Recipe is 1/2" copper tube, washers big and small, a nylock nut, a regular nut, and one fancy knob in the threading of your choice. I think it's about $5 per pin, but I bought a value pack of fancy knobs a while back 10 for $20 or something.
4 Gal Rotopax - stock 570 roof rack
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That was me. It’s anecdotal for sure but I had tons of expansion the first year and had to vent all the time. At one point I had gas bubbling in the rotopax from the pressure, enough that it sprayed out at me. Last summer I put premium in it instead and it hardly expanded and never seemed to really need venting
I’d be curious if others do the same what their results are
I’m definitely going to give it a try the next time I haul extra fuel for a weekend trip. Locally we don’t have extreme altitude changes, but camping excursions in July / August are pretty hot
Will definitely report back, good tip @linuxgod !
Expansion seemed to happen with both heat and elevation. 2 years ago we went from Chicago to Telluride then Santa Fe and Big Bend, all in July/Aug. I had one stretch between Denver and Telluride where we nearly ran out of gas on 285 in Jefferson IIRC... apparently the gas station there was no longer open. I'd vented the Rotopax that morning, but I went to use the Rotopax (which was bulging) and it sprayed fuel out as I opened the can. I had to let it vent for 5-10 minutes before I could safely open it at which time the fuel inside seemed to be bubbling. I had several other days where I'd vent the rotopax in the morning, both in CO as well as in NM and TX, and regularly it was bulging when I opened it (though occasionally I'd descend in elevation and it would be under a vacuum). Keep in mind I mount it horizontally, but when I fill it vertically it's nearly full before I close it up. Each time I filled it was 87 octane (even in CO I ran 87 all trip).I’m definitely going to give it a try the next time I haul extra fuel for a weekend trip. Locally we don’t have extreme altitude changes, but camping excursions in July / August are pretty hot
Last year I put premium in it before I left Chicago (so I know it was 91+ octane and 10% ethanol content) as I decided to run premium while towing since I felt like I was losing power at times during the trip the prior year. We did Chicago->Ouray->Vegas->Sequoia NP->Yosemite last year and the RP rarely bulged and I only vented it every few days (and even then it was just a little puff). Mileage was basically the same but the truck ran better (never felt like it was bogging down) as well. Again all very anecdotal so I'm really curious your experience and others, but I'm going to do the same thing this year.
Incidentally despite all the bulging and boiling and the fact my RP is strapped horizontal to my roof rack, it's never leaked. I just strap mine down with kayak lashing straps, though they will stretch slightly and allow the RP to move 1/4-1/2" over time so they do need to be retightened every few days. I've considered a proper RP mount but (a) I've heard of people with locking versions where the locks rust and can't be turned, and (b) with the way the RP swelled the first year I'm afraid if it swells while mounted I won't be able to turn the handles to remove it - I had a helluva time trying to get the lashing straps loose when it swelled in the example above and I can imagine a situation where you can't turn the metal handles without venting which in the horizontal position would spill fuel all over the roof. That said mounted vertically it would be fine because the air would be at the top of the can and easy to vent.
Personally I'd really like to find some adjustable latches with J-hooks on both ends... something like this but with hooks on either side and with a more rounded J hook to fit around the handle, so that when you tighten the latch it would pull both sides tight. If anyone knows where to source what I'm thinking of please PM me.
Amazon product ASIN B07438CCTR
Side note: if you do buy a RP I also highly recommend throwing the carb-compliant nozzle away and buying the water nozzle for $10 from Amazon. I used the carb nozzle the first year and aside from it pouring about 0.5 gal/min it's a huge PITA to use and like others on the forum resulted in my spilling fuel more than once.
Amazon product ASIN B004ETRWLS
Anyone with more knowledge have a reason fuel can boil other than it simply being too hot for the pressure on it? My 80 boiled fuel right out of the tank on a trail in colorado. I can't remember whether it was ethanol free, but likely wasn't premium.
I do remember reading about someone with rotopax in the fancy mount expanding and not being able to get the thing off the bracket when needed. That's exactly what prompted me to ask about expansion.
I have five gallons of RUG in a MFC for parts cleaning, it expands like crazy even when not at high temps. I might try filling it with premium to see if it makes a difference, as an at-home experiment.
I do remember reading about someone with rotopax in the fancy mount expanding and not being able to get the thing off the bracket when needed. That's exactly what prompted me to ask about expansion.
I have five gallons of RUG in a MFC for parts cleaning, it expands like crazy even when not at high temps. I might try filling it with premium to see if it makes a difference, as an at-home experiment.
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- #26
I did get the yellow spout as well 
I could try ethanol free. I could get it at a Love's.
I could try ethanol free. I could get it at a Love's.
RET2
SILVER Star
Ever think about adding a couple of those 8020 aluminum crossbars?
- Thread starter
- #28
FIlled it up...and was curious...
