hmmm i know that the 85 model of the 88 had heat risers not sure about 87 though. ill see if i cant find somethin out for ya. -Intimidator68

Hi Brando, All,


Back in the dark ages before computers, a heat riser valve was part of the exhaust system in V type engines.

A butterfly valve on one side, between the manifold and exhaust pipe, would close during cold weather warm up. The closed valve would force the gas from that bank to enter the intake manifold passage under the carb and exit thru the opposite manifold. It supplied heat to the carb and choke during cold weather warmup. Exhaust would heat a bi-metal spring that opened the valve to allow normal flow.

Most were blocked open, and/or eliminated when the original pipe was replaced.

The only ones left, are probably on 100 point restorations.

Vacuum was not involved.

EGR valve drew exhaust gas from the same under carb passage, and it was vacuum controlled.

Regards, Norm

Good to know, I looked on eBay for heat riser before, and only saw them for older, carbureted vehicles.

Yea....this is fuel injected....hence the fuel injector tips being loaded with carbon.

TOC Admin
Brando

1985 is RWD, 5.0L 307 V8.

TOC Admin
Brando

Hi Brando, Intimidator68, All,


The heat riser valve and the heat stove for the choke were eliminated in, I believe, '73 CA and '74 the other 49 States. The manifold passage was still used for EGR and carb heat, and is still called a heat riser passage, "heat riser" for short.

Don't know about the 5.0, but I believe my '87 G body/307 has one.

If I knew how to find all this stuff on the internet or in books, I wouldn't have to rely on my memory.

Regards, Norm

I had a heat riser in my 84 caprice w/305... But newer cars with fuel injection dont use such things. The computer is capable of compensating for a cold engine using its many sensors.

I do remember though, that heat riser on my caprice was a peice of crap! I had to replace it when it rusted shut...

i figured newer cars wouldnt have this since it was in the carbeurator area of my book. Ill do more research. -Intimidator68

The 85 Delta 88 with the 307 does have the heat riser valve, the 85 Delta 88 with the 3.8 doesn't have a heat riser valve.

TOC Admin
Brando

k i dont know if this could be it or not, but a friend of mine had alot of carbon in his manifold after he drove it for the first 70k miles. he replaced the manifold gasket when he noticed it didnt have a good seal. he says he has driven another 115k since then and manifold is clean. so check the gasket. if that is not it ill think of somethin else. -Intimidator68

Here is some stuff a friend of mine typed up about the carbon. Hope this helps.

The carbon issue may be caused by improper maintenance. Make sure that the PCV is new, that the egr is clean and the passageways from the egr to the engine are also clean. All of these items can cause carbon build-up. Also with the pollution control devices on today's engines carbon buildup is going to happen. The use of a good fuel system cleaner on a regular basis can stop this build-up and help the valves stay clean too. The other issue is to use a good brand name gasoline. These companies use better quality engine detergents that can keep carbon build up to a minimum as well.

-Intimidator68