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Welding or Brazing Sump


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I have a spare engine sump i want to first baffle, then also add a temperature sensor boss for some electronic measurements. I don´t want to use one of those sump plug adapters, I´d rather keep this separate to the magnetic drain plug.

I have noticed (after removing the paint) that the original boss for the sump plug is brazed, would it be better to do this for the temp sensor boss as well? Is the sump sheet metal too thin to weld?

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I've fabricated water connectors in steel by Mig welding, and found it difficult to achieve a leak free weld. In fact, I had to resort to RadWeld in the end to cure a seep, despite repeated grinding back and careful re-application of the weld.

Braze, correctly applied, tends to 'wet' the native metal and flow into seams.  It is the usual method for radiators to be made, so I think that others experience prove this too, although I've never learnt to braze.

Havign said that, I've welded brackets inside the sump to support baffles, with no problems, but those didn't penetrate through.  I think sump metal is a bit thicker than body panel sheeting, so that isn't the problem - it's brazing's better sealing ability that you need.

For a temp sensor, I've used a dipstick with a sensor on the end.  That removes the need for a hole in the sump.  This is a popular idea with bikers, but the sticks are too short and the guauge is on the top, not on the dash.  VWs use them as well, longer and adjustable for length, see:http://www.ebay.co.uk/itm/5573-Oil-Temperature-Dipstick-Sender-for-Aircooled-1200cc-1600cc-VW-engines-/271444272585?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3f3356e5c9#ht_5425wt_1141

This part is supplied by VDO Guages, who also make a sensor that is bolted onto the sump, with gaskets, that may be more secure, certianly more adjustable, than a welded in boss.   http://www.justkampers.com/vdo-oil-temperature-gauge-kit-with-sump-sender-1200-1600cc-to-1979.html

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there are two problems with welding a boss to a sump,

first as mentioned is the difference in material thickness,

and second, if the sump has been subject to use  it will be contaminated by engine oil making welding very difficult as the oil somehow seems to penetrate into the steel.

I tried welding baffles in a used sump and even after grinding back to 'fresh' metal it still was a bugger to get a good weld.

brazing will burn off any residue and should allow you to uniformly heat both surfaces to get a good bond.

only my opinion of course. :)

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John is onto something above.
Why not just drill the sump and use a copper/dowty washer and nut on the sensor so it is just bolt on? The only downside is you would have to remove the sump to fit a new sender?
That leads onto the idea that just tacking a bolt inside the sump and relying on a washer to seal against the outside face may also work?

Just ideas.....

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Hello Bainzy,

brazing is fine but you need a good heat source, oxy/acetylene is great but I doubt if you have the kit? It's harder to do with a large propane torch as it is such a broad spread of heat. Soft solder (which is what copper radiators are built up with) is easier as long as the boss has a reasonably sized face to attach to the sump.

Is there nobody around who could do the work for you; if you are in my neck of the woods, I'd happily braze it in for you?


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Thanks for all the replies! Looks like brazing is the way to go then.

That's very kind of you Alec, I'm in Yorkshire so a bit far from Shropshire, but are you visiting any shows in the near future such as the NEC classic car show or Stoneleigh in Feb? There's no rush for me to do it as the car will be off the road for a while now.

It seems brazing is pretty handy. I may need to get hold of some oxy/acetylene kit eventually as I need to also braze some other joints on the car such as the sill to rear wing and the windscreen frame gutters (replacing both)....

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