Antifreeze Leak, closed coolant system

[390Express]

I was sitting on the back of the boat having a couple "sodas" last weekend with my buddy Dan, he left, I was messing around in the cabin, and the port motor started sounding different. Not bad, not knocking, not even a hot oil lifter tick (motors just sound different when they're running hot), it just didn't have the same sound or frequency to it. So, I went to the helm and the temp gauge was reading 220+ (I didn't get a good look, it wasn't pinned, but it was hot). I immediately shut it down and opened the hatch, damn antifreeze everywhere - couple gallons at least, and the reservoir was empty. I checked it over pretty good, but it was around 2am, dark and I didn't want to mess with it while it was hot, so I buttoned it up, and went home. I figured that I would see the worst of it when I got down to the boat the next morning, but... Nothing...

It was still obviously out of coolant, but no visible signs of where the coolant leaked from. I checked it over real good, no water in the oil, no visible cracks, no blown hoses. I added about a gallon of water, and fired it back up, and it ran great. It did get hot (180) after running for 35-40 min, but that was somewhat to be expected, I didn't top off the coolant, and I didn't bleed the system. However, the boat had no visible signs of a leak, crack or blown hose... I don't get it? No water in the oil, no smoke in the exhaust, nothing. The little bit of water that was left in the reservoir was rusty colored, but not oily. Not sure what could have happened.

It was pretty hot that day, and the lake temp is up at the end of the year. Is there some sort of blowoff valve, or pressure relief valve that could have opened up? The seaweed growth is up a ton too, I'm wondering if my pickups to the freshwater side are clogged, but that wouldn't explain the puked antifreeze all over the bilge. Thoughts?

[Midnightsun]

I think you are on the right track. Boats have no air cooled radiators like cars do. They depend on water cooling from the lake and without it they will boil over. I am suspecting blocked intakes like you mentioned. Maybe a good idea to put on a mask and take a peek, also check your stainers as they may be in the verge of plugging also. Don't forget to turn off the seacock before you remove the strainer cover.

[390Express]

Source of the post I think you are on the right track. Boats have no air cooled radiators like cars do. They depend on water cooling from the lake and without it they will boil over. I am suspecting blocked intakes like you mentioned. Maybe a good idea to put on a mask and take a peek, also check your stainers as they may be in the verge of plugging also. Don't forget to turn off the seacock before you remove the strainer cover.

I'll take the freshwater (city water) pressurized hose into the bilge, and shove it into the strainer, and back flush the pickup, and see what happens. There is a nice sandy area that I can take it to this weekend, put a mask on and see what's going on, but the marina water is pretty nasty. I doubt I could see anything if I tried.

If it pukes because it's running hot/boils over, where does it puke out of? The expansion tank/reservoir?

[Midnightsun]

Not sure but I would think it is like the rad cap just like your car. They are spring loaded and will puke after X psi.

[km1125]

Either something was restricted on the intake side, or you are lacking circulation inside. The first guess would be on the intake side. Do you have a strainer? Is it possible you have something loose and you were sucking air in somewhere?

Is the 'sandy area' you speak of Art Van's'? That would be a good place to check out the bottom, just make sure you're far enough south to avoid the rocks.

[390Express]

Source of the post Either something was restricted on the intake side, or you are lacking circulation inside. The first guess would be on the intake side. Do you have a strainer? Is it possible you have something loose and you were sucking air in somewhere?

Is the 'sandy area' you speak of Art Van's'? That would be a good place to check out the bottom, just make sure you're far enough south to avoid the rocks.

I'll put out to the 10 mile cove this weekend to check it out. If it's good, I'll head out to Muskamoot. Supposed to be 80 this weekend, probably the last one!

I'm just relieved, I thought for sure it was some damn catastrophic failure, after all of that work getting the damn thing running right.

[LaBomba]

The majority of heat exchangers have a rad cap that lifts when the temperature and pressure get above the set point, usually 10 to 13 psi. When this happens the boiling liquid is pushed to the reservoir tanks and overflows it to the bilge. My guess is a blocked inlet as well as this happened to me. Aqualarm and others sell both exhaust hose temperature alarms as well as no flow alarms that would have alarmed prior to the overheat and may be something you want to look into. I added one after my incident. Could save an engine and they are not expensive.

[bud37]

390 is that the same engine that the coolant was missing from before ? If so you are going to have to pressure test at the very least....sorry man.

To add....you can blow crud out of and check thru hulls with a shop vac on blow.Thru hull valves have been known to fail internally and maybe be partly open.

[390Express]

Source of the post 390 is that the same engine that the coolant was missing from before ? If so you are going to have to pressure test at the very least....sorry man.

To add....you can blow crud out of and check thru hulls with a shop vac on blow.Thru hull valves have been known to fail internally and maybe be partly open.

Same motor that had the missing coolant, but I don't suspect that the two are related. The port motor had low coolant in the block, but had full coolant in the reservoir. The reservoir in both motors was low to start the season, but I filled both. Starboard motor was fine, and never had a cooling issue. Port motor had hot manifolds and a full coolant tank. I believe the port motor had air in the system (and a significant amount) that precluded it from creating suction that would allow it to draw from the reservoir. The manifolds were getting hot due to not having a proper coolant level in the motor. That issue has been rectified.

The motor got hot and puked out the coolant that I put in to fill the issue above. Motor gets hot at idle, but cools down immediately at 1500 rpm. I'm guessing the cause is a partially clogged exchanger, and/or worn fresh water pump. Coolant isn't disappearing anywhere, no leaks, no water in the oil, and not losing coolant out of the exhaust.