What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Heat riser question

COCHEV

COCHEV

1/2 ton status
Joined
Jul 9, 2002
Posts
4,054
Reaction score
5
Location
Washougal WA
Did some searching and couldn't find a straight answers. In my pic, is it open until heat/ vac applied or closed. When I manually operate the linkage its pretty damn stiff. My guess is the coil heats up as the exhaust does then opens? Don't know how the vacuum part comes in...

Trying to determine if its working and if not, is that side closed all the time...

uploadfromtaptalk1363056552728.jpg
 
Last edited:
it's just a butterfly inside the housing
the vacuum pulls the arm, which closes the butterfly

without vacuum, the butterfly stays open (unless mine was more broken than I thought, ended up gutting it anyway)
 
Im pretty sure they dont use exhaust. It attaches to a shield that wraps around the manifold and uses heated air to warm the truck up faster. Assuming we are talking about the same thing. Anyways, you can just wire it open or gut it if you dont have emissions. That may or may not be a big deal in your area.
 
The butterfly is designed to stay open without vacuum,or in the case of older heat risers with bi-metallic springs,they use spring tention to keep it closed until heat builds up and makes the spring unwind--those can seize shut,thats why it was an important part of a tune up years ago,it can restrict the flow of exhaust and make the carb run too hot,boil off the fuel in the bowl,vapor lock,etc...the vacuum type are designed to stay open if they screw up,but can still stick shut sometimes..

The heat riser blocks off one side of the y-pipe or dual exhaust,forcing the gasses to flow up thru passages casted into the intake under the carb,over to the opposite cylinder head,and out that sides exhaust pipe...this pre-heats the intake and air-fuel mixture for more efficient vaporization and combustion....increases cold weather performance,mpg and driveability when lean mixtures are used...also prevents carb icing and lowers emissions...its very noticeable if the heat riser system isn't working in cold weather here,a few chevy's I had wouldn't idle and would stall after I put an Edelbrock carb with a spacer on an aluminum intake,without it rigged up to stay closed,they iced up and ran too cold!...the hot air stove on the exhaust manifold also helps a lot to prevent icing,it pre-heats incoming air in the air filter...
 
Well this thing starts great cold, but crappy when hot...I'm also wondering if my funky electric fuel pump plumbed through the mechanical pump was a bandaid/ incorrect fix for this. If I just run the mechanical pump it starves out on hills

So if I'm getting this right, the spring holds the valve shut when cold. So shouldn't I be able to start the rig and watch it open as it warms up? Or do I need some RPMs for the exhaust to open it up?

This is also the side that has the bad exhaust leak...
 
I thought it was open to warm up the truck then closes when warm so it doesn't keep putting more heat into the mix when the engine is at normal temp.
 
I gutted mine out when i did an engine swap, never had any issues. It does get cold here in Central Washington but it did not make a differnce. If your going to pull the manifolds to fix an exhaust leak, thats the perfect time just to cut it out.
 
Two different things. You are talking about THERMAC (in the air cleaner snorkel) they are talking about the heat riser in the passenger exhaust manifold.

FWIW certain Corvette's had a "blank" heat riser piece, which can be bought repro. That way you don't have to modify the exhaust to get rid of it, if needed/wanted.
 
As my picture showes I'm talking about the one in the exhaust manifold, in line with the exhaust

I would prefer to have it functioning, but on the interim I'm trying to figure out if it is closed until heated or if vac opens it etc. I can manually operate it but without taking it apart I can't tell if I'm opening it or closing it.

One thing for sure , the spring tension is stiff.

Was thinking of wiring it open until I can fully address it.
 
A vacuum operated heat riser needs vaccum applied to the diaphram to close the butterfly,so it'll stay open due to the spring inside the diaphram unless it gets a vacuum signal applied to it via a thermal switch usually located in the thermostat housing that lets vaccum go to it when its cold ,then it denies it as the engine warms up...

Some V8's had heat riser block off plates installed at the factory,between the heads and intake---usually on heavier duty trucks,they also come in the fel-pro intake manifold gasket sets and you can install them so the heat riser wont affect the intake temparature...I'd assume such engines had no heat riser installed...

Here where its often cool,damp and rainy,a heat riser and thermac air cleaner are almost a must have if you want to be able to drive it during those days...my carbs used to frost up so bad someties the throttle would actuallly stick!..the butterflies in the carb would freeze to the venturis..it wasn't until you droveat least 10+ miles at highway speeds it would finally get warm enough not to ice up--somedays it never warmed up enough,thats when I decided to re-rig the heat riser hoses so it stayed closed all the time ,when it got above 40 or so,I put it back to normal...
 
My vac line goes to this thing on the t stat housing. When I pull the vac line off down by the heat valve I do not feel any vac at idle

uploadfromtaptalk1363102338646.jpg
 
Those all look to be thermostatic controlled switches. Cold only you should feel vacuum. No idea at what temp they switch. I would make sure the engine was ice cold before testing just to be certain.
 
I don't think our weather out here ever gets bad enough for those to cause an issue.

All that extra garbage is one strong reason to upgrade to EFI, even if just TBI. The cost of some of that replacement stuff is way too much.

I suppose if it actually works why mess with it, just not really fun to have to play with.
 
Well I took everything apart last night, which turned into a big ordeal with broken bolts and parts stores not being able to find the right replacement ones or the correct gaskets I needed.

Sooo... I decided while I was in there, to replace the manifold bolts, which required removing the AC and power steering pump....on and on and let's just say the burb is staying in the driveway the next couple days
 
Those PVS switches used to be cheap,but now I suppose many states require vehicles with emission controls to be intact and operable,so the manufacturers of them are taking full advantage of that fact and poking anyone hard who needs one...

I'd search boneyards ,you can get the whole t-stat housing with the switches for peanuts there--I always shop at junkyards first for things like this that I looked up online,and saw they want a ridiculous price for---..they dont fail that often,so I would not be afraid of a used one..most got the nipples snapped off them,than failed,in my experience...a short hunk of 3/16" brake line tube can be heated and inserted into a broken nipple to resurect it for further use...
 
Well after several late nights and all damn day today I got it back together. Most the collector bolts broke. Had to drill one completely out and use a through bolt. Pretty much sucked across the board to just fix a leak and return to stock. Headers and exhaust just isnt in the budget tho.

Ended up just removing the flapper inside the heat riser and getting all new gaskets and putting it back together. The exhaust leak is gone.
 
Should be good to go. I see by your photo someone already plugged the smog tube holes. When i did my swap it was all factory emissions. And everything was hooked up, i could not believe all the junk i took off, vac-hoses everywhere, temp housing activated vac switches or whatever they are. Then there was the charcoal cannister with a mile of hoses coming off of it. All gone and no issues. We dont have emission testing here.
 
I plugged the smog tube holes. We have emission but no visual inspections, except to see if you have a cat or not - which mine doesn't from the factory.

Pretty sure this rig will end up injected down the road anyways:D
 
You must log in or register to reply here.

Latest Posts

Top Bottom