Heater y-pipe - question

[functionoverfashion]

Hey all. I have a heater in my 2003 SANTE that appears to be set up the way it was from the factory, with the water return going back into the pump. I had a y-pipe in my old boat and I really felt like it helped give better heat at idle, so I bought one for this boat. I'm curious about the construction, though - there is only a tiny hole between the "Y" and the larger pipe itself - it's nowhere near the full 5/8" or so diameter of the smaller Y piece.

Have others used this same piece with good results? I'm tempted to drill it out larger before installing it. But I'm also thinking it would be easier to try it as-is, because it would be much harder to fill in than to drill out later. But why would that hole be so small in the first place? Edit - I do know it can be hard to get the system primed (it can suck air from the heater line) at initial startup. But if you have the system filled with antifreeze, and/or prime it with water, I don't see a downside to the y-pipe.

[functionoverfashion]

I feel dumb because I just, you know, called Heater Craft directly, and they said that's absolutely by design. The guy couldn't explain the physics of it, per se, but he said they have tested them and found it to be most effective with the hole being smaller than the ID of the pipe that's coming in right there (5/8").

It just seems to me like if the hole was bigger, more water would flow through per minute. It doesn't seem to be about creating more pressure, but just moving more water through the system.

Or am I thinking about it the wrong way? I know water would come out of the block if you took the plug out, but with how much pressure? Water has other ways to escape, too. So if the heater and its long run through a bunch of corners (namely the heater core) creates enough resistance... then water is going to just not going to flow out of the block with any kind of urgency, because it's meeting resistance, and the suction created at the other end isn't sufficient. By creating a point of high suction (relative to if the hole were bigger) does it then tend to "pull" the water out of the other end of the system?

I suppose this would be easy to test with some pressure gauges and a few of those y-pipes. Unfortunately, the pipes are a bit pricey to start cutting them up, or drilling bigger holes as the case may be.

Heater Craft says they "did testing" and this is the product they've been using for years. Who am I to question it?

I'm also installing a filter inline on the supply side, as I found in my old boat that the heater core would get a bit clogged with debris over time, little bits of rust flakes from the engine block, etc. which doesn't help.

[TRBenj]

The restriction improves heat output at low rpm (idle).

A simple plastic tee with a restriction on the heater return line serves the same purpose and can be assembled for a few dollars.

[functionoverfashion]

The restriction improves heat output at low rpm (idle).

A simple plastic tee with a restriction on the heater return line serves the same purpose and can be assembled for a few dollars.

I had one of these in my old boat and it worked... except I never had it plumbed any other way so I can't compare. I guess it just seems like putting the return just "upstream" of the RWP would be the goal, and that a larger opening would create better flow. But intuition and physics aren't always aligned. I do believe it's better than the factory setup.