Boiling Gas

[Jimbenge]

Several times I have opened the gas cap on my 1993 K1100RS and seen my gas boiling.  I think the problem may be the fuel regulator, it being metal I believe it is absorbing engine heat and when you stop I think its pushing that hot gas back up to the fuel pump and it must be boiling as you get air bubbles as well.  The tank seems to have an awful lot of pressure as well, sometimes the check valve moans like crazy and when I open the gas cap there is a lot of pressure ?  Has anybody else observed this ?  Has anyone ever relocated the Fuel regular to a different spot that is not exposed to so much heat.  I pull a trailer which is probably contributing to the heat problem.  I did the K100 3 row radiator swap and fan switch mod which have helped but it is still one hot ride.  Any ideas would be greatly appreciated.

[Motorhobo]

I've never had my fuel boil...ask Johnny about that and maybe get yerself  a 'Johnny blanket'.

Actually I have no useful contribution to make to this topic and am only replying so I can say, "Cool avatar -- wish I'd thought of that!"

[Inge K.]

Some of the Aussie members at the "K100 Forum" have added a fuel cooler and isolated the fuel hoses and rail,
have used oil coolers from cars if I remember correctly.
About your vent problem, search the "cup" in the Lieberry.

[johnny]

this is what boiling ethyl looks like...





j o

[racinrich]

alcohol is the enemy, oil cooler on return line will help and a johnney blanket . puregas.org find no alcohol fuel near you.

[Jimbenge]

Now that you mention it, a couple of weeks ago my wife and I (and trailer) went from San Diego to Saint Paul Minnesota (and back) to the BMW National Rally and were forced into using fuel all thru the central states that had corn in it (never more than 10% though) although I did see several places that had 20 & 30 % alcohol in it.

[Jimbenge]

Hey Johnny:

Those pics look just like my tank and gas boiling problems, Same color of bike too.  You been drinking alcohol too?

[johnny]

nopes... butts ive been known to have a bowl of corn weed chowder to take the edge off...

j o

[K75RT Keith]

If you ride with a tank cover, take it off.  I remember reading that they trap the heat and can cause the tank temperature to increase. 
Check the insulation under the tank and consider adding a johnny blanket made of mylar sheeting or Koolmat. and insulate the return fuel line from the FPR to the tank.  Apparently the routing past the radiator increases the temperature enough that when added to the heat from the fuel pump it's enough to bring the ethanol to a boil     

[pdg]

the fuel regulator, it being metal I believe it is absorbing engine heat and when you stop I think its pushing that hot gas back up to the fuel pump

The fuel is circulating all the time the engine is running. The pump runs all the time and the FPR just keeps the rail at the right pressure. Anything 'over' is returned to the tank. The fuel goes through the pump, then to the rail, then the FPR and returns to the tank.

This is where some of the 'problem' comes in - the fuel is constantly picking up heat from the engine and taking it to the tank. If it weren't for the return line you would never get enough heat in the tank to notice.

It's not a regulator like you would use on a gas bottle (LPG/propane, not gasoline - just to clear that up), it's a bypass regulator, hence the return line to the tank.

Relocating the FPR and lines is certainly possible - put them anywhere you like, they don't care, they don't even have to be under the fuel level so if it really bothers you put the FPR up on the 'bars or fairing to get some air around it.

[WayneDW]

I put a piece of left over foam pipe insulation like you can buy from Home Depot around the return line.  I think it helps!

[hartrepair]

I did relocate my regulator to the left side NACA scoop. I also made a duct to blast the air past the regulator and down the fuel rail. I insulated the fuel lines as well. There is a "show and tell" on the forum somewhere. The super hot fuel tank is not a problem now. However at ride to Mojave Cal was hot...everything was hot, fender to fender.

[The Mighty Gryphon]

I am doing the blankets and manual fan switches on my two K's this winter to keep the tanks cooler.  Looking at the fuel system plumbing on my 100 I wonder why I can't run the fuel pump output to the front of the rail and connect the return line with the fuel pressure regulator to the back end.

Putting the regulator outside the fairings should get it away from most of the engine heat.  Can anyone think of a reason NOT to do the switch?  Seems to me the rail doesn't care which end it's fed from.  Looks like it will make the hose routing a bit neater as well.

[Scott_]

One small advantage of the current hose routing and length, tank front to rear of the rail, allows you a small amount of flexibility to be able to remove/relocate the fuel tank to the rear of the bike without totally disconnecting the lines 1st.

[F14CRAZY]

Aside from dealing with the heat on your legs, is boiling gas really a problem? Seems like it would remove any moisture in the tank

[billday]

Could a blocked or malfunctioning gas cap/gaskets cause or worsen boiling gas?

