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So my '66 Toronado has a small exhaust manifold leak, looking for a bit of advice. There's actually a couple leaks going on, one is at the exhaust donut connection to the pipe and the other is up by the #2 cylinder. I knew the one at the donut was leaking so I replaced the donut and even put a little red Permatex Optimum around the area but it's still leaking like crazy. Well, to be more accurate, you can only really hear it when you have it in gear and you accelerate. At idle, or when you rev it with no load, you really can't hear it without using a length of hose up to your ear. It's decently loud when you go for a drive though.
The second leak, at the #2 cylinder area is buried beneath the AC compressor so I can't quite find the source yet. What would even cause a leak here anyway? Do the manifolds warp on their own over time? These manifold have never been off the car as far as I know, maybe the bolts have just come loose? I'd like to pull that manifold off to take a look but I am just wondering what I have in store for me? The bolts will probably be pretty gnarly I assume so I'll have to use some common sense there and not get too hog wild. There's no gasket here right? Just metal to metal?
It's too bad that it's the RH side with that AC compressor in the way. Not a lot of room to work in there!
Classic Oldsmobiles came from the factory without exhaust manifold gaskets. Years of use have made them a necessity now unless you have a machinist true the exhaust manifold surface on the head and touch up the manifolds.
Unfortunately, exhaust manifold gaskets aren't an easy task. Especially with the AC compressor in the way. Still preferable to lying on your back under the car. You might get to do that too loosening the exhaust pipes though.
I did the ol' shop vac in the tail pipe + soapy water to see if I could sort out where the leaks are coming from. Check out the little Youtube short I made attached below. It's leaking from both exhaust donuts plus at the #1 and #2 manifold to cylinder head connections. These look like pretty significant leaks, however, the donuts at both locations have already been replaced last month. I bought replacement FelPro ones and they fit snugly. I also added just a little of some Red RTV as when I first started the car up after replacing the donuts, I could still hear a leak. The RTV seemed to help but, obviously, they're still leaking.
I have no idea how to deal with these leaking manifold donuts, honestly. They fit nice, sealant added to help and they still leak terribly as shown in the video. I mean, what else can I do here??
Before you put the new doughnuts in, are you sure you cleaned all the remains of the old ones? I think you'll need to pull them to verify what is causing the leaks at the front. If its cracks in the manifolds or warped, or exactly what is causing it. Be very careful as these bolts can be brittle from heating and cooling over the years.
Before you put the new doughnuts in, are you sure you cleaned all the remains of the old ones? I think you'll need to pull them to verify what is causing the leaks at the front. If its cracks in the manifolds or warped, or exactly what is causing it. Be very careful as these bolts can be brittle from heating and cooling over the years.
When I pulled the original drivers side donut, it pretty much fell out. At least, I'll call it "original" as it was what was in there when I got the car.....I'm sure it was changed out over the years but it was toast when I first got the car and it was really loud. When I put the new one back in there was quite a bit of slop so that's where I used the RTV sealant to help fill the gap. Seems like someone might have cleaned it up a little too well the last time they changed the donut because it's quite a sloppy fit. Despite the air leak shown in the video, the drivers side seems relatively quiet.
The passenger side however, which I have to change from below, had to be slide hammered out with a vice grip attachement but I got it all in one piece. The replacement donut for the passenger side fit super tight and I had to gently tap it in with a seal driver and a brass hammer. Oddly enough, this is the side with the worst leak noise.
The bolts didn't fight me at all actually. I'd like to replace them along with the springs if I can find em that is. The manifold-cyl head bolts, however........maybe I'll just deal with the exhaust donut leaks first and see how quiet the thing is before I even think about touching those. Still, I don't know what else I can do with it.
If you plan to pull the exhaust manifold, start by unbolting the A/C compressor. You can leave the lines attached so you don't lose any freon. Just lay the compressor out of the way. This will make removing the manifold infinitely easier.
If you plan to pull the exhaust manifold, start by unbolting the A/C compressor. You can leave the lines attached so you don't lose any freon. Just lay the compressor out of the way. This will make removing the manifold infinitely easier.
And the A.I.R. lines as well......just RIGHT in the way!
Classic Oldsmobiles came from the factory without exhaust manifold gaskets. Years of use have made them a necessity now unless you have a machinist true the exhaust manifold surface on the head and touch up the manifolds.
Unfortunately, exhaust manifold gaskets aren't an easy task. Especially with the AC compressor in the way. Still preferable to lying on your back under the car. You might get to do that too loosening the exhaust pipes though.
So is it decently common on these old engines to have to run a manifold gasket? I'm assuming these gaskets don't have a long life so you're back replacing them fairly often?
Your surfaces are either good enough, or you use a machinist, often for both sides, or you use a gasket. If the car needs help, the gasket is much less work than pulling the manifold and head and taking them to a shop.
