Packard Forum Index » Pre-War (1899-1942)

My own experience with the heat riser on my V8 Caribbean is that I omitted the entire unit when I installed a new exhaust system, and I regret it. The car is very "balky" for a few minutes until it begins to warm up, even with ambient temperatures as high as the 60s. I intend to reinstall it.

The latest issue of Hemmings Classic Car that arrived in my mailbox has a feature on the development of the Rochester mechanical fuel injection system (1957). One of many things they had to take in account was that at 60^F, there was only something like 50% vaporization of gas. This important because only vaporized gas burns - the rest gets wasted.

As such, in a carbureted car the manifold heat valve is very important to performance during warm-up.

My father worked as a mechanic in a Packard dealership, but when the dealer switched to Chrysler product (when the Studepackards came out), my dad moved on to a Chevy dealer, where he soon became Service Manager. He swore by a chemical supplied by GM as (IIRC) "Manifold Heat Valve Lubricant", which is still available through GM dealers under the same part number (#1052627), but now called "Rust Penetrant and Inhibitor", with "Heat Valve Lubricant" as subtitle on the can.

If that doesn't free the valve up, then it may be "hammer-time".

I thought that's what the electric choke is for (AFB). Until an educated guess is actually tested, it still just that.

Joe H

IIRC, the electrically-heated thermostatic choke coil was a replacement for the tube on earlier cars (like our Packards), through which heated air was drawn across that bi-metal coil. The air drawn into that tube was heated by the flow of exhaust gas passing through the exhaust crossover passage in the intake, but that only happens when the manifold heat valve is closed. Heating the choke coil causes the choke valve to be unloaded, but that force is counterbalanced (at least in our Packards) by vacuum applied to a piston in the choke housing (via an internal passage).

Yet, heating the choke was a secondary function; the primary purpose of that exhaust crossover passage was to heat the intake manifold so vaporized fuel wouldn't condense back into liquid following a cold start.

Of course, I am talking from a perspective of V8 experience, in response to Owen_Dynetos' post, and drifted from an initial offering of info on chemicals to free and lubricate the heat valve. How it all works on an old straight eight is beyond me, but the underlying reasons for having the heat valve still apply.

The electric choke is only for choke operation. There is still some kind of exhaust manifol heat wheather thru the intake manifold or thru a hose from the exh manifold to the air cleaner snorkel. Many people thing the hose from ex manifold to air cleaner is some part of emmisions. It's not.

A certain amount of carb heat is necessary except under hi speed HOT conditions. Carburetor icing can occur at ambient temperatures as high as 50 degrees F. NOTE that many small air planes have MANUAL carburetor heat controls due to altitude and temperature changes. Cord L29 had a manual choke and a carb heat push pull knob on the dash.

My 56 Exec runs just fine without the heat riser even in very cold weather. HOWEVER, i have two different mufflers and one is a so-called turbo muffer so i'm guessing that a small amount of heat is always passing under the carb. It should yield better mileage. Also note that the 45XLS plugs area rather HOT plug which yields good cold engine performance.

Well day #3 Ive been soaking it 2 times a day and tapping on both ends of the heat riser shaft while hand twisting the counterweight but nothings happening yet. Still as solid as a rock. I'll keep trying until monday then I think I'll remove the exhaust pipe and have at it with a sawsall with metal blades. So far that PB Blaster hasn't done much.

Have a little patience. The Blaster can't undo in a day what has taken years to build up. If anything can free it, it is PB Blaster.

I agree with Randy. PB has worked miracles for me. It works great on brake/fuel line fittings also before using a flare nut wrench.

It also works wonders on pertified rubber. Just spray the heck out of a rubber part with PB, and put in a ziplock bag for a couple of days, and you would swear it was a brand new rubber part.

WAAAAAHOOOO! Day #4 just went to garage and gave it another squirt. wacked it with the hammer and ITS FREE.
Stiff but I can move it all the way up and down by hand. Now all I have to do is figure out which is open and closed.
You guys came through AGAIN - A BIG THANK YOU

The counterweight should be fully up (held by the coil spring tension) when the motor is cold, and down when the motor comes up to temp (as the coil expands).

The spring should just hold the counterweight in the full up position when cold, but no additional tension.

Also it should move freely. If it is still stiff, then keep spraying cause you want it too move freely. You could pull the exhaust pipe and give it a couple sprays from the inside if it doesnt get any looser.

I hope this helps.