[Scott_]

Could a blocked or malfunctioning gas cap/gaskets cause or worsen boiling gas?

I would doubt it as the tank is supposed to be vented, either to the atmosphere or crankcase.

[jayskerdoo]

Hey, sorry to resurrect an old thread but I am looking to do the fuel cooler on my '95 K11LT and am in need of quick piece of advice. Should I install the cooler into the fuel plumbing after or before the fuel pressure regulator. It looks like there is one hose from the right hand rail into the back of the fuel pressure regulator, one vacuum hose into it from the bottom, and then a hose from the top of the fuel pressure regulator back into the gas tank. My initial thinking was to do it after it comes out of the fuel pressure regulator.


What do you think? Has anyone done this one way or the other and had a successful result?

[Laitch]

. .  am in need of quick piece of advice.

How quick?

Read this thread. The Mighty Gryphon also elaborated later: The cooler goes in the return line from the pressure regulator to the fuel tank so there is no real backpressure.  I have been running a cooler for two years and 15,000 miles now with no adverse effect on performance, if anything by keeping the fuel cool the higher density makes the mixture a tiny bit richer, possibly increasing the power by an infinitesimal amount.

[jayskerdoo]

Thanks for the response. I have time as it is still under 40 degrees here in Chicago and my 5000 mile round trip is 3 months away. I read this thread and the only clarification I was able to receive from it was that the cooler should be placed on "the return line where the pressure is only high enough to push the fuel back up to the tank"[/size]and that I should make sure it is[/size] "[/color][/size]installed on the return line so it's not under fuel pump pressure".[/color][/size] This was a tad bit confusing to me which is why I was seeking clarification. So the fuel needs to already be under pressure from the fuel pump regulator for it to be cycled through the cooler fast enough? This would suggest that my initial thought of installing it [/size]after[/size] the fuel pump regulator while it's on the way back to the fuel tank was correct? I'm assuming this is the norm and that there would be adverse effects if installed otherwise.
[/size]
[/size]Jason

[jayskerdoo]

I think my response got cut off by some formatting anomaly. Anyways, so the cooler must be installed after it has pressure from the fuel pressure regulator to properly cycle the gas through it? I'm assuming (at this point) that this is the normal installation procedure and that there would be adverse effects if installed otherwise....


The other posts I read never clarified on which side of the fuel pressure regulator it should be installed on, and only that it should be insterted "in the return line where the pressure is only high enough to push the fuel back up to the tank". This means after the fuel pressure regulator then, correct?


I apologize if this is obvious information to some, but this is my first fuel injected bike. I'm used to dealing with carbureted systems and gas tanks that don't boil gas! :dunno

[beemerphile]

From this retired chemical engineer with a lot of heat exchange experience, either will work.  If you are concerned about the pressure rating of your cooler, the pressure is lower after the regulator.  Some will say that it is also later in the line, so you won't pick up as much new heat after you cool it.  That is true, but is offset by the fact that the fuel will be hotter before you START cooling it.  I wouldn't expect a significantly different return fuel temperature either way.  Theoretically it will be lower if installed later in the line because the "approach temperature", which is the difference between the temperature of the exit fuel temperature cooling air temperature, would be a bit higher. 

[The Mighty Gryphon]

I installed mine in the line from the regulator to the tank.   Mainly because it made the plumbing easier.  Mine is on a K75RT and the 3 cylinder motor being shorter made it possible to put the cooler in front of the engine.  Not sure where I would put it on a K100 or an 1100.


My only advice would be to avoid coolers with thin walls.  You don't want any small holes to occur in your cooler.  I used a cooler with an extruded body which should be able to take anything the front wheel can throw at it.

[bizzaro]

Aside from dealing with the heat on your legs, is boiling gas really a problem? Seems like it would remove any moisture in the tank

It makes my bike stall. Vapor lock or something like that I guess?  And before it stalls it will cough n sputter intermittently.  I pull over and let it cool down, then put some fresh gas in it pronto.  And it doesn't happen again till the next time the stars all align just right.  IE: Very hot day..above 85.  Driving hard, mid day and high sun beating on my tank, and usually about half a tank or less of gas.  I almost never run corn, and I don't have a tank bag.  I do have the original tank insulation and added a Johnny blanket. 

I like Gryph's idea of moving the FPR. It is buried right on top of the engine. But it happens so rarely, it is usually not a problem.

[The Mighty Gryphon]

Boiling gas isn't hot enough to boil off any moisture.  While I've had boiling fuel before the cooler, I haven't had any issues with vapor lock.  My cooler has kept the fuel cool even in 110F temperatures in New Mexico and Utah.

I wasn't the one who relocated the FPR, although it sounds very attractive to put it out where it is easier to get at the plumbing.