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  1. #1

    Default Mercury 650 3 cyl cooling issues

    I have a 1972 Mercury 650E 3 cyl. I have a water oil whitish foamy liquid coming out the upper starboard engine mount. I removed the power head and exhaust plate from the middle section drive shaft housing. There was only a little water near the engine mount. I have a few questions. Is it normal to have water below the exhaust plate? Where does the cooling water get expelled from the power head? Does the water drain down around the exhaust tube down and through the prop? Today I plan to remove the exhaust plate to make sure that the gasket is not leaking water to below the exhaust plate and onto the engine mount. I plan to replace the upper engine mounts or packing U cup if the mounts look OK or both. Is it normal to have some water mix with exhaust causing the whitish foam to come out somewhere? I also plan to replace the water pump impeller since I found a few bits of rubber in the port just below the elbow pee vent on the port side of the engine.
    Also, when I removed the power head, the water inlet tube sleeve was resting near the bend of the tube. Should that sleeve be secured at the top or bottom of the tube or simply reside near the bend where it was? Your guidance and comments are greatly appreciated.

  2. #2

    Default Re: Mercury 650 3 cyl cooling issues

    The cooling water travels down the driveshaft housing around the exhaust tube and exits out the "vents" in the LU, if either of the gaskets in the in the exhaust extension plate are missing or damaged water will leak out; you can't silicone these parts together they need gaskets!Click image for larger version. 

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ID:	26513The guide tube "water inlet tube sleeve" sits on the waterpump outlet to help you guide the watertube into the pump.

  3. #3

    Default Re: Mercury 650 3 cyl cooling issues

    Quicksilver, thank you for your quick reply. I removed the exhaust extension plate. I don't see something obvious on either gasket but will clean the surfaces up and replace both gaskets. I did notice one of the studs seems a bit out of square. I can't seem to upload photos.
    Are the stubs threaded into the block? I can replace it or try to bend it back into square. Thoughts on this?

    If I understand your comment, the water inlet sleeve is simply an extension to the tube to help get the tube in the proper place on the water pump to align the tube into the water pump. Then it just sits on the tube once one pushes the tube into the water pump, correct? I will rebuild the water pump assembly as well since I found some rubber pieces in a water port near the pee tube elbow on the starboard side of the engine.

    Since my previous post, I removed the LU. I first drained the gear oil only to find what came out was predominately water. I have a video but can't upload it.

    So, I have added the LU rebuild to my engine project. Iím surprised the engine performed as well as it did with no gear oil.

    When I dropped the LU, several washers fell to the floor as well as an interesting looking rubber bushing. Iíll try to post pictures but Iím not sure where it came from or where it should be installed. Any clues you can provide would be helpful.

    I have the parts manual; the same one you posted in your reply. It helps quite a bit but often doesnít show how things actually go together. I have the Seloc repair manual but it leaves much to be desired. I find the forum a terrific place to get advice from helpful mechanics who have done what Iím attempting.

    I recently rebuilt the carbs. It was when I brought my boat to the water to adjust the carbs that I noticed the white foamy liquid coming out the starboard, upper engine mount that got me going with this middle and lower end overhaul.

    Any tricks to rebuilding the gear assemblies in the LU?

  4. #4
    Join Date
    May 2007
    Ireland,the only country in the world you can go North to go South

    Default Re: Mercury 650 3 cyl cooling issues

    To upload pics, click Go Advanced, click Manage Attachments. A separate window will open. Click Add Files

  5. #5
    Join Date
    Sep 2003
    New Tripoli, PA, USA!

    Default Re: Mercury 650 3 cyl cooling issues

    I've seen that whitish milkshake every time I pulled the PH on my three cylinder Mercs. "Bad seals," I concluded nd replaced them, only to see the same condition next time the PH came off.


  6. #6

    Default Re: Mercury 650 3 cyl cooling issues

    The studs that attach the powerhead to the exhaust extension plate are threaded into the base; I have had white goo on my driveshaft and the manual says to fill the LU then drain 1oz out, you might have a bad seal under the waterpump which could explain the water filling. Rebuilding the lower unit requires the use of a bearing carrier toolClick image for larger version. 

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ID:	26531 that is available from Mercury
    here's a parts diagram of a lower unit
    Click image for larger version. 

