Diagnosis and Repair of Problems With Your Imperial's Gas Cap


Imperial Homepage -> Repair -> Fuel -> Gas Cap

Question from George (1955):

What other caps might fit my 1955 Crown Limo??? I think that it should be the same as other '55 Imperials, as the filler is under the Sparrow Strainer, but the cap from my 1956 Crown Limo will not fit. The inside dimension of the filler neck is 1&3/8" and the outside dimension is 1&3/4" and the total outer size of the cap can't be much bigger than 2&1/4" also the lock notches are on the inside. Would there be one that might fit from another make that I could use until I can find the "real" thing?


From Dick:

I have gas cap application data going back to 1948 for most cars. Unfortunately, the-55 up Imperial in any style is one of the few cars for which the demand was so small that the aftermarket never tooled up to make replacements. Considering this fact, I'd be amazed if anyone listed a cap to fit the 55 Crown Limo - I think you are going to have to just inspect the caps for other cars and try to find or adapt one to fit. If you have access to a parts book, you might find a part number that would interchange with some other car, or find a vendor with a stash of parts that might have one.

From Bill:

There are good used & NOS original gas caps out there you just have to find them. Call Lowell Howe, Bob Hoffmiester, Murrey Park or others for used original caps. If no luck call the NOS suppliers found throughout Hemmings Motor News each month. A few months ago I bought a surprisingly good used gas cap for my 1955 C-69 from Lowell in California. If you don't have a copy of Hemmings pick one up from almost any place magazines are sold.

From John:

I would try contacting some of the car yards first. Most of these have interchange books to find what will fit. You should also have a factory parts book of your own, this way you can look up the part number & see if it fits accross the rest of the 55 model lineup. I'll bet that once you find the part number, you'll find someone, Probably Mitchells has one on the shelf.

From Bob:

According to the Parts Manual, 1675 193 should fit 1955-6 Crown Imperials and 1955-9 Imperials, but no other Mopars. The filler tube (1616 495) is unique to all 1955 Imperials, including limos.

If the cap from your 1956 doesn't fit, the filler tube is likely non-stock. You should be able to replace your tube and cap with one from any 1955 Imperial. (The 1956 limo filler tube is unique to the 1956 limo.)

Question from Don (1967):

When I fill the tank up I get a leak, but only when it is full. My investigation yesterday revealed that the gas tank, underneath the vent tube, is clean as a whistle and shows signs of gas. Fine, looked like the rubber vent tube hose should be replaced. No sweat. However, I did notice that my tank has TWO vent tubes, side by side. One is as shown in my Shop Manual (page 14-33), the other, to the left of it, comes out of the tank, goes straight up into a frame-like brace, curves around and stops. It looks like a 'Hook". This is not plugged and after a short drive, a stop for coffee while sitting behind the level car, I saw drip-drip. Investigation revealed that gas was infrequently dripping out of the end of the 'hook' vent tube as the frame-like brace was just dripping wet with gas. BTW : I've probably got around 1/8th of a tank of gas currently. Any suggestions? Since the shop manual doesn't show a second tube I'm totally lost. Should it be plugged?


From Norm:

Maybe someone put a non vented gas cap on the car and the vacuum created by gasoline flow is sufficient to push gas through the vent tube when the fuel level is high enough.

From Paul:

My '66 Newport convertible did the same thing that you describe while on a trip several years ago and worried me a bunch but it has never done it since???? I wonder if both of the vent tubes are completely clear? I think I would pull the tank. This will make changing the sending unit much easier and you will be able to inspect the inside of the tank for any corrosion that might cause later problems. Tanks can look great outside and be a mess inside! (been there) If there is any sign of corrosion, I would coat the tank with one of the various gas tank sealers. Be sure to keep the vent tubes clear of sealer by blowing compressed air through them several times as the sealer cures. There is a chance that you will find that the float on the end of the sending unit has perforated and is not floating because it is full of gasoline. In this case just replace the float. The same brass float is used at least into the middle '80's in the Fifth Avenues and similar cars. While you have the sending unit out, you can check it's operation by connecting it and providing a chassis ground connection to the body of the sending unit. If it is OK, you should be able to get various readings on your gas gauge depending upon the position of the float lever arm.

