I have 2 bass boats right now, one in storage and one covered sitting by my house. I haven't fished lately because of these high temperatures. I checked my boat in storage and noticed it had a oil leak either from the top screw on lower unit or its coming from the prop shaft seals. I went home and low and behold my other boats had the same exact issue. My question is, can this have anything to do with the constant high temperatures we have been having? Is it possible for the heat to cause the rubber washers to expand and the night temperature to cause them to shrink back? Has anyone experienced this?

Haven't had that issue and it's unusual that both boats have the same problem. High temps will expand the oil and may leak around the seals. If the seals are old, the high temp can put more oil pressure on them and cause a leak. Sitting for long periods may contribute also. Usually the lower unit is not that full of oil to cause a leak with high temps. Not sure how hot the oil gets when the engine is running, but the lower unit is in the water so it's got some natural cooling. There's a seal on the prop shaft and one on the drive shaft under the water pump. A leak in the seal under the water pump can be hard to detect as it's on top and usually doesn't leak unless the motor is in gear and the oil goes out thru the exhaust. May not know it's leaking there until it's too late. Time to have them checked.

When any type of seal, car, boat, tractor, etc sits for an extended period of time it can cause the seal to become brittle and leak. Pull your prop and see if it’s leaking from the prop shaft. If you have a bunch of fishing line wrapped up that could be a giveaway that you probably need propshaft seals replaced. If not it could be as simple as it just needs a new o ring on the drain/fill screws. What type of motors are they?

The boat in storage, I had the water pump replaced this spring.

The boat in storage is a 225 yamaha vmax and the one at the house is a 300 yamaha vmax.

Sea Pro 21.... What did you finally do? Maybe post pictures to help the readers. Is it motor oil or gearcase oil? very unlikely to have motor oil dropping off the lower unit; but gravity never fails.

At one time, I had too much two cycle oil in the gas and very black, tarry oil would leak from exhaust hub on prop.

Yes a photo showing type of oil would help. I would drain and fill the lower unit first. If very milky that’s a dead giveaway your propshaft seal is leaking.

Well I kept doing more research and I had the motor tilted down to where if it was leaking from prop shaft seals it would be more noticeable. I wiped everything down real well and checked it the next morning. Apparently now no leak. I have no idea except somehow these constent high temperatures had something to do with it. I see that we are going to finally get some temperatures below a 100 next week so plan on going fishing. Im gonna pull my prop off, drain my lower unit and do a pressure test on propshaft seals. If everything looks good, fill lower unit and take her out. It was very little oil that had leaked so again I truly cant explain it. I can tell you that the oil was definitely lower unit oil. Im praying the seals are good and the oil doesn't come out milky. I truly appreciate everyones input. Im a retired veteran and I know a lot about the military but not so much about these overpriced motors. I am finding out the definition of BOAT is actually true

Luckily they’re pretty simple to change and cheap. Lower units are pretty forgiving if you get some water in them

my 115 mercury optimax has been doing some strange things this summer as well. on 3 seperate occassions this year we put the boat in started it up and it would not pump water., so we took a piece of weedeater string and pushed it down the telltale hole, and it started pumping fine for the rest of the trip.. when we stick the weedeater line down the telltale hole, a sticky, thick yellow substance comes out ,,
when it first happened at lake athens, I thought it was pollen from a water lilly flower had got sucked in and stopped it up,, then it happened again at a cleaner lake with no vegetation again.. Im starting to think that gear oil from the lower unit is somehow leaking into the water cooling circuit and stopping it up. anyone ever have this happen? my optimax has the "cool fuel" system on it where water circulates around the fuel pump on the powerhead, so I dont know if theres seals in that system that can leak or not. have owned outboards for many years, and never saw this happen before. entire motor was serviced and lower unit serviced before I aquired the boat around 3 years ago..

on a seperate note, this year my 115 yamaha 2 stroke quit pumping while running on the garden hose and bubbler.. when I changed the impeller myself, (which had been in since new in 07) it had taken on a set, but looked like it should still pump.. I replaced it and it pumped fine again.. not sure what is going on this year.

also some outboards exhaust thru the prop holes, as well as other places on the lower unit,, you will get carbon and some oil build up in the exhaust housing, especially on a 2 stroke engine . when u park the boat, and have temp changes, and high humidity, moisture will form inside the exhaust housing and cause the carbon and oil to wick downward and drip. you could get a new drain plug oring seal for the to vent hole, remove the plug, and stick a piece of wire down the lower unit a couple inches and check the oil level and also the condition of the oil. this will give u some direction on what to do.
very few outboards stay 100 percent water tight 100 percent of the time, so getting into a routine of draining the lower unit and replacing the oil once a year is a good idea.. if you start seeing the water and oil milkshake mix, then you know its time to get it serviced.

My 225 vmax actually was doing the same thing earlier this summer. I did the same thing shoving some weed eater cord down the pee hole. In the end I had to replace the peoppet valve.

Hey folks I finally got around to pulling my boat home to change my lower unit oil and do a pressure test on my prop seals to see where a small leak was coming from. I just got up and made this video to show what I found this morning.

https://youtube.com/watch?v=9kzG-lIvkiM&si=kOnDLjWXqzLiRuDm

Whats the problem, I don't give clicks to youtubers here

Not sure what you're asking but it was the only way I could get the video uploaded. Could care less about anything else with the video.