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  7. #7

    Default Re: Mercury 650 3 cyl cooling issues

    i made the photos smaller and was able to attach.
    Here's the slightly bent stud. What do think about trying to bend it back with a pipe while protecting the threads?

    Here's the rubber bushing piece which fell out when I removed the LU. What part is it and where does it install? The 2nd photo shows the ribbing on the interior.

    The ragged edge at the top of the bushing in the photo below seems to say that there was a section ripped off.

    The piece seems to fit the splines at the top of the drive shaft.

    One more question, since the lube chamber was filled with water, does that mean that the seals in the prop shaft are good because the water doesn't leak out when sitting out of the water? I'm asking if I also should rebuild the prop shaft and gears or just rebuild the drive shaft water pump seals? And the special tool... is that for the removing the prop shaft or the drive shaft or both. I would be surprised if it was the same tool for both.

    What is the ideal dilution ratio for using Simple Green to clean parts?

    You guys are terrific. Thanks for your help.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  8. #8

    Default Re: Mercury 650 3 cyl cooling issues

    That torn rubber piece fits over the driveshaft splines as a seal, when it's new; the tool is used to remove the bearing carrier nut at the prop end of the LU which lets you remove the internals. I don't know if you can straighten out that stud but if you have a straight one lying around go ahead and replace it. If you use a LU oil pump you can pressurize the LU and see where it leaks but since there was water in it I think all the seals should be replaced and you can check for bad bearings and rust at the same time. Use the serial Nr. to locate parts.

  9. #9
    Join Date
    Sep 2010

    Default Re: Mercury 650 3 cyl cooling issues

    The gearcase on that motor is not considered to be robust.----Nearly identical to the 40 / 50 hp models.---So yours needs tear down , inspection and seal kit.--And there were issues with top cylinder dome cracking due to cooling issues.--Needs a new impeller every 3 years at least.-----Coupled with hard to find expensive ignition parts.----I have some of these motors for parts.----I would never have one on my own boat.

  10. #10

    Default Re: Mercury 650 3 cyl cooling issues

    Quicksilver, if I understand, that rubber piece is not needed but was there to protect the spline when new, correct? I like the idea of pressure testing.

    Racerone, thank you for joining in.

    A little background on this engine and boat. Both were seen at the end of the seller's driveway with a FREE sign on it. That was April 2019. After a quick walk around, I towed it home. The engine ignition was in parts. After numerous conversations with CDI about the installed system as well as replacing the distributor, I was able to get the engine up and running. I must confess. I didn't check the LU oil level. Anyway, in Nov 2020, I was getting a loss of power while accelerating. In my wisdom, which is not a whole lot, I decided it was time to rebuild the carbs. That was fun. But it took me a while to get it done. A few weeks ago I took it down to the lake to adjust the idle mixture and rpm. That's when I noticed the whitish liquid coming from the upper starboard engine mount. So, I figured a gasket was leaking and pulled the power head. Both gaskets, above and below the exhaust plate, did not show signs of being blown. In order to inspect the engine mount, I removed the LU to get the drive shaft out of the way. I figured, I could change the impeller. I drained the LU to find it full of water. And that is where I am today. It is all torn down except for the gears box. I have a second 650 which is a '73 from which I have taken a few parts.
    Upon inspection of the disassembled water pump, it seems a previous "mechanic" used a wrong size O ring on the lower portion of the water pump body.

    My parts diagram shows item 23, p/n 26-32121, oil seal upper water pump body, which was not installed on the upper water pump body. I presume this seal is necessary. This plus the O ring may explain the gear oil filling with water.

    My upper water pump body has a one piece water pump body to water tube seal. The parts diagram shows two parts, a seal and a cupped washer, p/ns 26-38452 and 12-38453, respectively. Were these two parts replaced with a combined part?

    Does anyone know of a water pump kit which will include all seals and gaskets of the water pump?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  11. #11

    Default Re: Mercury 650 3 cyl cooling issues

    Parts are available on this site or from a Merc dealer, you'll need your serial Nr. for exact year. It sounds like you should give the motor a thorough inspection, it sounds like there are a lot of problems.
    Last edited by Quicksilver; 04-08-2021 at 07:40 PM.

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