2000 PCM 5.8l Exhaust Manifold leaking

[Winger63]

Out on the lake last night for an evening tour and about 45 min in the engine overheats ( up to 200) and starts to miss fire with a big reduction in power. Open the engine cover and notice the port side exhaust manifold leaking from what looks like a rusty crack on the bottom. Would this cause the issues? The impeller looks fine and I just replaced the thermostat

[windsurfnut]

Rusty crack along the bottom sounds like a crack from water freezing in the manifold. If its cracked internally (likely) then you're likely getting water in the cylinder. Quick check on the dipstick may show milky oil, or take the spark plugs out on that side and look for a wet plug(s).

[Winger63]

Thanks for the reply Windsurfnut. The manifold has been removed, nothing but a PITA, as we all know how brutal exhaust bolt are. Spark plugs removed and checked, luckily no moisture is noticeable in the cylinder. Oil is not milky. I have gone through the entire raw water intake system and only thing other than the manifold leak is the 90 degree strainer fitting on the outflow side is slightly loose so I removed it and retightened it. The riser appears in really good shape so I ordered a new manifold and gasket kit , hopefully that helps. Would I need to remove the other side manifold to pressure test the water jackets or can this be done while still on the motor?

[jpwhit]

Loose fitting on the strainer could easily have caused your issue. That’s on the vacuum side of the raw water pump. It’ll let air into the suction side of the raw water system. That air will turn into large bubbles due to the low pressure and displace most of the cooling water. Manifold crack likely had nothing to do with the overheating.