56 Buick

56 choke thermostat tube issue

Recommended Posts

Now the carb is running and the choke set. I am hooking up the thermostat tube that runs from the exhaust manifold to the thermostat housing. The housing is pulling vacuum from the tube but from what I can see the hole where the tube inserts is blocked off - meaning the vacuum cannot pull hot exhaust from the manifold through the tube and into the housing to move the thermostat coil. Attached is a photo of the tube going to the manifold ... is this the correct location? If so then why would it be blocked?

15775946407202773965018019193028.jpg

Share this post


Link to post
Share on other sites

It should not be blocked unless someone did it on purpose, who just wanted to eliminate the choke heat tube after it rusted off and didn't want an exhaust leak.  I pulled one that I have on my shelf now that somebody did that with.

 

Yank or drill it out and replace the tube that runs through the manifold.  It's most likely rusted out inside the manifold.

Edited by lancemb (see edit history)

Share this post


Link to post
Share on other sites

Just to be clear, the choke does not draw exhaust, that would destroy it. It draws clean air heated by the exhaust. If exhaust is getting in the tube, you will need to take care of that.

 

The pictures don't show enough for me to tell, but on some engine designs the tube runs clear through manifold and exits the other side. That way, there is exhaust heating the outside of the tube, and hot fresh air inside the tube for the choke. On some other engine designs, there is just a cast iron fresh air chamber in the manifold that gets hot from exhaust on the other side of the cast iron.

  • Like 1

Share this post


Link to post
Share on other sites

Another photo showing the hole the existing tube sits in. Feeling around with a dental pick, it definitely feels like a blind hole. And there is no hole directly on the other side of the manifold. There is a hole at 90° to this blind hole. It directly faces the dipstick and engine block and is difficult to access but using a piece of wire I can tell it goes in  fair way. It is certainly likely these holes could meet up but again the hole that the existing tube is sitting in, is blocked.

 

15776057847071195066053318195698.jpg

15776061779363187672770864266090.jpg

Share this post


Link to post
Share on other sites

The one on my '56 is attached to the port in the back side of the manifold.  Difficult to see or photograph.  

Share this post


Link to post
Share on other sites

Hi John, when you say 'back side' do you mean where the arrow is on the attached photo?  The arrow shows the location of a port or hole where the hole opening faces the engine. Thanks

 

location - Copy.jpg

Share this post


Link to post
Share on other sites

I am very familair with 57-58 design, and am guessing 56 was same way.  As bloo stated, the tube is meant to go all the way across the manifold, not letting exhaust gas in.  As one can imagine, they rust out easily.  When this happens it's better to block it off then leave it be.  Even better, replace the tube.

Share this post


Link to post
Share on other sites

To my knowledge these tubes are not reproduced, which is surprising to me.  They are very easy to make yourself though.  I made my last one out of stainless tubing I bought on Amazon for like 12 bucks.

Share this post


Link to post
Share on other sites
3 hours ago, 56 Buick said:

Hi John, when you say 'back side' do you mean where the arrow is on the attached photo?  The arrow shows the location of a port or hole where the hole opening faces the engine. Thanks

 

location - Copy.jpg

 

Went through this on both a 55 and a 56. The arrow above is the correct side where the heat chamber is.  If you stand at the passenger fender facing the passenger bank of the engine, the port that the carbs heat pipe plugs into is almost directly behind the leftmost (nearest the firewall) bolt that attaches the exhaust manifold to the cylinder head.  Now - assuming all the passenger side 56 manifold designs are the same for this feature, just feel around the back left side of the manifold and you should feel a small pipe about 1/8-1/4 inch sticking out.  I believe the heat passage is fully cast into the 56 manifold.  The chamber does not allow exhaust gas to enter, rather pulls air across some risers cast inside the manifold that act as a heat exchanger.  On the 55 manifold (mine at least - early 55), there was a metal plate riveted over the top of the chamber which disintegrated over time.  WIth that plate gone you could see the inside the chamber = the cast "risers" that the outside air was pulled across to warm the outside air to the choke. 

