5.7 manifold errosion

[cdavisdb]

Thanks all.

I suspected a mismatch involving the gasket or in how it sealed. The manifold side is perfect, the problem only on the engine side and on both sides of the engine. The old gaskets did not separate the two center exhaust holes, which I thought was strange. I'll check tomorrow and try to see how the old gaskets went on and how the new ones will. Old ones are some kind of tough, fiber mat encased material. New ones are more like paper. Maybe I can trim the gasket to fit better around the eroded space.


Engine is fresh water cooled. I had envisioned the possibility of eroding through and allowing hot gas to escape to the outside. Never occurred to me that it could erode or crack into the water jacket. Ugh!

[Bushwacker]

Hey Connor,

The exhaust manifolds are obviously running a lot cooler than the heads if there is no oxidation on them. Since the engine is fresh water cooled, the risk of keeping those heads is minimal and I think I'd just put the new manifolds on it and press on, but keep a close eye on coolant level. If you see it start to drop, loosen the Hex cap to eliminate pressure in the system that would force coolant out thru any cracks. The gasket surface is at the extreme outer edge of the cylinder head casting, so I'm guessing the head is fairly thick in that area. If you can trim the gaskets to match the ports and eliminate any flow restrictions at the head/manifold joint, that would help. I'd trim the gaskets to match the ports on the head, and then see how they match up to the exhaust manifold. The old gasket might have been some sort of asbestos material that's no longer available, but carbon fiber would be an excellent material if you could find some, as it will probably withstand about 1900F! If the manifold is smaller than the trimmed gasket, then I'd break out a grinder and open up the manifold to match the gasket. Maybe use some of that muffler repair putty as a gasket sealant. It's basically a ceramic material and will take some fairly high temperature. Those siamesed exhaust ports are the hottest spots on a small block Chevy and are one reason the Fords tend to be a bit more durable in that area since they have individual exhaust ports. The big block Chevy and Chrysler Hemi also have individual exhaust ports to minimize hot spots. Interesting that they didn't even try to seal the area between the ports, but I think I've seen automotive exhaust manifolds with just one big opening for the center ports. That would explain why you've lost material from the rib between the ports, but that's no big deal. I'm guessing you didn't see any problems on the end ports.

Although I've heard that you generally can't justify the extra cost of FWC in a gas engine, this is one situation where it allows you to keep running a set of cylinder heads where it would be a lot riskier in a raw water cooled engine! Your valve seats are obviously in good shape with those compression numbers, so good thing you were observing the 7" limit on manifold vacuum! It's strange that the exit of the exhaust port is evidently running hotter than the exhaust valve itself or the valve seat area, although maybe Volvo uses better materials in those areas! Denny

[FishStretcher]

A few thoughts.

A 99 engine will be tuned for non ethanol gasoline. I am not sure if this is a MPI or a carburetted engine, but either way, it will be running lean. Lean and hot probably contributes to this as there is excess oxygen at the siamesed ports. More so than a properly tuned system.

If you can re-jet or change program or injectors, that isn't a bad idea for this port and the exhaust valves. A little bit rich wouldn't hurt. If it has carbs and you can just go up a bit on the main jets, that might be the ticket. Without excess oxygen in the exhaust, that erosion and oxidation will slow down considerably.

And I am with Bushwacker on the muffler putty.

[Bushwacker]

If it's an EFI engine, just buy another temperature sensor, mount it somewhere cool and connect the wire from the engine computer to that one instead of the one on the engine. This will fake out the computer and make it think the engine is cold so it needs a richer mixture to adequately vaporize the fuel. Might hurt your gas mileage a bit, but should generate a little more power, plus it's probably cheaper to burn fuel than cast iron, valves and valve seats!

[cdavisdb]

Fishstretcher. I run exclusively what is supposed to be non alcohol gas in this thing. Caveat: I've noticed over the last couple of years that there is no water at all in my fuel filters. I suspect there is some alcohol in what I'm buying.

Bushwacker., Its an early EFI, throttle body system. Sensor in a cooler place is a good idea. I'll explore how to do that with my mechanic.


Raining today, it may be a while before I can get back to the boat.

[Bushwacker]

Connor, you could rig up the sensors with a switch to select either one, sort of like an economy mode using the OEM sensor for lightly loaded operation and then a power option with the other sensor for heavy load and/or hard running. Denny

[FishStretcher]

If you are running non ethanol gas, then you are already taking pretty good care of it. I hear you can reprogram the 555 based systems. I don't know if that includes the TBI. The colder sensor or resistor in the wiring harness is a trick on older systems like that.

I suspect this would help. Maybe a fair amount. But at some point it is just cast iron in a condensing marine environment, so there will be a finite life. Which means I should look at mine, too.

edit: I wonder if edelbrock etec 170 heads would fix this. They are aluminum and supposed to be a replacement for the vortec heads. Something I am interested in, but haven't fully researched.

Originally Posted by cdavisdb

Fishstretcher. I run exclusively what is supposed to be non alcohol gas in this thing. Caveat: I've noticed over the last couple of years that there is no water at all in my fuel filters. I suspect there is some alcohol in what I'm buying.

Bushwacker., Its an early EFI, throttle body system. Sensor in a cooler place is a good idea. I'll explore how to do that with my mechanic.


Raining today, it may be a while before I can get back to the boat.

[Bushwacker]

Originally Posted by FishStretcher

. . . I wonder if edelbrock etec 170 heads would fix this. They are aluminum and supposed to be a replacement for the vortec heads. Something I am interested in, but haven't fully researched.

Aluminum heads might actually work very well for a couple of reasons. It's improved conductivity relative to iron makes it easier to cool down hot spots. And although it has a much lower melting point than iron, the aluminum oxide that forms at high temperatures is actually a tough ceramic that tolerates very high temperatures in addition to acting as insulation. Although turbine vane alloys are nickle based, the better ones contain a significant amount of aluminum, which forms a protective oxide on the surface. The oxide will eventually spall off, exposing fresh material which then forms more aluminum oxide on the surface, so it's a self-healing process. We used to enhance it by just packing the parts in a retort full of pure aluminum powder and then cooking them at high temperature in a vacuum furnace. The aluminum would diffuse into the outer 5-10 mils of the surface and then create a very robust aluminum oxide layer when run in an engine. The same thing will happen in the exhaust ports of an aluminum head!

This oxide formation is one reason why the V-4/V-6 outboards can get away with dumping hot exhaust gas into the V of the aluminum block, but it also forms on bolt hole threads, which is why you often had to use a propane or acetylene wrench to remove the bolts from the exhaust covers on the old cross-flow motors! I'd be sure to use plenty of Never-seize on the exhaust manifold bolts!

[Billpotter]

FWIW/FYI: In twenty five years of high volume outboard service experience with aluminum engines, we preferred to stay away from "never seize/ anti seize" compounds because of galvanic corrosion coupling between the aluminum/ metallic never seize anti seize compound/ stainless components. We maintained and serviced the same client's boats for years and years, and found that a Teflon type anti corrosion grease seemed to work best at isolating the different metals, and preventing seizing and corrosion.

[FishStretcher]

So does that mean tef-gel versus nickel or copper anti-sieze? I figure nickel and copper are more noble than aluminum (without looking t up).