Just venting Re: vapor lock

[ElZilchoTX]

Scot - thanks for that, it further solidified my decision.

I am going the overkill route on the exhaust in the two sections it is passing under the fuel lines:
Thermo-tech exhaust wrap then wrapped in ceramic insulation for good measure.

[Alantbird]

My 72 toro- same thing. Am seeking non ethanol for next fill. There’s a web site for that. Not concerned w 81 diesel Seville.

[Scot Minesinger]

For me I like to drive my 1970 Cadillac authentically as they did in 1970.  I always buy premium standard pump gas and my car operates wonderfully.  While non-ethanol gas and leaded premium, even racing gas may provide for a better running 1970 Cadillac, I just cannot be bothered.  If using special sell at only a few places gasoline is required I'm out and my Cadillac will be for sale.  I can tell you that I have driven my 1970 Cadillac in 100'F weather powered by standard premium pump gas with the ac on and it does not overheat, but it does get to 215-220'F idling for ten minutes in a traffic jam.  Normally on a 100'F day the sun is out and the top is down and she runs around 205'F (I have a real nice Autometer temperature gauge), if caught in a major traffic jam 210'F with no ac.  I just replaced my 10 year old radiator, former one sprung a leak.

Bottom line, if you have to use special gasoline to keep your car from vapor locking or overheating, then something is wrong with the car.

It is understood that this hobby has room for everyone from preservationists to consumers of classic cars (I'm more of a consumer).  It is fine to use special gasoline or not, I'm in the not crowd.

Enjoy your Cadillac!

[Dan LeBlanc]

I guess I'm lucky in two ways up here, Scot.

1.  We don't get temps in the 100's up here.  93 is about the hottest I've seen in my 40 years on this planet.  Even then, that only lasts a day or two.  A summer full of low to mid-80s is normal here.
2.  Premium unleaded fuel is ethanol free in our province by legislation!  No worries about ethanol here.

[ElZilchoTX]

I only put in the highest octane available in her. The problem is definitely the exhaust routing 1” under the fuel lines.

[Scot Minesinger]

heat rises, so insulate exhaust and provide a metal heat shield (both at the 1" separation point) and that should be an excellent starting point.

[jdemerson]

For me I like to drive my 1970 Cadillac authentically as they did in 1970.  I always buy premium standard pump gas and my car operates wonderfully.  While non-ethanol gas and leaded premium, even racing gas may provide for a better running 1970 Cadillac, I just cannot be bothered.  If using special sell at only a few places gasoline is required I'm out and my Cadillac will be for sale.  I can tell you that I have driven my 1970 Cadillac in 100'F weather powered by standard premium pump gas with the ac on and it does not overheat, but it does get to 215-220'F idling for ten minutes in a traffic jam.  Normally on a 100'F day the sun is out and the top is down and she runs around 205'F (I have a real nice Autometer temperature gauge), if caught in a major traffic jam 210'F with no ac.  I just replaced my 10 year old radiator, former one sprung a leak.

Bottom line, if you have to use special gasoline to keep your car from vapor locking or overheating, then something is wrong with the car.

It is understood that this hobby has room for everyone from preservationists to consumers of classic cars (I'm more of a consumer).  It is fine to use special gasoline or not, I'm in the not crowd.

Enjoy your Cadillac!

I'll differ somewhat with Scot on this one, at least for older Cadillacs. I use only 91 octave ethanol-free gas in my 1952, and it is easy to find here in Vermont. Since ethanol lowers the boiling point of gasoline, the use of ethanol-free gasoline significantly lowers the chances of vapor lock. I've found from experience that it does matter in the real world. Remember: gasoline did not have ethanol in the 1950s! So i haven't thought of ethanol-free gasoline as "special gasoline"...

John Emerson
1952 Cadillac Sedan 6219X

[Jim Miller]

Maybe it's overkill but, in my '41, I use ethanol free 91 octane. For every ten gallons I use 6oz. lead additive, and 4oz. of marvel mystery oil. This was suggested by a friend in the collector car business about 40 years. Figure if something goes wrong I can't blame ethanol or lead free. It's been 91 all week and heavy humidity and no vapor lock issues.

