defroster on a raw water cooled Mercruiser 3.0 140HP

Hi guys, I was terribly annoyed with fogged up windows last season. and I want to install a defroster so I can have some nozzles pointed on the window. tried everything last year but I realized i need something more to get rid of the condensation.. got plenty of space to put it under the windshield and everything.

but wondered if anyone had any experience connecting up a defroster to a raw water cooled engine? where would I get the outlet and anything I should be thinking about before going head in.. I know it have been done before, but dont know the results or how it was done.

this is the boat in question. both pics is not of my boat, but exactly the same..(mine is mint though )


here it is done with some fan nozzles under the windshield.

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

You can run hoses up to the cabin and install a cabin heater that has defroster ducts. Here is how you hook up to the engine.

View attachment aux heater.pdf

May not get really warm being as it's raw water cooled, but it should be warm enough to make a good defroster if you duct it right.

Since it's not really an engine question, I'm going to move it over to boat topics. May be others with other engines that have installed defrosters in their boats.

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

Don, you`re as always fast and of much help as I`ve seen before.. thank you so much! really appreciate it.

I know I wont get to much heat out of this, but hoping some will come. trying to insulate the hoses good will probably help..

what do you mean by "duct it right"? just trying to avoid mistakes. thinking two ducts under the window and 2 down that i can shut close by the floor for some leg heat on a cold night.

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

With improperly sized ducts or vents, or too long, you may not get the air flow to even blow on the windhield. It depends on CFM of the blower on the heater core setup you use.
I'm not good at ducting for a defroster, tried it on the boat I had in Alaska, with a closed cooling system and it would only get a small spot. I thought about putting a 3" bilge blower in to help the air flow but never gave it a try.
A lot had to do with the layout of the boat, and mine was nothing like yours.

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

Bubba1235 said:

Don, if he taps in before the T-stat wouldn't the water temp be 160 F. (or what the T-stat is made for) once the engine is up to operating temp? If so then the defroster won't be much different than what you get in the average car I would think.

To the original poster: A forum member (Opps is his handle) did this last year with great results, you might send him a PM and ask about it.

Click to expand...

Oops! hasn't been on the forums in months, not sure where he went.

The info I gave came out of the #13 manual, and they were using 140? stats on many of the older engines, and 140 is cold by the time it gets forward. It's not so much the temp I was talking about, but blowing the "slightly warmed" air onto the windshield that turned into a problem for me. Of course, I had a 28' boat and his doesn't look that big.
Just saying it's not going to be something that might work the first time and may take some trial and error work to get what he wants.

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

rbuljo said:

Hi guys, I was terribly annoyed with fogged up windows last season. and I want to install a defroster so I can have some nozzles pointed on the window. tried everything last year but I realized i need something more to get rid of the condensation.. got plenty of space to put it under the windshield and everything.

but wondered if anyone had any experience connecting up a defroster to a raw water cooled engine? where would I get the outlet and anything I should be thinking about before going head in.. I know it have been done before, but dont know the results or how it was done.

this is the boat in question. both pics is not of my boat, but exactly the same..(mine is mint though )
View attachment 180306

here it is done with some fan nozzles under the windshield.
View attachment 180307

Click to expand...

Ayuh,.... I've done a cabin heater on a boat, 'bout that size with a 4.3l raw water cooled...

Mounted under the seat, it heated well, but no defroster...

Have ya considered goin' with a Dash Fan,....

For deFoggin' they do very well,... deFrostin' not so much,...

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

Something like this, perhaps? ACC Climate Control AUXILIARY DEFROSTER KIT - JCWhitney

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

hi guys, im just getting started with the heater/defroster setup. bought this heater

its a 10kw @ 172 degrees F. if i get 0.5kw im happy..

the "outlet" on the engine is the plug on the termostat housing if im correct? the manual only states return hose.

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

shameless bump

Re: defroster on a raw water cooled Mercruiser 3.0 140HP

rbuljo said:

hi guys, im just getting started with the heater/defroster setup. bought this heater View attachment 190519

its a 10kw @ 172 degrees F. if i get 0.5kw im happy..

the "outlet" on the engine is the plug on the termostat housing if im correct? the manual only states return hose.

Click to expand...

Ayuh,... Ya need hot water from the head side of the T-stat,...

Donno what you've got for ports, but a "T" can be put into the temp gauge sender port...