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Cracked Exhaust Manifold


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Hi all. I am new to the forum and need some advice. I just bought a 1997 Tantrum Monsoon 320 with 420 hours on it. The fit and finish is great for being 17 yrs old. After sitting all winter it fired right up and ran great on the test drive. Last night I ran it for 30 minutes to warm it up for an oil change, again ran great. As I was changing the oil filter I noticed water leaking out of bottom outside part of the exhaust manifold. Yep, it's cracked. The guy I bought it from explained his winterizing process about filling it with antifreeze but never said anything about draining the water out of the manifolds, so I'm guessing that is why it cracked. Also the crack has corrosion on it so it didn't just happen this past winter, it has been like this for a while. My fault for not catching it on the inspection.

So I know it needs to be replaced but my question here is could there be more damage that I can't see even though the engine is running top notch. My limited knowledge with manifolds is that there are two chambers, one carries the exhaust coming out of the engine, the other carries the cooling water. If it has also cracked between the two inner chambers then water could be draining into the cylinders when the motor is shut off, which could cause it to hydro-lock. Is there any way to test for this. The water dripping out of the manifold is clear and not discolored. Also the engine oil did not appear to be contaminated with water either. Boat runs great but I am worried it is a ticking time bomb.

Does anyone know of a good place to buy manifolds or should I just go through the dealer? I was also thinking about doing this job myself and am welcome to any advice. I know there is a torque sequence you have to follow (anyone know where I can find this) but other than that is it just a bolt off / on job?

Thanks

Steve

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I would check around the block and heads also for leaking. it is very possible that they may have cracked internally also. they are just a remove and replace job, nothing hard about it at all. you will want to check inside the exhaust hoses coming off the risers to make sure they are not coming apart inside from excess heat. without the proper amount of water, the insides of the hoses will be destroyed. proper torque is about 30 ft lbs for those 3/8ths bolts.

while the manifolds are out of the way, i'd change plugs and wires.

discount inboard marine, bakes marine, or ebay to find a replacement.

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Or establish a relationship with your local Malibu-Indmar dealer, as you may want other items and parts as time goes on. People replace them when they are cracked, so I would not suggest purchasing a used one.

Peter :)

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Or establish a relationship with your local Malibu-Indmar dealer, as you may want other items and parts as time goes on. People replace them when they are cracked, so I would not suggest purchasing a used one.

Peter :)

:plus1: This may not be the cheapest option but could pay dividends when you need service or parts or when you decide you want to upgrade to a new(er) boat.

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Only thing, I would ad to the good advice above, don't start the engine again until after the manifolds are replaced as you could do more damage than you want to think about.

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I'd pull the manifolds (both) ASAP to see if they are cracked on the inside as well, allowing water to enter the exhaust ports.

If the block or heads are internally cracked, the oil will become the consistency and color of a milkshake (don't ask how I know).

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@sdennis: if you remove the riser you should be able to see if any water has gotten down the inside of the manifold as there would be some witness marks. You might potentially get water down the exhaust port and not have the milkshake oil look if the rings happen to keep any water in the combustion chamber. If not mixed, the dipstick would appear to have gained oil level. You could also remove the spark plugs and take a look in the cylinders for any corrosion or water.

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My buddy has a older Mercruiser that he ran with a cracked exh. manifold for 2 years. And he surfed a lot. Last year his motor dropped a valve seat and trashed the motor. We were both wondering if it was from the manifold leak or from surfing (the fail happened on the high side when listed). Most of our crew surf goofy, so it had a lot of time running listed (6 years).

Reminder to everyone: if you get the boat out-recommission-for one last ride in the middle of winter, double check your winterizing. He missed pulling the hose off the exh. manifold.

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My buddy has a older Mercruiser that he ran with a cracked exh. manifold for 2 years. And he surfed a lot. Last year his motor dropped a valve seat and trashed the motor. We were both wondering if it was from the manifold leak

This is one of the common things that are damaged from exhaust water leaks. cold water on hot metal doesn't work well.

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Hi all. I am new to the forum and need some advice. I just bought a 1997 Tantrum Monsoon 320 with 420 hours on it. The fit and finish is great for being 17 yrs old. After sitting all winter it fired right up and ran great on the test drive. Last night I ran it for 30 minutes to warm it up for an oil change, again ran great. As I was changing the oil filter I noticed water leaking out of bottom outside part of the exhaust manifold. Yep, it's cracked. The guy I bought it from explained his winterizing process about filling it with antifreeze but never said anything about draining the water out of the manifolds, so I'm guessing that is why it cracked. Also the crack has corrosion on it so it didn't just happen this past winter, it has been like this for a while. My fault for not catching it on the inspection.

