Heat Riser Valve

[JERRY88GW]

What exactly does the heat riser valve do? Does it force the exhaust back into the engines intake?

My jeep does not have the pre-heat hose comming up from the passenger side exhaust manifold and into the intake. Do I need the heat riser valve?

One more question:
I under stand why they put the pre-heat hose onto the intake, but it just doesn't make any since to me. I allways thought that colder air is better air for an engine. And since the flap in the aircleaner snorkel only opens when the engine is cold, wouldn't the cold air be good for it?

Thanks

[This message has been edited by JERRY88GW (edited July 19, 2000).]

[Veepster]

heat riser valve and pre heat hose are completely independent of each other.

purpose of pre heat hose:
warm air allows the engine to warm up quicker, therefore less emissions.

cold air makes more horsepower.

so the flap is open when the engine is cold to allow air from around exhaust to enter intake and therefore the motor comes to temp quicker.....then flap shuts and intake air comes from the grill area..assuming all parts are present

Peace...............BartG

[lanierboy]

I believe the heat riser valve restricts the exhaust of a cold engine thereby heating up the manifold quickly. This intern supplys the warm air to the pre-heat hose to warm up the engine quickly on those cold mornings. Once the engine reaches temperature, the heat riser valve opens.

Since I'm in the process of installing a Holley Projection efi, I had the muffler shop weld open the heat riser when he installed the oxygen sensor in the Y pipe.



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1987 GW "Global Warmer"
AMC360 / NP229 / TF727

[Shane]

The heat riser valve when closed blocks off exhaust on one side only. There are passages through your intake manifold that the exhaust will use to find its way out the other side. This in turn heats up your intake manifold quicker than the coolant ever could.

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1982 J10 Model 25
My Daily driver since
1988

[Ralph]

Shane has it right. The purpose of the heat riser valve is to create just enough back pressure to cause hot exhaust gases to circulate under the INTAKE manifold; this warmth aids fuel atomization when the engine is cold.

The heat riser valve is not forcefully shut (unless it's frozen shut); even when the engine is cold exhaust will come out of that manifold strongly and smoothly.

It is very worthwhile to do a little PM by spraying high-temp lubricant or penetrant into it once in a while, and work the flap a bit to ensure it moves freely (although it's sprung).

P.S. It's also an OEM emissions device, which makes it technically illegal to remove it.

[This message has been edited by Ralph (edited July 19, 2000).]