TAC Tech => Mechanical => Topic started by: BlueBaron762x39 on September 06, 2021, 08:18:41 PM
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I'm having issues with fuel boiling/vapor locking lately on my stock 1979 Olds 403 Trans Am. The engine is not overheating but sometimes runs warm (between 210-220 degrees sometimes). This seemed to start when the temperature warmed up during the summer. Have any of you tried these phenolic carb spacers to help address this issue with the fuel? I purchased one but haven't installed it yet. Not sure if this is something people use more for racing or if it's appropriate for a daily driver but I need to try something so I can drive the car still this time of year.
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If you can find one, I believe the P/N is 3969837 Its an Aluminum Heat Shield.
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You may have multiple issues.
220 degrees is on the high side. Keep in mind the factory temperature gage is not known for its accuracy. How old is your radiator, could it be partially plugged? What kind of fan, if it’s a clutch fan is it good. Is coolant topped off and coolant recover tank still in place with coolant? The coolant recovery system eliminates air pockets and will allow for cooler running.
I am pretty sure all 403 engine cars had a return fuel system so cooler fuel was being pumped into the carb. Having this functional is a great defense against vapor lock. Someone may have disconnected or blocked the return line, or switched to a fuel pump without the return.
Keep in mind any carb spacer could raise the shaker scoop higher causing clearance problems.
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You may have multiple issues.
220 degrees is on the high side. Keep in mind the factory temperature gage is not known for its accuracy. How old is your radiator, could it be partially plugged? What kind of fan, if it’s a clutch fan is it good. Is coolant topped off and coolant recover tank still in place with coolant? The coolant recovery system eliminates air pockets and will allow for cooler running.
I am pretty sure all 403 engine cars had a return fuel system so cooler fuel was being pumped into the carb. Having this functional is a great defense against vapor lock. Someone may have disconnected or blocked the return line, or switched to a fuel pump without the return.
Keep in mind any carb spacer could raise the shaker scoop higher causing clearance problems.
Sorry...They have a Fuel Return from the "Pump" only.... a single inlet line to the "Carburetor" only.... I can't think of one Carburetor Equiped GM Vehicle I have ever seen with a return line from the Carburetor. The Heat Shield I mentioned is very thin, and I doubt seriously it would create a problem with the "Shaker"......I have one installed on several of my vehicles, works great to keep the heat off the Carburetor..... But as you said, there may be other problems.
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Sorry Langss I did not make myself very clear on the fuel return. I was referring to the fuel pump. The fuel pump will have an inlet from the tank, an output to the carb and another output/return to the tank. This keeps the fuel cooler as it is constantly recirculating from the tank.
Also, I was referring to the Phenolic spacer that BlueBaron mentioned causing problems as they are often thick, not an aluminum heat shield.
Such as this. Sorry for not making myself clear.
(https://live.staticflickr.com/65535/51437532001_10ed29f0e9_h.jpg) (https://flic.kr/p/2mnmNd2)IMG_8604 (https://flic.kr/p/2mnmNd2) by Lawrence Alexander (https://www.flickr.com/photos/188552644@N06/), on Flickr
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No Worries....I've just been doing this stuff since I was 13....I'm 73 now. Believe me when I say I have seen a lot of people take one well meaning statement, and the rest is history. Perfect Example: Some 57 Chevy's had Fuel Injection.... So this guy I used to know drives his "Pristine" 57 Convertible home and yanks the 2bbl Carb off...Bends the Fuel Line down towards the open Intake.... Hops behind the wheel and gives it a few cranks.....FUEL IS INDEED being injected....just not the way GM had intended.
Nothing happens (Or So He Thinks) So he tries it again...It pops but that's it. In frustration, he closes the hood, goes in the house, makes himself a sandwich, and plops down in the sofa to watch TV..... Less than 10 minutes later the Fire Department is banging on the front door advising that the car has BURNT TO THE GROUND, and there was nothing they could do to save it.
I think you can guess the rest of the story...(The Burn Spot Is Still IN The Driveway) and that was 1966. I tell this story for the humor of it, because people don't always realize that what is in one case, may not be in another. Got to admit a cooling fuel line would have eliminated a lot of people stuck along side the road with Vapor Lock...in the hot days of the past....lol..... And I have been there as well.....lol.....
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You may have multiple issues.
220 degrees is on the high side. Keep in mind the factory temperature gage is not known for its accuracy. How old is your radiator, could it be partially plugged? What kind of fan, if it’s a clutch fan is it good. Is coolant topped off and coolant recover tank still in place with coolant? The coolant recovery system eliminates air pockets and will allow for cooler running.
I am pretty sure all 403 engine cars had a return fuel system so cooler fuel was being pumped into the carb. Having this functional is a great defense against vapor lock. Someone may have disconnected or blocked the return line, or switched to a fuel pump without the return.
Keep in mind any carb spacer could raise the shaker scoop higher causing clearance problems.
I also have a 79' 403 that gets to 220 temps (new 3-row radiator; not aluminum) if I drive in 90 F weather. Is there a way to test the OEM fan? What's a good choice if I indeed need a new fan? TIA
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I cant add anything intelligent, but I was at a Pontiac show last month and there was a guy that swore by his wood spacer block. Said it was the best thing to use. Another stand by guy in earshot second' his comment. I thought he was crazy, bs'ing about a wood block. But he was completely serious.
