Mercruiser Cool Fuel Module (Gen III) cooling passages routing question

[ostrichegg]

I have a Gen III cool fuel module. It has a few caps that are bolted on, one over the filter and one over the pump. It also has water intakes/outlets that pump cooling water through.

Some of the bolts were really, really corroded in there so I took it to a machinist to get them out. I'm not 100% sure what happened but I think one of the bolt holes got drilled out too far and it drilled into the cooling passage. So now, it's possible to stick a wire into the cooling passage and you can see it through the bolt hole.

So in the photo below, the cooling passage (red) travels through the casing. The bolt in the yellow hole was corroded, so a machinist drilled the bolt out. But now, you can stick a wire (aqua) through the cooling passage and it can continue down the cooling passage, but if you turn it towards that yellow bolt hole, you can also see it sticking out into that bolt hole.



So here's my question. Is this supposed to happen? If so, great! Like maybe that bolt hole is supposed to connect to that cooling passage for some reason.

If not... how bad is this? What should I do to fix this? Some options, none of them good:

1) plug the bottom of the bolt hole with sealant or JB weld or something, essentially recreating the bottom that apparently got drilled out.

2) Drill the hole out larger, and put some kind of plug in there. Maybe just some aluminum rod, and seal around it. Then drill/tap the rod so a bolt can go in but don't drill out so far that the bottom opens up again.

3) Accept the fact that water will get up into where the bolt is. Use some material that won't corrode as much as stainless. Put some kind of gasket or washer on top of the bolt so that water can't get into the fuel.

4) Get a new module. But they're like 2 grand!!

5) Something else that I'm just not thinking of?

Any thoughts appreciated.

Thanks!

 

[ROY WILLIAMS]

I have a Gen III cool fuel module. It has a few caps that are bolted on, one over the filter and one over the pump. It also has water intakes/outlets that pump cooling water through.

Some of the bolts were really, really corroded in there so I took it to a machinist to get them out. I'm not 100% sure what happened but I think one of the bolt holes got drilled out too far and it drilled into the cooling passage. So now, it's possible to stick a wire into the cooling passage and you can see it through the bolt hole.

So in the photo below, the cooling passage (red) travels through the casing. The bolt in the yellow hole was corroded, so a machinist drilled the bolt out. But now, you can stick a wire (aqua) through the cooling passage and it can continue down the cooling passage, but if you turn it towards that yellow bolt hole, you can also see it sticking out into that bolt hole.

View attachment 419044

So here's my question. Is this supposed to happen? If so, great! Like maybe that bolt hole is supposed to connect to that cooling passage for some reason.

If not... how bad is this? What should I do to fix this? Some options, none of them good:

1) plug the bottom of the bolt hole with sealant or JB weld or something, essentially recreating the bottom that apparently got drilled out.

2) Drill the hole out larger, and put some kind of plug in there. Maybe just some aluminum rod, and seal around it. Then drill/tap the rod so a bolt can go in but don't drill out so far that the bottom opens up again.

3) Accept the fact that water will get up into where the bolt is. Use some material that won't corrode as much as stainless. Put some kind of gasket or washer on top of the bolt so that water can't get into the fuel.

4) Get a new module. But they're like 2 grand!!

5) Something else that I'm just not thinking of?

Any thoughts appreciated.

Thanks!

 

[ostrichegg]

@ROY WILLIAMS thanks for replying! For some reason, I can't see your post (looking on mobile so maybe it's just weird) but could I trouble you to re-post it? I'm very keen to solve this Thanks so much!!

 

[alldodge]

Haven't looked at one close enough but I would say none of those holes should be open to the fuel @muc can you advise? Could use something like Gasolia E seal.

I've thought about changing out the Gen 3 cool fuel module for the older style Gen 2. Reason for this is the motors would come with Gen 2 if they had an Alpha drive and Gen 3 with a Bravo, always thought why? This way you could go back to the cheaper canister fuel filter.