So I know it needs to be replaced but my question here is could there be more damage that I can't see even though the engine is running top notch. My limited knowledge with manifolds is that there are two chambers, one carries the exhaust coming out of the engine, the other carries the cooling water. If it has also cracked between the two inner chambers then water could be draining into the cylinders when the motor is shut off, which could cause it to hydro-lock. Is there any way to test for this. The water dripping out of the manifold is clear and not discolored. Also the engine oil did not appear to be contaminated with water either. Boat runs great but I am worried it is a ticking time bomb.

Does anyone know of a good place to buy manifolds or should I just go through the dealer? I was also thinking about doing this job myself and am welcome to any advice. I know there is a torque sequence you have to follow (anyone know where I can find this) but other than that is it just a bolt off / on job?

Thanks

Steve

You could have a single crack or multiple cracks. "assuming" that the manifold cracked because of poor winterizing its unlikely that you did any internal damage. It usually takes more than a single run to do any damage to the valve or valve seat. Replace the manifold and you should be fine. If he did one manifold wrong, he probably did the other wrong too, so it may or may not be damaged. Based on the year of your boat, when you pull the riser off, you are going to find that the mating surfaces are pretty coroded, so you may need to replace them also. The gasket between the manifold and riser MUST have a flat clean surface, or it will leak.

When I do them, I take to 8" long 3/8 bolts with the heads cut off. I replace the 2 end manifold bolts with them and then remove the rest of the bolts and slide the manifolds off. They are heavy and this makes sure they don't drop where you don't want them too.

Check the exhaust runner length on the exsisting manifolds. Indmar used 2 different lengths. I replaced my manifolds, and they used the longer one. Thats not what most places sell. There is a thread on here about it, that I will link here when I find it.

Torque the bolts from the middle out. There is a Tq spec given here which is fine. you are going to have to recheck them a couple of times after the engine heat cycles.

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This thread

http://www.themalibucrew.com/forums/index.php?/topic/41004-new-exhaust-manifolds-question/#entry568831

shows what I'm talking about with the exhaust manifolds and their distance from the head. I seem to have deleted the shorter ones from photo bucket,(ooops) but the longer ones that I needed are still there so you can use those numbers to tell if you need them, or the shorter ones.

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Thanks everyone for all the good advice.

I removed the manifolds last night which was much easier than I expected. The bolts came right out, being almost 17 years old I expected some bolts to be seized. Good news the exhaust ports didn't crack so there was no water damage to any of the cylinders. Just cracked and leaked on the outside. Going to order new manifolds today through the dealer. Whats everyone's thought on using anti seizing lube on the manifold bolts? I have heard multiple opinions.

The risers look to be in good shape so there isn't any need to replace them correct? Also the plug wires look to be original so should I replace them also even though everything is running good? I would rather do a little preventive maintenance now than wait for them to fail.

Again thanks for the help.

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That's all good news. If I remember right, those bolt holes are blind (don't go into the water jacket on the heads) so anti seize or sealant isn't really critical, you could put in on if you got it.

Plug wires are so easy to replace now or later it doesn't have to be of this job, but 17 years is on up there...

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some have mentioned working with your Malibu dealer. not sure of your location or how far away your nearest dealer is. in my case its 55 miles away and while its been a great dealer to buy boats from, I learned early on that the parts & service department and mechanics were nothing like the sales department. several unreturned phone calls and parts that were supposed to be ordered, charged to a credit card and turns out were never ordered. missed several weeks of boating over the years because of this and I've bought 3 boats from them. always seem to be able to get a return call when we were buying a boat though. from what I understand things haven't changed much. not saying this is the norm for all Malibu dealers but it is for the one closest to me. I mentioned discount inboard marine because vince and Richard go thee extra step. they are full of great information to help trouble shoot and share this knowledge. great people to deal with and 10% off every order doesn't hurt either.

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some have mentioned working with your Malibu dealer. not sure of your location or how far away your nearest dealer is. in my case its 55 miles away and while its been a great dealer to buy boats from, I learned early on that the parts & service department and mechanics were nothing like the sales department. several unreturned phone calls and parts that were supposed to be ordered, charged to a credit card and turns out were never ordered. missed several weeks of boating over the years because of this and I've bought 3 boats from them. always seem to be able to get a return call when we were buying a boat though. from what I understand things haven't changed much. not saying this is the norm for all Malibu dealers but it is for the one closest to me. I mentioned discount inboard marine because vince and Richard go thee extra step. they are full of great information to help trouble shoot and share this knowledge. great people to deal with and 10% off every order doesn't hurt either.

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Went through the local (2.5 hrs away) dealership for the parts. Went to pick them up and it was the wrong manifold (shorter exhaust ports that were mentioned on this topic). They apologized and said they would contact Malibu for the correct part as soon as possible. I called back noon the next day and the guy said he hadn't had time to call, but he would when he hung up the phone and call me right back. That was five days ago and no call back yet. The next day I called Discount Inboard Marine, they new exactly what I was talking about and had the parts to me in two days. Won't be going back to the dealership anytime soon.

Thanks for everyone's advice.

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