Repair Information For Your Imperial's Heat Riser


Imperial Homepage -> Repair -> Exhaust -> Heat Riser

Tip from  Norm and Ross:

"Heat Riser Valve Lubricant" on the pins about once a month; 90-days without fail.   Mopar still makes a manifold heat riser lubricant that is available at any dealership. I use it and it works better than any other thing out there. 

Tip from Greg:

The heat riser on Chrysler cars are a real pain. No after market venders sell parts off the shelf, they were all MOPAR parts kits which have been discontinued. I was able to find a complete NOS kit for my 66 at Brads in North Carolina. You will have to search the NOS parts venders to find one. Andy Bernbaum used to have the springs but the last time I called him he was out of them and did not for see getting any replacements. I am considering getting some of the parts made locally but the cost is over whelming. To produce a complete heat riser kit for a 66 Imperial the estimated cost is around $400. EXPENSIVE! Mostly the coiled bimetal spring fails, if a source for the springs could be established that would cure many problems.

Question from Adam:

I need a heat riser - any help out there?  What does the heat riser do?  Do I need it if the car sees only warm weather?


From Pete:

The heat riser is a thermostatic valve located in the RH exhaust manifold at its outlet (on Mopar big blocks, anyway). When the engine is cold, the bimetal coil mounted on the valve shaft closes the valve to essentially close off the RH manifold outlet. As a result, nearly all exhaust gases from the RH cylinder bank are forced to flow upward through the crossover passage in the cylinder head, through the crossover passage in the intake manifold, through the crossover passage in the LH cylinder head, and into the LH exhaust manifold. The heat added to the intake manifold has two purposes: 1) it acts on the choke coil to open the choke 2) it heats the intake manifold floor to improve fuel vaporization when the engine is cold. The butterfly valve doesn't pivot "on center." This means that the valve will be forced open under hard acceleration when the engine is cold by pressurized exhaust gases (as long as the valve is free). If the valve is stuck OPEN, no real big problems occur. The choke opens much slower than normal so you may experience bogging and black smoke during warm-up operation. If the valve is stuck CLOSED, however, you have a real problem. Obviously exhaust flow from the RH cylinder bank is severely restricted so performance will suffer. More importantly, tons of excess heat will flow through the intake manifold floor. The extra heat can cause engine overheating, vapor lock, carburetor warping, fuel boil-off after shutdown, and head warping. The heat riser on my 70 LeBaron was shot so I got an NOS repair kit from Frank Mitchell years ago. He must have cobbled the kit together, though, because the valve never opened. Unfortunately, I don't think anyone reproduces parts for the big block valve. Year one offer small block kits, though.

From Norm:

Many times if a heat riser is stiff but moveable, I just place it in the open position and forget about it. No problems encountered to date.

From Roy:

You seem quite desperate for a manifold heat riser, but you do not mention what is wrong with the old one. Pete did a great job of explaining how it works, so that should give you some more insight. Complete NOS replacement kits are hard to find, but may not be necessary if you can explain what is wrong. Are you doing the work yourself or did someone merely tell you that you needed a new heat riser? The parts of a kit are the counterweight, bumper, thermal coil, anti-rattle spring, the shaft and flap. In some extreme cases the shaft is excessively worn and exhaust can leak out around it, or it may just be stuck. In any event to replace the entire heat riser, you need to remove the manifold and cut the old shaft off to replace it. The new flap has to be welded on the shaft once it put through the manifold. A whole lot of work for little gain! What I am saying here is that if it is stuck in the open position, don't worry about it. Also if the counter weight is present and you absolutely want it to work, try loosening it up with penetrating oil over a period of days. Once it is loose, you will probably only need the thermal coil to get it working. Andy Bernbaum lists them for older Mopars, but they are similar if not alike.

From John:

I've never seen very many of these that work. Make sure it is in the open position or you will likely have an overheating problem. With it in the open position all the time, the only problem you will have is that it will take a minute or two for the engine to idle smoothly when started from cold. If it were mine I would let it be.

From Bill:

I seem to recall seeing one in Year One's catalog. Call them at 1-800-YEARONE and they can tell you or steer you to some place if they don't have it.

