5.7 Vortec dist, trying to seal the cap/rotor due to constant corrosion. Merc 350 Mag MPI Horizon.

[c1steve]

I have an older boat where the deck water drains into the bilge. Due to the high moisture in the engine area, and that it is in saltwater for months at a time, the distributor contacts corrode quickly. My current method to keep the engine running smoothly is to clean the contacts with a soft wire brush in a Dremel tool every 20-30 hours. This works, but am looking for a better solution.

I tried using a thin O-ring inside the cap, but it did not seal well. Any suggestions? I have purchased a distributor cap with an O-ring for some other engine in the past, and this appeared to work well. Does not appear available with this OEM distributor. Are there any distributors that would work with this engine, and have a sealed cap?

 

[Lou C]

My OMC/BRP original Prestolite caps & even Sierra aftermarket caps come with gaskets. Not sure why Merc doesn’t use one…
That said I can get thru a season with my boat on a salt water mooring & it will show very little green corrosion after 6 months out there that can easily be cleaned off.

 

[Scott Danforth]

merc also has a breather fitting. not sure a gasket would help

 

[Lou C]

Mine have a screen in the bottom, and same unit was used on Merc 4.3s, I have 2 spares one painted OMC grey and the other Merc black.

 

[c1steve]

I recently installed some weatherstrip at the engine cover. This appears to be helping, however there are always a 2-3 gallons of saltwater present in the bilge under the engine. I believe moisture through out the engine compartment seeps in under the cap. Engine uses the "crab cap". A paper gasket might work, but the o-ring definitely did not.

I have to check on this, but I believe this distributor has no screen/vent at the bottom. It is sealed except at the cap.

 

[QBhoy]

I’m afraid they are notorious for it. So easy for them to gather moisture and damp.

 

[Scott Danforth]

I recently installed some weatherstrip at the engine cover. This appears to be helping, however there are always a 2-3 gallons of saltwater present in the bilge under the engine. I believe moisture through out the engine compartment seeps in under the cap. Engine uses the "crab cap". A paper gasket might work, but the o-ring definitely did not.

I have to check on this, but I believe this distributor has no screen/vent at the bottom. It is sealed except at the cap.

The crab cap has many issues

 

[QBhoy]

The crab cap has many issues

I also genuinely think that lots of them may have been cracked when installing them. Very easily done without knowing. Don’t ask me how I know

 

[Lou C]

You should not be getting salt water in the bilge only fresh water from rain. If salt water is getting in around the transom mount somehow that’s going to cause a lot of other corrosion damage.

 

[c1steve]

Even if the weather is mild, when we wash down the deck with saltwater it goes in the bilge. In September I went albacore fishing, we caught 400 lbs. of albacore in two days. Lots of deck wash water drained to the bilge, but I run the pumps often to keep the bilge as dry as is possible.

If there was a different distributor that would work the the Merc computer system, I would be interested in trying it. I have been using the PCM caps, and they have not been cross firing or cracking.

 

[Lou C]

Ah ok that explains it. Salt water is tough on inboards due to the materials used. Too bad you can’t keep it out of the bilge and have it exit overboard via scuppers. If your boat does have scuppers maybe you can build a dam to force it to divert around the engine bilge & out the scuppers. I’d be most concerned about the oil pan with salt water laying right under it. I spray mine with Corrosion X at the start of each season & after 20 seasons in salt water still in good shape.

 

[c1steve]

Oil pan has quite a bit of clearance, and I run the pumps on manual override often. So far the oil pan is rust free.

 

[tank1949]

I have an older boat where the deck water drains into the bilge. Due to the high moisture in the engine area, and that it is in saltwater for months at a time, the distributor contacts corrode quickly. My current method to keep the engine running smoothly is to clean the contacts with a soft wire brush in a Dremel tool every 20-30 hours. This works, but am looking for a better solution.

I tried using a thin O-ring inside the cap, but it did not seal well. Any suggestions? I have purchased a distributor cap with an O-ring for some other engine in the past, and this appeared to work well. Does not appear available with this OEM distributor. Are there any distributors that would work with this engine, and have a sealed cap?

Build a drip tray similar to a gutter. You will have to figure out best place. Also, a piece of hard plastic across dist. and trim pump electrical will help

 

[Drcoffee]

So condensation forms when there is no airflow. Connect a vacuum line from the air intake to the nipple on the distr cap. Use a port before the throttle plate so it doesnt affect AFR

 

[c1steve]

So condensation forms when there is no airflow. Connect a vacuum line from the air intake to the nipple on the distr cap. Use a port before the throttle plate so it doesnt affect AFR

That is an interesting idea. I will try it, thanks.

 

[crazy charlie]

Had similar issue with an old Searay I once owned .I used a spray can of "Wire drier" inside the cap and outside .Made a big difference however the cure was to STOP any water from coming down from above.Large drip tray as mentioned is a great idea.I changed out my camper back screens to plastic
and problem solved forever. Charlie