Volvo MD7A Thermostat / Manifold Problem

[gandy]

Hi,

I'm trying to replace the thermostat, but have run into a bit of a problem. The thermostat housing is not the same as shown in the manual (PDF)
On our engine the two bolts are at roughly 5 and 11 o'clock when facing astern, rather than 7 and 1 as shown in the manual.

The problem is that instead of a flexible pipe connecting to the bottom of the housing, ours has a horrible piece of copper pipe that starts as a push-fit in the water pump and runs all the way to the thermostat, with a brand half-way along going into the manifold. I can't separate that pipe either from the manifold or from the thermostat housing, and can't actually see how they're held together in any case.

See photo ..

Any suggestions? Obviously I can't separate the thermostat housing from the manifold unless I can get that pipe undone.

Thanks in advance, as always ...

 

[double_ender]

The copper tube into the thermostat joint is just a push on fit with a rubber ring seal.
So undo the 2 thermostat bolts and prise open the gap between manifold and thermost.
The tube is a similar fit into the underside of the manifold.
I have the 7B, and have a spare I've mostly stripped.

 

[gandy]

Cheers. It must be pretty tight, I had the thermostat housing unbolted and was giving it a good wiggle before accepting defeat and taking the whole manifold home. First thing I think is to see if the copper pipe is still available. Then I know its not the end of the world if it doesn't come out intact.

 

[scottie]

the copper pipe is used on the 7a and depends on the pipe not being deformed to seal so do not bend it when you remove it watch aou for the small o ring in the thermostat housing although the manifold is blank you need the o ring to seal the housing

the pipe may still be available but pricey

 

[Bilgediver]

Seems you have a later version engine where the pipe connections have been made in a similar way to the 2002 series using push fit sealed by o rings.

The pipe is held in position between the housing and the pump.

I would suggest you buy about 4 of the square section O rings and change both the O ring on the engine inlet and the thermostat housing keeping the others in your spares box.

 

[VicS]

If necessary you could cut the copper pipe and rejoin it with a short length of rubber hose. Some MD engines are like that any way. There is some variation amongst the MD6 and 7 series as well.

You see what I mean if you look at the various diagrams on http://www.marinepartsexpress.com/VP_Schematics/DIESEL/MD6_MD7/COOLING%20SYSTEM/

 

[scottie]

DONT cut it you depend on the original shape for it to seal

 

[double_ender]

I've got a spare copper tube if you have a problem.

Malcolm

 

[VicS]

[ QUOTE ]
DONT cut it you depend on the original shape

[/ QUOTE ] If the pipe was just cut through and then rejoined with the cut ends butting up against each other inside a piece of hose it'll be alright. Far better than damaging the pipe getting it disconnected from the t'stat housing I would think. Important to be sure of getting the correct size hose first though.

 

[scottie]

If the pipe was just cut through and then rejoined with the cut ends butting up against each other inside a piece of hose it'll be alright.

NO it wont be rigid and seal in to the manifold

 

[VicS]

Surely its the seals, shown as #70 on some of the diagrams in my link that make the seal. They will be sufficiently resislient to allow a little bit of movement but of you rejoin the cut section as I suggest the amount of movent possible will be imperceptible. If the pipe is distorted in attempts to get the t'stat housing off then they won't seal.

If it can all be separated without damaging the pipe then all well and good,it can just be reassembled with three new seals.
If it cannot be separated without damage then cutting it is an optionI If it is damaged then it may mean a new pipe, if my suggestion proves to be no good then again its a new pipe. Nothing to lose but the possibility of saving the price of a new pipe to gain.
If the new pipe is no more expensive than a bit of hose and two clips then agreed don't bother. Rip it out and buy the new pipe and 3 new seals and be done with it.

 

[gandy]

I'm still in a bit of a dilemma on this. Keypart can get the copper pipe, but its expensive and they don't have it in stock. I think I really need to try and separate the parts without damaging it too much.

Cutting and reconnecting is a possible option, with rubber hose as suggested. I wonder about soldering it back together?

A rubber hose jointhas the disadvantage that its a bit less rigid, and the whole thing seems iffy enough to me as it is, with the main cooling water supply just reliant on a push-fit with a rubber seal.

 

[scottie]

[ QUOTE ]
I've got a spare copper tube if you have a problem.

Malcolm

[/ QUOTE ]

there is your answer

you could try boiling water to loosen the pipe the only thing holding it together after you take the end cover off is stiction and the o rings

 

[VicS]

[ QUOTE ]
I wonder about soldering it back together?

[/ QUOTE ] That would be better but it rather depends on the diameter of the pipe. If it matches readily available fittings from a plumbers merchant, either solder ring type or end feed type, then that would be great other wise you would have to find a bit of tube that was s decent fit to slide over it as a sleeve. Unlikely IMHO. Silver soldering would make a stronger joint than soft (tin/lead) solder.

You say "the whole thing seems iffy enough" but it is firmly held at one end by the water pump. at the other by the t'stat housing and in the middle by the joint with the manifold. Solid as a rock!

 

[gandy]

The "iffy" comment really refers to my installation where the copper tube is seriously squashed in the middle, although I don't think the design is that brilliant in any case.

Thanks to the kindness of a Forumite, I now have a serviceable spare copper tube.

The thing is now in bits, and it looks like the "old" copper tube was distorted and had been sealed with silicone (hence firmly glued in place) More silicone seems to have been used around the thermostat, so it looks like this overhaul of the manifold and pipework is well overdue.

 

[Pandour]

DONT cut it you depend on the original shape for it to seal

Hi I have taken off the manifold thermostat etc - did not bend the pipe but now its back together it leaks at the pump press fit and at the fit into the manifold - seems to be good at thermostat end. the pipe seemed to be too long from the middle t fitting to the thermostat fitting and so getting the fitting into the manifold was not a straight in fit had to wiggle it a lot. Any suggestions as to getting it to seal - the square o rings cost $12 NZ each.

 

[Beneteau381]

do as Vic says, cut it and butt fit it inside a rubber hose, the cut will allow you to get it square in the hole and to the O rings