View Full Version : ManifoldRiser Service Life

George Whittet
07-18-2000, 09:14 PM
" I've just bought a 1978 Carver with raw water cooled Crusader 220 hp inboards (Chevy 305s). I'm satisfied with the overall condition of the boat but have concerns about the manifold systems. Hours total about 800, the last 150 in saltwater, prior to that it was moored in freshwater. Engines were overhauled about 200 hours ago and at that time a "manifold inspection" showed no problems. There are no symptoms of manifold leakage.

I've been told by some that since the greater portion of service has been in freshwater, the manifolds are probably in fairly good shape. I've been told by others, however, that 800 hours, salt- or freshwater, is a lot, and I should be prepared for a failure.

I'm not convinced an inspection is of any value, I mean no one has x-ray vision! Or am I wrong and would an examination be useful?

Anyone have an opinion that could help me? I'm prepared to go ahead and replace them now but before spending $2k-$3K I'd like some advice from some with perhaps more experience. "

07-19-2000, 09:58 AM
" 800 hours is a lot, but very subjective. Fresh or salt doesn't really matter, manifolds suffer a 'scaling' effect... good today, gone tomorrow. The only inspection I'm aware of that is reliable is a pressure test, which must be done with the manifolds removed. If you manifolds have good water flow they will last longer, if the flow is decreased and they operate hot, they will break down faster. It's relatively simple to remove one or more plugs on the manifolds and install temperature sensors if you'd like to 'track' the operating temperature, but on a raw water cooled engine you should be able to monitor well enough on the block. Most people just watch the exhaust and get to know the way their system performs. Some steam is ok, if you notice an increase in steam you could have a problem. If the water spits out the exhaust at idle rather than a smooth flow you should start pulling plug wires to see if you have a piston pushing water. Another good practice is to let your engine idle after a good run to cool the manifolds. The manifolds drain after you turn off the engine and what water that's left will absorb into the hot cast iron and promote scaling, it only takes a few minutes at idle to cool them down. I don't turn mine off until the block temp is below 180 which only happens on a hot day in July. If you're manifolds fail it will be at the intake end and should be visible by removing the end plate. Also, your engines will be hard starting if one or more manifolds leaks and you'll have a rough idle with exhaust spitting. I have seen saltwater in engine oil from failed manifolds but that's extreme failure. If you have water leaking into one or more pistons you'll get a hesitation when starting that seems a lot like a failed starter or bendex, if this happens check for water in the oil. It only takes a tablespoon of water or so to make your oil foam up. There would be a build up of foam stuck inside the oil fill cap. Another check is to have someone start the motor while you watch the stern and see if you see an initial discharge of oil at start-up in the water. This means that there's water sitting in one or more pistons and it's got some gas or oil mixed with it. In extreme cases you'll see the un-burnt gas from the bad cylinder(s) constantly forming an oil slick behind the boat. It doesn't cost as much as you think to replace them, about $160 each plus gaskets. Don't waist your time with stock gaskets, high performance gaskets are $25 a pair and well worth the investment over the $12 stock gaskets. Replace all your bolts with stainless if necessary and make sure you turn the studs all the way in using two nuts locked together before you install the new manifolds. Don't use any Teflon tape or gasket cement on any of the installation. Good luck "