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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10597
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1974 Christ Craft Lancer 24 ft. It had a 307 GLV

Customer Question

I have a 1974 Christ Craft Lancer 24 ft. It had a 307 GLV Engine but the Block cracked.
I have replaced it with a 350 chevy Marine Engine. and everything just bolted up nicely but my exhaust risers get so hot now that they melt the Rubber union on the 90 down pipe that connects with the Y pipe.
a) Shouldn't the risers be cold to the touch enough to Sweat on a hot day
b) does that exhaust system have an actual thermostat what should it run at 150? 160?
c) is my Exhaust system a "3 Pass" system?
Submitted: 4 months ago.
Category: Boat
Expert:  Jason replied 4 months ago.

Good morning, my name is ***** ***** am I speaking with?

Exhaust manifold/risers should run cooler than engine temps, not hotter than engine temps. I have a feeling the cooling plumbing is not correct on your engine. Can you take a whole bunch of pictures of your engine so I can see how all of the cooling houses are routed? The more pictures the better.

Customer: replied 3 months ago.
Ok will do Thank you, ***** ***** is Andres.Ok so what I am sending you right now are pics of the original Engine and cooling set up. I need to take some pics of the new Engine with the Old Cooling system bolted on. I will get back to you with those. perhaps you can tell me what you'd like to see.Otherwise I need a better way to get you a bunch of pics.
Expert:  Jason replied 3 months ago.

I don't recognize that system. I will opt out and leave this open to the community.

Customer: replied 3 months ago.
Ok Thanks for trying Jason. I am told it is a Thermacon system for or from Chris Craft?
Expert:  Tan replied 3 months ago.

Hello Andre. My name is Tan.

The thermostats are in the sides of the risers where the water hose connects originally. Pull the fitting off the side of the riser are the thermostat in there? If they aren't there they are at the front of the motor in the housing where all the hoses connect.

Customer: replied 3 months ago.
Hi Tan,
there is in fact something in the front of the Engine in what appears to be a Thermostat housing. the housing says 8496 K1 on it not sure if that is of any use to you. I can send you a Pic of that I have oiled that up so that the spring moves reasonably freely. what's your suggestion?
Expert:  Tan replied 3 months ago.

Did you test the thermostat to see if it opens? What you do is with a cooking thermometer put the thermostat in a pot of water and bring the water up to about 150*F. Then pull t stat out is it open?

Customer: replied 3 months ago.
Hi Tan,
sorry I did not see this most recent response, But yes my Thermostat Works. The engine temp is bang on at 160 and sits there very nicely. The engine is happy, but there is not enough water to cool the exhaust so the Y pipe and the 90s that connect to it get hot enough to start to melt the rubber union. The Cooling system is something that is unique to Chris Craft, the Thermacon Develvo 3 pass system. I have signed up with some Chris Craft Forums and started to ask questions. But Thanks for trying.Andres
Expert:  Tan replied 3 months ago.

Ok Andre. Have you checked for blockage in the risers them selves not letting water to flow? Blockage and water volume are the usual causes of this kind of problem. Since the engine is staying cool is it possible the risers are clogged or restricted?

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