So, short answer, yes, they run them unless you are doing an engine overhaul in which case you'd machine, and probably run a gasket even then. Lifespan should be quite a long time.
I run the FelPro exhaust manifold gaskets. I've tried fancy ones and they don't work any better.
So if you end up just running the manifold gaskets, do you still get the manifolds trued by a machine shop or do you just do a quick and dirty gasket install?
Without knowing how much either of the surfaces are warped or pitted it is a guess as to whether or not a gasket will be enough. My guess is that a gasket between the head and the exhaust manifold will work.
Clean any exposed threads and soak the bolts repeatedly on a warm engine (not hot) so that the penetrant wicks in as the engine cools. If any of the bolts put up a fight, stop don't break them and re-group. Use six point wrenches and sockets, don't use twelve point tools. Heat may be needed particularly on the blind center bolts
The bolts may have locking tabs that need to be bent back and out of the way.
Last edited by Sugar Bear; May 5, 2025 at 06:05 PM.
Without knowing how much either of the surfaces are warped or pitted it is a guess as to whether or not a gasket will be enough. My guess is that a gasket between the head and the exhaust manifold will work.
Clean any exposed threads and soak the bolts repeatedly on a warm engine (not hot) so that the penetrant wicks in as the engine cools. If any of the bolts put up a fight, stop don't break them and re-group. Use six point wrenches and sockets, don't use twelve point tools. Heat may be needed particularly on the blind center bolts
The bolts may have locking tabs that need to be bent back and out of the way.
Good advice here. I noticed that most of those locking tabs on mine are broken off......they rusted off by the looks of things. Access is an issue on my car as the AC compressor is right in the way along with the A.I.R pipes. I'll have to move the AC compressor out of the way, which isn't too big of a deal because I can leave that connected, but I don't know about the AIR pipes. Will have to see how she goes.
I started working on the passenger side exhaust manifold today. 3 hours later, 0% progress! I've been working on the easiest to access manifold bolt, just so I can see what kind of forces are involved to remove a bolt. Haven't been able to budge it thus far.
I warmed up the engine for a bit before starting. Cleaned and sprayed the accessible threads with Kroil. The 14mm seemed to fit best so that's what I've been using. I have only been using 3/8" drive tools so far as I'm hesitant to step up to 1/2" drive but I may have to yet. I have been hitting it with a gentle 3/8" angle impact driver from time to time but it's not getting it done.
I don't know where I'll go from here. I've been using a hand held torch to heat the cylinder head but I may have to step up to my oxy/propane torch.
Warm the area that the bolt goes into not the bolt itself, juice it, impact in both directions, rejuice it and walk away.
Agreed, baby steps. I'm heating the head where the bolt threads in and then juicing. I don't think the handheld propane torch is up to the job, however, so I'm going to try to use my mini oxy/propane torch. I'm a little leary of running an impact wrench on the bolts though.....I'm not sure.
Impact it with a wrench and hammer if you can. Apply torque in the tightening direction and strike the wrench while under torque then in the loosening direction many many times.
Ok so a little success. I removed that easy to get to bolt. Just used heat, Kroil, and patience. I put the bolt back in and snugged it so that the rest of the manifold doesn't start to twist as other bolts are removed.
The next bolt, however, yikes! I decided to move on to the center, blind bolt. I don't know what's going on with this bolt head but 14mm is just way too big. 13mm and 1/2" are both too small. There's way too much play on that 14mm socket when I lay it on the bolt head and move it side to side. Using that 14mm on there will be disastrous.
I can't get a straight shot on it either, from down below in the wheel well, because of the shock upper mount. I actually have no idea what I'm going to do next. I guess a Turbo socket could work but that's probably gonna be a one shot deal. I'm walking away from this one for a bit to regroup.
View of manifold center, blind, bolt from underhood.
View from wheel well opening.
View of shock mount, blocking straight on access to bolt head. I can get at it with a universal.
Last edited by ourkid2000; Dec 30, 2025 at 03:03 PM.
The bolt heads are rusted, which is why sockets don't fit correctly. If 1/2" is too big, get a 12mm six point and hammer it onto the bolt head.
Just to be clear, these are 3/8"-16 bolts that are supposed to have a 9/16" hex on them. They're rusted down so that 14mm fits better, except for this one bolt.
13mm and 1/2" are both too small for this particular bolt. I'll try hammering on the 13mm to see if I can get it to fit.
The bolts in the blind holes are definitely difficult. Vise Grips may be the answer. If you use them clamp them on as tightly as possible or tighter it is important that they don't slip and destroy the hex. I'd try hammering a socket on first even if the head of the bolt has to be filed slightly.
