Offshoreonly.com - Not so good find on my 502 MPI

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Where did you place the the PRV? I have pipes across the back of each motor that replaced the 420 oil coolers (just after the trans cooler and before th 502 oil cooler). Is that a good spot to add them?

Thanks again for posting that link!

I put it downstream of the PSteering cooler, and before the cool fuel exchanger. Rear port side of motor. The 1" dump hose just goes outside the boat with a thru hull fitting. In my case the boat had the fittings already, next to the bilge pump fitting.

Remember these are not just pressure regulators with one inlet, one outlet. It is a Tee. These let the water go straight thru, wide open fitting. There is a tee that dumps water thru the 3rd side fitting that needs to go overboard. I guess this way if it breaks and closes shut you still have your original water pressure.

Same here on never checking the block water pressure. i never would have started checking it if i hadn't seen all the corrosion below both heads on both motors. It doesn't take a whole lot of pressure to move a lot of water.
I will go see if i can get a pic.

Heads are off. I had water intrusion on 7 and especially 8. It doesn’t look like it happened for long, and could have been caused by condensation (I keep the boat tilted pretty high on the trailer to keep water flowing to the bildge). Otherwise everything looks good.

I may have been a little overzealous with going after this issue.

And unless GM uses Felpro head gaskets, this motor has had the heads off in the past.

I’m water pressure testing the headers now, and so far I have not seen any leaks.

The deck surfaces look good, and nothing shows signs of water intrusion or burns between cylinders. I’m going to have my shop go through the heads to make sure they’re sound, and then I’ll button her back up. I’m going to clean up the rust and treat the block areas with Ospro then paint fresh. Both sides of the block had this happen (the Cool Fuel module and oil lines were obscuring the view).

I have an electrical connection on the #8 injector that feels loose. I’m going to ship these off to BUP to have them cleaned and flowed. Might as well since they’re out. (BUP if you could send me a PM on particulars for sending these to you, I’d be much appreciative).

On the power building front, I’m going to source new parts to build a set of motors so that I can keep my sewing machines on standby. Not necessary to mess with these motors, and the boat will do 69-70 all day long.

Cap’m,

My PRVs are like the Mercury part but without the diaphragm. It’s a 3-way that puts excess water overboard. I’ll add the dumps to the transom more than likely.

GM does not assemble the engines for marine use...found out when found a scat crank in my new GM 454, so easily could have been assembled with felpro gaskets. Also what I have seen is terrible condensation build up in a lot of boats, after running one day, parking overnight open hatch looks like someone used a hose and soaked everything down. I would ck you boat and if it is doing that try leaving hatch open some. Also seen the manifolds leak and run water down like this, only takes one spot in the paint for the corrosion to start and spread like cancer. If blocks savable sand down and repaint with rustoleum. Merc has had this issue for years, oil pans used to rust thru, would not even know till oil started leaking, so they went to a undercoating type crap on the steel pans now..

Quote:

Originally Posted by TomZ (Post 4677417)

And unless GM uses Felpro head gaskets, this motor has had the heads off in the past.

My 496HO had Felpro headgaskets stock from GM. Mercruiser sourced GM longblocks for their "black" engines.

Good call on BUP for your injectors. He does a very thorough job!!

So finding Felpro head gaskets is normal?

It had a Merc p/n intake gaskets. None of the head bolts, intake bolts, water pump bolts, etc, had tool marks so I was assuming that it had not been touched.

Hoping to have her buttoned up pretty quickly. The water in 7 and 8 bothered me hence sending them out. I want to make sure their solid.

Just an update...

The port engine is done. The cylinder heads were in excellent shape, and only needed minimal refreshening. While I had it all apart, I went ahead at had BUP hook me up with a new set of injectors (for both engines). All I have left to do is cleanup the bilge and drop her her back in.

While I was doing some cleanup last night, I found that the other block was in just as bad shape. Considering that it’s been fine up to this point, I’ve decided to leave that one for the off-season.

WPRs are going on both engines before going out next.