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Low RPM heater Mod Question


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I'm installing the low RPM heater mod today and I had a few questions.

I was wondering which hose is the return line from the heater core? I'm assuming it is the hose the connects to the engine water pump. Is this correct? Should I just buy another plug from an automotive store to put in the block where the return line went?

Also, should I install the Y-fitting before or after the raw water pump? I was thinking I would just install it before the pump since I had more room there.

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I was wondering which hose is the return line from the heater core? I'm assuming it is the hose the connects to the engine water pump. Is this correct? Should I just buy another plug from an automotive store to put in the block where the return line went?
You are correct, and yes, you need to buy a brass plug to seal off the hole in the water pump housing. You don't need to go to an automotive store to find that plug - most hardware stores would carry it too (if that is more convenient for you).
Also, should I install the Y-fitting before or after the raw water pump? I was thinking I would just install it before the pump since I had more room there.
Most have it installed before the raw water pump (mine is - works great), I'm pretty sure the instructions indicate as much too. Some have installed after the pump, I'm guessing because that hose is easier to cut (not reinforced hardwall hose like on the inlet side). But I'm not sure it works as well there. Don't let having to cut the hardwall hose be a deterrent - a hacksaw works just fine.
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I would skip it.

Mine didn't work and there are numerous others that report that it does not work.

Instructions tell you to mount AFTER the impeller (to keep the boat from sinking if the heater hose fails)

Just had mine pulled off last week as it not only didn't provide heat at low RPM...but not at any RPM.

Dave

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Sorry to hear yours didn't work, Dave. I was wondering how that turned out for you. :(

I do find it interesting that you say numerous others have had the same experience though - I'm not sure I'd ever heard a negative report until yours. Dontknow.gif I definitely heard a lot of people speak highly of it, both here and on the old MBO. I know mine works much better with it installed than without it.

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I installed the y-adapter on my old boat before the impellor and it improved the low rpm heat. I plan to install before the impellor on my new boat as well.

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Mine didn't work and there are numerous others that report that it does not work.

Instructions tell you to mount AFTER the impeller (to keep the boat from sinking if the heater hose fails)

Just had mine pulled off last week as it not only didn't provide heat at low RPM...but not at any RPM.

Dave

Dave, if your heater is not pumping heat with the Y fitting, at low RPM or any RPM, then it is installed incorrectly or there is another problem. Haven't heard the numerous reports of it not working, though perhaps performance is affected if installed after the impeller. Not sure when you bought/installed your Y, but my instructions indicated before the impeller. I'm not worried about sinking--boat is in a lift--but if someone was, they could always just throw the intake valve. Which direction did the stem, or bottom, of the Y face?

trevorb, mine works great. Wouldn't be without it. I used a hacksaw as well on the reinforced hose.

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Mine didn't work and there are numerous others that report that it does not work.

Instructions tell you to mount AFTER the impeller (to keep the boat from sinking if the heater hose fails)

Just had mine pulled off last week as it not only didn't provide heat at low RPM...but not at any RPM.

Dave

Dave, if your heater is not pumping heat with the Y fitting, at low RPM or any RPM, then it is installed incorrectly or there is another problem. Haven't heard the numerous reports of it not working, though perhaps performance is affected if installed after the impeller. Not sure when you bought/installed your Y, but my instructions indicated before the impeller. I'm not worried about sinking--boat is in a lift--but if someone was, they could always just throw the intake valve. Which direction did the stem, or bottom, of the Y face?

trevorb, mine works great. Wouldn't be without it. I used a hacksaw as well on the reinforced hose.

Installed by the Malibu dealer after the impeller...and it WAS installed correctly with the bottom of the Y facing the motor (same direction as if you put it before the impeller)

For some reason, the Y ends up pushing cold water the opposite way through the heater and back into the motor.

This is the second one that they have run into this year....seems to be a random occurance.

On this and the old MBO there are numerous people who have either pulled them or drilled out the hole inside of the Y.

FWIW...they pulled it this week and the heat is HOT now :-)

Dave

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Dave, glad to hear your boat is hot. :)

Though I have heard a few questions about y install after the impeller, including if/why factory does it this way, I haven't heard of problems with the pre-impeller install.

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For some reason, the Y ends up pushing cold water the opposite way through the heater and back into the motor.

This is the second one that they have run into this year....seems to be a random occurance.

Glad you got heat Dave, but it still isn't adding up.

I can imagine with the Y-fitting after the impeller that this could happen because the impeller is pushing water in that direction. If there was any kind of restriction downstream of that fitting (such as weeds in the trans oil cooler), the impeller would push the cold lake water through that fitting and into the heater core. This failure mode cannot happen if the Y-fitting is on the intake side of the impeller, because the impeller can't push water that direction.

