GM Vortec distributor cap - corrosion

I have a ski boat with a PCM 2003 GM 5.7 (350 ci) marine motor that uses the Vortec distributor cap - it is flat and the plug wires come off of the sides. GM has a technical bulletin included in the new cap that speaks of a lack of ventilation which can cause pre-mature corrosion of the cap. It recommends taking out the wire screens located somewhere on the base of the distributor. I only get 1-2 years before the distributor cap gets so gunked up it misfires and has to be replaced. The inside of the cap is a mess. I can’t seem to see what technical bulletin is referring too, but I’d like to do something to improve the life of the cap. At $60 for a cap and another $20 for the rotor this is getting pricey. The boat is in the water all summer so it is a moisture rich situation to begin with and the design of this distributor and cap isn’t handling the moisture well.

Gunk inside the cap and not outside means (to me) the stuff is coming up from the bottom of the distributor, where it’s geared to the camshaft.
I thought all distributors have a shaft seal to stop oil etc. from coming up towards the dist. head.
Crankcase fumes.
A problem with the PCV system could aggravate the problem.

You might have to remove the distributor to find the screens mentioned in the bulletin.

sorry “gunk” isn’t a very specific term - nothing oily, debris from arcing, and a white fuzzy coating on all the electrical contacts. Looks almost like a coating of fresh snow. Moisture is there too. There is a sheet in the NAPA box for the cap that refers to GM Technical Service Bulletins #03-06-04-041A and #05500.

Maybe periodically coat the inside of the cap with something like Gunk silicone spray?

What about the possibility of drilling some tiny hole in the cap at some non-critical spot, add a nipple, and run a small vacuum line to a vacuum nipple on the engine?
Over the years various car makes have used something like that. It allows engine vacuum to keep all moisture out while running and pulls any accumulated moisture out after it’s been sitting and upon startup.

Can’t blame you though. That 80 bucks a pop would grate a bit.

In marine applications you have to consider spark suppression. An inboard motor has many components designed specifically to reduce or eliminate the possibility of an erroneous spark igniting fumes in the hold. I would spray the inside of the cap with WD-40 but avoid drilling holes, removing screens or any other modifications that might compromise the safety aspect of the component…

You might get on some ski boat forums, those SBC engines are used a lot, I’d think others would have your problem, and maybe a solution.

my google search turned up some more info on the TSB’s. It seems this was a common issue on GM cars and trucks in the late '90’s and early to mid- 2000’s. I got a drawing of where the “mesh screens” are located and to remove them if they are still present. It is a tough place to get to and get a visual with a flashlight but now I know more about where and what to look for. On cars and trucks there was an AC line that produced condensation running near the distributor that was the source of the moisture.

If you happen to have one of these GM motors with the “flat top” style of distributor cap it might be interesting to pop off the cap and see what you’ve got going on inside there. The symptoms are a P0300 code, misfiring, backfiring, poor starting, no start, rough running, etc. GM used the style cap on V6 and V8 Vortec motors. You need a throx t-20 to pop the cap, and t-15 to take off the rotor.