The Stovebolt Site Forums The Shop Area Engine Shop Heat Riser Valve

My truck has a heat riser valve that moves freely and seems to open when it's supposed to.

I haven't experienced problems that can be attributed to this device. However, I generally remove them or disable them on all cars I own due to the possibility of sticking closed or partly closed.

Anyway, I assume that the default position is closed and that unhooking the spring from its post will allow the counterweight to keep the valve in the open position at all times.

I live in Atlanta so cold weather warm-ups aren't really a concern.

Should I leave the spring unhooked and run with the valve fully open all the time or should I leave well enough alone and leave it hooked up to open with the exhaust flow?

Removing the the thermostatic spring will cause the heat riser valve to close blocking the exhaust from heating the bottom of the intake manifold.

The pictures came from Trifive.

The spring is also an antivibration spring. Some say they can hear vibration (valve shaft against manifold) if unhooked.

Do you need a working heat riser in Atlanta? Wikipedia says:
"Carburetor icing most often occurs when the outside air temperature is below 70 degrees F (21 degrees C)
and the relative humidity is above 80 percent."

Fortunately when the temperatures are that low in Atlanta, the humidity is also low.

We get the high humidity in the summer when the temps are well above 80F.

I actually experience carburetor icing once in my life about 21 years ago.

It was in my '56 Cadillac in February. It was a fluke temperature and humidity thing. Temp was in the upper 30s but the humidity was extremely high. There was a wet fog/mist in the air - some freak weather thing that never happens around here and I've never seen since.

My car conked out and I opened the hood and saw a thin film of ice on the base of the carb. Inside the carb was choked with ice. It thawed out pretty fast after the engine was turned off just from the ambient heat under the hood. I was literally within sight of my house so I drove home and it's never happened again.

Can this valve contribute to vapor lock on these engines?

Think about all the research, development and manufacturing money GM could have saved if a heat riser really was not necessary. Of course, hotrodders have always been smarter than the guys who make a living designing engines.
Jerry

Jerry, I agree with you and don't hotrod or modify any of my vehicles to any significant degree. I generally believe the designers knew best.

However, today's fuel isn't the same as it was 70 years ago. Sometimes what worked then can be a hindrance today.

I was forced to block the exhaust crossover passages on my Toronado intake manifold because it heated up the carburetor base so much I was experiencing vapor lock.

70 degrees is cold when taking into consideration that the operating temperature is 180 degrees. Disabling the heat valve will cause atomized fuel to come out of suspension, resulting in puddling of liquid fuel at the bottom of the "cold" intake runners which will not burn, but rather, leak down past the piston rings and into the crank case, contaminating the oil. This will shorten the life of moving parts throughout the engine. This will occur even in Georgia.
You probably don't notice the engine stumbling when taking off right after startup on a cold day like us folks further north where it gets much colder, but the oil contamination is still occurring.

Otto, please don't rattle Jerry's chains.

I can see your point about vapor lock.
There should be a thick insulator below the carburetor.
If this is not good enough I would install a heat shield.
I've seen one on an Oldsmobile flat 6.
Another solution is to install an electric fuel pump.
Please open another topic if you wish more discussion.

I haven't disconnected the heat riser and don't intend to. I was was just asking to see what most people do.

Haven't had any problems with the engine running or with vapor lock.

The counterweight, plus the volume of exhaust gas at any speed above idle, will force the heat riser to the "cold" position as soon as the engine starts if the bimetal spring is disabled. It really is necessary for a quick warmup even in so-called "warm" climates. It should be completely released due to the geometry of the flap and pivot shaft within 5 minutes or less after startup.
Jerry

Mine is installed backwards so I leave it jammed open. This is not ideal of course, but it is better than running with the heat shield closed.

How did that happen?

My 59 235 was missing the heat riser valve when I got the truck. It seemed to run well but had a few issues I thought were related to missing valve. I replaced the manifold with a working heat riser and indeed it ran better and no longer had the hard start when warmed up well. It also no longer showed frost on carb body at times. One time in about a thousand miles of use it iced the carb to the point I had to wait for the ice to melt from engine heat before it would re start. I am happy with the result of the repair.

Someone must have disassembled the manifold and valve and reassembled it wrong.

Otto Skorzeny Here in Illinois where it gets colder than a well diggers butt,I cut the flap out,weld the holes shut with stainless. Then using new forklift propane carburetor fix my trucks so they will start and run in cold or heat,no sludge,oil stays clean,no fuel pump,no dirty lines or tank. Just one filter,can trouble shoot easily,keep an item or 2 with you on the road. Also never cold natured,don,t wash cylinders down every day with gasoline !!

Otto Replied...went in cloud

Post pictures of your conversion. Do you keep the propane in a tank behind the seat?

How many miles per gallon (or pound) of propane do you get?

Otto replied to you,went in cloud.

What do you mean?

Otto nearly missed your question,Never keep propane in the cab,will smell it from fueling. Any propane forklift system is the same thing.I do a few things to the system to get the best service. Economy is not over 8 or9 mpg, now my injected 04 GMC 1/2 ton does as hi as 14. This is mostly a buying at the right time (summer) situation,it's great to have fuel at home. You do however have to become a storage specialist (tanks,valves,fittings,pumps,gauges) . Right now while gasoline is 6$ am winning some with 1.41$LPG. Have not become a very good internet photographer yet,hope this message gets to you.

Otto I have a hard time getting messages to stay up,may be because I live in the wilderness,however I am close to L.A.right now so don't know.