1936 4 door sedan fuel/vacuum pump and vapor lock issues - ClassicOldsmobile.com


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Old June 18th, 2017, 04:56 PM   #1
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1936 4 door sedan fuel/vacuum pump and vapor lock issues

I just bought a 36 and I'm having issues with the fuel/vacuum pump. The vacuum doesn't appear to be working as the wipers do not operate at all. I'm having issues locating a rebuild kit for the 36. Can I use 35 37 38 rebuild kits? Can I use a pump from a other years? The line for the wiper was plugged directly into the manifold, so I tried changing it to the correct way, to the pump. I am getting poor acceleration and thought maybe it was sucking air through the open pump line on the firewall. Would that make sense? I tried running it, but the wipers didn't work at all after I made the change. The previous owner said he rebuilt the pump, but I'm wondering if he just did the fuel pump and not vacuum portion??

On a separate note, I'm also having issues with vapor lock and can see fuel boiling in the bowl. I've already rerouted the fuel line the correct way as the previous owner put in a new line but didn't run it right. I'm thinking adding a heat shield around the pump and wrapping the fuel line from the pump to the carburetor. Any other suggestions?

I appreciate the help and apologize if this has already come up in another post. I've only had the car about 3 weeks. Original car, no rust. I'm the 3rd owner. Engine runs great... until it quits after 20 minutes of driving.
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Old June 18th, 2017, 07:57 PM   #2
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I'm thinking adding a heat shield around the pump and wrapping the fuel line from the pump to the carburetor. Any other suggestions?
Sounds like a nice car!

I'm not knowledgeable about the cars of that era, so I won't try to give you advice about specific pumps and years, but I will say that it sounds as though your fuel pump is not functioning as it should. Vapor lock was a real thing back when these cars were new, and definitely happened on occasion, but it was not so common that you could expect it to happen every time you drove the car. That being said, in these cases, once you've confirmed correct fuel pump function (generally measured by volume of fuel pumped per minute at a given RPM, plus correct fuel pressure), and likely rebuilt the fuel pump again, the best insurance against vapor lock is an electric fuel pump mounted close to the gas tank, and activated by a separate switch, when needed. It can also serve to refill the float bowl when the car has been sitting, for fast starts.

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Old June 18th, 2017, 09:17 PM   #3
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Before you start pulling parts off double check that there are no air leaks in the fuel line joints. A old farmer test on these fuel pumps was to disconnect the fuel line at the carburetor pull the coil wire so it won't start then place a 16 oz coke bottle over the gas line end. In fifteen seconds of cranking if the bottle isn't 1/2 full you have a fuel pump problem. This isn't a definitive test because of no resistance on the line but it will tell you if the pump is shorting gas at the carb at free flow also will tell if there is bubbles in the system on a cold start.... Tedd
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Old June 18th, 2017, 09:43 PM   #4
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Get a Hollander Interchange Book

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Originally Posted by cozmo3710 View Post
I just bought a 36 and I'm having issues with the fuel/vacuum pump. The vacuum doesn't appear to be working as the wipers do not operate at all. I'm having issues locating a rebuild kit for the 36. Can I use 35 37 38 rebuild kits? Can I use a pump from a other years? The line for the wiper was plugged directly into the manifold, so I tried changing it to the correct way, to the pump. I am getting poor acceleration and thought maybe it was sucking air through the open pump line on the firewall. Would that make sense? I tried running it, but the wipers didn't work at all after I made the change. The previous owner said he rebuilt the pump, but I'm wondering if he just did the fuel pump and not vacuum portion??

On a separate note, I'm also having issues with vapor lock and can see fuel boiling in the bowl. I've already rerouted the fuel line the correct way as the previous owner put in a new line but didn't run it right. I'm thinking adding a heat shield around the pump and wrapping the fuel line from the pump to the carburetor. Any other suggestions?
_________________________________________________

Fuel Pump: It does make a difference whether your 36 is a six or eight cylinder. My Hollander 16th Edition Interchange manual lists a different pump for each. BUT.... some had a vacuum chamber and some did not. It looks like any possible interchange would go back to 1933-35 but not beyond 36. Its sort of confusing. In one case it apears a LaSalle fuel pump would work. In a few cases it looks like some years of GMC trucks may have the same fuel pump. You really need your own Hollander. Since I got my 16th Edition some years back they have condensed a lot of older car information into fewer editions. You can find used ones on Ebay sometimes or you can find Hollander on the Internet and contact them. A good reference manual is more valuable than tools.

