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Old 04-01-2015, 08:55 AM   #1
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When to replace the exhaust manifold?

It's a 30 year old Perkins 4.236. I've removed the original cast iron exhaust manifold to access other areas of the engine and while it's off I'm inspecting the water jacket. I can imagine that if it rusts through it will do serious damage letting water into the engine. All I can tell is that it's, well... rusty, but there are no obvious signs that its necessarily going to rust out anytime soon. I'm debating if I should replace this now or not. The new ones aren't cheap, so I would like to get as much life out of this as I can. I guess my question is how do I know when it's time to replace an exhaust manifold? Is this something that is routinely replaced or should it last as long as the engine?
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Old 04-01-2015, 09:54 AM   #2
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The best answer is to replace the exhaust manifold just before it fails. Its a lot like how do you keep from breaking the lead on a pencil. duh You lift up just before it breaks.

You are changing the timing belt, should you also change the water pump?

I think you are going to get a lot of opinions with your question. Mine is if the exhaust is deteriorated replace it.
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Old 04-01-2015, 10:13 AM   #3
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This is an integral exhaust manifold and heat exchanger right? If so there are three fluids that need to be kept separate: exhaust, raw water and engine coolant.

I don't think a failure is going to have catastrophic results, like sea water getting into your crankcase. You can look for bubbling in your coolant to detect exhaust gas leaks and you can look for the coolant level rising due to salt water leaking to that side.

I would just watch these indicators and act accordingly. Cast iron lasts almost forever in coolant/exhaust service and a long time in sea water service.

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Old 04-01-2015, 10:22 AM   #4
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OB - I'm back at the ranch in Montana. I'm replacing the water pump on my John Deere, with that said, I'm also replacing all the hoses, belts, rubber buffers, etc. while the radiator & fan are removed though they look ok. My manifolds are in good shape - so I'm not doing that. Bottom line, replace the manifold if you can. Don't wait till it breaks.
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Old 04-01-2015, 10:30 AM   #5
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Some Perkins have sea water in manifolds, some have coolant in manifolds. Ones with coolant last forever unless cracked by heat. Ones with sea water, tough call. Clean out the rust and try to get a feel for how much "meat" is left.
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Old 04-01-2015, 11:08 AM   #6
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It's just an exhaust manifold with raw seawalter running through it, not a combined manifold/heat exchanger, like a Bowman.

I'm considering maybe converting to one of those if I do replace the manifold. But those are really expensive.
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Old 04-01-2015, 11:50 AM   #7
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Quote:
Originally Posted by Ski in NC View Post
Some Perkins have sea water in manifolds, some have coolant in manifolds. Ones with coolant last forever unless cracked by heat. Ones with sea water, tough call. Clean out the rust and try to get a feel for how much "meat" is left.
I know of 8 people who had T6.354 Perkins with raw water exhaust manifolds that failed.
3 failed externally, meaning they saw a leak and replaced the manifold.
5 failed with an internal leak. 4 of those times it took the engine out before they knew they had a leak.
So roll the dice.
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