Question from Dennis (331):

Does anyone know if I can just eliminate the heat riser butterfly valve in the spacer between the engine manifold and the engine exhaust pipe on the passenger side of the car (the other side does not have one). No amount of heat, penetrating oil and coaxing can move it.  It is now open about one third to one half of its travel, and before I put the system back together I know this must be addressed. It seems that leaving it rusted and in place is just inviting trouble. I want to just cut the butterfly valve off and reinstall the spacer. What is the purpose of this thing in the first place and why is it only on one side? I do not suppose this part is available anywhere. 

Reply from Paul:

Most cars will run fine if you remove the heat riser. If it is stuck closed or partially closed it will cause the engine to overheat and possibly other more serious problems. The purpose of it is to send heat to help warm up the manifold on a cold engine. I would say in a perfect world if you can get a new one and plan on maintaining it, go ahead and replace it. Otherwise, having it won't solve any significant problems, and not having it won't cause any.

Question from Adam (413):

So I just got my baby back form the garage and found out that they removed the heat riser completely. Now there is a steady exhaust leak pouring out my side. Wondering what the long term effects are and how I can seal it. The riser valve was restricting the flow , so it had to go, and the mechanic has worked on Imps before, so he sounded like he knew what he was talking about, does he?

Reply from Joe:

Braze the holes shut.

Question from Bob (440):

I was wondering if anyone knows were I can a rebuild kit for my 68 imperial 440's exhaust manifold heat riser. Mine has a broken spring.


From Pete:

As far as I know, no one reproduces this part or sells an equivalent. You have to find NOS.

The heat riser on my 70 didn't work so I bought an NOS kit from Frank Mitchell (years ago). Cost $75 then.

Despite careful installation and great expectations, the heat riser simply didn't work; it stayed closed regardless of temperature.

I have several used exhaust manifolds (hipo 383) in my parts inventory and compared my Imp manifold to them. All the parts looked the same and were oriented the same, but the Imp manifold valve simply won't open by itself. The thermo spring seems to be for the wrong temp range.

I was baffled and disheartened. The heat riser is now wired open to avoid intake manifold and carburetor roasting.

From Dick:

Out here in the balmy southwest, most of us balmy car collectors just torch out the butterfly valve from the center of the heat riser when it fails or begins to rattle. If the axle holes leak exhaust, braze them shut.

Question from Zeke (440):

My valve is in the open position due to gravity, and I think I will leave it this way. If need be, I will search for a new thermostat valve in the winter. Next question: My 67 runs extremely hot. Not on the gauge but in the engine bay. The car does not overheat, hasn't really come close since I've owned it. The problem is I have an exhaust leak on the driver's side exhaust manifold. Will this (relatively small) leak lead to such a hot temperature that my fenders are too hot to touch?


From Roy:

Several have given advice regarding what you now know is a manifold heat riser, ranging from its absolutely unnecessary to important for the petrochemical health of an engine. What has been missed is to point out that it has a bearing on the proper operation of the factory carburetor and choke. The factory 67 carburetor, either Holley or Carter, has a choke which is operated by a lever attached to a thermal sensor in a well on the passenger side of the intake manifold. The passage of diverted exhaust gas goes right by that well. There are many starting or running problems associated with the incorrect adjustment of this type of automatic choke. If this type of choke is adjusted properly, the engine will both start and run properly, but all the components must be present. Now if your car has an after market carburetor with an electric or manual choke, the heat riser will only effect the temperature of the air/fuel mixture at start up. Something else that hasn't been mentioned is what the manifold heat riser consists of and how it works. As was mentioned, there is a shaft through the manifold with a flap attached to the inside which diverts the exhaust gas. On the outside there is a counterweight and a stop tab attached to one end of the shaft and a thermal spring (clock spring) and anti-rattle spring attached to the other end of the shaft (closest to the engine). There is also a pin next to the shaft on both ends, one is for the stop tab and the other is to anchor the thermal spring. How the valve operates is that the thermal spring expands or contracts with the change in temperature, and since it is wound concentrically with one end anchored to the pin and the middle attached to the shaft, the shaft rotates in turn moving the flap. You indicated that your valve flaps around, which is good because that means it is not seized. If there is a half-moon shaped piece of metal attached to the outside of the shaft, then you have a counterweight, if not, they can be found at a wrecking yard. Next, you need to look (feel) behind the manifold at the other end of the shaft for the thermal spring which will most likely be missing, and you will have to search long and wide for a replacement. Once you find one, the thermal spring slips into the slit in the end of the shaft and over the anchor pin, and the anti-rattle spring loops over the outside end of the pin and shaft. YearOne has manifold heat riser kits for LA engines and street hemis but not the 440, and occasionally you see some parts on eBay.

