Why is my BOATS Engine OVERHEATING? Thermostat Replacement

In this video Why is my BOATS Engine OVERHEATING? (Thermostat Replacement) for 2004 Mercruiser 5.7 MAG MPI engine. We replaced our boats Mercruiser 5.7 engine thermostat because it was overheating at speeds around 35 mph at 4500 rpms, and when we slow down it would go back to normal. Can't understand why it was overheating? Thanks for watching! Peace from the Keys!
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#boatoverheating #boating #mercruiser5.7 #engineoverheating #floridakeys #thermostat #keysboatingchannel #mercruiser #Islandparadise #keysbesthangout #happydance #taverniersandbar #saltlife #overheating #keysbestsandbar

[@paulmarkland8907]

Hello there! I just went through the exact same thing you are experiencing with your Mercruiser overheating. I replaced every cooling pump, hose, thermo-stat, exhaust manifold, elbow riser, engine sensor and the problem persisted! It turned out to be the connection that goes through the transom of the boat. The raw water hose the comes in from the Bravo outdrive connects to the raw water hose that goes to the seawater pump on your engine. In the transom of the boat there is a threaded insert that connects the hose outside to the hose inside. Oxidation and debris build up in the passage over time partially clogging and restricting the flow of water through the transom of the boat. There are two choices to fix this: 1. Replace the insert . The part cost about $4. You'll need the part and the extration tool. Problem is actually getting it out. Very limited space behind the motor. It comes out on the motor side of the transom. Plus, Since its connected to the hose in the outdrive you need to remove the outdrive as well to get to the hose connection on that side. I didn't do this. I used option 2: Re-plump the raw water coming in using a new through hull water pickup. I already had a small 3/4" water pickup in the hull for my washdown and live well. I removed it , enlarged the old hole in my hull and installed a 1.25" Groco scoop type water pickup in its place with new ball valves and hoses for about $250 all in. This completely fixed my over-heating problems!

[@paulmarkland8907]

Here's a quick test to see if your raw water hose coming in from the outdrive has a partial blockage causing overheating at cruise RPM's: Remove the incoming seawater hose from the back of your rawwater/seawater pump. Adapt a 3/4" or even a 5/8" garden hose to connect to the rawwater hose you disconnected. You can use the existing hose clamp to tighten down on the garden hose connector. You need an airtight seal from the rawwater hose to the garden hose. I use a small 6' hose extension so as not to have 25' of garden hose to contend with. Then all you need to do is blow (using your mouth) into the garden hose. Once you clear the residual water from the hose. There should be zero resistance. If you feel any resistance while blowing through the hose your transom is clogged and this is your problem! You could also remove the raw water hose from the transom behind the motor to look for a clog. There's only two bolts to take if off. You may need to turn your steering all the way in one direction to get to the two bolts.

[@KeysBoatingChannel]

Hi Paul! Wow! thanks so much for your experience on this issue, this will help me, and anyone else that may have the same problem. Great Idea! Thanks again! I will be posting a follow up video on this problem. Have a great weekend! Peace from the Keys!

[@DavidSkolnickteam]

​@KeysBoatingChannel was the information Paul offer about the line being clogged the case? I have a 2015 SeaRay 240 Sundeck with the same problem. Thank you

[@gm1937]

A stuck thermostat caused me a massive overheat in the middle of Long Island sound in the dead of night and I could not move an inch. That earned me a one way ticket on Sea Tow back to the dock for the bargain basement price of $500. And since I did not know it was the thermostat at the time I brought it to a dealer who charged me $800 to fix a $40 part. So the moral of the story is make sure you change your thermostat periodically and spare yourself the aggravation and cost.

[@KeysBoatingChannel]

Hi GM1937! Wow! $1,300 for just a $40 Fix...that hurts, I feel you Brother! Good lesson learned, and great testimonial for other boater's. Thanks for sharing your experience, and watching our video. Peace from the Keys!

[@alligatorcampers611]

Thank you Bro. With your video I saw that my thermostat was misplaced with some monkey. Hopefully it didn’t kill the engine. I started to figure out why wasn’t the gauge showing the temperature. And the hand was only moving slightly when the thermostat opened.

