Steam/reversion
 

Ok, So I got the boat up and running (496 stroker Chevy bb)and am having some issues with steam out the exhaust. Talked to Crane before I fired up the engine and asked if the stock exhaust (manifolds and risers) would work and I was told it would. The cam is a 571/556 228/234 with a 114. I have a 142 degree t-stat in it. When I run the boat at 3000 to 3500 the temp is about at 150 but when I throttle down the temp shoots up to 170ish followed by ALOT of steam, the risers and manifolds are only warm, the temps drops quick (about 40 sec) and the steam clears after a min or 2. I had restricter riser gaskets (2 long open with 2 pin hole open) and thought that might be the problem. I pulled the risers off and water laying the the bottom. Did a compression chk and all good. I have seen 3" spacers. Should I look into them? All the parts in the cooling system are new. Raw water cooled. I need some help with this one. :poopoo:

When I took the risers off I did see a small amount of water in the base and I had a few tiny droplets on the #3 spark plug.

I'm guessing here, but it sounds like you may have two problems, reversion due to the cam, and lack of coolant flow perhaps due to restriction. I take it, this is an open cooling system.

Michael

Yup the system is open. Not sure what to make of the restriction problem though. I have gone through everything and even pulled the t-stat and ran it to see if that would eliminate the problem but no such luck.......

id also ck that gauge . boiling water not good .maybe hotter than u think .

i think u r getting sone reversion at low rpm,s.also,you might want to replace your wp impellor,it might be getting tired.

wp impeller is new also and just to be safe I checked it yesterday and it was fine.

You could have a leak /crack in one or 2 manifolds /risers /gasket are you using the cowhorn ? maybe it is just pulsing just enough to pull a little water back into the combustion chamber...
I installed a new thermostat in my engine in the start of the season ,my water temp was fluctuating all the time ,we looked everywhere ,changed a lot of stuff ,finally I change the thermostat for a new one again ,and all was good !!

I do not think that longer risers are going to help that much. I came to this conclusion on my boat after reading this article http://www.michel-christen.com/ExhaustElbows.pdf. It is really the design of the riser and/or how far back you introduce the water into the exhaust that will help reversion (IMO). If it was me I would look for a manifold/risers that have a known history of preventing reversion (cheaper than a new motor).

You also touched on two other possible issues for the problem - restriction in the cooling system and/or bad joint. Wet joints in the exhaust/manifold system are know to have trouble. That is why you see so many systems that have now gone to a dry joint. The joint itself may be the source (although it does sound like reversion caused by the cam) so at a minimum if you are going to change your system out consider a dry joint system. Now restriction; it would be a little curious to me that a motor stays cool at high RPMs and then the temp rises excessively as you slow down due to a restriction. This is just based on my experience with the Bravo One cooling hose delima. The hose gets restricted such that the water pressure can cool the engine at lower RPMs but once the throttle is increased the water flow cannot increase enough to meet the demand of the higher RPMs. I just can't see how pulling back on the throttle would make the temp go too high?? It will be interesting to see some more responses.

Thanks for the all the input guys. The manifolds and risers are new and without defect. Had them on my other motor a few weeks ago with no issues. I did make a phone call to a very well know marine exhaust company and after talking to the tech and explaining what I do for a living (own a metal restoration and plating shop) I asked about simply moving the exhaust exit point on the riser further down stream away from the exiting water up top. All of the aftermarket seem to have the water as far down the tube as they can get. I cant change that aspect on my riser but I can move the exhaust witch is what I did. I added an additional 4 1/2 inches to the (brazed in muffler pipe then high temp heat paint) discharge giving me just about 16 1/2 inches from the manifold. The same as aftermarket.