 

Where the pipe is in your photograph looks more like something that was drilled pr a casting hole to accommodate the pipe.  On my 55 manifold, since the heat exchanger was useless without a cover and the nipple to attach the heat tube to also gone,  a heat stove "kit" was installed into the manifold - basically a bolt that has about 1/4 - 1/2 inch hollowed out in it that threads and seals into a hold drilled into and through one wall of the manifold.  The carb heat tube sits inside that hollowed out bolt section.  Not original but worked great and the choke opened up quick.  No running issues.  So the way the heat tube is sitting in your original picture reminded me of that. 

 

The heat tube routes from the carburetor alongside the inside back of the valve cover, follows the block down near the oil pressure line and connects unseen behind the exhaust manifold.  When I switched to the 56 motor I made it a point to remove my earlier fix and return it to proper configuration.  Looks better too.

 

Pictures below courtesy of eBay. Look to far left of the manifold you can see the pipe sticking out. The hole in the middle near that square feature below looks like where your inlet pipe is setting. 

 

image.thumb.png.fa7db8e92bc0bf84f4c19ab745a7b0c2.png

image.png.1bcf4f9ce091b56137b5cbccf7bf7c00.png

 

The car was just running today so its uncovered and accessible - could probably snap a pic if you really need it.  Hope this helps.

 

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites

Check out the thread "Vacuum Line routing to choke" from two weeks ago in this same forum category, bought the kit from CARs, flared one end, bent the other end around so it slipped into that inside manifold nipple then simply bent it toward the choke, slid on provided insulation, screwed the brass nut on the choke threads, easy! had what appeared to be plumbers putty plugging up the hole, it dug out easily when I did the carb rebuild. 
couldn't figure out how to gather the frayed insulation ends, thus the tape for now 

6F3B7F6E-AFBA-4D62-8CF3-A8316E83F0FD.jpeg

CAC407EF-BC29-430B-A1EF-5AAB475EB88E.jpeg

Edited by jw1955buick (see edit history)

Share this post


Link to post
Share on other sites

Okay great. Thanks all. I have located the tube sticking out of the manifold. The existing tube was clearly in the wrong spot.

  • Like 1

Share this post


Link to post
Share on other sites

FYI after some investigation I have found that the other side, of the tube sitting out at the rear of the exhaust manifold, is actually the hole in the centre of the manifold that faces the engine block (see arrow in photo within previous post above). I have now bent my existing tubing to run from this hole up to the choke thermostat housing. Appears to operate the choke thermostat but the tube certainly gets hot. Is there a danger of overheating the carburettor with these thermostat tubes?

Share this post


Link to post
Share on other sites

No. You just need to be sure it is pulling hot air and not exhaust. It is meant to get hot.

Share this post


Link to post
Share on other sites

I will pull it off after a drive and see if there is any soot as that should indicate if it is pulling exhaust. Thanks

Share this post


Link to post
Share on other sites

To clarify, here is a pic showing the tube path on a 57 manifold.  The 56 manifold uses the exact same tube, through at least 59 (and I think 60).  The pencil shows the path of the tube and you can see it sticking out on the bottom.  The other pic is of the tube itself when not installed (an NOS example).

20200105_141153.thumb.jpg.026f0da307bf1491400f98047a03d5c2.jpg

 

20200104_213317.thumb.jpg.b79dbfb22608f8d2a1ab125963ab54cd.jpg

  • Like 2

Share this post


Link to post
Share on other sites

Just for info, how hard are those tubes to pull if they were to be replaced?

Share this post


Link to post
Share on other sites
19 minutes ago, 56 Buick said:

Just for info, how hard are those tubes to pull if they were to be replaced?

Easy.  You can just drill out both ends and it will then be loose.  You can then fish it out pretty easily.  It's easy to make your own, too.

