The heat riser valve. Really important, or really NOT important?

The heat riser valve on my 1967 Mercury Park Lane is functional, but it rattles. I've had people say you don't need it and to replace it with a dummy (which I have yet to find). I believe the heat riser valve was installed for a reason, otherwise why would the designers include it? The shop manual sure makes a strong case for it, but the majority of people I speak to say to take it out.

Which is it, then? Keep it or toss it?

Plus, isn't it keeping the car "original" by leaving the heat riser valve intact?

I would suggest trying to keep it original. In all truth, in a nice warm southern environment, you could get away without it, but I would suggest keeping it original.

if its rattling, its notworking

Use wire to hold it in the open position until you can find a new one, it will help the car run better in cold weather startups.

It's not necessary...even in cold weather. Car will run fine w/o it. Maybe in Alaska in the winter you might want one...

I would repalce it w/the proper part for the sake of originality LONG before replacing it due to any concern about drivability. It's just not an issue.

It's not necessary...even in cold weather. Car will run fine w/o it. Maybe in Alaska in the winter you might want one...

I would repalce it w/the proper part for the sake of originality LONG before replacing it due to any concern about drivability. It's just not an issue.

Odd. In the very benign climate I live in I do find that having a working heat riser makes a difference in cold start drivability especially during our "winter" when the morning temperatures are in the 40F range. That first mile or so takes a bit more futzing with the choke and hand throttle if the heat riser is not functioning properly. I'd expect that it would make an even bigger difference in places where it actually gets cold.

Maybe it is just me and my car....

I think that you're talking about an entirely different animal. I don't know what your car is but you mentioned hand choke and hand throttle; sounds like the 20's to me?

The OP is talking about a '68 Ford. IT should have an automatic choke and run "good enough" w/o the heat riser, until the choke fully opens on it's own...at which point the floor of the V8 engine's intake manifold will be hot due to the exhaust crossover passage.

The heat riser is necessary for proper operation and not only is the choke involved but as mentioned by the previous post,the heating of the base of the manifold where the gas/air mixture enters the combustion chamber. Probably not the answer you want to hear. Most questions posted already have the answer.

I have no compelling reason to remove the heat riser valve, except that it does rattle. And when I said it's functional, it does really work as it should, but one side, opposite the spring, has lost its bushing, so the little tiny axle just rattles around inside the shaft. At idle, it sounds like a very loud rattling coming from the engine.

I just need to fix that somehow and I'll be set.

Rebush and/or add an anti rattle spring...........Bob

The heat riser valve ... Which is it, then? Keep it or toss it?

I'm absolutely NO expert, but something tells me that you should have a functional one.

I have just started working on a 1978 Dodge van with a 400-V8. Several hours of service later, it's finally running well. After taking it out on the highway for a 20-minute workout, it was HOT. Very HOT. Faulty heat riser valve? Not sure just yet.

I posted some questions about fuel on another web site (http://www.forbbodiesonly.com/moparforum/showthread.php?76681-new-Dodge-Tradesman-200-Funcraft-campervan-(400-cid)-running-rough). One user said he cooked an exhaust valve because of excess heat due to a faulty heat riser valve (HIA (Heated Inlet Air) System).

If it's there, it's needed. Not my opinion but the opinion on hundreds of professional engineers working on engines for many decades.

Hope all works out well!

Years ago I had a slant six Dodge pickup with hand choke. One year I went to the trouble to get the heat riser valve, hot air stove,and hand choke working to factory specs and was absolutely amazed at the difference it made. The motor started and ran just like fuel injection with no hesitation or warmup required. It also warmed up in half the time, with an improvement in convenience and gas mileage.

This and a few other experiences convinced me that it is always best to keep to factory specs.

On the other hand, it will probably run acceptably without the heat riser especially in warm weather. But will run better with it.

This assumes the passage in the intake manifold that carries exhaust from one side to the other, is clear and functional. On old cars they usually aren't.

If it isn't necessary why did the auto makers put it there? They aren't going to spend money on something they don't need. As Rusty says, the drivability of any vehicle will improve dramatically with a properly functioning heat riser and a clear exhaust crossover. At best, it will run poorly until it warms up. At worst it will stall repeatedly when it is put in gear with a cold engine.

Terry

Well, ^that question could be asked of a plethora of systems on any vehicle, and if that was our method for determining the importance of OE equipment on a car, we'd never modify anything!

