospace engineer, my initial thoughts were that BMW had done a poor job insulating the bike. The RT faring trapped a lot of heat, so in theory one should try to keep heat from reaching the tank in the first place. The plan is to add insulation wherever possible to prevent engine heat from rising up and around the fuel tank.

During the winter of 2013-14 I disassembled the RT faring and began looking for ways to add some basic insulation. There are three places where insulation is easily added; on top of the engine, under the fuel tank itself, and on the sides of the tank around the faring.

The results of the test were very satisfying. I can now report that adding insulation was successful in reducing heat build-up within the fuel tank. At most the tank got slightly warm, but only barely perceptible to the touch. The fuel lines were still exposed to engine heat, which resulted in gradual warming of the tank even while running at speed. The '85 model has an amber 7L low fuel light that comes on when the tank reaches a certain temperature, and this light came on fairly regularly during summer operation.

My recommendation is to follow good insulation practices on all models before considering the added weight and complexity of a fuel cooler. Granted, here in New England, the temperatures rarely get above 90degF, but in all likelihood the insulation kit should make a vast improvement over non-insulated bikes no matter the environment.

Give it a try, it's easy to do and doesn't cost much.

Most everyone should appreciate the difference it will make.

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The air box covers the rear half the engine, and that does a good job of insulating. However, there's a large patch of engine exposed between the air box and the rear of the radiator.

Cut a piece of pink insulation to fit this space.

Apply some reflective tape to the bottom side to keep the heat from rising up. Bolt the insulation down at the spot indicated.

The thickness of the insulation should not interfere with normal air flow passing through the radiator.

good recommendations aj .....well at least for the more heat challenged  environments  that many of us experience

I  must admit that in 20 c  or so environments the heat issue does not really exist as a major concern in fact it is a benefit an temperatures below 20 c



but for us 30 - 40 c ambient riders there is a major comfort issue

I might add that the fuel cooler only adds about  600 grams to the weight  of the bike ( a little over a pound  if im thinking right )
tank is consistently at ambient now days ,




cheers  !!!!

The tank has reflective tape underneath, but still there are regions where heat can accumulate due to poor air flow.

Cut two strips of pink insulation and lay them into the channels under the tank on either side of the frame. Do not disturb the fuel cap overflow container (top right).

Heat can still rise up and around the fuel tank, and this creates a problem for the rider as well. By insulating these gaps both the fuel tank and rider are removed from engine heat.

Cut two strips of insulation to fit alongside the tank under the glove boxes.

These strips are visible in gaps between the tank and the faring, and so if desired one may spray paint the insulation black so it doesn't stand out so much (unless of course you have a pink bike).


Caution: With the underside of the faring exposed to the elements the front edge of the insulation can get wet, causing it to stick to the surrounding materials. This is a minor problem for which there is no solution as of yet.

charlie99 wrote:good recommendations aj .....well at least for the more heat challenged  environments  that many of us experience

Thanks Charlie. Few bikes approach the sophistication of the Grey Ghost (the mighty K, etc.).

I'm really surprised that BMW didn't insulate the K100 more. Did they really go straight from testing the naked K in northern Germany to a fully fared bike without considering heat build-up? It's crazy. :suspect:

Ah, pink batts, an obvious solution.  No need to burn the Midnight Oil here.... 

Just a thought, as there appear to be a few people with electronics background on the forum, but how about a couple of extractor fans.  The type fitted to computer towers for example.

I had a yarn with Charlie via pm protocol a couple of summers ago, with regard to using a smaller radiator and ducting cooler air under and over the radiator to cool the engine compartment and the tank and ducting a fully enclosed exhaust duct to remove the heated air. We bounced the idea of a 2nd radiator under the engine to carry the 1st cooling effort then allow it to go into the main radiator before the thermostat, also considered a new radiator but fitted in the R/H side fairing side panel with ducting to send the heated air out that way. Don't know if Charlie ever started any of it, but I tore mine down for a new paint job and clean up so maybe next summer it will become a priority again. I wonder if the pink batt would sogg if riding in the wet? and whether that would lead to corrosion under it?????

TacKler wrote:Ah, pink batts, an obvious solution.  No need to burn the Midnight Oil here.... 

Just a thought, as there appear to be a few people with electronics background on the forum, but how about a couple of extractor fans.  The type fitted to computer towers for example.

computer fans will flow some air ....but nowhere near enough ...they are low torgue devices with only a few watts (3 or 5 or so watts)   of energy ...good for ventilating a small enclosure if kept out of the main airsteam, they have little if any volumetric flow if placed in a low pressure suck type situation ...they cavitate like crazy and the bearing structure is terrible in an external environment .
compared to radiator fans in the many 10 s of watts ,  like 70-90 watts for the main fan for example  and a heap more volumetric flow at pressure .

there are purpose built smaller fans for this heat flow function if you search around

I agree pink batts around under the tank electrics section is a little risky ...the ecu relies on some airflow through there to  keep cool , in fact the plastics around the head stock directs  air up under the tank whilst in motion ...I would have thought they would have gone to that design lengths unless some need existed .....

just a contribution

Hey Charlie did you go ahead with the ducks bill air duct idea at all????

things are still progressing keith

have a few of the things I need already , but looking for others as time goes on . currently looking for a bit of 6mm aluminium plate for the afm to mount up to and a bit of profiling for the inlet area  so it all looks nice ...and will take a standard car filter on that mount . 

the flow through the radiator will bypass my legs and exit about the battery from the tunnel created down the centre

currently hopefull of picking up as head gasket and valve stem seals from alby , in the not to distant future ...there is no rush at all with this.

K75cster wrote:I wonder if the pink batt would sogg if riding in the wet? and whether that would lead to corrosion under it?????

Good question.

Ya, some insulation got a little wet under the glove boxes because the faring is open around the forks. But, it's mostly plastic and rubber in that region, so not a rust hazard. I'm considering covering those insulation strips in reflective tape to alleviate any future problems.

Doubtful the bit on top of the engine and behind the radiator could wick any moisture since that area is high temperature to begin with. Does rainwater get past the radiator? I hadn't considered that.

The strips under the tank are too far removed from any source of moisture, so no problem there.

charlie99 wrote:
I agree pink batts around under the tank electrics section is a little risky ...the ecu relies on some airflow through there to  keep cool , in fact the plastics around the head stock directs  air up under the tank whilst in motion ...I would have thought they would have gone to that design lengths unless some need existed .....

Good point.

The ECU has some ribs on it and looks like it was designed to shed heat. The unit resides in the front of the cable bay, but the insulation only begins at this point. So, the ECU still receives the benefit of air flow passing through the radiator and beyond. The other bit of insulation on top of the engine also helps keep air temperatures in this region from rising while bike is moving or stopped (assuming the radiator fan is working too).

Pondered the question of air flow under the tank for a good long while. Hot air seems to linger in this area, keeping the tank warm even after the bike is parked. Initially thought of installing small exhaust ducts around the relay box to allow hot air to exit from under the tank while the bike is in motion. But, there are just too many obstructions to permit good air flow.

So, that's when I decided to go the opposite direction and look at insulation. So far it's working great. Cheap, easy to install, and easy to remove for maintenance. Anyone can install these strips. It's just two bolts under the seat to lift the tank enough to lay them in.

one good thing if the insulation does get wet when you are out in the rain, I suspect it will dry rather quickly behind the radiator when the rain stops, be interesting to hear what you find out after it rains.

K75cster wrote:be interesting to hear what you find out after it rains.

This winter I'll remove the faring and have a look. Will post pics.