[font size="1" color="#FF0000"]LAST EDITED ON 29-Sep-00 AT 02:25 AM (EST)[/font][p]I have a 1984 F-150 with a 300 c.i. inline 6 cylinder. I purchased it 7 years ago and have always had trouble with a leaking intake/exhaust assembly. A few years ago I noticed an exhaust leak at the connection between the manifolds. I removed the assembly and realized that the butterfly mechanism (heat riser flapper) had completely disintegrated. I temporarily fixed this by sandwiching a piece of galv. sheet metal between the intake and exhaust manifold. Of course, now the heat riser no longer functions but the only consequence is that it takes a little longer for the engine to warm up in the winter.
Now I believe this temporary fix is wearing out. I have noticed the exhaust sound is getting louder and it is leaking between the manifold assembly again.
My question is does anybody know of an aftermarket parts house that sells replacement exhaust manifolds for the 300 I6? I checked at a Ford dealer two years ago and they wanted $400 for it. Could I get one from a junkyard off a later model f-150? I don't know if the later model exhaust manifold would work. Also, does anyone know how to make a long lasting seal between the intake and exhaust manifolds?
I know when I had the 300 in my truck, It was a Dual Exit manifold. These are not the one piece assemblies like yours, if I'm not mistaken. But you can get a used one from a wrecking yard, but BEWARE of cracked bolt flanges.
My father also had a 300 in his 82. He went through 3 intake manifolds before he finally got one that didn't break when he put it on the truck. But, don't let that discourage you. Just letting you know what to look out for.
If you get a good(fel-pro or the like)gasket set, there will be a gasket for between the manifolds with it.
82 F100 FlareSide
HD 300-6, 240 head
2.73 Geared 9"
Blue & Silver
Pracklam, Be very careful with what you find at a salvage yard. I have been there and done that twice. 83' and 86' f-150's. By the time you find good manifold set (intake/exhaust) for your 300, then have them plained and cleaned up, you could have a set of new one's on the truck. Yes they are expensive, but I have found that 95% of the time junk yard manifolds can haunt you in the future. As for after market, my best guess would be JC Witney. I myself prefered Ford originals. Including the gaskets. Felpro gaskets are very good, and they do come with a little gasket for the joint between the intake and exhaust where as Ford did not have it available when I needed it. I felt that the Ford gaskets just seemed to work better. I have had the exhaust bolts loosen up from time to time with Felpro where as the Ford gasket application seemed to keep the bolts tight. My trucks are used for construction daily and I don't have much room for down time. Just a thought. Good luck.
If I put the newer style 2 piece exhaust maifolds on my 300-6 (carbed), what do I do with the opening at the bottom of the original intake manifold (between intake and exhaust manifolds)? My impression was that the split manifolds came out when Ford went to EFI. Is there an intake that went with the split manifolds on carbureted 300-6's?
Hooker makes an awsome complete bolton set of headers for the 300I6. I have a set on mine and it was worth the price ($275), i gained 10hp at the rear wheels and my fuel economy went up 2 mpg. I had the same problem, manifolds always leaked. The headers have been on a year and not one problem.
Before you start installing replacement manifolds make sure that they will pass your smog testing if you need to have that done. In California I have not found any headers for a 300/I6 that were compatible with the California Air Resources board. So changing out to smog approved headers is out here in california. You can still do it if when smogging time comes you change back to your stock manifolds.