I have a Mercrusier 3.0 and one thing you didn't mention is the Exhaust Manifold. If that is plugged from years of use and a build up of rust, it will overheat the boat. I had to replace everything from the risers to the exhaust bellows. Hope this helps a few of you.
How did you determine the exhaust manifold was plugged? I'm assuming that if the manifold is plugged that you'll notice that the amount of water coming out of the engine will be a lot less than normal due to the restriction? Just curious to know how you figured this out short of removing it and looking as it. Any tell tail symptoms?
@@richmac918 If you put the muffs on and you don't see any water coming out of the back, good chance the exhaust manifold and/or risers are plugged. I replaced everything from the exhaust, riser, & all rubber bellows. Runs great now.
What if you accidentally forget to take the ear muffs off and you run the boat in the water for 10 minutes. I know that it would reduce water flow to the recirculation pump of water but wouldn’t it still get some water? There is a connection on them for the hose. What should you check after that?
what great video , I learn alot , I did first step replace impeller in outdrive still overheat now will check thermostat let you know what happen thanks, you are a profesional . teaching showing is a profession .
Did you guys ever get it figured out? I had a 3.0 that kept overheating, went thru and replaced everything, pump, impeller, hoses, t-stat, still overheated. It wasn't until I tore the engine down that I found that upon removing the t-stat housing/ hose manifold from the head that a piece of old impeller had found its way up to the head and got lodged right there, it had rust and barnacles or rust bubbles all over it and had clogged that passage completely, come to find out on that block, that is the bypass passage and if it doesn't have flow, the coolant system just doesn't work at all. The actual explanation is more technical but that's the jist of it.
Thanks for the video, big help. I'm still overheating. Wracking my brain trying to figure it out. I noticed in your video u don't have water coming out of the prop. Maybe my mercruiser 3.0 is a different engine design. I have 2 exhaust ports on the upper part of the outdrive, one expelling water and the other exhaust. I also have about 1/3 of water volume coming out of center prop. I've replaced impeller, thermostat, poppet valve assembly, thermostat and poppet valve housing. I guess I'll change the pump even though it looks and sounds decent. I found a lot of crud caked in the thermostat housing and fear the exhaust manifold may be choked with it. Any ideas or input u may have would be great-Steve
Sorry I just saw this. It does sound as if you may have a blockage somewhere. The manifolds like to plug up with age. Not sure what else it could be. Under load a bit more water come out my prop but not much. Mine is a 1st gen that's as far as my hands on experience goes
I feel like I need to check my impeller after watching. That could be one of the causes. The previous owner left it docked and a thousand baby oysters attached themselves all over in the nooks and crannies of the out drive. I enjoyed hours of picking them out of the crannies with a sharpened flat bladed screwdriver and a cold beer in my hand. However I noticed them inside of the water intake ports and I guess I just thought they would somehow get flushed out. I haven’t attempted taking that stern drive apart yet. I will search on RU-vid to see if anyone attempted that.
There's quite a few videos of the stern drive impeller replacement. There spoase to be replaced ever 3 years or so many hours. It's the number one cause of failure out on the lake. So many people neglect it, and it can cause such major issues.
My boat was overheating so I took the thermostat out and started it without the top on and no water was circulating. It was bone dry. I just had the impeller replaced. Could it be the impeller again? I’m sort of at a loss
@@daleofalltrades followed everything and ended up replacing my impeller and doing a backwash one the tube that goes from the impeller to the motor and now I’ve got much better flow and no over heating!!!
2010 Bayliner 175 - 3.0 TKS MerCruiser My boat was running perfectly in the lake when I heard a strange sound coming from the engine or drive and immediately the alarm sound, the engine temperature was 250 degree, I stopped the engine and look for any visual damage. Didn't find anything from inside the boat and wait for the engine cool off. After a while started the engine and start boating again, about 2-3 minutes later the temperature when to 250 degrees again, I shot down engine and call for a tow. Back at home I run the engine with fresh water thru a hose and was no circulation at all. What could be the problem?
Only thing to to is start investigating the cooling system. Use the video as reference points. Only thing not mentioned in this video is that the exhaust manifold can get plugged as well. Good luck.
The it could mean that the impeller in the out drive may be worn out and time to be serviced. As they wear out they tend to lose blades which would make less or no resistance. May be a good idea to tear it apart and inspect it.
I have a 88 sundancer, with a 7.4L, it only overheats at idle 800 rpm, the temp is at 200F, once i get to 1200-1500 it drops back to 160F. It ran cool all last year after i replaced the thermostat. I had a marina winterize it, not sure what they did, but I started it on the muffs myself, ran it across lake st clair for 12 miles from storage to my marina, only found the overheat when i was docking. any idea on how to check ? not sure if / what they did towinterize, odd its only at idle
I don't think it's do to the winterization. When you moving faster things are also spinning faster pushing more water. Sounds like a flow issue. Time to start inspecting. Check the impeller, check theanifolds for plugs,. Check hoses for debris inside ect.