MDchanic is right that vapor lock used to be a real thing on carbureted cars. I remember it well during hot summer days. If you are willing to use aftermarket items on your 36 an electric pump, as he recommends, is a good solution. Just be sure to get a low pressure pump meant for carburetors. There should be specifications on your car re. normal fuel pressure. Get as close as you can. I'm thinking it would be in the 3-6 lb. psi range but get the actual data. If you stay 6 volt you will have to get a 6V pump. Summit and others have them.
A heat shielded fuel line in the engine area is a good idea. So would be a Nylon reinforced flexible fuel line as it wouldn't soak up heat. Another thing to do is create a heat block between carburetor base and intake manifold with a non heat conducting fibre or plastic maybe a half inch thick. If the fuel is boiling in your carb float chamber this can prevent that and it can help stop the heat from the engine going up thru the carb and into a steel fuel line.
There are a number of videos on you tube about fuel vapor lock. One thing some point out is that modern gasoline blends with ethanol have a lower boiling point than non-ethanol fuels. If you can find non ethanol fuel in your area try using that as well as the other things mentioned in replies to your post.

Jerry

Last edited by 47 Convertible; June 18th, 2017 at 09:49 PM.
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Old June 20th, 2017, 05:35 AM   #5
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Quote:
Originally Posted by cozmo3710 View Post
I just bought a 36 and I'm having issues with the fuel/vacuum pump. The vacuum doesn't appear to be working as the wipers do not operate at all. I'm having issues locating a rebuild kit for the 36. Can I use 35 37 38 rebuild kits? Can I use a pump from a other years? The line for the wiper was plugged directly into the manifold, so I tried changing it to the correct way, to the pump. I am getting poor acceleration and thought maybe it was sucking air through the open pump line on the firewall. Would that make sense? I tried running it, but the wipers didn't work at all after I made the change. The previous owner said he rebuilt the pump, but I'm wondering if he just did the fuel pump and not vacuum portion??

On a separate note, I'm also having issues with vapor lock and can see fuel boiling in the bowl. I've already rerouted the fuel line the correct way as the previous owner put in a new line but didn't run it right. I'm thinking adding a heat shield around the pump and wrapping the fuel line from the pump to the carburetor. Any other suggestions?