From Ross:

The exhaust heat riser valve is, like the PCV and leaner choke settings of the late 60's era of early emissions devices an ironically good thing for motor longevity. Ironically, because those of us who bemoaned the 1970's crude technology came to hate emissions devices due to the lack of appropriate technology to keep them serviceable over the long run.

Yet this is not true with the above-mentioned: A properly operating riser makes a significant contribution to motor longevity -- and this is important -- in conjunction with a well-calibrated carburetor whose intake air is ALSO regulated. You'll notice that vehicles with "heat stoves" on the exhaust manifold which lead pre-warmed air to the carb, or a BLEND of air heated and not heated, finally only "cold" air as the motor warms up and under-hood temperatures rise above about 85-115 degrees F have a demonstrably shorter warm-up period than those cars not so equipped. The heat riser passage which leads from one end of the passenger-side exhaust manifold (valve closed) through the underside of the intake manifold and on out the driver's side is, when kept clean and operating properly, making a noticeably significant difference in keeping the fuel/air mixture IN SUSPENSION. Once those fuel droplets "fall out" the differences in mixture cylinder-by-cylinder are aggravated, thus making a fair running car lose efficiency. The valve is on the passenger-side on most American cars (trivia time) because Cylinders 5 & 7 always fire one after the other: too strong an exhaust pulse for a valve, yet it aids in "pulling" the charge thru the intake area. It also (heat riser valve) has the benefit of warming the underhood air a bit faster as all that cast iron is being cooked thus enabling the valve to close faster and the carburetor come out of cold operating parameters. Chrysler was ahead of the game in emissions also in the late 60's as GM's needed the dreaded smog pump (A.I.R.; "Air Injection Reaction") to pass the minimal guidelines of the day.

Yes, the heat on the intake underside reduces what is called charge density, but that is really only significant to full-throttle acceleration, and then it is a gain of perhaps 5%. Our kind of ultra-low rpm driving (off-idle thru about 3500 around town) benefits from the "constancy" of temperature regulation, and the attending leaner carburetor calibration. In short, better BSFC numbers on the dyno, (fuel usage versus work performed; most especially in numerous part-throttle transitions), and a LONGER-LIVED MOTOR!

With all that said, no, probably none of us bother to keep the valve operable, it needs a shot of "Heat Riser Valve Lubricant" on the pins about once a month; 90-days without fail (GM used to market the best version of this). Obviously it is also a significant exhaust restriction and eliminating it (not just pinning it open) probably saves more gasoline than it ever did operating. Yet it is fundamental that to have the longest-lived motor, one must shorten the interval from dead-cold to @ F 180 as much as possible as this is where the really nasty shit (sorry, it's the only correct word) gets in the lube oil, very corrosive acid compounds which it takes at least 10 miles/20 minutes of driving @ 35-40 mph before they BEGIN to burn off.

So disabling the valve has a price, albeit over a period of time. Some of us know this and forget it, yet we're the one's who also know that ol' granddaddy who kept that Imp in ideal condition for us to buy also understood it. If it'll work, free it up and let it do its intended job. A low performance Imperial motor needs whatever Ma Mopar gave it. (At least up through 1970). And pull that intake manifold once in a while to clean out the accumulated carbon buildup in the passage. This can solve more than a few mysterious "lowered gas mileage" woes.

Question from Eric (440):

Hello fellow land yacht owners. I have a question about heat riser repairs. The heat riser on my 69 Imp is leaking and swinging in the breeze. I believe most of it is there, but it certainly is not functioning and presently it leaks. I am looking for others with experience in either repairing or eliminating their heat risers. I am considering pulling the manifold, removing the heat riser assembly and filling the holes with the manifold repair compound sold by POR-15. Of course, it would be nice to repair the heat riser, but in the interest of quiet operation, repair parts cost and the fact that I probably won't be driving the car between November and April here in upstate New York, do I really need it? If anyone has been down this road before or has any ideas, I'd appreciate your input.


