Electrolosis issue

Could be location, or how the raw water flows through them, change them more often.

671s or V92's ? My cooler (6v92) only had one small zinc at the exit of raw water to the exhaust system. It used to burn faster than the large heat exchanger zinc. I was told to plug it and don't worry about it because the big zinc ahead of the cooler in the exchanger will provide the protection. Been running like that for several years with no problem. If you want to keep the small zinc, meter the zinc heads and zinc to be sure they are grounded to the cooler and that the cooler is grounded good to the engine. Paint rust etc can add some resistance.

Work a thin straight screw driver between the hose and cooler, then try to work the hose side to side to break the seal, then once you do that twist side to side and pull.

I had some galvanic corrosion issues awhile back. I walked in to the marine electricians office to discuss this, and I also used the word "electrolysis". He asked me if the project involved removing hair from women's legs. Lesson learned. Anyway, hope you get it figured out. My other lesson is that it is somewhat of a black art, and there a lot of people who claim to understand it, but don't. It is one of those areas where I like to see some grey hair on the person doing the investigating.

I have 671's too. I use roughly three sets of trans zincs over the 7 month season. This lets me still unscrew them before wearing so much they break off. Mine are small, I think the E1's, so you are talking about a 1/2 x 2" zinc getting the full flow of cooling water past it plus protecting quite a bit of metal. If you are comparing to the large Detroit sized zincs in the main cooler, I have two of those so that is probably 10 times more zinc to wear. I replace those once a year.

You could have an issue, but probably not if your zincs overall (rear plate, trim tabs) are lasting for your season.

No, do not use Silicone hose on the suction side. You only want to use marine exhaust hose with wiring.

Very close to where the shorepower inlet is, usually.....

My 91 did not have one. I put one in behind the breaker panel where the green wire AC ground comes in from shore power. It has a remote LED that gets mounted to the panel.

Most boats didn't have a galvanic isolator in 1988. They're easy to install and generally I install them right after where the shorepower comes into the boat.

My 75 did, and it appeared to be original before I replaced it. Look on the bulkhead above the generator.

I had noticed through the years that some zinc manufacturers last longer than others, I did prefer using B&S marine anodes.

Sorry for the delay. Had to dig through my books to find it.