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Old 21-05-2020, 18:15   #1
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Volvo Penta MD7a Water cooling system

Hi
I have recently taken off the exhaust manifold, exhaust elbow and thermostat housing - it needed cleaning out badly - I put the parts into caustic soda then rinse then Hydrochloric acid then rinse then Peroxide and this started to clean out the bits quite well. I still had to use some small scraping tools and drill bits to try and remove the remaining crud. Have put it back together BUT cannot get the copper pipe running between thermostat end, middle join into manifold and join onto water pump to seal. I paid $12NZ for one new square o ring and thought the other two were in OK condition so did not replace them. Prior leaks seems to have put salt deposit into the manifold hole in the miiddle and I did my best to clear this but still no seal. Image shows that pipe is off to one side and so does not seal.
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Old 21-05-2020, 18:28   #2
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Re: Volvo Penta MD7a Water cooling system

Hi Pandour, thanks for posting. I have the same problem I've assembled and disassembled it several times . I bent the tubing up some hoping for a better seal. It seem to be ok but not perfect I'm hoping that it will seal itself. I don't see it dripping just a little rusty residue arount that area. Search md7a mystery hole and you will find much on the cooling system
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Old 21-05-2020, 18:58   #3
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Re: Volvo Penta MD7a Water cooling system

So are you saying it won’t seal going down into the water pump?

Almost like the pipe is too long?

No I’m not gonna tell you to do this, I’ll tell you what I did. I cut the pipe off a wee bit, damn near too much. Then it fit right in.

Those square washers? Take one and go to a Lowe’s or Home Depot. In the plumbing aisle they generally have a selection of sink washers. I found one there that worked well.

Someone else recommended this.

Quote:
You can get the correct washers at West Marine. WM part 10511004 about $10 for the kit. That includes 4 of the square washers and the O ring and gasket for the thermostat.
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Old 21-05-2020, 19:33   #4
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Re: Volvo Penta MD7a Water cooling system

Mine sealed at the water pump. There is a bracket that holds it in place. Mine is leaking some at the manifold like in the photo. I don't remember any square washers??. I pulled the gearbox and the v-drive and sent them in for service and I noticed rusty stains bleeding down from that connection at the manifold and the pipe.It's only been about 2-3 months since I had the manifold off. I was thinking of leaving well enough alone. Oh I looked up the part number I got those round washers. I paid a premium from the volvo shop
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Old 21-05-2020, 20:14   #5
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Re: Volvo Penta MD7a Water cooling system

Those leaks in small Volvos are common. Some people cut the pipe and connect with hose to get a better alignment for the seal.
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Old 22-05-2020, 04:44   #6
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Re: Volvo Penta MD7a Water cooling system

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Originally Posted by Lepke View Post
Those leaks in small Volvos are common. Some people cut the pipe and connect with hose to get a better alignment for the seal.
I had to do that between the transmission and the water pump. Otherwise impossible to seal reliably.

Last summer I came across some place on line selling MD7 parts and it had these water distribution pipes listed as in stock. I think they were just under $200.

When we say “square” washers, the washer is round but square in cross section.

On mine the connection to the transmission requires a soft copper washer to seal. They often can not be reused. You can buy little kits of copper washers at Harbor Freight.
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Old 22-05-2020, 08:42   #7
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Re: Volvo Penta MD7a Water cooling system

The pipe uses a square cut o-ring. The pipe or tubing must be perpendicular to the surface or straight in for it to work. Bend the tube if you have to being careful not to deform the end (put a snug fitting socket in it or bend it about 2" away from the end with a flat bar). You can get the o-ring from any Volvo car dealer or most car parts stores. At Volvo the sealing ring is listed in the climate control section for any 440, 540, 122, 144, P1800, 240, 260, 740, 940 series cars. A generic part is available as a "water pump sealing kit" for these same series cars. Volvo made it this way for about 40 years. O-ring gets installed with a bit of liquid soap or rubber friendly grease.

Or you could tap the hole for a 3/8 NPT pipe to hose nipple fitting.
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Old 22-05-2020, 08:56   #8
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Re: Volvo Penta MD7a Water cooling system

That’s useful info. Thanks.
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Old 22-05-2020, 13:29   #9
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Re: Volvo Penta MD7a Water cooling system

I have just used a stack of several O-rings from a Harbor Freight assortment kit.
If you want to make custom pipes, the tubes are standard rigid copper plumbing size, use wrought copper sweat solder elbows and such.
I had to make some custom plumbing to reverse the raw water flow through the heat exchanger on my MD11C, since the geniuses at Volvo ran the water in at the top and out at the bottom, resulting in an occasional trapped air bubble which caused overheating.
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