Hi folks! My name's Matt. Long time observer (I've owned 3 classic Plymouths, all with Slant Sixes), first time posting. I'm working on restoring a 1973 Valiant right now and I'm having a little bit of confusion as to whether or not my MHCV is functioning properly. Truth be told, I've usually kinda ignored them on my previous cars, but not this time.

I've noticed in previous posts about the MHCV there is a debate as to whether or not it is necessary. My stance right now is: It came with the car so I would like it to function correctly. So, I am hoping someone out there might be able to give me advice on whether or not mine seems to be working right.

The real question I need answered is: Is the wheel always supposed to be spring loaded? The spring is clearly present on the wheel but it does not create any tension. The wheel freely turns clockwise and counter-clockwise but the spring just turns with it. Does the spring only provide resistance to the wheel turning counter-clockwise when it is hot or is my spring simply old and broken?

Here are some pictures to help clarify my situation:






Again, I would really like to have this system functioning properly because I am aiming to use this car as a year-round daily driver in New England. If the spring (or thermostat I guess it is technically called) is no good, is there any chance of me ever finding a replacement? I've looked and looked and it doesn't seem to be a part that anyone offers... Any advice is GREATLY appreciated! THANK YOU!!

-Matt

You are correct to want this valve working correctly. The thermostatic spring's broken on yours. Time to hunt up a replacement (getting tough to find) or install a complete brand-new exhaust manifold with brand-new heat control valve, such as this one. It is very much worth your while to get the good gaskets for the manifolds-to-head and intake-to-exhaust junctions.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks for confirming my suspicions Dan! How do you feel about the Exhaust Manifold offered by 1AAuto? It's only $98 with free shipping. Saw it referenced in another post and checked it out, sounds like a great deal. Here's a link to it. And I might as well get a new manifold considering all the NOS 340 MHCV kits I see going on eBay are usually well over a hundred dollars so I'd assume a kit for the 225 would run me the same or more. Either way, when I replace the manifold I will definitely order the gaskets you recommended.

-Matt

No way is it worth saving a few bucks to buy that Chinese copycat item versus the much better quality American-made real Chrysler one.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan, if you don't mind, I'd like to ask one more question of you before I buy the manifold you recommended on eBay.

To your knowledge, is there any chance at all that there could be any characteristics of that exhaust manifold that won't match up with the mechanics of the Slant 6 in my 1973 Valiant? I ask because I know that there was a slight variation between the exhaust manifold on my 69 Valiant and my 73 Valiant. I don't knowing exactly the function or name of it, but the 69 had a small pipe running through the manifold that connected to a tube on top and, I believe, a metal pipe underneath that ran along the engine block. The 73 Valiant has no trace of any such thing.

The guy on eBay is marketing his manifold as being for a truck... he doesn't specify any particular year range. It LOOKS exactly like the one in my 73 Valiant but before I spend my hard earned money I just want to make sure I'm not setting myself up for any unpleasant surprises.

If it's an exact fit, the manifold on eBay is as good as sold and you've successfully diverted the sale of a Chinese knock-off! THANK YOU!

-Matt

None whatsoever.
That's inconsequential to interchange. See here.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Okay awesome. Dan, you ROCK! Just bought the manifold on eBay and also placed an order for the hotbox gasket from GPRS. I'm gonna get the the Remflex gasket too. THANKS FOR STEERING ME IN THE RIGHT DIRECTION!!!

-Matt