heat riser: necessary or not?

[fullsizeBlazer]

Hey,

is the heat riser (mounted on the end of one of the exhaust mainfolds) a necessary / good eqipment, or don't you necessarily have to replace it (when the old one is shot) ;)


thanks

Flo

[DmaxMaverick]

It is necessary for two purposes, both are emission system related. It helps with warm-up (after a clean start, and before it is up to operating temp), and provides back-pressure for efficient EGR operation. It kept the EPA happy (they are never happy for long). If you live without EGR, then it's extra (unnecessary) baggage. Otherwise, it is required for emission system compliance.

If you eliminate it, you can either remove it (and adapt the pipe/manifold connection), or leave it in. If you leave it in, remove the butterfly and shaft, and plug the hole with a carriage bolt (inserted from the inside, about 5/16" X 1.5" long, IIRC), secured with a nut on the outside. This also eliminates an exhaust system restriction, for whatever that's worth.

[Robyn]

Technically its called the EPR valve = Exhaust pressure regulator.

Its sole function is to cause a flow restriction so that the exhaust will flow up though the intake manifold to the EGR valve.

As Maverick mentioned it causes a back pressure.

A valve that has all the linkage and other goodies in place but has the butterfly either removed or fixed open will give the best performance.

EGR skunks up the intake on these engines terribly, even if the system is working properly.

On a high mile EGR equipped engine large chunks of carbon form in the intake runners and around the valves.

Every so often a large chunk of that carbon falls off and heads right into the cylinder.
The results are a terrible knocking and banging inside the engine due to the pile of smashed carbon on the top of the piston.

There is only about .035" clearance between the piston and the head, add to this a chunk of carbon the size of a hall closet and you got troubles :eek:

The EGR also causes loads of power loss if it fails to work properly and that is only a matter of time before that happens.

If you have to pass emissions testing and the tech knows what he's looking at, the EPR valve and the related hoses and pieces had better be there.

To be real honest though, there is little way to tell if the stuff is working or just taking up space unless the test facility has some
very sophisticated test equipment.

The EGR bleed at idle reduces peak burn temps and helps lower NOX levels.

If the EGR pops open at highway speed the result will be enough smoke to kill a whole swamp full of skeeters.

The reason is that the exhaust dilutes the intake air stream and robs the engine of oxygen.

The "Horse pressure" will go right out the window too if the EGR is open when it's not supposed to be. :eek:

Hope this helps.

Missy

[fullsizeBlazer]

Hey,

thanks a lot for your answers! According to what you wrote, I think I'll have to throw out the whole EGR system soon/ or not reinstall it on a new or rebuilt engine (I planned on doing that anyway) ;)

Greetings

Flo

[DickWells]

I assume you're talking about a gas engine? Anyway, a carb throat can freeze up at anything bleow 55Deg F. Especially, if it's humid. A 71 Toyota Corolla 1200 didn't have any heat rizer in it, for some reason! Took me several weeks to figure out that in humid weather, it'd choke up like crazy after about 30 minutes of steady driving. Finally, one morning I jumped out and tore off the top of the air cleaner, and there was a ball of ice, allmost completely blocking off the carb throat! I busted it up with a screwdriver and after the smoke cleared, finished the trip into work. That night, I built a little shroud around the ex manifold and used a flex hose up to the air cleaner, and had to leave it in place as long as I had the car, except through the hottest of summer weather.

[Robyn]

Hmmm
I assumed he had a 6.2 powered rig with the "C" engine.
These have a device that looks similar to a "heat riser" but is simply a restrictor in the LH exgaust manifold to route exhaust over the top and supply the EGR with enough gas pressure to function.

The heat riser was all but eliminated on later gassers in favor of a hot air feed off the exhaust manifold.

The "hot box" supplies heated air right off the exhaust manifold and feeds this into the air cleaner assembly.

Works much faster and is more effective at controlling Iceing in the carb throat.

Now with the fuel injection, most engines inject the fuel right into the intake ports and the manifold runners are handling air only so the issue is a moot point anymore.

The early TBI units still had heat supplied as they could ice up due to the fact that fuel was sprayed into the throats above the throttle plates.

A flap type heat riser has been a thing of the past for many years now.

The EPR valve on the "C" series 6.2 engines was a real PITA as it could and would fail in the closed position, causing all or most of the exhaust from the LH cylinders to be forced across the passage in the manifold and making it much harder for the engine to beathe.