[@KeysBoatingChannel]

Hi, glad our video helped you. Thanks so much for watching! Peace from the Keys!

[@perfectfitboating]

Man I was hoping the thermostat was the issue. Either way it’s good to change them. Praying it’s an easy fix. Those boats can be money pits but man do we love them! 🤙

[@KeysBoatingChannel]

My Brother thanks so much for watching! Hope you guys are doing great! Yes, B.O.A.T. But we love the salt life! I will be doing another follow up video, on this problem, Paulmarkland8907 give us very good information on his experience. Peace from the Keys!

[@paulmarkland8907]

Based on the overheat failure mode you definitely have a restriction in the system somewhere. My boat did exactly the same thing. I'd run approximately one mile at cruise speed until the temp went just above 170. I'd pull the throttle back let her cool off a few minutes then do it again and again. I could run the boat this way without actually overheating. But, If I stayed on cruise RPM ( about 3200 rpm ) for over a mile the engine alrarm would go off as the temp went just above 175. Drove me absolutely nuts for over a month and $3000 in parts replaced ! When's the last time you changed the impeller in the raw water pump? I'd check that first and do the hose blow test I gave you since you'll have the raw water hose off anyway. If you have back any back pressure in that raw water hose going to the transom you have a restriction in the system and its most likely the transom insert. Its a design flaw. The insert that connects the two hoses together is only 5/8" ID . Any restriction = overheat!

[@sharronhumphries6727]

Thank you for sharing brother !!!. Looking forward for the next video and hopefully a resolution to the over heating issue.

[@KeysBoatingChannel]

Thanks for Watching our video, next video coming soon. Thanks so much. Peace from the Keys!

[@Bryan_One87]

Not sure if you've changed it yet or not but it sounds like the impeller that's inside your lower unit that helps the motor intake water at speed and if they wear out then the boat can't take on enough water to properly cool the engine and then would slow down it's able to suck water in through the motor with the water pump I know I just had a similar issue

[@KeysBoatingChannel]

Hi Bryan! thanks so much for your comment. Its been a headache with this issue, we've changed the raw water pump, the thermostat, serpentine belt, and our next move is our engine circulating pump its 19 years old. I believe on the Bravo 3 outdrive there's no impeller in the outdrive, we have a raw water pump with the impeller in the engine compartment, this is separate from the engine circulating pump. My Brother again thank you so much for your comment & watching our video. This information will help point us in the right direction. Peace from the Keys!

[@artsirx]

impaler, sound like it broke or some piece broke off and there is a blockage somewhere in the system. had the same issue

[@KeysBoatingChannel]

Hi, thanks so much for watching our video. Yes, that could happen, and I thought about this. But it is really difficult to pinpoint that issue, especially when there's very minimal space to work in. Thanks for your comment. This is very helpful information for anyone going through this problem. Peace from the Keys!

[@ReelifeFishing]

Pretty cool you know how to dothis stuff. Save a lot of money

[@KeysBoatingChannel]

Thank you for watching my Brother! Yes, save money, and nowadays you can't trust too many out there. That's why I do most of the work myself. Hope you guys are doing Great! Peace from the Keys!

[@michaelhusky9736]

the 1st guy is probably rite...the insert from the drive through the transom

[@KeysBoatingChannel]

Hi, thanks for watching! Yes, it was my 1st guess too. Peace from the Keys!

[@markdimaio8396]

Did you say that the housing in 3 years old?

[@KeysBoatingChannel]

Hi Mark, 3 years since the last thermostat change and repaint of the housing. The housing is 19 years old. Thanks for watching Brother. Peace from the Keys!

[@markdimaio8396]

@@KeysBoatingChannel those oem housings are expensive!!!!

[@KeysBoatingChannel]

@markdimaio8396 Yes, they are. I searched, and they are around $340 plus. Thanks, Brother! Peace!

[@eagle5720]

Sounds like low water pressure

[@KeysBoatingChannel]

Hi, thanks for watching our video! Yes it could be, but in our case it ended bad with an internal blockage. See our new update video: kzbin.info/www/bejne/gp-xp5uYfNSnbLs Peace from the Keys!