This is somewhat complicated and maybe difficult to explain but here goes I will be using my ‘48 Willys Jeep with the 134ci flathead 4 (I know, not a hot rod) At as high as 13,000 feet and vapor lock is a huge issue. My thought is to use an electric pump at appx 12-15 psi right at the tank and run the fuel through an oil cooler (so in this case, a fuel cooler) mounted in front of the radiator and then use a pressure regulator as close to the carb as I can get it and drop the pressure to 2.5 psi-ish. It seems to me that the higher the fuel pump pressure the better but is there too much of a good thing? Can a pressure regulator reliably drop the pressure that much? To combat vapor lock as I understand it is pressure and cooling. Any problems with my thought process? I have never known of anybody to do this but it seems workable to me.
Wow. This is a tough one. Here are my thoughts. 1. Make sure you have the carb itself as isolated from heat as possible with phenolic type insulator, etc. 2. You are correct that pressure and temperature are the two variables you can use to try to control vapor lock. I think I would try using an electric fuel pump and a by-pass type regulator that keeps the excess fuel circulating. Mount it as close to the carb as possible while avoiding hot spots. 3. As far as a cooler goes, how about a small cooler with an electric fan that was mounted away from everything warm? Something like this. I think I would put it in the recirculation line. Good luck! https://www.amazon.com/Mishimoto-MM...Electric+Fan+Oil+Cooler&qid=1721155523&sr=8-5
Even at higher altitudes, vapor lock should not be a huge problem, given that you are running a flat head and not a 12 to 1 chevy 350 or 383. Your underhood temperatures shouldn't be sky high... a much simpler retrofit would be a momentary dash mounted push button to prime the carburetor after it may have sat overnight on a very warm day. Have the button energize an electric fuel pump which, when you install it, takes it's suction from the entering side of a check valve and discharges the fuel to the leaving side of the same check valve. That way, if the carb IS dry, and after you take your finger off the button, there is no restriction for the fuel flow to resume normal flow to your mechanical fuel pump. I have a 383 stroker in a '49 Ford and live in Texas, and in the summer, the carb would go dry after maybe 4 hours after shut down.. here is how you do it... Note: If you check this link on your phone, do not click on the individual photos, just scroll down. If you click on a photo, you lose the narrative. https://www.49fordcoupe.com/Fighting-Vapor-Lock
I will be interested in your results if you do this. My initial thought was, any benefits will be marginal, considering the radiator fan blows hot air from the hot water being cooled. Even mounted in front of the rad, heat will still transfer to the oil/fuel cooler at slow speeds or stops. I think the shortest run from the tank to carb possible, shielded from heat sources and a return line to the tank is the best solution for keeping the fuel cool.
If you use a return line as many electric pump systems do, you shouldn't have a problem, as the fuel will be continuously flowing back to the tank and remain somewhat cool. Electric pumps come with different pressures, so you may want to use a little higher pressure and then regulate it to the lower pressure to keep pressure constant. I would also consider installing 2 electric pumps so that it's easy to switch them if one does fail. When electric pumps fail, they seldom if ever give you any warning. I've had a few fail, and had no warning. One failed while I was driving on the expressway. Running perfect .....then nothing. The others were working fine till I stopped somewhere, and then would not start when I got back in the vehicle. Don't want that at 12,000 ft back in the boondocks. So plan ahead if you use an electric pump. I would also recommend having an extra battery......not because of the electric fuel pump, but just because you might be a long way from getting help.
I'm not an expert or a scientist but it seems this way to me regarding the higher-pressure pump........... The higher pressure in the fuel line will raise the point at which vapor bubbles appear in that section but as soon as the fuel is exposed to the high altitude, lower ambient pressure past the regulator, vapor bubbles will pop into the suddenly lower pressure fuel. Even in the carb fuel bowl itself. I think you would be better off focusing on keeping the fuel temperature as low as possible. The cooler idea may help but don't overlook simply heat insulating the fuel line.
I wouldn't recirculate the fuel back to the tank. Even a small electric pump will recirculate ALL the fuel in the tank to the hot, close to pavement and hot air; in a matter of minutes.