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No Worries....I've just been doing this stuff since I was 13....I'm 73 now. Believe me when I say I have seen a lot of people take one well meaning statement, and the rest is history. Perfect Example: Some 57 Chevy's had Fuel Injection.... So this guy I used to know drives his "Pristine" 57 Convertible home and yanks the 2bbl Carb off...Bends the Fuel Line down towards the open Intake.... Hops behind the wheel and gives it a few cranks.....FUEL IS INDEED being injected....just not the way GM had intended.
Nothing happens (Or So He Thinks) So he tries it again...It pops but that's it. In frustration, he closes the hood, goes in the house, makes himself a sandwich, and plops down in the sofa to watch TV..... Less than 10 minutes later the Fire Department is banging on the front door advising that the car has BURNT TO THE GROUND, and there was nothing they could do to save it.
I think you can guess the rest of the story...(The Burn Spot Is Still IN The Driveway) and that was 1966. I tell this story for the humor of it, because people don't always realize that what is in one case, may not be in another. Got to admit a cooling fuel line would have eliminated a lot of people stuck along side the road with Vapor Lock...in the hot days of the past....lol..... And I have been there as well.....lol.....
That's the sort of thing that sometimes worries me about these old cars. You get someone who doesn't know what they're doing working on them or you accidentally do something wrong yourself you could risk burning down the whole car.
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You may have multiple issues.
220 degrees is on the high side. Keep in mind the factory temperature gage is not known for its accuracy. How old is your radiator, could it be partially plugged? What kind of fan, if it’s a clutch fan is it good. Is coolant topped off and coolant recover tank still in place with coolant? The coolant recovery system eliminates air pockets and will allow for cooler running.
I am pretty sure all 403 engine cars had a return fuel system so cooler fuel was being pumped into the carb. Having this functional is a great defense against vapor lock. Someone may have disconnected or blocked the return line, or switched to a fuel pump without the return.
Keep in mind any carb spacer could raise the shaker scoop higher causing clearance problems.
My radiator is a new copper 4 row and I'm using the original fan with a standard duty fan clutch from Autozone or Orielly. The water pump is a new Flowkooler pump and the thermostat is a new Robert Shaw 180 degree. I also have the spring installed inside the lower radiator hose. Coolant recovery tank is in place and the system is full of coolant. The fuel pump is stock with a return line.
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If you can find a station that sells 100% gas that will help out too. Alcohol has a lower boiling point than gas does.
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No Worries....I've just been doing this stuff since I was 13....I'm 73 now. Believe me when I say I have seen a lot of people take one well meaning statement, and the rest is history. Perfect Example: Some 57 Chevy's had Fuel Injection.... So this guy I used to know drives his "Pristine" 57 Convertible home and yanks the 2bbl Carb off...Bends the Fuel Line down towards the open Intake.... Hops behind the wheel and gives it a few cranks.....FUEL IS INDEED being injected....just not the way GM had intended.
Nothing happens (Or So He Thinks) So he tries it again...It pops but that's it. In frustration, he closes the hood, goes in the house, makes himself a sandwich, and plops down in the sofa to watch TV..... Less than 10 minutes later the Fire Department is banging on the front door advising that the car has BURNT TO THE GROUND, and there was nothing they could do to save it.
I think you can guess the rest of the story...(The Burn Spot Is Still IN The Driveway) and that was 1966. I tell this story for the humor of it, because people don't always realize that what is in one case, may not be in another. Got to admit a cooling fuel line would have eliminated a lot of people stuck along side the road with Vapor Lock...in the hot days of the past....lol..... And I have been there as well.....lol.....
That's the sort of thing that sometimes worries me about these old cars. You get someone who doesn't know what they're doing working on them or you accidentally do something wrong yourself you could risk burning down the whole car.
That is exactly why I took the time to relate that story. Unfortunately Experience Shows Up, Right After You Need It.
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If you can find a station that sells 100% gas that will help out too. Alcohol has a lower boiling point than gas does.
When I replaced the lower hose on my 79' 403, the new hose did not come with the spring. Would that be the issue?
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BlueBaron,
You didn’t mention under what conditions you get vapor lock. Can we assume this happens at low speed and maybe bumper to bumper traffic? At this point I have only a couple more suggestions.
If your car has air conditioning what does the condenser coil in front of the radiator look like? Dirt, debris, fuzz balls, bent fins can impede air flow to the radiator. Refrigerant oil leaking from the coil will attract dirt and reduce air flow.
Do you have a fan shroud installed and is it the correct one?
You mentioned the fan clutch was replaced. Is it correct? You can find procedures online to verify the clutch is working properly.
Have you pressure tested the radiator cap? A cooling system under pressure has less air bubbles and is more efficient.
When the water pump was replaced did you check out the condition of the metal sleeves and rubber doughnuts that are in the timing cover? They should provide a tight seal to the rear housing plate.
While the fuel pump is stock and connected that doesn’t mean there couldn’t be crud in the return line. The line could also be crimped.
Last but not least what have you or anyone else done recently to the fuel or cooling system before you started having this issue?
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When I was in Colorado (high altitude) and warm summers, I was having the vapor lock issues. My engine was a 455 but the principle is the same. I did put one of the spacers under my carb and I added an electric fuel pump under the rear of the car, near the gas tank, to help "push" the fuel through the fuel line to the carb.
Worked like a champ and never had anymore vapor lock as long as I owned that car.
It is a low cost fix. You can try the spacer first, then add the fuel pump. I cannot remember the PSI but sure someone can help with that, just hook up to start the pump when the ignition is on.
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When I replaced the lower hose on my 79' 403, the new hose did not come with the spring. Would that be the issue?
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Its possible, ive heard the lower hose can collapse and restrict flow, thats why the spring is in there. Get the engine up to temp to get the thermostat open then rev the engine while watching the lower hose.