Hi all, I've done a lot of searching and keep finding mixed results. I currently have my 496 out of the boat for the winter while I clean up the bilge and give everything a good once over (this is a new to me boat). I've been reading a lot about cooling issues with the Merc 496, either from bravo-itis or the PCM going into guardian by reading low water pressure under acceleration.
I figured if I was going to dive into this project, now is the time with the engine out, however I'm concerned about cooling the Bravo drive without the water flow... I've seen some people say its fine, and other people say its not good so I'm a bit nervous about this aspect. I also don't love the added cost of the thruhull, misc fittings, strainer, etc...

I'm not going for any speed records and this is in a cabin cruiser so probably not tons of time spent at WOT, but it does annoy my OCD that the ID of the bravo water hose is like 7/8" until is gets thru the transom, and then jumps up to 1 1/4" and then the output of the seawater pump is 1 1/2"... This is 100% backwards of every well designed pump. The inlet should ALWAYS be larger or at a minimum the same size as the outlet to limit the risk of cavitation.

Looking for any feedback from the experts here, especially anyone that may have done this modification.
Thanks

Hi ashipshow, I'm not an expert but I'm running 496 hos with drop tubes and strainers. Never had a low pressure alarm with this setup other than when running on a hose that didn't have enough supply.

This method did cause warm drive problems which was solved with a drive shower plumbed thru the water channel in the upper. My xdim is high and a cavitation plate intake for the drive shower didn't work.

Water flows from normal intake holes in the lower to upper thru water channel then thru hose to drive shower. A cutoff plate and gasket is installed on inner transom assembly after removing hose fitting.

Don't cut hose between gimbal and outer transom assembly so flow goes to the shower. The mercury provided instructions with cutoff plate say to cut a window in the hose between the gimbal and outer transom assembly which provides flow and some drive cooling if not using a drive shower. Hope this helps. Todd 989-289-9240

I've installed this kit on numerous boats with great results, I know what you mean about the transom assembly inlet being smaller than a hose, but don't overthink it. It works.

I agree with boatnt. I'm pushing 800HP through my 496HO and the outdrive supplied cooling water keeps everything plenty cool. I'm even taking some of the flow for my intercooler. Just make sure you install the updated transom inlet hose style that won't get bravoitis, and have your seawater pump and impeller in top order. Make sure your oil cooler and heat exchanger don't have any debris.

Wow! That makes me feel a little better about a stock 496 Mag lol.. I just installed a new Hardin gen7 sea water pump and a brand new heat exchanger so should be good to go there.. thanks for the advice

On a previous boat, I ran a drive shower plumbed off the water jacket as pictured above along with a separate water dump connected to the water hose coming in from the transom assembly. My current boat has simrek drive showers and has water dumps. Another idea is run your water dump directly above your drive and angled so it dumps the water onto the top of the drive.

That all being said, I don't think you need the thru hull pickup for any added cooling purpose on a stock 496.

Take the Hardin pump off and throw it in the trash.

Use the stock merc pumps and don’t worry. My buddy has a DONZI with same motors and has went through 6 of those pumps.

There is no advantage to them.

On the drive like BoatNT said upgrade to the new kit and go head put some strainers in. Plumb your flush to them and you can even flush in the water.

I have twin HP500efi’s with that setup and never have any water pressure issues.

if I do the strainer is plugged or the pump is bad. I am sure on your cruiser the drives are deep so the water pickup in them will be fine.

curious what your issues have been with the hardin pump? My merc pump was badly scored internally so the whole body needed replaced... I like the idea of the hardin pumps being rebuildable with end plates for a fraction of the price..

I did order the upgraded transom kit and will use that.. also not sure I see the purpose of the strainer if im keeping the thru drive setup? Maybe im missing something but seems a little redundant

The hardin pumps keep leaking around the shaft.

my pumps are a little different design but I always change the housing and impeller, they are a bit over $100 how much are the 496 pump and housing?


I didn’t see where you boat but sea strainers are there to strain out weeds small shells etc. we get a fair amount of that in FL.


depends on where u boat.

The best price ive found for the oem merc housing for mine is just north of $400, and it's still bronze which will wear out much faster than stainless... I'm not saying the hardin pump is magic, it just seemed to make sense for the price.. buy once cry once sort of situation..

I'll be boating mostly northern chesapeake and it will also be my first time so not entirely sure what to expect.. I know it's very low salinity but not sure what the seaweed situation is.