From Mark:

I have a '71 coupe and recently removed the heat riser. I couldn't notice a difference either way - except now it doesn't rattle. I have been told the heat riser mainly helps in cold weather starts - I live in Florida, so maybe it makes no difference here.

From Pete:

I've both repaired (sort of) and eliminated the heat riser setup. Either operation requires RH exhaust manifold removal (which is no treat) but the biggest difficulty will probably be finding the thermostatic spring. I bought an NOS repair kit from Frank Mitchell many years ago to repair my 70 but there was obviously something wrong with the kit because the valve wouldn't open automatically after that. It's wired open 'til I feel light pulling the manifold again. A complete repair kit gives you the SS shaft, butterfly flapper, cup seals, bushings, counterweight, thermostatic spring, end stop clip, and anti-rattle spring. If you're lucky, you'll probably only need the thermostatic spring, end stop clip, and anti-rattle spring. Installing the "full" kit requires grinding, welding and reaming. A big hassle is that the end stop pin that is pressed into the manifold is often rusted to a fraction of its original diameter or gone completely. Then you've got to find where it went and drill out the hole, and drive in another one. I completely removed the valve guts on a 71 and welded the holes shut. I don't think that POR or any other sealer will stand up to manifold heat for long. When the heat riser works it's great, but they are problematic. The valves really help reduce pollution by causing the intake manifold to warm up and promote fuel vaporization -- they were used at least into the mid 80s but fitted with vacuum operated servos instead of thermo springs.

Question from Brad (440):

The heat riser on my 68 rattles like crazy. IT doesn't seem to stop when the engine warms up. Any ideas?


From Pete:

Mopar used an appropriately named "anti-rattle" spring to prevent noise. The spring was only about 1/2" long and one end slipped into a groove at the end of the heat riser valve shaft. The other end hooked onto a 1/8" diameter steel pin driven into a flat surface next to the valve. Problem is that the pin often erodes to almost nothing where it enters the manifold casting and then it breaks off. This is a unpleasant fix as you have to remove the manifold, locate the pin stump, drill the remains out, and drive a new pin in.

From Brad:

My exhaust also rattles.   It does eventually quit, but it takes a while. I just live with it for now. If nothing else works, wire it open with a length of coat hanger and forget about it. If you don't drive it all winter as some of us do (don't) it won't affect drivability all that much. As previously posted, and you probably know, it may run rich for a while until the choke has a chance to come off. If it still runs too rich, back off the choke plate another drill bit's width.

Question from Tim (413):

The choke is not working on my car making it run very rich. My brother thinks that the crossover tube that warms the choke is plugged up with carbon deposits. He suggests changing the intake manifold over to the newer electrically heated kind. (The kind with a little half-circle cut out.) He says that they're much more reliable. The question...Is this feasible? We've found one on a '78 New Yorker that we could use. (I really, REALLY don't want a manual choke as he suggested.)


From Paul:

I almost gave up on my original choke until I noticed that the reason it wasn't opening completely was because the carb choke linkage on the driver's side of the car was improperly assembled. Either I did it during rebuilding the carb, or someone else did on a prior rebuild. It's easy to mess up, and only by studying the pictures in the Factory Shop Manual did I find the problem. I wouldn't think the crossover could get clogged enough to matter, but the heat riser valve on the passenger side exhaust manifold might be jammed open. This can be freed up and then lubricated with the special lube for this purpose. Don't use anything else, or it will just jam up again. If you go for converting to electric, I wouldn't think it would require changing the intake manifold other than if you are changing the carb also to something with a different mount. I'm not familiar with the setup you are talking about, so maybe I am missing something. The electric chokes I am familiar with are in a little circular device that attaches to the side of the carb. My stock '65 AFB carb has the choke thermostat spring down in a little well in the intake manifold.

From Tony:

When I bought my 1969 LeBaron, it got 5 mpg in the beginning. I discovered (among other things) that the original thick carburetor-to-manifold gasket had been replaced by a thin one. Since the choke is in the intake manifold, this had the effect of keeping the choke half closed all the time.

This page last updated March 9, 2003.  Send us your feedback, and come join the Imperial Mailing List - Online Car Club