Aftermarket intake manifold for stock 96


3rd Gear Poster
Oct 5, 2023
Country flag
Howdy all. So I started to replace my spark plugs today. I'm not sure what the cylinder numbering scheme is on a 4.6. I'm assuming that drivers side closest to the radiator is #1 and the same cylinder on the opposite bank is #2. Suppose that this numbering scheme is correct. #1 and #3 were fine. When I pulled the plug boot for #5 it has coolant in the hole. I haven't gone any further as I was loosing daylight.

I'm assuming that the intake is cracked. Obviously I'm going to check the rest, but the engine was missing badly when accelerating and I suspect that I might find more holes with coolant in them. Assuming that the manifold is toast, I'm wondering where I can get another. Keep in mind that this is not a performance vehicle but more than likely a daily driver. I certainly wouldn't want anything that would decrease fuel mileage.

Any recommendations? New is probably the way to go. There are no salvage yards around here that have 96 Tbirds in them. I have a 95 aluminum manifold but I didn't want to use it unless I couldn't find another. I'd sure appreciate some help...
First up, fords are generally numbered in straight banks, or at least the 4.6 is #1 is pass side front, #5 is drivers front, and drivers rear is #8.
I think the one you mean is #7, which is 3rd one back on the drivers' side.
Any misfiring issues you have there, or #8, look in the spark plug wells for coolant. That's a common issue with the 4.6. You probably have a manifold gasket leak. If that's the issue, replace the gasket, replace the wires, and clean the plugs with brake parts cleaner.
The 96 Thunderbird I drove years ago had the Dorman intake installed. It worked fine, I couldn't tell a difference between that and the OEM besides it looks a bit different. They are designed to be easily installed so for a stock setup they are a great choice
Thank you folk for your very helpful replies. Grog, Thanks for the instruction on cylinder numbering. I wasn't aware. Also, I'd be wary of pulling the intake and just replacing the gaskets only to put it back on and find it leaks again. I've read the threads concerning cracks in the plastic manifolds and with the way this car has been proceeding in trying to get it back on the road, it's has had very little in terms of regular maintenance. I COULD take the manifold off and inspect for cracks but if found faulty, that will mean that I won't have it back in running condition for at least 2 weeks because of my schedule. I may do that depending on the cost of a new unit and hope for the best. Thanks again.
From what I've seen, cracks in the intake tend to happen on the older, all-composite models without the aluminum crossover. That's not to say that they're unheard of on the updated models, but they tend to be isolated to the heater core outlet above cylinder 4, which starts leaking. Other coolant leaks tend to be caused by electrolysis around the mating surfaces at the crossover between cylinders 1 and 5, or between the composite gasket mating surface between the crossover and head or the O-rings that seal the crossover to that composite component.

Pull the intake tube and plug wires, and use compressed air and a vacuum to clean the plug wells and top of the heads as well as you can to help you easily identify the source of the coolant leak. Check after a day or two of normal driving to see where new coolant stains are coming from.
Thank you "theterminator93" I can't really check after normal driving as it's not been registered or insured yet. I will tell you that it's missing so bad under medium to hard acceleration that I wouldn't drive it other than for testing. To be honest, I'm sure that coolant in the plug holes is PART of the problem, but I think there may be more contributors. I haven't yet cleaned the MAF sensor. I've had one that wouldn't run because it was so dirty. I haven't even checked this one.

Now that it's daylight, I've inspected holes #7 & #8 (just to make sure I'm talking about driver's side, two holes closest to the firewall). Both plug holes have coolant in them, mostly #7 but #8 had some as well. I do not see any obvious signs of where the coolant is coming from but the head/manifold joint is moist, but not wet, even after a 2 mile test ride with the temp. gauge reading about straight up or even to the right a bit. Do these intakes use O-rings to seal them to the head platform or do they use gaskets? If the latter, I noticed something that looked like part of a gasket sticking out from the manifold. You can see the bit I'm talking about in the first photo.

On an unrelated issue, when I pulled plug #8 out it was tough at first like someone put Locktite on it. When I got it out, the entire first half of the threads had gunk in them, like JB Weld putty or maybe even Locktite. I cleaned it off and put it back in and gingerly tightened it, expecting it to strip, but I think I got it tight enough. In the second photo, you can see all the junk on the threads nearest the insulator.


  • 20240221_121241.jpg
    1.7 MB · Views: 6
  • 20240221_124804.jpg
    1.3 MB · Views: 6
The aftermarket replacement intakes have O-rings around each port (coolant and air). If the manifold is improperly torqued, they will deform and the manifold can warp/leak. The factory intakes use a gasket, though that itself is just O-rings embedded in a plastic mold. Again, properly torqued intake bolts are the key to a lasting seal. Based on your photos, it's the factory intake and gasket.

There is a coolant port at the front and back of each head (they are the same casting, just different plugs sealed on each side for the oil galleys); the one behind cylinder #8 is just capped off by the intake once it's installed. There's still pressure and a gasket seal above the port, though, so that could be where the leak is coming from.

These heads only have 5 threads for the spark plugs, so the gunk on the upper threads of the plug would seem to indicate a partial seal allowing residue to build up on it.

Sounds like some TLC is just what the doctor mechanic ordered!
Well, I just searched through my stash of 4.6 parts and I happened to find a Fel-Pro intake gasket set (MS 95728-2). On Saturday I'll be busy picking up the 94 V6 car I bought in Georgia a few weeks ago, but the intake manifold job is on the list! Thank you to all that posted replies and special thanks to the admistrators and moderator for their excellent tips and advice.

I suppose I'll sound lazy if I ask if anybody knows the torque spec. to the intake bolts instead of looking it up myself? :)
It's 8-10 ft lbs, not much.Clean the head surface, and see if there is pitting under where the gasket was; if there is, clean out the pits, and backfill them with black rtv. I had this problem on Lazarus. I ended up gluing the manifold on with rtv, lol. If you don't clean the aluminum rust under the gasket seal, it will wash out when the coolant gets hot. then it leaks again.
I cannot remember if the NPI gaskets have the locating pins. When I use the PI gaskets on my NPI heads I have to cut the locating pins off. To keep the gaskets in place I have a set of four studs that I cut a slot into the top. I install those into the heads, then the gaskets, and then the intake. Once the intake is down and I have a couple of bolts finger tight I remove the locating studs using a flat blade screwdriver and reinstall the intake bolts in their place.
npi gaskets have locating pins but they’re in different spots than PI due to the port shape changing, hence why they need to be cut off.

Similar threads