The Stovebolt Site Forums The Shop Area Engine Shop 228 GMC question What is this?

I have a question about a part on my 228. There is a length of tubeing that originates on the intake manifold under the carb and runs up to the top of the intake and goes into a fitting between 5 and 6. It seems like an unecessary loop of vacuum. Anybody know what and why this is there? Mine is made of copper and looks like someone put it there. Anyone got a pic of a stock engine that shows this? Thanks for any help, advice!! Sincerely, Smitty

what year truck? Pics? Does it go in on the left or right side of the engine?

Sorry for not supplying enough info. The year is 52. It is all on the intake manifold. I just can't figure out what it is for.

It is a common modification to use water for heating the intake manifold instead of using exhaust.

Does the mystery tube go from under the intake to a large fitting on the top of the head? If so it is to return the hot water returning into the temperature sensor hole.

Is there another copper line going from under the intake back to the water pump or thermostat housing? If so my guess is right.

Thanks to all for responding! There is no water in play here. It is merely a fitting on the manifold on the side under the carb. Tube then travels over to another fitting on the manifold in between cylinders 5 and 6. It is just a loop from one part of the intake to another.

I just thought of something. My truck has been converted to electric wipers. I wonder if one of the fittings was origionally the vacuum wiper tap? Any thoughts, Thanks

well, looking at my 228, I have a vacuum fitting on the top of intake, between cylinders 4 and 5. Although this is not hooked up, I believe that is the vacuum port for my windshield wipers. the vacuum under the carb, I would guess goes to your vacuum advance on the distributer.

I may be wrong. Do you have a line hooked up to the vacuum advance on the distributer? Maybe somebody connected the tube to seal up a vacuum leak for those missing accessories.

well, if only I could've typed a little faster...

Hey bigbad! Guess what!! You were right about the fitting and also I discovered that my vacuum advance was not hooked up at all! The copper line was connected together way down in the darkest area of the engine with a piece of rubber tube. It had come apart and as a result, she wasn't running too hot! Got it all straightened out, Thanks! Smitty

As a sidebar, I am wondering what the reason for the other taps for engine vacuum would have been used for?

Maybe a hydra-vac? A vacuum powered wolf-whistle?
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