I appreciate the help and apologize if this has already come up in another post. I've only had the car about 3 weeks. Original car, no rust. I'm the 3rd owner. Engine runs great... until it quits after 20 minutes of driving.
The Olds parts book says the fuel pump diaphragm kits (group 3.925) are the same for 1935 & 1936. It shows no difference between engines.
Vacuum side part number 1538496
Fuel side part number 1538502
Unfortunately I don't know where to get either.
The kits for 1937 & up have different part numbers, hence, you probably can't use them.
If you're unsure about what the previous owner did with the pump perhaps you should ask him.
Vacuum wipers quit working for different reasons. Sometimes the fault is with the vacuum "motor". If the valve is defective it won't work. If the "wiper" portion has dried out and lost its seal, it won't work. If the line to the vacuum motor leaks it won't work. The pump is intended to boost vacuum to the vacuum motor during low vacuum periods in the engine like harder acceleration. If the vacuum motor is O.K. and gets enough vacuum to it, it should work the windshield wipers. The pump booster isn't needed when the engine vacuum is high.
Many things can cause poor acceleration. A vacuum leak is one.
Vapor lock can be a problem especially in high ambient temperature operational conditions. If the fuel is actually "boiling" it could be a significant indicator. Try to keep the fuel as cool as possible.
Try to confirm proper performance of each component separate from the rest. That should reduce the need for a lot of guesses.
If the engine "runs great" for 20 minutes and then stops, my guess is that it has lost either fuel or ignition. Try to narrow it down to which it is, then pursue it further.
People have successfully driven the car you own for extended periods without distress. You will be able to do the same after resolving the shortfalls.
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Old June 20th, 2017, 06:51 AM   #6
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The last time I worked on a 36 the screw in fuel line from the main fuel line to the pump was leaking and sucking air. You might try Fusick for a kit.
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Old June 20th, 2017, 06:01 PM   #7
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Originally Posted by cozmo3710 View Post
The line for the wiper was plugged directly into the manifold, so I tried changing it to the correct way, to the pump. I am getting poor acceleration and thought maybe it was sucking air through the open pump line on the firewall. Would that make sense? I tried running it, but the wipers didn't work at all after I made the change. The previous owner said he rebuilt the pump, but I'm wondering if he just did the fuel pump and not vacuum portion??
The best way to tell if the vacuum pump is working is to use a vacuum guage .
Hook up the guage to the hose that goes to the wiper motor . If you have at least 14 inches of vacuum at idle , then the wipers should work . If not , then the problem is probably with the wiper motor. You should be able to move the wiper arms by hand , with the engine off . If not , then something is siezed in the wiper linkage or the motor .
Make sure that the "in" vacuum port on the pump is connected to the intake manifold , and the "out" port is connected to the wiper motor .

The wipers should work if directly connected to the manifold . If the manifold vacuum is sufficent . (like at idle or cruise )
The vacuum pump was just there to provide vacuum when manifold vacuum was low . (accelerating , going uphill )
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Old June 26th, 2017, 01:00 PM   #8
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Thanks for all of the info. I went ahead and ordered a New Hollander Manual. That will be a huge help to me.

The wiper motor was hooked up directly to the manifold when I bought the car. I discovered that was incorrect, so I tried it the other way. Before I switched it, the wipers worked. And now they don't. So that tells me the wiper motor works, but my vacuum pump doesn't.

For the fuel boiling... I'm going to make up a heat shield to put around the fuel pump. I have already ran new fuel line, the correct way. I've also read about mixing diesel or kerosene in with the gas, about 15:1 mixture. I may try that as well.

I also found an old 6 volt timing light in an antique shop that still works, so I'm going to check the timing on the car as well.

I also found that the car isn't charging the battery while running, so that is a new issue to figure out... My battery was dead when I went out to start it last.
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Old June 26th, 2017, 03:18 PM   #9
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I also found an old 6 volt timing light in an antique shop that still works, so I'm going to check the timing on the car as well.
Note that in a pinch, if you need to time a 6v car and only have a 12v timing light, you can connect the 12v light to a 12v source (such as another car parked next to the car you're working on), clamp the sensor lead on, and use the timing light on the 6v car.

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Old July 4th, 2017, 03:54 AM   #10
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Originally Posted by cozmo3710 View Post

For the fuel boiling... I'm going to make up a heat shield to put around the fuel pump. I have already ran new fuel line, the correct way. I've also read about mixing diesel or kerosene in with the gas, about 15:1 mixture. I may try that as well.
The L.36 actually had a heat shield that wasn't available on the F.36 but they aren't terribly effective at all. I'm an Aussie and back in the mid '80s spent a great deal of time in Philadelphia with another '36 fanatic that had an L.36 Convertible with the exact same problems. Much research revealed that the additive that fuel companies use has the most dramatic influence on this issue with cars of the '30s & 40's . You need to keep in mind that if the fuel in your tank was put in during early spring or fall then there is a high probability that there will be far less of the additive that lowers the boiling point. The reputable gas companies that I called indicated that some low cost (less reputable brands) tended to use way less additive until it's really needed in summer and even then it can be a much lower concentration (causing increased risk of vaporisation). Just something to be mindful of.
All the recommendations above on insulating the fuel line etc are very appropriate including the use of an electric pump.
Good luck and I hope you have some success with all the suggestions.

Last edited by 35olds; July 4th, 2017 at 04:56 AM.
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