Volvo Penta MD7a Water cooling system

[Pandour]

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.

[JD-MDR]

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

[hpeer]

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.

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.

[JD-MDR]

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

[Lepke]

Those leaks in small Volvos are common. Some people cut the pipe and connect with hose to get a better alignment for the seal.

[hpeer]

Originally Posted by Lepke

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.

[Scubaseas]

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.

[hpeer]

That’s useful info. Thanks.

[Bill Seal]

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.

[Toddy693]

Originally Posted by JD-MDR

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

My question is before they leak. How do you remove them from the pump? Are they just pressed in? I need to pull pump but haven’t figured what hold them in and how to remove them

[Scubaseas]

They are held in place by the metal pipe which has a ridge on it. The metal pipe is secured with a bolt. Remove pipe and the o-ring usually comes out with it or if not is easily remove with a pinky finger. or pick of some kind. The pipe and o-ring simply slide into the pump which is why it's important to have the pipe perpendicular to the pump so the o-ring sits flat and seals properly.

[Don C L]

There really should be a Social Group for Volvo owners... maybe I'll get on that someday... even though I don't have one but my buddy does..
Try this: (I just searched MD7A here) There's a lot

https://www.cruisersforum.com/forums...rchid=32629274

Then get back and tell us what worked!

[hpeer]

Don,

That’s a GREAT idea. Hell the MD7A/B could have its own sub group.

There is a LOT on this forum but it takes diffing to back through it all.

[hpeer]

A nice water pump rebuild kit.

https://www.ebay.com/i/112375767496?...YaAh3kEALw_wcB


Here is the exploded parts diagram.

You are looking at parts 69 and 70.

https://www.marinepartseurope.com/en...26-13636D.aspx

[Toddy693]

Originally Posted by Scubaseas

They are held in place by the metal pipe which has a ridge on it. The metal pipe is secured with a bolt. Remove pipe and the o-ring usually comes out with it or if not is easily remove with a pinky finger. or pick of some kind. The pipe and o-ring simply slide into the pump which is why it's important to have the pipe perpendicular to the pump so the o-ring sits flat and seals properly.

Where is the bolt located that secured it?Can’t seem to find one?