[James Landi]

Have to agree with Jim about the Marvel additive.  My 72 was hard starting when hot.  I could not figure out if I need to give it a couple of pumps of gas, or no accelerator at all... finally, when it did start, even though the interior of the car was over 100 degree F, I was always in a cold sweat.  Someone on this site suggested Marvel oil ---  I used it in the summer every time I needed gas--- I call it Marvel Miracle Oil...  I think it may drop the boiling point of gasoline in the carburetor... the started instantly with it in the gas mix.   Try it--- Happy day,  James

[cadillacmike68]

Maybe it's overkill but, in my '41, I use ethanol free 91 octane. For every ten gallons I use 6oz. lead additive, and 4oz. of marvel mystery oil. This was suggested by a friend in the collector car business about 40 years. Figure if something goes wrong I can't blame ethanol or lead free. It's been 91 all week and heavy humidity and no vapor lock issues.

Where do you get that lead additive??
I use only Shell or Chevron 93 octane and then I mix in a little 110 octane from a few places around here that sell it.  I cannot make the engine ping or knock with that combo,  but if I only run the 93, then the higher compression ratio (10.5:1) can ping under load so i ease off on the pedal. The compression ratio on a 1941 is nowhere near that of a 1968.

Never had it vapor lock with or without AC on and it gets REAL hot here. It was like 95 today. No issues, didn't even creep up on the temp as much as it did before the overhaul.

[Jim Miller]

When I called it lead additive I misspoke, it's lead substitute. The substitute supposed to protect the valves. I use this same mixture, with non-ethanol gas, in my old wooden boat. It has a 1967 225 Chrysler V8 sitting in a mahogany box with about 2 inches of clearance - no vapor lock. 

[robert G. smits]

Scott, if your Cadillac is vapor lock free you are lucky.  The flatheads vaporlocked when they were new so why wouldn't you expect it now?  You obviously have not sat in a stalled sedan without AC for 30 Minutes in 105 degree Texas weather listening to your wife complain about how unbearable it is.  Marty Roth swears by adding a gallon of diesel to each 10 gallons of gas in the summer.

[cadillacmike68]

It's a Lot more temperate in Virginia than it is in Texas - or Florida for that matter. Different driving conditions. Scot has it easier than we do.

[Scot Minesinger]

Mine is a 1970 overhead valve V-8, not a flat head.  There are days where it is over 100'F, but not often.  I never get vapor lock.  However, if it is not raining and over 55'F the top is down and ac off.  If raining the load on ac and cooling is low when top is up.  I got stuck in a 3 hour traffic jam (94'F and sunny), driving home from GN going less than 2mph (only drove 5 miles in 3 hours).   Top was down so ac was off. 

If I have a 1970 SDV, but I never drive it if the weather is hot and sunny because the top does not go down.

[ElZilchoTX]

100+* yesterday
Drove 60 miles in stop/go traffic with the A/C on (including idling for 15 min) with no issues. The only change I made was to add a piece of spun silica furnace insulation between the fuel lines and exhaust in one loaction (about a 3"x6" patch).

[Giant Jason]

You guys all have modern cars too, I expect? You don’t get vapor lock in those modern cars, right? My tundra doesn’t have wrapped fuel lines and it has never vapor locked. So other than computers, Efi, and higher psi of fuel force, what’s the difference? The difference is the electronic fuel pump at the fuel tank. I put one in my 68 DVC and it ended my vapor lock issues- though I put it in to fix my hard start issues, which it did.

Octane rating is never going to fix vapor lock because fuel is designed to turn into a vapor. The issue is where the fuel turns into a vapor. Mechanical fuel pumps can’t “push” vapor. (Actually, the pump doesn’t really push, pull, or suck the fuel. It creates a low pressure situation on the carb side and a high pressure situation on the tank side.)

When I am replacing fuel lines for clients- I own a company that cleans very large fuel tanks- the most common issue is a blockage in the line, tank, filter, or vent. (You’ll note that when you are at the gas station pumping fuel and it’s going really slow, or you’re pumping and someone on the other side of the pump starts pumping and it goes super slow- that’s a blockage.) By watching all the pumps at a station, I can generally localize where the blockage is. The problem of a blockage for the pump is that it lowers the pressure on the tank side, thus forcing the pump to work harder.