Share this post


Link to post
Share on other sites
54 minutes ago, lancemb said:

Easy.  You can just drill out both ends and it will then be loose.  You can then fish it out pretty easily.  It's easy to make your own, too.

 

I just looked at my spare '56 manifold and saw that tube, just like you said.  However, the end of the tube is plugged just like @56 Buick said.  That hole on the engine side does appear to be the air inlet, but the tube appears to be solid.  So I am wondering if the tube is perforated in the area underneath the label.  If not then how does the air get drawn into the tube to be heated?

 

 

Share this post


Link to post
Share on other sites
Posted (edited)
39 minutes ago, JohnD1956 said:

 

I just looked at my spare '56 manifold and saw that tube, just like you said.  However, the end of the tube is plugged just like @56 Buick said.  That hole on the engine side does appear to be the air inlet, but the tube appears to be solid.  So I am wondering if the tube is perforated in the area underneath the label.  If not then how does the air get drawn into the tube to be heated?

 

 

 

The air does not need to get drawn up the tube to the choke. The  tube itself slowly gets warm allowing the choke coil to slowly warm until it kick down the high idle cam.   If direct smoldering hot exhaust was pushing up that tube the plastic choke cover and probably the housing would melt 

Edited by avgwarhawk (see edit history)

Share this post


Link to post
Share on other sites
42 minutes ago, JohnD1956 said:

 

I just looked at my spare '56 manifold and saw that tube, just like you said.  However, the end of the tube is plugged just like @56 Buick said.  That hole on the engine side does appear to be the air inlet, but the tube appears to be solid.  So I am wondering if the tube is perforated in the area underneath the label.  If not then how does the air get drawn into the tube to be heated?

 

 

The tube is not perforated (that would be bad, to draw in exaust) and goes all the way through like a straw.  If yours is plugged, it shouldn't be.  It should draw in fresh air through the bottom.

Share this post


Link to post
Share on other sites
16 minutes ago, avgwarhawk said:

 

The air does not need to get drawn up the tube to the choke. The  tube itself slowly gets warm allowing the choke coil to slowly warm until it kick down the high idle cam.   If direct smoldering hot exhaust was pushing up that tube the plastic choke cover and probably the housing would melt 

Hmmmm if I disconnect the tube on my engine then the choke thermostat housing is definitely pulling a vacuum through the tube attachment, so it appears that when the tube is attached then it will be pulling hot air. My choke thermostat housing cover is metal.

Share this post


Link to post
Share on other sites
Posted (edited)
56 minutes ago, 56 Buick said:

Hmmmm if I disconnect the tube on my engine then the choke thermostat housing is definitely pulling a vacuum through the tube attachment, so it appears that when the tube is attached then it will be pulling hot air. My choke thermostat housing cover is metal.

 

If I'm not mistaken the vacuum is present in the choke housing to open the butterfly valve. There is a passage with piston type set up that opens the butterfly valve. 

Note the cylinder shape inside the choke housing with a arm attached. This operates the butterfly valve via vacuum as I understand it. 

 

Q1222-w600-2l.jpg

Edited by avgwarhawk (see edit history)

Share this post


Link to post
Share on other sites
21 minutes ago, avgwarhawk said:

 

If I'm not mistaken the vacuum is present in the choke housing to open the butterfly valve. There is a passage with piston type set up that opens the butterfly valve. 

Note the cylinder shape inside the choke housing with a arm attached. This operates the butterfly valve via vacuum as I understand it. 

 

Q1222-w600-2l.jpg

I believe you are correct but I am sure I can feel suction at the point where tube attaches to the choke thermostat housing cover plate.

Share this post


Link to post
Share on other sites
48 minutes ago, 56 Buick said:

I believe you are correct but I am sure I can feel suction at the point where tube attaches to the choke thermostat housing cover plate.

 

I'm sure you do as this port is now open and free to pull vacuum. When the tube is attached to choke housing and the other end is plugged into the manifold dead end a open vacuum source is now eliminated. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now