Here is the answer; The OEM's need to meed criteria that we don't (always) care about. Emissions -and I'm not talking about the same emissions that our cars have to "pass"...OEM emission criteria are much more stringent. COLD weather drivability. HOT weather drivability. CAFE (depending on year). Engine/vehicle life expectations. And so on. Using just the temps criteria as an example, the OEM's have to produce cars that will start and run (for even the "lowest common denominator") in the arctic.....and also not over head, boil fuel etc, climbing Davis Dam in Arizona, in July. That is quite a spectrum. Using a catalytic converter as another example, "why did the auto makers put it there? They aren't going to spend money on something they don't need."....right? So is that "proof" that a car needs a catalytic converter in order to run well? Of course not and in many cases, that converter makes the car run/perform WORSE. So why did the automakers spend money on something that in many cases, makes the car run/perform worse? THey had to meet emission criteria. So the fact that (some) cars came w/converters isn't proof that cars need converters to run right. That cars came w/heat stoves isn't proof that they NEED a functioning heat stove to run right. When we understand the function of a part or system, how we use our car, and our own expectations....we can then make our own decisions, as to what's important, and what is not.

How do WE operate our cars? I'd guess that most on this forum operate their cars in mild, temperate to hot conditions, so we aren't exposing our cars to the conditions that the OEM's had to consider. That is why in the context of this thread, "The heat riser valve. Really important, or really NOT important?" I say it's not REALLY important. It may help drivability for the first 30 seconds....maybe, and I'd submit that in temperate conditions, if it IS helping, it's "covering" another problem or system that isn't functioning properly. Rusty OToole made a good point that in many old cars, the exhaust crossover in the intake gets plugged up and isn't as effective. In this case, the heat stove/hot air intake could help for the first several minutes, until the coolant and oil temps warm the intake. And there are plenty of older cars that don't have properly tuned/adjusted carbs, chokes, timing, etc. I've owned plenty of carb'ed cars that have no hot air intake and start and run absolutely fine -my boat is a prime example; '92 Mastercraft w/a 351w and a Holley 4160 carb. Electric choke, open element air cleaner (flame arrestor). Fires instantly (cold) w/one pump, and idles fine. The heat stove is primarily there for subfreezing conditions, and to meet criteria that we generally don't care about.

It is my experience that on a cold start on a cool day (below 5 to 10 deg. C or so?), the carburettor ices up just below the venturi. The heat riser valve prevents this. The icing is caused by the expansion of the air & fuel mixture, which requires heat, so it takes it from the environment. My heat riser butterfly is frozen and has no operating lever so does not work. I start the car, idle for 5 mins and shut down. Five mins later I can restart and drive off - the area has warmed from the exhaust manifold. This is in the 1930 Dodge. The 1939 Studebaker also has a heat riser valve, which operates with a bi-metal spring. The Dodge one is manually operated.

In later models, I expect the same effect would occur but improvements in carburettors and engine design in general perhaps make it less noticeable.

I've heard of carb Icing...never seen in in my life on cars ranging from 1910 to the mid 80's, bikes, even snowmobiles. I was taught about it in auto school...but never have seen it happen. Have you looked in the carb and seen ice build up?

Spinneyhill is 100% correct.

I started my 53 Plymouth and drove straight to Ellensburg from Seattle in the early damp AM in the fall.

Pulled into the gas station and the car imediately died. Opened the hood to find a 1/2" of ice surrounding the carb base. % minutes later the ice melted and the engine idled and ran fine rest of the trip.

I did free up the heat riser and tjhat did not happen anymore plus the car ran smoother during warm ups.

I have seen this many times here in the NW-Dodge 318/360's being one of the worst to throttle plate ice up. Intake heat passages carboned up.

I've heard of carb Icing...never seen in in my life on cars ranging from 1910 to the mid 80's, bikes, even snowmobiles. I was taught about it in auto school...but never have seen it happen. Have you looked in the carb and seen ice build up?

I had the carb ice up on a '72 Cutlass one very cold Wisconsin night when the flexible tube that ran between the exhaust manifold and the air filter intake became disconnected.

Crazy. My '83 Trans Am got driven all over New England in all typed of conditions, out to Colorado for ski trips, never seen it happen. I'd like to witness that once.

My 1973 Honda XL175 "trail" bike iced up one day when we were out playing in the snow. The bottom of the carb was a block of ice. When it stopped I kicked and kicked it to no avail until I looked and saw the ice. Once I allowed it to thaw, it started first kick and off we went. BTW, it was an excellent day playing in snow and ice in an area of plantation forest that had been logged and was ready for replanting. I got about 1 m onto the ice on the lake before landing on my side. Power slides all over the gravel forestry road with no traffic to annoy us.

Oh, we were late back to our photogrametry class too, wet and cold from thigh downwards and elbows down. What a blast!

It might have a lot to do with humidity. I suppose low humidity air is less likely to form ice. Remember you also have a 6 or 8 mm thick insulator between the carb and manifold too. Engines have higher volumetric efficiency on cold air (and mixture) than hot air.

God is protecting you from cold high humidity flowing deep into your carburetors venturi's.

http://www.atsb.gov.au/publications/2009/carburettor-icing.aspx