Even without a blockage (I think I remember you saying in the other thread that you had checked and there wasn't any weeds at the cooler), I've never understood how that Y-fitting is supposed to work on that side of the impeller. I thought the whole point was to use the raw water pump to suck water through the heater. I suppose one might argue that it's relying on the venturi effect, but that doesn't seem like it would be very effective (maybe that's the problem, eh? ;) )

As for the potential of sinking due to a heater hose bursting - I'll take that risk any day. That heater hose is pretty serious duty - I'd bet Jack's house that the core is a bigger risk to burst than the hose. Heck, I've seen many threads of people sharing their experience with a popped heater core and water getting all over - yet none of them sank as a result. I don't think I've ever seen someone post that their heater hose burst.

Bottom line for me - I'd love to see you install it on the intake side of the impeller and see what happens. I'll bet Jack's boat that you'll be pleased with the results. :)

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For some reason, the Y ends up pushing cold water the opposite way through the heater and back into the motor.

This is the second one that they have run into this year....seems to be a random occurance.

I'd bet Jack's house that

I'll bet Jack's boat that

You're awfully quick to gamble all my crap, aint'cha? Though I agree with your above post, perhaps we could start the ante at a case of beer or spring water?

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I've never understood how that Y-fitting is supposed to work on that side of the impeller. I thought the whole point was to use the raw water pump to suck water through the heater.

I agree...never made sense to me either but that it the way the dealer did it...and they are supposed to know right? ROFL.gif Doesn't malibu do that from the factory as well?

Anyway...I have heat now so I am happy.

I may mess around with moving it later this summer...but high RPM heat is better than none for now...

dave

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I put mine in last fall. I put it in after the pump, and couldn't get it to work at all. After a coupe trips to heater craft (they are very close to my house, and very nice guys) I had tried everything to get it to work. I moved it over to before the pump, and now it works great. There was too much back presure putting it after the pump.

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So I put the Y-adapter in yesterday. It only took me about an hour to get it put in. I put it in before the raw water intake and used 2 hose clamps on each side of the fitting. (4 in total) I was concerned about the hoses falling off too. I also have a valve at the water intake to shut off the water if anything did ever pop off. The hacksaw cut through reinforced hose very easily.

I took the boat out last night and now I have heat at idle Yahoo.gifYahoo.gif

It's not exactly hot enough to burn my toes at idle like it does at 1000 RPM, but it's alot better than blowing cold air. Mine would blow COLD air at idle before. I would say the heat is now at about 75% when idling around. It is soooooo nice to not have to turn off the heater every time I stop. Today I'm installing the extendable tube on the driver's side to replace one of the fixed vents, so I don't have to keep stealing the heat from the passenger.

For those of you who cannot get the low rpm mod to work, I've heard that you can just throw in a circulation pump into the heater line. I think they actually do this on some other boats. I'm not sure if this true, I just heard it the other day. Maybe someone could try using a circulation pump and see if it works better than the Y-adapter.

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Installation after the raw water pump is incorrect, I don't care who says it is right. There is more pressure after the pump than pressure from the block even with the Y facing the pump, therefore creating an air conditioning unit instead of a heater.

If you are using the Y, it must go inline before the raw water pump in order for the pump to suck hot water out of the block and through the heater core. Of course, it's especially screwed up if the Y is after the pump AND the Y faces away from the pump. This purely ensures that the heater will be cold.

:::getting down of my soapbox:::

Peter.

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Installation after the raw water pump is incorrect, I don't care who says it is right.

If only we could get advice from someone who spends a lot of time around these boats. . .

Whistling.gif

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The instructions that I recieved from heatercraft also say to install it before the raw water pump.

Can you scan those and email or fax to me? Would love to show them to my dealer and have them redo for free...

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The instructions that I recieved from heatercraft also say to install it before the raw water pump.

Can you scan those and email or fax to me? Would love to show them to my dealer and have them redo for free...

These are the instructions that I got directly from Heatercraft.

scan0004.jpg

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So this all sounds great and is a mod I intend on doing but Why in the world would Malibu not install their heaters this way? There has to be some drawback. Please help me understand this one. Thanks!

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Our Response came with the heater factory installed.

And guess where the y-pipe is mounted - After the impeller!

I was always disappointed about the cold air coming out of the heater hoses when idling... :(

I think I have some mods to do now...

I love this site! :)

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Does anyone know if drilling out the hole in the 5/8" line will improve the heat at idle? The heat is pretty good right now (about 75%), but I know it can get hotter. At 1000 RPM's I can burn my toes on the heater. I would like to burn them at 650 RPM's too. It's cold up here in Canada! Crazy.gif

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