72 Heat riser valve

[Gary S.]

I had posted a while back about a rough idle issue, thinking it might be vacuum related, for my 72 LT1. After a complete tune-up to GM specs, I measured the vacuum at 15" @ 850 rpm. I troubleshot the vacuum-using components and tubing and all was good. Btw, this is an original, unrestored 37000 mile car.

Last week someone posted that idle issues, with a warm engine can be a multitude of things including heat riser valve failure. I just got back from running my car until it is fully warmed up. With the engine temps normal the heat riser valve only appears to open about 30% or so. I pulled it off and a visual inspection reveals a very nice looking heat riser valve, with smooth operation of the butterfly valve and no sticking throughout its entire range of motion. I held the valve over my gas range, about 6" above the flame and got it very hot. The butterfly only opened about 30-40%.

Can I assume that this unit is toast? If so, who makes the best replacement heat riser valve. I have an LT1 with the 2" exhaust manifold swedged to 2.5" so I will need the 2" inch valve. I see that Doc Rebuild, Paragon, Volunteer, etc all offer these units. Is anybody, including GM, a standout as far as original looking?

TIA,
Gary

[Bob R.]

Re: 72 Heat riser valve

The riser appears to work the same as mine. Many on this board have recommended wiring the riser open as it is only needed for winter driving. It also causes the exhaust system to rot out more quickly. I have had mine wiried open and left it to operate on its own with no noticable difference in the idle. You may want to try wiring it open all the way and see how the car runs.

[Duke W.]

Re: 72 Heat riser valve

The themostatic springs on the heat risers appear to go out of calibration with time. Your best choice it to just wire it open. If you drive the car in cold weather it might exhibit some early warm up driveability problems, but that's it.

Duke

[Gary S.]

Re: 72 Heat riser valve

Thanks Duke & Bob, can one also use a Dremel with a mini-cutoff wheel and just totally cut off the butterfly, leaving the shaft, spring, and counterbalance intact? A friend was suggesting this to me as an alternative to having a piece of wire holding the butterfly open.

Gary

[Steve Junkersfeld]

Re: 72 Heat riser valve

Gary,

I agree totally with your friend. I have the butterfly cut out of my 56 and my 77. They run fine, it looks much neater, and there is never any concern about the valve not opening. They do run a little balky when cold - but it's only temporary. Steve

[Patrick H.]

Re: 72 Heat riser valve

Gary,

Yes, you can cut it out or wire it open. Just be sure to remove the wire before judging.

The alternative is to purchase a new GM one. I'm sure Joe can give you the number. I have a new one on my 71, and a spare for the future. Of course, you'd have to wait to install it until after any possible Bowtie judging unless you like swapping valves a lot.

Patrick

[Joe L.]

Re: 72 Heat riser valve

Gary------

Most of the heat risers on the market are configured pretty much the same. I don't think that GM produces their offering internally anymore, if they ever did. The GM part number for the valve is GM #362652 and it looks virtually the same as the original valve save, possibly, for some of the obscure markings on the counterweight.

You can cut out the butterfly to obviate the valve's function and keep it stock appearing. However, you will then likely still get the annoying rattle out of the valve. That's almost the worst part of having the thing. Dr. Rebuild will sell you an anti-rattle spring seperately (GM doesn't have this part available seperately anymore) and that may cure the rattle they produce. Generally, however, the only thing that I've found effective to cure the rattle is wiring the valve tightly open or eliminating it with a spacer.

[Eric Fairclough]

Re: 72 Heat riser valve

I just turned my heat riser to the open position on mine and it has been like that for a year now. No wire.

[Eric Fairclough]

Re: 72 Heat riser valve

I should add the i thought the open position was up. I found out that open is down. I drive short distances thats probably why i did't have a problem. Thanks Eric