Our Winnebago Class A with it's Ford V10 just joined the ranks of those with broken manifold studs and a leaking exhaust manifold. When it warms up next week I'll dig in and fix it. Thought I'd try to reason out why this is such a common issue, particularly on the F53 motorhome chassis. I'm harkened back to the 70's when I first started tinkering with motorhomes and am reminded of all the "classic Flying W" Winnebagos that came on the Dodge chassis with the old 413 V8. Toward the end of their existence, almost all of them ended up with tubular headers as the stock cast iron ones just couldn't stand the heat under an RV doghouse and cracked. That was so common it got pretty much impossible to find a good used RV 413 header in junkyards and as Dodge had discontinued that engine in favor of the 440, they soon (10 years) stopped selling new 413 manifolds making aftermarket "racing headers" the only game in town for the 413. I'm leaning towards my theory two things are contributing to the V10 manifold gasket issue. One is that the V10 is part of the "modular" Ford engine family where many parts are common across the multiple size engines. The metric manifold studs are about the size of a 5/16" bolt. This is no doubt sufficient for a V6's short manifold but probably borderline for a V8 and CERTAINLY too wimpy for the V10's longer exhaust manifold. The V10 should have been built with 3/8" studs. This leads to what I'm thinking is the REAL culprit causing the manifold leaks. First off, I see it's most often the passenger side that starts the tick-tick-ticking leak first. As the manifolds, bolts, and gaskets are the same on both sides, you would expect there shouldn't be a preference for the passenger side to leak first. What I propose as the problem has to do with the fact that the F53 chassis has the engine offset towards the passenger side. Crawling under the wheel well, the right manifold is quite exposed to air and road splash water from the tire. I'm thinking this uneven heating of the manifold coupled with the undersize bolts for such a longer manifold gives more "leverage" for the manifold to try to warp up and this is what causes the often seen broken rear manifold studs. The driver's side is much more protected being further to the right and more removed from the left front wheel (and has a bunch of cables, hoses, and other stuff between the engine and wheel). The older 70's Winnebago engines actually set up inside the taller doghouses where the engine was more removed from road draft and splashing from the tires (and transmitted a LOT more heat and noise to the passenger compartment). This made them run much hotter though, and more prone to cracking manifolds from the heat. With the "basement" design of modern motorhomes, the drivetrain is now mostly down below the cabin floor, much more exposed. I think what happens is that going down the road, particularly during hill climbing, the right exhaust manifold ends up very unevenly heated, the side against the engine much hotter than the side toward the wheel. Once I do my repair, I'm going to mount a piece of galvanized metal on the passenger side to the frame that will extend up to the bottom of the cabin floor. Mounted to the outside of the frame rail will put it about 5-6" inches away from the manifold so it will still get plenty of cooling air from the front like the left side but will be protected from most wind and water splash directly from the right front tire. I feel this will make the right manifold's environment much more like the left's hopefully making this a one-time repair. You can see YouTube videos and read about owners having to do this fix several times which I want to avoid. If you need to do this repair, also be advised that it is very important to take the manifold down to your local automotive machine shop and have the mating surface planed flat again. The manifold starts leaking because the rear of it has warped up and "curled away" from the cylinder head surface and this distortion is permanent but easily fixed by planing it . I'm pretty confident the machine work and my DIY shield will make this a one time repair for me.