The only reason cool fuel came about is because Merc doesn't want to do a return to tank option

 

[muc]

Pretty sure that bolt hole shouldn't be open to the cooling water passage and a dealer would recommend replacing the entire module.
If it was my engine, measure the depth of the threads in the hole and add the thickness of the cover, now make sure the bolt you have is that long (you want the bolt to reach the bottom of the threads when installed and no more) get a new steel bolt (just a regular bolt-no fancy washer) if you need to. Clean the bolt and hole with brake cleaner and paint the bolt threads with Perfect Seal and bolt it back together. Is it doesn't leak when you run it - good. If it does leak - time for a new module.

 

[ostrichegg]

Haven't looked at one close enough but I would say none of those holes should be open to the fuel @muc can you advise? Could use something like Gasolia E seal.

I've thought about changing out the Gen 3 cool fuel module for the older style Gen 2. Reason for this is the motors would come with Gen 2 if they had an Alpha drive and Gen 3 with a Bravo, always thought why? This way you could go back to the cheaper canister fuel filter.

The only reason cool fuel came about is because Merc doesn't want to do a return to tank option

Thank you! Luckily, I don't think the bolt hole is open to the fuel, just to the raw water cooling passages. And I run in salt, so... my worry is that eventually the bolt will corrode through or something, or it will leak enough that I end up with a stream of water coming out the top of the bolt or eventually leaking into the fuel. Although, I hope the gasket will prevent any leaking into the fuel.

But I would definitely worry about the bolt corroding. But then again, all these bolts were so corroded as-is that I had to take it to a machinist, so... maybe a little extra corrosion won't hurt either way.

Re: The Gen 2, are you talking about just entirely swapping out the Gen 3 module for a Gen 2? What are the downsides of this? The Gen 2 module looks to be about half price ($1000 vs $2000) over the Gen 3, so if that's a safe and easy swap, I might consider that as well.

Thanks

 

[ostrichegg]

Pretty sure that bolt hole shouldn't be open to the cooling water passage and a dealer would recommend replacing the entire module.
If it was my engine, measure the depth of the threads in the hole and add the thickness of the cover, now make sure the bolt you have is that long (you want the bolt to reach the bottom of the threads when installed and no more) get a new steel bolt (just a regular bolt-no fancy washer) if you need to. Clean the bolt and hole with brake cleaner and paint the bolt threads with Perfect Seal and bolt it back together. Is it doesn't leak when you run it - good. If it does leak - time for a new module.

Thanks! Let's say it doesn't leak. Is there any downside to running it like this, with perfect seal? Is that generally pretty good about resisting salt water and stuff? I have never used perfect seal, and I just wouldn't want it flaking off and clogging my cooling system or anything. Is this the recommended fix, at least as a test, and if it doesn't like maybe it's all good for at least a while?

Luckily the leak would be between the bolt hole and the cooling, so it's not like water would get into the fuel, I don't think. So maybe low risk in terms of running it like this but I just want to double check

Thanks

 

[Bondo]

No, there's no chance of prefect seal(aka: permatex form-a-gasket #3) going anywhere, other than where you paint on on,...
If yer worried 'bout a steel screw rusting, use a SSteel one,...

 

[alldodge]

Re: The Gen 2, are you talking about just entirely swapping out the Gen 3 module for a Gen 2? What are the downsides of this? The Gen 2 module looks to be about half price ($1000 vs $2000) over the Gen 3, so if that's a safe and easy swap, I might consider that as well.

The motor needs 43 psi +/- a few.
How it gets that specific pressure it doesn't care, there are no fuel pressure sensors to tell the ECM this have changed.

So you can use "any" fuel pump setup so long as the regulator keeps pressure at what the ECM thinks should be there.

I'm planning to dump my Craparrell and buy a Formula 270 bow rider with a 8.2 CAT motor. Shortly after getting it, I'm looking at dumping the Gen 3 cool fuel piece of crap and maybe go Aeromotive fuel pump, canister filter, and specific Reg with return to tank setup