5.8 Exhaust Manifolds
 

I have a 92 F-150 5.8L, and have a major "spit" coming from the RH side of the engine; obviously an exhaust leak. Before I dig into the issue, I'd like to know if the RH exhaust manifold for a 5.8 is the same as for a 5.0. The 302's seem to be considerably more common in the salvage yards than the 351's. If I need to replace a cracked manifold, it'll be easier to find a 302 manifold. Also, which years are interchangeable?

Thanks!

JD

Not interchangable. You'll have to have 87-96 truck 5.8 manifold. Sorry.

(On edit) check your manifold to egr valve riser pipe. They frequently split in their expanded bellows area & are covered with a heat resitant cloth that hides the split.

Excellent point there Scndsin. It is common on these trucks to develop cracks in the manifold and also have issues with the EGR tube. Either one can be replaced with a few tools and a torch for heat.

I will second your input for the manifolds, no they are not interchangeable if you want to retain the factory y-pipe.

Yeah issues with the EGR Tubes...like falling out while driving down the road!!!! idk how, but it did. :) just thought I'd throw that in there. ^_^

Just had the 5.8 rebuilt on my 91, the EGR tube was split and and several exhaust manifold bolts had broken during removal.

Thanks for the info. My EGR tube was broken, and I replaced that last year. Still have the leak. It's sounding like I have a cracked manifold. I'll pull it apart to confirm. Hope it doesn't take long to find a replacement.

JD

I ordered cheap offshore made Dorman replacement manifolds two years ago. They fit ok, but not nearly as well as the factory pieces.

What kind of fit issues did you have? I don't want to have to egg-shape any of the head mounting holes, and I hate when the collector doesn't line up. As long as I don't have to start modifying parts, I'm okay with "persuading" a few things.

Thanks,

JD

The mounting holes were plenty big. Good thing I planned on using some larger washers. The fit to the y-pipe was no problem-o. :-X10

On the positive side each manifold came with a nice assortment of different plugs for the holes it had cast in it to fit different year/model trucks/vans.

I had posted the following on another thread I started dealing with some EEC IV codes and drivability issues. I thought it might be better to tack it onto this thread that deals with my exhaust manifold issue:


I pulled the RH exhaust manifold off, and it is clear that 2-3 of the exhaust ports were leaking between the manifold and head. Only one cylinder looks like it has a good "seal-off". The other three show exhaust blackening on the mating surface, and the head is sooty in corresponding locations.

I'm going to take the manifold to work tomorrow, and check the flange with a straight edge, as well as inspect it under mangnification for any cracking. I didn't see any on initial inspection. Are these manifolds known to have warping or cracking problems?

Also, there was no exhaust manifold gasket in place when I disassembled the engine. I don't think this is unusual, as I've been into several engines that don't use exhaust manifold gaskets from the factory. I bought a set today as a "just in case". Assuming my manifold checks straight/flat, and has no cracks, can I just reassemble using the manifold gasket and have a reasonable assumption that it will seal up? I definately don't want to have to dig back down to the manifold again to replace it.

Any and all feed back continues to be greatly appreciated.

Thanks!

JD <!-- / message -->

DO NOT buy Chinese/Dorman exhaust manifolds!.........I did...they both cracked on the 350 Chevy in my motorhome, in less than 2,000 miles. Buy OEM and don't look back.

Mine have been on for over 2 years now. So far, so good. If they break that gives me a reason to go with something better.

Yes I would recommend using a good quality gasket with the factory manifolds when you re-install them.

I checked my manifold at work today, and it is not cracked. That's the good news. However, it is pretty warped. I checked across the head-mating surface with a straight edge, and it has about 0.050" variation across the surface. I cleaned it up with a wire wheel, and the mating surfaces were pretty pitted and uneven.

I put the manifold on a large disk sander and worked it for awhile to try and get the surface flatter and cleaned up. I was fairly successful; to the point where I think a manifold gasket will seal it up. I may go with double-gaskets if it looks like it's not going to seal up with one. I know this isn't the best practice, but it will give me time to get a replacement.

I purchased brand new hardware for the head mounting flange, as well as the collector end. Even thought I got all the original fasteners out without breaking them, I don't want to risk re-using them. I figure the $20 for new studs & bolts were cheap insurance. I'm going to reassemble it with anti-seize compound in case I need to go back in to replace the manifold. Hopefully not.

I should have it back together by early tomorrow afternoon or so, and will post up what kind of success I had. I'm going to take the opportunity to do some cleaning/detailing while I have some things pulled off. Wish me luck.

JD

Good luck! Thanks for the update.

No-go on reassembly. The original manifold is just too warped. Fought with it for over an hour and the closest I could get was 1/2 a hole off on one end with a bolt in the opposite end. This thing is warped in too many directions to work.

I'm off to the parts store to get a Dorman replacement. I need the truck back on the road, and if the Dorman gets me a year or two, I'll be happy. Any other used one I find is likely to be warped just as bad. I'll check into an OEM replacement, but it's probably too expensive and likely to warp just like the original.

I'll post when everything is back together this afternoon/evening.

Thanks!

JD