My mercruiser 3.0 alpha1 overheated yesterday. Got towed... Back at the house I am trying to figure out why it is not starting anymore before the finding the overheating pb. Just put a new battery and sparkplugs. It almost starts, but do not idle or stay on at all. Could you please help?
my 1999 5.0l mercruiser alpha one heats up, sets the alarm off then cools off and starts the cycle again. i replaced the thermostat, impeller, circulating pump and risers and still have the same problem. its seems to take a long time for water to reach the thermostat housing. any thoughts?
Have you checked the elbow located inside the housing of the outdrive by the bellows. The water feed hose for the outdrive runs from the outdrive to that elbow through the transom into the hose that goes to the thermostat housing. Anyway those like to crack and cause a water bleed not allowing enough water to get to the engine fast enough... Worth a check
@@daleofalltradesthanks for responding. will check it out. also, i have a 1970 6 hp johnson outboard (6R-70B) that i cannot find wires for. amazon has a coil/wire set but i dont know when i can get it as it hasnt been released.
Hi not sure if you are still answering posts but I'm lost my 3.0 is running hot but only at speed. I can idle around all day and it's fine. I have replaced the impeller, thermostat ,water pump, head and gasket (the head had a small crack) also the exhaust. Please any help would be appreciated.
I am forever and always answering questions 😃. I have a few thoughts 1st though perhaps the inlet in the out drive is clogged? When impellers failed sometimes chunks of rubber can make there way up the unit clogging the inlet lines causing poor water flow. Try on the trailer blowing some compressed air through all the inlet lines maybe tear the whole out drive off and go through it really good looking for obstructions. It definitely sounds like a flow issue considering when the engine is idling (not working hard) it's fine and when your cruising (working hard) it's heating up. Lack of water flow would cause that. I like hooking muffs up on try land and observing water flow out of the exhaust. You could have someone sit in the boat while it's idling watch the water flow out and then have someone rev the engine as if you were cruising and still observe the water flow. If there's not very much coming out I'm guessing you have a blockage somewhere. Hope that helps you in some way.
I'm having an issue with my 3.0 Merc. A couple years ago I started noticing that my temp gauge was reading higher than normal (went from 165 to over 200). No noticeable changes in engine operation like pinging or run on after shutting it off, just a higher temp indication. Changed the impeller (even though the original was in perfect condition) and changed the thermostat (though testing showed the original was working perfectly). Pulled the wire from the sending unit and gauge stopped reading so I know that it is doing something. Water seems to be flowing well through the engine and out. Used an infrared non contact thermometer to measure temps along all the water lines coming and going from the thermostat housing - nothing above 165. Water pump on the engine looks good, no leaks. I'm not certain I trust the temp gauge (most of the gauges on the gauge cluster jump around quite a bit) or maybe sending unit? Suggestions as to what to look at next?
Gauges go bad all the time I would try hooking up a different gauge to verify even just a cheap test gauge. If it's not that then I'd have to say sending unit. Infrared thermometers don't lie there's definitely no issue with the engine.
@@daleofalltrades My water flow appears to be fine. It started as overheating only at plane, so I figured water flow. Now overheats at idle. Replaced both temp gage sending units in thermostat housing.
I am not 100% sure, they may be the same or close I do believe the block is the same. Manufactured by GM. However I am not entirely sure, could you call a service center and see if they could give you the specs?
Yes you are correct about that I took valve cover off and it says gm right on top on the block I have a guy at the local marina who is supposed to be looking for them for me but he says he has to find book and has no idea where it is
I was just going to use the chart you put up when you did your head gasket as your engine is same size as mine also yours is 140hp as well correct? I would think it would be same pounds if it’s same hp right? I just don’t want to do it and then blow gasket again because I don’t have it torqued right
@@natesignor3442 I'm guessing they are probably the same torque specs, did you happen to watch my video of the second time I put my head gasket in? I ended up doing it a second time and used aviation permatex on both sides of the gasket. Has not blown again would highly recommend using it
I cant believe he said thats all it could be when at least 60% of the time it is indeed the manifold or risers or elbow!!!and yes you can still see water shooting out the back. That dosnt mean It isnt PARTLY obstructed.. my boat only over heats on wide open throttle. With NO thermostat even. There could be obstructions, , hairline cracks,,, rust, even old impeller poeces from over the years from different owners. Stick to something other then boats bro. And circularion pump... 30 bucks?? Lol try 102.00 plus shipping of 80 in canada. E years
The video was intended to give a general idea of how the cooling system on an I/O works with general ideas as to the cause of possible overheating. I have brought up the manifolds in the comments as it is something that plain slipped my mind while making the video as I don't do scrips. From my personal experience most the time it's blockage or impeller issues. Ether way thanks for watching. Every video is a learning process for me and my viewers
Check this video of a a clogged exhaust manifold that creates overheating on the same engine. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-qLu_VFrz5NQ.html