First thing is to figure out where the heat is affecting the fuel in the line the most. On that Jeep there isn't much line so it should be a pretty easy task and if you were to insulate the whole line it wouldn't take a lot of insulation. Assuming that you have a CJ rather than a Pickup or wagon this page shows the fuel line routing real close to what it was originally according to the gent posting it https://www.thecj2apage.com/forums/fuel-line-routing-tank-to-fuel-pump_topic34789.html In the photo off that page note that there is a pretty good clearance between fuel line and exhaust. someone at some time didn't tuck the exhaust up closer to the floor and in turn the fuel line by chance?
Putting Diesel into Gasoline https://www.bellperformance.com/blog/accidentally-mixing-gasoline-and-diesel-fuel You’re mixing a higher flash, heavier fuel into a base fuel (gasoline) that’s lighter, more volatile and burns at a much lower flash temperature. Some might think that this "diesel-in-gasoline" scenario isn't as serious as the reverse. But that's not really the case. One big concern with contaminating your gasoline with diesel fuel is the reduction in octane. Thinking about how gasoline burns in an engine, octane rating is the measurement of gasoline’s ability to ignite at the right time – not too early. Gasoline with lower octane rating will ignite too quickly once it is injected into the chamber. The gasoline ignite and explodes, but the piston is still on its way up and the resulting pressure wave collision gives you (at best) a knocking sound and (at worst) damage to the piston and rod. In a sense, octane slows down combustion, it delays it. Gasoline needs to have an octane rating of 87-91 to fit today’s car engines. Diesel fuel has an octane rating of 25-40. Mixing 2% diesel fuel into gasoline will lower the overall octane rating by 1 point. Getting 10% diesel contamination lowers octane by 5 points, which is enough to create problems in most engines. The octane depression rises linearly with increasing percentages of diesel fuel in the gasoline. And that's just the first potential problem. Because diesel fuel is heavier than gasoline, it can sink to the bottom of your gas tank, resulting in the injection of both gas and diesel into the intake manifold or the cylinder. Depending on the mix, you can get partially-burned diesel fuel which leaves bigtime deposits on pistons, valves and spark plugs. You get a car or truck that runs terrible, and if you keep driving it, you can cause serious damage If enough diesel fuel gets in the cylinder, you can hydro-lock the cylinders, resulting in a blown head gasket, cracked cylinder head or other serious problems that can lead your vehicle down the road to a quick and final death. This diesel fuel in the cylinder can also seep past the piston rings into the oil crankcase, diluting the lubricating oil. This can damage all internal engine lubricated parts resulting in major engine failure from rapid wear. If unburned diesel fuel makes its way into the exhaust system, it will ignite in the catalytic convertor. The fire will plug the holes in the catalyst, destroying it and leaving you with a repair job well into the four-figures.
I am not an expert, though I play one on the internet. I would not think a single regulator can make the drop from 15 to 2.5 psi. I run 2 regulators on my 34 ford. I have a tanks inc in tank pump delivering 190 LPH and over 35 psi. I used a Holley 12-887(?) that knocks the pressure down to 6 psi and has a return line to the tank the same diameter as the delivery -6AN SS. Bad photo but it is tucked under the car on the right side frame rail with a gauge. Another Holley regulator 12-804 sits on the back of the blower reducing the 6 psi to 2.5 for the Stromberg's. This system has worked beautifully for a few years and a few thousand miles.
Absolutely no idea but it seems to have been a favorite trick on older lower compression motors (model A, model T etc).
Don't forget, the fuel we get today is very different from the fuels used when such ideas were created. What could help back then might not help today.
Well folks are still doing it according to the T and A forums I am on.... and still seems to work. No idea why but it is what it is
as stated above, need to isolate carb from heat with a phenolic (fiber, not plastic) spacer. only possible if have long enough carb mounting studs. also, cover fuel line with heat resistant covering. sometimes may not be a true vapor lock but, gas boiling in carb from heat.
glennpm. So 1qt in 15 gallons will not stay in mix if you add the qt prior to filling your tank. I’m definitely not a petrochemical engineer but it seems to me since both are derived from oil, crude or not, they would mix and stay in solution…..thanks.