The EPR was only supposed to function at Idle or at times when the throttle was very low.

There are two vacuum solenoids mounted on the LH Valve cover.
These supply vacuum from the vacuum pump to the EPR valve and the EGR valve itself.

Failure of the vacuum pump would render the whole system NON OP as well as the heater doors on the older rigs.
Failure of the solenoids could cause either an "ON ALL THE TIME" or a NON OP of the EPR/EGR

More garbage to keep the EPA happy for a few minutes and drive technicians and owners nuts.


If you have ever had the oportunity to open up a 6.2/6.5 that is equipped with the EGR you would question the addition of this stuff.

The intake systems look like 100 miles of nasty dirt road after only a short time.
The buildup of soot and other crap is Horrible.

The oil vapor from the crankcase is vented through the CDR valve and into either the intake manifold proper (NA engines) or into the turbo on the TD engines.

Mix this oil vapor with an abundance of soot right straight off the exhaust manifold and it makes a nasty black paste that coats the entire inside of the intake system.

As the gooooo reaches the intake valves the heat from combustion cause this goop to stick to the backside of the valve and build up into a huge cone shaped lump of crap.

Let one of these engines sit for a few months without a startup especially in a cold damp area and the lumps of crud loosen and fall into the engine.

I have seen engines that had been running fine and then sit for a while, upon a restart turn over and then come up hard and stop.

YUP due to all the crap that fell into a cylinder.

If the engine fails to start it is usually not fatal, but if the thing starts and then gulps in a mouthfull of that carbon it can break a piston, crack a cylinder wall (piston cocks sideways) or bend a rod.

The least it will do is make you mess your shorts while the little beast digests and blows that stuff out.

I have seen two engines come apart from this very happening.
Needless to say, I dont think much of the technology.

While keeping exhaust emissions to a reasonable level is certainly a good idea, the design used should place the overall health and longevity of the engine first.

Just some thoughts





Missy

[DmaxMaverick]

I assume you're talking about a gas engine? Anyway, a carb throat can freeze up at anything bleow 55Deg F. Especially, if it's humid. A 71 Toyota Corolla 1200 didn't have any heat rizer in it, for some reason! Took me several weeks to figure out that in humid weather, it'd choke up like crazy after about 30 minutes of steady driving. Finally, one morning I jumped out and tore off the top of the air cleaner, and there was a ball of ice, allmost completely blocking off the carb throat! I busted it up with a screwdriver and after the smoke cleared, finished the trip into work. That night, I built a little shroud around the ex manifold and used a flex hose up to the air cleaner, and had to leave it in place as long as I had the car, except through the hottest of summer weather.

You are correct, of course, and offer good advice. However:


is the heat riser (mounted on the end of one of the exhaust mainfolds)

....is not the "stove pipe" common on many gasser vehicles. He is referring to the EPR. The gasser heat risers, or stove pipes, are a shroud around a portion of the exhaust manifold, either near the head ports, or near the collector. It's function is as you described, but the inlet valve is located in the air cleaner housing or duct work. Many gassers also have (had) an EPR.

[fullsizeBlazer]

... no, talkling about the 6.2, maybe there's also some misunderstanding though, it is the valve at the end of the left exhaust mainfold that I'm talking about. Maybe it is not a heat riser, just a EGR valve, found this part on ebay.com and there it is called "heat riser for 6.2 diesel"... oh, btw, the lmctruck. com catalogue also lists that part as "heat riser" wtf?! :confused:

[JohnC]

... no, talkling about the 6.2,

thought so. Moving to the 6.2 forum...

[fullsizeBlazer]

ok, no problem, but I'm thniking about getting a 6.5, well, but I do not think that i need that part according to the postings on this thread :cool::cool:

[DmaxMaverick]

Correct. As a matter of function, it is not needed. The EPA doesn't agree, but who asked them, anyway?

Just removing it isn't that simple. Once "out of the way", the pipe won't match up, and it's a real PITA to get a leak-free coupling. If you remove the butterfly shaft and plug the hole with a bolt, the fit and leak issues become a non-issue. It doesn't hurt anything being there, if you don't mind the extra pound of iron.

For all intents and purposes, the 6.2 and 6.5 is the same engine. The difference between them depends on what is bolted onto them. The blocks/heads are essentially interchangeable. Most N/A 6.5 discussions are best posted in the 6.2 forum for this reason.

[fullsizeBlazer]

@Dmaxmaverick:

hey, thanks for that information! ;)