2015 PCM ZR409 - Exhaust Manifolds - Overheating

[scotchipman]

My 2015 ZR409 exhaust manifolds are overheating then my boat goes into some kind of limp mode. My ZR409 has coolant in the engine block and fresh water in the manifolds with a heat exchanger in the rear. No engine light is coming on and the water temp is reading normal. What I think is happening is the exhaust manifolds are getting clogged up? When I pull the plugs on the manifolds I get a lot of debris coming out with the water that looks like silt or hard water that has been baked onto the inside of the manifold then has flaked off. This is the second time this has happened, the first time was only about 20 hours prior.

Do you think I'm correct in assuming that the overheating is due to the manifolds getting clogged? If so is there anything I can do beside pulling the four plugs and removing the debris? Could my issue be something completely different and if so what can I check?

[CarlitosAir]

I am by no means expert at this, but will take a shot. Can you check to see how the sea strainer looks? Typically that should indicate whether the water your engine intakes is dirty or clean, and you'll see it on the screen. Also try running it in your driveway connected to a clean water source, and see how the water comes out from the exhaust. Best of luck

[jpwhit]

How many hours since the raw water pump impeller has been changed? The exhaust manifolds need a much higher flow rate of raw water to stay cool than the engine. So, if the impeller is marginal, the manifolds will always overheat long before the engine. Recommended impeller replacement interval is every 50 hours, but in practice will often go longer. But since you're having an issue, if it's been much more than 50 hours, then that is the first thing to do. And as CarlitosAir suggests, make sure the strainer is cleaned out and also has a good o-ring w/o any cuts, abrasions, or stiffness.

It takes a lot of debris to clog exhaust manifolds. I don't think I've ever seen enough debris getting through the raw water strainer to do that. Unless by chance someone removed the raw water strainer from your boat or it's a salt water boat.

[scotchipman]

I'm on a private lake, there is no debris going into the system besides very fine sediment and dissolved which are around 1,000 ppm. None of the 20+ boats on the lake get anything in the strainer, I actually removed my strainer since it was leaking a little and was one more thing to winterize. The debris is coming from inside the exhaust manifolds, dissolved solids and/or fine sediment is baking on the inside then flaking off. The impeller does have more than 50 hours on it but when I start the boat up with the hose disconnected just after the pump I get a lot of water flow, also a lot of water flow when I start the boat and pull the exhaust manifold plugs. I'm at the end of the season in Utah, I will replace the impeller when I start up again in March.

[pauldixon]

Not sure on the Nautique but I had clogged manifolds on a 2016 Mastercraft. There is a ring in them that is fairly tight to not let too much water through and it became clogged due to running in “hard” water. I ended up running through a dilute solution of muriatic acid to clean the manifolds. Worked great!

I used 1 cup of pool acid (33%) for 4 gallons of soft water. Drain your manifolds and any raw water out of the engine and then refill with this mixture. Let it sit for 4 hours. I guarantee this will fix your issue based on what you are describing with how hard your water is. You may have to do it more than once.

[scotchipman]

Thanks for the timely reply! I just started skiing in Utah (last skied the first week of Nov) and the first time out my exhaust manifolds overheated. I did install a new impeller before my ski set. One thing new I noticed is a little water leaking between the manifolds and exhaust corners. My plan now is to remove the exhaust manifolds and let them soak in phosphoric acid (thinking of using this http://www.starbrite.com/item/marine-descaling-fluid-2) or taking them to a radiator shop and let them soak in their acid. Once I have cleaned them with acid I will reinstall with all new gaskets which should fix my leak. I'm also considering using http://www.starbrite.com/item/descaling-motor-flush which has hydrochloric acid. It sounds like I could even use muriatic acid.

Does anyone know which acid is best to use between phosphoric, hydrochloric, and muriatic? What kind of acid does the radiator shop use?

[MN Ryan]

Muriatic and hydrochloric are the same thing, just a different name for the same acid.

I honestly don't think phosphoric acid would do the trick. It's not that strong of an acid, and at higher concentrations, it's quite viscous, almost like corn syrup (but not quite that thick). I think hydrochloric/muriatic would be the ticket. Make sure you rinse the heck out of anything that comes in contact with it when you're done, though, as HCl is quite corrosive. And wear gloves and safety goggles!

[scotchipman]

Thanks for the acid information, if I do the cleaning myself I will likely go with http://www.starbrite.com/item/descaling-motor-flush which has hydrochloric acid in it. I need to call a radiator shop and see what they charge and what kind of acid they use.

[Paul W]

Since you're going to have them off, I would take them to the radiator shop and have them boiled out. Then you don't have to mess with the acid.