Question from Tim (1967):

What are the implications of the fact that I have to remove the gas cap in order to start the car when the engine's warm, but not when it's cold?


From Norm:

The car has the wrong gas cap. It is probably a non vented model when what you need is a vented one. You are allowing a huge suction to develop that is beyond the fuel pump's ability to pull after a certain period. My guess is that if you drove it long enough it would stall and/or you would see a caved-in gas tank. Take a look , it may be slightly caved in now.

From Dick:

I hope this continues to work for you. The caps on these cars are specified as to type or existence of vents. I don't recall for sure which is required for a 67, But yours seems to require a vented cap to prevent vacuum in the tank from stopping gas flow. I had a 69 Newport that did that too - the key was that when I removed the cap after driving a ways, there was a WHOOSH! from the air going back into the tank. I put a vented cap on it and no more problems. But the symptom that caused was that the car would just plain stop after driving a few miles (Like 20), and not restart until the pressure equalized in the tank. Your symptom seems different, so I remain to be convinced. The problem with all the low fill location tanks is that a vented cap can cause gas to leak out under some conditions (full tank, car facing up a steep hill, high temperatures.) I always had to be very careful where I parked my 69 Newport when the tank was over half full. But that car has a lower fill location than yours, so maybe you'll be OK in any situation. 

From Bob:

When the car has sat for a while, natural leakage of air back into the tank can occur (fuel systems are rarely ever completely air tight) which relieve the vacuum enough for the fuel pump to overcome. Continuous withdrawal of gasoline from the tank without air venting results in lack of fuel.

From Roger:

I strongly suggest that you get a vented gas cap and don't drive the Imp to get the cap.

From Kerry:

Ohh! Good idea. We had a similar problem with my Dad's 61 Desoto when I was a kid. Gas tank vent was plugged. Easy test. When it does it, open the gas tank cap. If you hear a "whoosh" there was a vacuum. Another thing would be to put a se through gas line filter so you could be sure there is gas at the carburetor.  Though I do think your gas tank vent line is plugged up. Some cars have vented gas caps and others a rubber hose. Since the Imperial filler cap is low, a vented cap will allow gas to slosh out. Replacing the hose should be easy. 

Question from Roger (1969):

Should gas cap on 1969 Imperial be vented or non vented?


From Eric:

As far as I can determine based on my own 19694DRHT LeBaron and my 1969 Chrysler/Imperial factory service manual, the gas cap is not vented. You should find 2 vent tubes at the front of the tank near the rear axle.

From Kerry:

This reminded me of something that happened in 1963 with my Dads 61 DeSoto (last of the marque). It would run great for a few miles then cough a couple times and then just plain quit running. We tried everything but nothing would help. In a few minutes the car would start and run for another 5-10 miles. My Dad had been a mechanic back in the late 30s/40s but nothing helped. FINALLY we determined that the gas vent was plugged. After a few miles the vacuum created in the tank would cause the fuel pump not to pump and the car would starve for gas. As air leaked back in it would be fine for a few miles. We finally found it out when we stopped for gas and heard the whoosh when we pulled the gas cap. Solution? We drilled a 1/4 inch hole in the gas cap. Lost a little gas on fast starts but then gas was .25 a gallon or less.

From Leo:

I once owned a 61 Dodge Lancer (Dodges version of the Valiant) with the aluminum block 225 slant six.. One winter night I ran out of gas with the gauge showing 1/2 tank. When AAA arrived to tow it, the mechanic looked under the rear of the car and said, "no wonder you ran out of gas, the gas tank is gone" Well, not quite, the vent line had frozen shut and the fuel pump sucked the tank nearly flat. It bent the filler line so I had to keep the tank 3/4 full or more until I replaced the line. Must have been an excellent fuel pump, Huh?

Question from Chad (1973):

When I stop to fill up my Imp, I always get a large "whoosh" once I pull off the gas cap. Is this right?  I don't remember either my 73 Nyer or Newport ever doing this, I only remember a slight pressure difference. Is it something to do with the charcoal canister?

Reply from David:

Either the charcoal canister is about to go or has gone or the vent is plugged up.  I would check the vent first as it should be the easiest to check.

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