FrazzledHunter
SILVER Star
I have indeed. I followed a thread a while back that did just that.
I'm also thinking about getting 1 or 2 more additional OEM crossbars for extra strength or to just use one to add a fairing on the front.
Here you go...
Octane number as a function of boiling range
The octane number decreases in general with increasing boiling range [1], [2]. This. effect is, however, different for different types of fuel. It is more pronounced for straight-run gasoline [2]. This is probably due to greater variation in the composition of straight-run gasolines as compared to reformate or racked gasoline.
Increasing the mid-boiling point tends to decrease octane quality [2], [3]. Increasing the mid-boiling point from 40 °C to 180 °C is accompanied with a decrease in the motor octane number. The magnitude of this decrease depends on the type of fuel. It ranges between 42 for straight-run gasoline to 6 for catalytically cracked gasoline [2].
Effects of the initial boiling point (IBP) is significant because light compounds in gasoline (C4 hydrocarbons) have high blending octane values and increasing the IBP can substantially reduce octane quality.
Similar effects are observed if 90% boiling point or final boiling point is changed, because even though the higher boiling fraction of gasoline is relatively high in aromatic content the total gasoline fraction is low in octane due to the diluting effect of a high paraffin content. Hence, a reduction in the final boiling point can result in higher overall gasoline octane [2].
Increasing the 90% boiling point seems to decrease the octane number in most cases with the exception of the catalytically-reformed naphtha where a slight increase in the octane number is observed. The octane number of the catalytically-cracked naphtha on the other hand, is not greatly affected by the 90% boiling point. The different relative amounts of aromatics and paraffins in the naphtha fractions is the most likely explanation for this anomaly.
A close study of the relationship between the octane number and boiling range indicates that for higher octane numbers and lower boiling temperatures (50%, 90% etc.) the correlation tends to be more significant. The change in octane number ranges from 5 for gasolines of 40 °C mid boiling point to 41 for gasolines of 180 °C. Similarly the change in octane number ranges from 19 for gasolines of 140 °C (90% boiling point) to 41 for gasolines of 200 °C [2], [3].
Method of Study and Results
To ascertain the relationship and correlation between the octane number and the boiling range, data were collected from the Octel Co. [4] and the Horns Oil Refinery (HOR) in Syria (platforming unit) as well as from other sources including the Banias Oil Refinery in Syria. A total of 1142 value points were used in the analysis. Regression Analysis of these data (using the least squares method) was carried out using a specially-prepared computer program [5], [6]. The boiling points considered in this analysis were the 10%, 50% and 90% boiling points as measured by the test method ASTM D86 (measured to the nearest 1 °C). In each case correlation factors and average errors were computed for the best correlations.
These optimum correlations did not however lead to simple easy-to-apply equations. For this reason straight-line correlations assuming linear relationships were included for comparison purposes.
Three runs were tried for each boiling temperature. The octel data were used for the first run. Data from HOR-Platforming unit were tried next, and finally both Octel and HOR data as well as data from other sources were used. The results obtained are given in Table 1, Table 2, Table 3.
Table 1. Optimum and straight-line correlation between Research Octane Number and 10% boiling point
Octane number as a function of boiling range
The octane number decreases in general with increasing boiling range [1], [2]. This. effect is, however, different for different types of fuel. It is more pronounced for straight-run gasoline [2]. This is probably due to greater variation in the composition of straight-run gasolines as compared to reformate or racked gasoline.
Increasing the mid-boiling point tends to decrease octane quality [2], [3]. Increasing the mid-boiling point from 40 °C to 180 °C is accompanied with a decrease in the motor octane number. The magnitude of this decrease depends on the type of fuel. It ranges between 42 for straight-run gasoline to 6 for catalytically cracked gasoline [2].
Effects of the initial boiling point (IBP) is significant because light compounds in gasoline (C4 hydrocarbons) have high blending octane values and increasing the IBP can substantially reduce octane quality.
Similar effects are observed if 90% boiling point or final boiling point is changed, because even though the higher boiling fraction of gasoline is relatively high in aromatic content the total gasoline fraction is low in octane due to the diluting effect of a high paraffin content. Hence, a reduction in the final boiling point can result in higher overall gasoline octane [2].
Increasing the 90% boiling point seems to decrease the octane number in most cases with the exception of the catalytically-reformed naphtha where a slight increase in the octane number is observed. The octane number of the catalytically-cracked naphtha on the other hand, is not greatly affected by the 90% boiling point. The different relative amounts of aromatics and paraffins in the naphtha fractions is the most likely explanation for this anomaly.
A close study of the relationship between the octane number and boiling range indicates that for higher octane numbers and lower boiling temperatures (50%, 90% etc.) the correlation tends to be more significant. The change in octane number ranges from 5 for gasolines of 40 °C mid boiling point to 41 for gasolines of 180 °C. Similarly the change in octane number ranges from 19 for gasolines of 140 °C (90% boiling point) to 41 for gasolines of 200 °C [2], [3].
