News:

Due to a technical issue, some recently uploaded pictures have been lost. We are investigating why this happened but the issue has been resolved so that future uploads should be safe.  You can also Modify your post (MORE...) and re-upload the pictures in your post.

Main Menu

Heat riser necessary?

Started by Bob Kielar, January 15, 2018, 08:15:09 AM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

Bob Kielar

Hello all,
               When taking my old exhaust off my 55 Cadillac the heat riser luckily was stuck open. It has been stuck open for I don’t know how many years also the shaft was broken. When I tried to remove the shaft the housing broke in two. I bought a used one and it was also stuck but I got it to work. I’m not that confident that the used one will hold up what would happen if it won’t open? So my question is are they necessary my Cadillac ran fine with the riser stuck open.
Regards,
Bob Kielar
Keep Cruzin
1955 Cadillac Fleetwood

Dave Shepherd

The function was to warm the carburetor base, under certain temperature and humidity conditions  icing up of the butterflies could occur.  So based on your experience seems you don't need it.

TJ Hopland

I suspect there are a lot of them stuck open and it doesn't seem to hurt anything.   It was probably more of an issue when these were year round daily drivers that people expected be able to turn the key and pretty much immediately go.

If they stick shut it does seem to cause problems.    Both heads have an exhaust passage in them that connects to a passage through the intake.  When the valve is closed it basically forces all the exhaust from that side through that passage into the other head where it can finally go out that manifold.   Its very restrictive so performance is terrible.  Because its so restrictive and low flowing it gets really hot.  This could cause fuel to boil in the carb so you get vapor lock even on cool days.   Some designs the passage is actually open under the carb so it gets extra hot and burns out gaskets which then turns it into a massive uncontrolled EGR system which will result in terrible or no idle.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

"Cadillac Kid" Greg Surfas 15364

Bob,
If you are going to drive your car in your neck of the woods between May and September you should have no problems.  If performance is also not an issue, you can do without the heat riser.  Besides assisting in warm up, the exhaust heat diverted to the intake passage assures that when the temperatures are very low (below about 50 degrees,) and/or very humid the gasoline in the mixture that has just gone through the carburetor is kept in suspension and does not drop out and run into the cylinders as a liquid.
Liquid Gasoline does not effectively burn but can run down the cylinder walls washing out the rings, diluting the oil and in turn causing Havoc.
Depending upon your usage you might do without the heat riser, but I would have to believe that if they were not necessary those Engineers working for Automobile manufacturers around the world for many decades would have figured out a better way.
As far as keeping the heat riser valves operable, that seems to have been a maintenance procedure included in normal standard maintenance.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Caddy Wizard

#4
Stuck open is not a big worry in warm weather.  In cold weather, if the riser is stuck open or omitted, it will run rougher when warming up.  It can also lead to icing of the carb in cold weather (I think). 

Stuck closed is more of a problem, as it sends hot exhaust gas under the carb all the time, even when you don't need it (like when the engine is fully hot in the middle of summer).  This can lead to vapor lock issues by itself. 

I made heat riser eliminators for many years and sold them for about $25 including shipping.  But I stopped doing that and turned over my inventory to Fusick's.  I think they still sell them...
Art Gardner


1955 S60 Fleetwood sedan (now under resto -- has been in paint shop since June 2022!)
1955 S62 Coupe (future show car? 2/3 done)
1958 Eldo Seville (2/3 done)

Jon S

The heat riser valve is NOT required. GM used them to improve cold weather operation. Ford never used them. I eliminated mine years ago and see absolutely zero difference in cold operation.
Jon

1958 Cadillac Sedan De Ville
1973 Lincoln Continental Coupe
1981 Corvette
2004 Mustang GT

"Cadillac Kid" Greg Surfas 15364

I would venture to say it just might get a bit below "cold" where Bob is.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Mike Josephic CLC #3877

The maintenance of the heat riser valve to keep it working freely
is simple.

Lubricate it several times per year -- but NOT with just any old
lubricant.  Due to the high temperatures on the exhaust graphite
in alcohol is what you need.  It's sold nowadays under the name
"Lockease" (it's used for locks also).  The alcohol quickly evaporates
off leaving graphite on the shaft.  Any regular type of oil just burns
off and leaves gunk.

Mike
1955 Cadillac Eldorado
1973 Cadillac Eldorado
1995 Cadillac Seville
2004 Escalade
1997 GMC Suburban 4X4, 454 engine, 3/4 ton
custom built by Santa Fe in Evansville, IN
2011 Buick Lucerne CX
-------------------------------------
CLCMRC Museum Benefactor #38
Past: VP International Affiliates, Museum Board Director, President / Director Pittsburgh Region