Let’s consider your 98 degree day in TX. The pavement that you’re riding on is thus about 130-140 degrees and that is heating up your fuel tank.  This lowers the pressure of the fuel while increasing the fuel’s size in your fuel tank. Then you have a blockage/restriction in the tank- say an old filter hardened by ethanol. This lowers the pressure going into the fuel lines even more. This creates the perfect situation for vapor lock- space in the line to expand, an overworked pump, and too low pressure. It also explains why you should buy your gas early in the morning instead of during the heat of the day. (In a 20 gallon tank, I’m told the difference could be as much as a gallon.)

All fuel is a mixture of light and heavy hydrocarbons. The light hydrocarbons have a lower boiling point then the heavy ones. Seasonally the mixture is changed for mileage vs cold starting. Thus you have summer and winter fuel. They even make this change in Miami which very rarely gets below 50.

Marvel Mystery oil is no mystery. It has 3 ingredients. Naphtha (Naphthillitic hydrocarbons), Mineral Spirits, and coloring because nobody would buy it if it was clear. Naphtha (paint thinner) is heavy hydrocarbons and Mineral Spirits (refined paint thinner) is light hydrocarbons. Notice any similarities to gasoline? Here’s a difference. The boiling point of mineral spirits is 106F, the boiling point of Naphtha is 160F, and the boiling point of 87 octane is ... drum roll... 171F- this is different in different parts of the country based on regulations, altitude, and California. Here’s the kicker, the boiling point of 93 octane- in FL- is 140. So, beyond being a cleaner, if you use 87 octane Marvel will raise your octane, but if you run 93 octane it will lower it. Obviously, octane is figured on an average across all your fuel, so putting 4oz in 20 gallons has little effect on octane. Now, who can tell me what the main products the gas companies use to raise octane- without google? Hint, there’s 2.

Marvel’s Naphtha/Mineral Spirits ratio is 80/20, Stabil is 90/10, startron is 99.6/.4, pfd 85/15, Seafoam 75/15/10 - 10% isopropyl alcohol, etc. msds.com has all others as well. When we clean tanks, we don’t use any of those because they don’t fix the biggest issues.

My understanding is that older caddies have high compression engines. Octane is the measure of how much pressure a gasoline can take before igniting. This is the knock rating of a gasoline. Gas causes some engines to knock if it pre-ignites. If your car has a high compression engine, you must run 93 octane to avoid knocking and engine damage.

Diesel was great to run in gas before they switched from LSD to ULSD. Now there’s no point. The sulfur was the lubricant and killer of anaerobic bacteria. At 15ppm now, it’s virtually nonexistent.

I hope that this information helps. Profligate companies perpetuate so much disinformation in my industry just to turn a buck. However, recent medical expiraments have shown the power of the placebo on someone who truly believes.

[Glen]

The issue is where the fuel turns into a vapor. Mechanical fuel pumps can’t “push” vapor. (Actually, the pump doesn’t really push, pull, or suck the fuel. It creates a low pressure situation on the carb side and a high pressure situation on the tank side.)

I think you got that backwards.  The pump creates a low pressure in the tank side of the fuel line and a high pressure on the carb side. 

When the cam lobe for the fuel pump comes around it forces the lever and diaphragm to move and expand the pump chamber.  This causes a low pressure in the chamber.  The low pressure causes the check valve on the outlet side to close and the atmospheric pressure on the fuel in the tank pushes the fuel into the pump chamber while opening the inlet check valve. 

As the lobe of the cam rotates off the pump lever it releases the diaphragm and the spring takes over pressing on the fuel in the chamber.  This causes the inlet check valve to close and the outlet to open (maybe, depending on if the carb float valve is open or closed).  The spring strength and the size of the diaphragm govern the output pressure of the pump.  This pressurizes the fuel line all the way to the carb float valve. 

Notice that if the float valve does not open no fuel flows and the diaphragm does not move.  If only a small amount of fuel is used the diaphragm only moves a small amount.  The next time the cam lobe comes around it may only move the diaphragm a small amount, causing the pump to take in only the small amount to replace what was used.  The spring pushes the fuel out.   

From this description you can see the cam causes sudden spikes of low pressure in the pump.  As you know the fuel vaporizes depending on the temperature and pressure.  So, if the fuel is warm enough each time the pump goes in to suction mode the fuel flashes to vapor which takes up the space made by the movement of the diaphragm.  The low pressure is not created and no fresh fuel flows into the pump.  As the cam lobe comes off the lever, the pressure returns, and the vapor condenses to a liquid state.  After several cycles of this the pump does not have enough fuel in it to supply the carb.