So I own a 1985 F-150 5.0L and my problems started about 4 months ago while driving to work, after a lot of reading and studying and thanks to a lot of posts I read on this forum I determined it to be my distributor gone bad...

so after replacing it and fixing some vacuum lines that were plugged I took it for a drive, but what I didn't notice was that one of those vacuum lines went to the heat riser that hadn't closed in at least a decade...

Now I have what sounds to be a HUGE exhaust leak coming from what seems to be the heat riser or the manifold, I've checked to make sure its open now and disconnected the vacuum line but what I need to know is if the heat riser closed could it have caused the gasket to blow out beside the heat riser or could it be the exhaust manifold gasket itself? or maybe i damaged something internally (sounds kind of knocky?)

I'm not sure about how the heat riser actually works but from what i understand it redirects the exhaust gas into the intake but how? (My intake and carburetor setup is not original so i don't know if maybe this caused an increase in pressure when the heat riser closed)

Sorry for such a long newbie post but I'm not a mechanic really and I'm just trying to get an idea of what i might have done to it, and any help would be greatly appreciated

 

My experience with bad exhaust gaskets it's more a metallic chattering associated with the valves.

So that we know what you're dealing with, bring us some pictures of the block from the drivers headlight, and several shots along the passenger side.

 

Do you mean the EGR valve? Might look something like this:

 

no its not the EGR valve that was removed with my intake and carburetor when i switched from the stock 2bbl to a holly 650 4bbl

It "was" a California emissions truck but everything has been stripped off of the motor for the emission system including the smog pump, EGR valve, and all the Vacuum lines and plugs that went with it

 

here are some pictures of the manifolds and the block

first one is the drivers side manifold with the heat riser



this is the passenger side manifold


as you can kind of see in this picture under the manifold the original exhaust was cut and a plate welded over it on this side and a new pipe ran on the drivers side to make it dual exhaust it is not leaking where they welded this plate

and here is a pic of the heat riser


yes i know i have some bad oil leaks that i plan on getting taken care of next week if time allows it

also my intake is off of a mustang not sure really of the year/type just know its a dual plain low rise the last pic is a picture of the gap it has on the block im also not sure if this is something i need to be worried about but the truck had been running for 6 months with this intake on it


(sorry for ****ty quality/angles really didn't have much time to take them)

 

Yes, the heat riser in operation could have blown a gasket that was getting ready to go. What you need to do is wait till the engine is cold and you can touch the exhaust system. Lift the hood, start the engine, and then run out real quick and feel over the exhaust where it's leaking to try and determine where the leak is coming from before it gets too hot.

You can get the gaskets at the store, the problem is most of the bolts may be stuck. You will definitely need 6 point sockets, and sometimes metric ones help, since over time the bolt heads disintegrate over time, and sometimes you can drive a metric socket on to get it loose.

There is a exhaust passage in the center of each cylinder head, and this matches up with a exhaust passage in the intake manifold, and this passage goes underneath the carb to the other side. This creates a hot spot under the carb, which is needed for winter driving to keep the fuel atomized so the engine will run smooth and not be cold natured. Hopefully whoever put the manifold on left these ports open, it will not run well in cold weather with these ports blocked.

What I have found is you can usually run with these ports open, and also not use the heat riser(leave it open and unhooked) as long as you run the stock aircleaner with the heat tube hooked from the aircleaner to the sheetmetal housing around the exhaust manifold on the pass side. This will keep the carb from freezing up in the cold winter months.

You could try and get the heat riser working, and not use the heated air system on the original aircleaner, and see how that works. I have never tried it, but the extra heat under the carb with a working heat riser may be enough to keep the carb warm without using the heat air system on the aircleaner. You would have to hook the heat riser vacuum line to the vacuum switch hooked into the water jacket that would release the heat riser when the coolant got to around 100 degrees. You can't leave the heat riser on all the time or it will overheat the carb and boil the fuel in it.

 

Thanks for the information it might be a blocked port in the intake that's what i was afraid of, I'll have to take a look at that...

For now I think I will try and find and fix the leak and just wire the heat riser open and see if that fixes my problem i shouldn't have any problems in the cold since i live in the south and it was running fine last winter before my distributor went out

 

Another way to check for exhaust leaks is to slowly pour some (small amount) of transmission fluid into the carb.
Operate the throttle by hand and bring up the rpms a little while pouring in the trans fluid.
The smoke will come out of your leaks.
By the way, this is not enviromentally correct,but it will show you the leak.

P.S. Do not try this in your garage or living room....Trav...