Coolant leak on back of water pump housing

That looks like the hole for a nipple for a heater hose. There is an identical one on the top of that housing, just a few inches away. That nipple is not available separately. You can only get it as part of the front engine cover. Cost is very high. The people at the dealership I used to work for still like me, so they would have sold me one for "only" $650.00. Problem is the previous owner of my van didn't do any maintenance on it including never replacing the coolant every two years. As a result, it looked like brown mud and required two flushes to really clean it out. In my case, it was the top nipple that corroded away. My van doubles in value every time I fill the gas tank, so $650.00 was not an economical option.

The solution was to get a nipple from a salvage yard, but it would still be too expensive for them to remove the entire front cover. That would leave them with an engine they can't sell. Instead, I found one that was about to be crushed, and sawed off just the water pump housing part of the cover.

Once you have that part, we figured out that nipple can be pulled out very easily after heating around it with an acetylene torch. Next, my friend heated that area on my engine, and we already had the nipple slightly started in the hole. Once the housing was warmed up, all that was needed was gentle taps with a hammer on a long metal rod. The nipple slid right in and has never leaked. Did that repair two years ago, but my van is a '94 with the identical 3.3L engine. I did have to unbolt the AC compressor and move it to the side. You may find access on yours easier or harder.

We were also worried about the part of the nipple inside the hole. There wasn't anything to grab onto so we just let the new one push the old one into the water pump impeller. Apparently it just crumbled away because there was no noise when we started the engine.