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Just installed heater but not getting any heat


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I tapped into the top of the intake manifold as shown in the first picture and redeposited the water just before the transmission cooler with a Y pipe. There is hot water coming out of the intake manifold and I took it for a test drive to confirm that it's not getting warm. I didn't think about it at the time but it's possible one of the hoses is kinked. Is there anything else I should check, next time I uncover the boat? The blue hose just under the raw water pump is the cold water supply for the shower.



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That's definitely how I had it in my last boat because it was more convenient but does it really matter that it's after the raw water pump instead of before? The hose before the pump is a reinforced line and I figured that would be a pain to cut.

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That is a good question. I have always heard to have it before the raw water pump. My guess is that it wasn't getting enough water flow to prime and siphon the water through the heater. The hose wasn't bad to cut through. I just cut the rubber with a utility knife and then cut the reinforcement with wire cutters.

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Ok I'll check for kinks later and if I don't see any, I will move the return line. Maybe after the ramp water pump is pressurized higher than what comes out of the block not allowing the water to move.

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had the same problem a few years ago. you MUST plug the Y before the impeller to have a better return as the impeller with pump the returning water of the heater (if you have it on the other side, there is pressure from the impeller and you don't have a good water flow). The hole in the Y is too small. make it bigger with a bigger drill. if you do both operation, you will never feel the cold again in your boat....

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The highest pressure in the entire cooling system will be at the raw water pump discharge which makes it the best point for the shower take-off. If you have connected a pipe there, the pressure at that point will exceed the pressure anywhere else that you have connected to and water will flow from the raw water discharge, 'backwards' through the heater and into wherever the other hose is connected to.

The heater 'return' has to be connected to something that is at a lower pressure than the hot water take-off point. That will be the raw water suction.

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I guess I should pay attention, I thought he was referring to a 2/3 vent heater (title of thread) not a hot water shower. The cm30 won't do much for that application.

I was talking about a vent heater. I just happen to have a hot water shower as well that is more visible/obvious. Weather here is pretty dreary so I haven't had a whole lot of motivation to go work on the boat but based on what I've read so far, it just sounds like I have no flow because of where I put the return line.

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My 350 on my last vlx had the Y installed in the proper location and I still was not satisfied with the heat output. The cm30 really did help increase flow at idle and when engine is off. I wired it to automatically come on with the heater on both hi and low settings.

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Ok swapped it to the other side of the raw water pump and drilled the Y fitting hole a little bigger and it works like a champ now. Surprisingly with a 1/4"-ish hole instead of the tiny little 1/8" hole, I do manage to keep heat at idle. No real tests as of yet but idling at my dock makes it seem like it'll do well. Will see how it does at speed though as it seemed to cool off a little when I revved the engine in neutral.

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