Wow, a lot of comments in a short amount of time. The reason that I have vapor lock concerns is because numerous guys that have been on the same trails I will be on with the exact same vehicle as mine have had vapor lock problems. There seems to be no real explanation as to why one vehicle will be troubled by vapor lock and the same vehicle on the same trail at the same time does not have problems. Once I hit the trail there will be no runs to the auto parts store or internet so any modifications must be done in advance. Some say it ethanol causing the problem (or at least making it worse) others say no. I’m the kind of guy that goes all in when I decide to do something. Another Jeeper says that the gas tank is so small that at a half tank the recirculating system will have the whole tank hot in no time. On an old Willy’s there is a lot of room in front of the radiator such as to allow the cooler to be a ways away from the radiator. If I could carry enough ice I would run a cold can but I can’t. There are a lot of good ideas here and I will probably end up with some combination of them. I will be on the trail with 10-20 Jeeps like mine and my worst fear is to be “That Guy”, the guy that’s holding the group up. I think that the cooler idea has merit even though I don’t know of anybody that has ever done it (except with a cold can). My worries about diesel and octane levels aren’t to big because the compression ratio of the Willys motor is very low (6.5:1). Not being an expert I would think that because alcohol has a higher boiling point than gasoline that it might actually help prevent vapor lock but I don’t know of anybody that shares that opinion. Unfortunately I do not have an unlimited budget either.
I will be using a full 10 gallon of gas every day and bouncing all over the trails when I do so I don’t think that the diesel will have time to settle. I can test the diesel idea without any modifications and I have some time before the trip to try it out. I won’t learn anything about it’s effect on vapor lock, only about “will the engine run with it in the tank?”
Maybe you can add an electric fan somewhere under the hood to blow the hot air out. Seems trail driving might be pretty slow going with not much air movement. Also an insulated air tube to draw in cooler air might help keep carburetor cool.
The OP has a Willis with a flathead. They were 6.9:1 as standard. That will run on sub 80 octane. And no I would not try it on a modern motor either but like I said... it does seem to work according to the old guys that have been doing it for years.
Sounds scientific, but remember that when fuel goes from the fuel line into the carbs float bowl, it also suddenly has no pressure on it other than atmospheric pressure and it doesn't have that problem. Continuously circulating the fuel keeps it cooler than having a deadhead situation where fuel is parked in the fuel line near the engine for a longer time. Doesn't matter what the fuel in the pump is doing while its inside the tank, the idea is that the body of fuel in the tank is cooler than the air near the engine. If the fuel continuously flows out of the tank and past the engine ...and returns to the tank........it stays reasonably cool. Then there is only a short section of fuel line that has parked fuel going into the carb. It gets used before it gets too hot. Think about how many OEM vehicles are on the road using a recirculating set up and not having any problems . Most don't use any kind of fuel cooler and they do well even in places like Arizona.
I was going to say this….but you said it better! I always believed a small return line is best! Chrysler even put them on the latest carburetor cars they made from the factory. They did it at the filter , down low! I believe coming right out of the back of the fuel log is the best! Bones
Out of curiosity, how close is your fuel line entering the carb to the radiator hose? Some checking with your laser thermometer might help figure out the hottest part of the fuel line where it's closest to heat generating things for a potential fuel boiling point, can you post a pic?
I have picked up some (very expensive) industrial tubing insulation which I think will help. I have been trying to talk to Holley but there are always 35 callers ahead of me (that’s no exaggeration, it’s a fact).
If you are truly having a vapor lock problem, possibly due to extreme slow speeds while wheeling, you might try to ventilate your engine compartment to reduce the temperature there. Might raise the back of the hood some to let the heat out. Or even louvers. Like mentioned, a small return line from the carb inlet fitting , back to the tank will also help. And is cheap! Bones
I put 1 litre of diesel or sometimes kero, depending on what I've got, with 10 litres of petrol in the old grey Fergie. It doesn't slow the old bugger down and keeps the valve seats lubricated.
watching Roadkil Show and ad show called Driving Decarbonization of America came on about Chevron promoting a test blend of gasoline & soybean oil. takes new car system to run on blend. so if unsure about trying to run diesel maybe try soybean oil.
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