Method of Study and Results
To ascertain the relationship and correlation between the octane number and the boiling range, data were collected from the Octel Co. [4] and the Horns Oil Refinery (HOR) in Syria (platforming unit) as well as from other sources including the Banias Oil Refinery in Syria. A total of 1142 value points were used in the analysis. Regression Analysis of these data (using the least squares method) was carried out using a specially-prepared computer program [5], [6]. The boiling points considered in this analysis were the 10%, 50% and 90% boiling points as measured by the test method ASTM D86 (measured to the nearest 1 °C). In each case correlation factors and average errors were computed for the best correlations.
These optimum correlations did not however lead to simple easy-to-apply equations. For this reason straight-line correlations assuming linear relationships were included for comparison purposes.
Three runs were tried for each boiling temperature. The octel data were used for the first run. Data from HOR-Platforming unit were tried next, and finally both Octel and HOR data as well as data from other sources were used. The results obtained are given in Table 1, Table 2, Table 3.
Table 1. Optimum and straight-line correlation between Research Octane Number and 10% boiling point
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- #32
I plan on never needing it. As stated from the beginning of this I came close under all of the right circumstances once in 20+ years of going North, 3k miles each time, so took care of that potential. These days there's gas stations everywhere but even those remote ones can have bad gas - ask me how I know. Most likely from bad planning on my part but there's a lot of open space even on the freeways where I go. I bet 95% of those that carry extra fuel don't need it or use it - that's for another discussion and I'm sure plenty of threads about it.
Us guys with trucks that get 10mpg appreciate wheeling with wagons guys with extra gas. That’s for sure. Just rotate it out through your lawnmower from time to time
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- #34
Hope to provide more insight. First my wife had it out for a couple of hours and there was a little bulging, I'd say a little expansion. Temp maybe 105-107. I vented by opening just until I heard the hiss, after about 30 sec a little more and so on. Took maybe 1.5 minutes?
Also for those worried about getting the container off from it expanding I don't see how that's possible. The bottom handle doesn't go up or down at all. The top one does all of the tightening. So when you screw it in, using both at the same time, just enough to get the bottom handle onto the dimples, the rest is top handle only that tightens it all down. To get it off turn the top handle to loosen all the way. I can only see it happening if the can expands so much that you literally can't turn the top handle - but if the stories are out there I guess (elevation is most likely a whole different ball game). The bottom handle on the locking mount is square to you can't even turn that one into place, the top handle secures that one down on the dimples. Hope this helps. Just a rookie with these.
Also for those worried about getting the container off from it expanding I don't see how that's possible. The bottom handle doesn't go up or down at all. The top one does all of the tightening. So when you screw it in, using both at the same time, just enough to get the bottom handle onto the dimples, the rest is top handle only that tightens it all down. To get it off turn the top handle to loosen all the way. I can only see it happening if the can expands so much that you literally can't turn the top handle - but if the stories are out there I guess (elevation is most likely a whole different ball game). The bottom handle on the locking mount is square to you can't even turn that one into place, the top handle secures that one down on the dimples. Hope this helps. Just a rookie with these.
RET2
SILVER Star
As an example of how elevation affects things just buy a bag of chips anywhere close to sea level then go up to 5 or 6K. The bag blows up like a balloon.
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- #36
Oh I've been in elevation, same with water bottles. But you can still open them 
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That is exactly what I’ve read about happening.. they blow up locking the top handle in place with no hope of turning it until you vent pressure, and if they are mounted horizontal that means a giant mess.
FrazzledHunter
SILVER Star
Sound of tires squealing and smell of brakes overheating...
I was just going to order 2 sets of Yakima Mighty mounts and 2 Rotopax 4 gal gas containers when I read about the swelling preventing their removal due to the Rotopax lock getting stuck. What about using some other mounting method like straps in combination with their lock? The idea would be that you would not twist the Rotopax lock real tight and have the straps to actually hold the Rotopax; their twist lock would be a failsafe. Or am I not getting something basic? Thoughts???
I was just going to order 2 sets of Yakima Mighty mounts and 2 Rotopax 4 gal gas containers when I read about the swelling preventing their removal due to the Rotopax lock getting stuck. What about using some other mounting method like straps in combination with their lock? The idea would be that you would not twist the Rotopax lock real tight and have the straps to actually hold the Rotopax; their twist lock would be a failsafe. Or am I not getting something basic? Thoughts???
Read Linuxgod’s post above.
You've got it with not over tightening the Rotopax clamp. That's really the trick as if you overtighten, then it swells, that extra pressure could make it difficult to unscrew. I don't believe it'll ever become so tight that it become impossible, but it can get pretty snug. I also use a mounting handle without a lock mechanism as I just didn't feel I needed that level of security. I've heard of those corroding and binding.
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