The bolts in the blind holes are definitely difficult. Vise Grips may be the answer. If you use them clamp them on as tightly as possible or tighter it is important that they don't slip and destroy the hex. I'd try hammering a socket on first even if the head of the bolt has to be filed slightly.
That's actually a really good idea. Make it just a bit smaller so the 13mm fits. Great suggestion! My Turbo socket seems to fit it pretty well too.
Got the center blind bolt out. It required stepping down to a 13mm extractor socket. Crazy, that bolt has degraded from 9/16" all the way down to 13mm. My method was to heat the cylinder head with a torch, smack the bolt head with a drift, cool the bolt head with upside down computer duster freeze spray, smack the bolt head with the drift again. Repeated about a half dozen times. Then I pounded on the 13mm extractor socket using a 1/2" drive extension and universal 3/4" socket. I had to use the universal socket because the shock mount is in the way preventing a straight shot, Once it broke free it didn't fight me at all on the way out. I'm just going to continue this method on all the bolts (hopefully will not have to resort to the extractor socket like on this bolt).
I did not use any impact wrenches here, only a big *** 1/2" drive ratchet. I'm at two bolts now after a week so at this rate, I should be finished up in a couple years.
13mm extractor socket sitting in 3/4" socket. These extractor sockets are excellent Bite marks on the bolt head. This is the stackup required to get at that bolt. 1/2" drive extension, 3/4" universal impact socket, 13mm extractor socket.
Last edited by ourkid2000; Jan 2, 2026 at 08:56 AM.
Good work ...patience pays. Two thoughts, add penetrating oil when the bolt is warm and if you are stuck try tapping the bolt in both directions cw/ccw.
Good work ...patience pays. Two thoughts, add penetrating oil when the bolt is warm and if you are stuck try tapping the bolt in both directions cw/ccw.
Yeah, when you're down to using bolt extractors you're unable to go back the other (tighten) direction as you'll lose grip on the bolt. They only work in one direction (well, mine do anyway). I think some of the newer, really expensive bolt extractors are able to work in both directions which would be a great feature. In my case to do this, you'd have to switch sockets.....tricky. Once I got the bolt moving, I did put the torch on the cylinder again and sprayed with kroil.
Good work ...patience pays. Two thoughts, add penetrating oil when the bolt is warm and if you are stuck try tapping the bolt in both directions cw/ccw.
Well if these aren't trophies I don't know what is! Pretty happy with this as only one of them gave me significant trouble where I had to use an extractor socket. Interestingly, the very last one in the line which would be in the #2 cylinder area, was extremely loose and came out by hand if you can believe that. I didn't have to use any tools to remove it, I just used my fingers. It had been soaking in Mouse Milk all day, not sure if that's what did it but I'm happy it came out easy. I didn't heat it, hit it, or anything. If it was that loose, I bet it is the reason for the exhaust leak I was hearing at the front of the engine on that side. Anyway, I'll see if I can finagle the manifold out of the car. If not, no big deal, I'll just slip my new Remflex gasket in there. I've got all new replacement hardware as well.
It wasn't easy getting that AC compressor out of the way and it's going to be a huge pain to put back in for sure. Thanks everyone for your help. I will move on to the drivers side later as it's much much easier to get access. At least I can get at every bolt directly and not have to work through the wheel well with extensions and wobbles. Bloody AIR injection lines make this even more challenging. The bolts connecting the manifold to the downpipe were removed last summer (I put new donut gaskets in them) and I put fancy nickle based turbine engine anti-seize on the bolts so they should come out just fine.
Last edited by ourkid2000; Jan 3, 2026 at 04:17 PM.
There they are.....all 10 of 'em. Only took me better part of two weeks to get them out, haha. There was some praying involved. Lots of various penetrating oils (Kroil, Deep Creep, Mouse Milk, Liquid Wrench) and my torch. Some of them came out easy but others were setting off my "danger" alarm so I really took my time with them. Heating, spraying, smacking them with a drift.
Anyway, on to giving the manifolds a spiffing up with some sandblasting and POR-15 manifold paint. Then the Remflex gaskets and re-install. High temp anti seize as well.
What does everyone like to use for replacement manifold bolts anyway (I don't require stock looking bolts)? I've got some new grade 5 bolts but should I use grade 8 instead maybe?
[img alt="Trophies!
"]https://cimg6.ibsrv.net/gimg/classicoldsmobile.com-vbulletin/655x584/manifold13_57a0640a10a0b31092dde542ea77b426ce68e80 7.png[/img] Trophies for sure.
Grade 5 should be more than adequate. What were the ones removed?
I have no idea what grade these are. I'm assuming they're the original ones that were installed back in '65 or '66 when the engine was assembled. Maybe that's a grade 5? It kinda resembles the modern grade 5 marking, but not quite.
