Metal conduit for coolant pipe?

I need to make a coolant bypass pipe about 24" long with a couple bends midway along. It looks like electrical metal conduit is the simplest cheapest option. Any reason this won't work, or is a particularly bad idea?

Some Conduit has a gray paint inside that cracks and flakes off when you bend it.  Also i have some that was used for coolant pipes and it’s really crappy inside.  I’d rather use copper and braze some elbows in for the bends.

I've done copper.

I have done copper as well. 24" should not be too expensive. Aluminum might also be a good idea instead of steel

I used aluminum, but the bends I had to make were all large radius, small degree bends. Should react less with the coolant than steel or galvanizing.

I've fabricated coolant hard lines with exhaust J-bends and U-bends many times.

The water pump is half steel and the inside of the engine is steel, aluminum, and iron.  Don't worry about materials one bit.

Electrical Metallic Tubing (EMT) has a coating inside like Patrick mentioned and it will likely contaminate the system. Copper would be a better choice and is easy to bend.

02Pilot said:

I need to make a coolant bypass pipe about 24" long with a couple bends midway along. It looks like electrical metal conduit is the simplest cheapest option. Any reason this won't work, or is a particularly bad idea?

Yes, electrical conduit will rust really quickly (BTDT).  There are other pipes out there that will to a lot better job, as listed.

OK, got it - no steel. On balance I'd prefer aluminum over copper, I think, but I have a feeling copper would be a lot easier to bend.

There's already plenty of steel in your cooling system. Stop over-thinking things.

ShawnG said:

There's already plenty of steel in your cooling system. Stop over-thinking things.

There may be steel, but some steel is better than others when put in a corrosive environment.  The electrical conduit is not good for passing water all the time- and it's not what it's made for.

I ran 1.5" aluminum tube quite a few feet to plumb a Cadillac radiator in the back of the BatVan.  Knurl or somehow pecker up the end where the hose clamps to so it has some bite.

I used some leftover bits of 304 stainless (from my wastegate dump tube) to extend a couple radiator hoses…. Back in like 2005.  Still works fine.

I used aluminum in my rear radiator setup through the cockpit

alfadriver said:

ShawnG said:

There's already plenty of steel in your cooling system. Stop over-thinking things.

There may be steel, but some steel is better than others when put in a corrosive environment.  The electrical conduit is not good for passing water all the time- and it's not what it's made for.

If coolant is corrosive, then it needs to be changed.

If the liquid you are running in your cooling system is harmful to steel, then the conduit will be the least of your long term problems.

I would use something whereI could somehow form up the ends with a ridge that I can slide the flexible tube over and clamp behind, so I don't blow the line off.  I'm not a lucky guy.

I will be that guy who has used emt conduit as coolant pipes when I relocated my radiator to the other end of the car, it worked well for 6 years and when I took the car apart it was spotless inside. 

If you want a really easy solution, you can buy generic coolant hoses that have a metal wire inside them which allows them to be flexible, while not pinching. They are somewhat rigid. At 24" it's probably a good idea to consider some sort of support bracing that connects in at least one place in the middle. Once upon a time, I used two of these with a few inches of pipe clamped in the middle. This allowed me to make use of a giant Howe radiator which had a connection on the opposite side from the factory setup.

I should point out that this is a small diameter line connecting the heater core to the water pump; ID is probably around 3/4" or so (will measure before buying, obviously). Factory part is metal, but also disproportionately expensive, hence my attempt to come up with a more grassroots solution. The existing pipe - installed by the PO - is just that: straight pipe, which means that it sits on the starter and rattles around. I've got the whole side of the motor apart for carb rebuilds and a new starter, so now's the time to improve it. It's got a ~45deg left, then a ~45deg right about halfway along to clear the starter.

I'm going to put eyes on some materials soon. If I can find steel conduit without an interior coating I'll be pretty tempted to try it (not worried about corrosion - I change coolant regularly, and everything in the system is nice and clean), but failing that copper seems like the way to go.

In reply to 02Pilot :

Full full of sand, then bend, much nicer bends

Alfaromeoguy said:

In reply to 02Pilot :

Full full of sand, then bend, much nicer bends

Yep. I learned that trick reading about a guy in the UK (Mike the Pipe, I think?) who hand-builds custom headers. Thankfully I shouldn't need to get the pipe red-hot like he does.

alfadriver said:

ShawnG said:

There's already plenty of steel in your cooling system. Stop over-thinking things.

There may be steel, but some steel is better than others when put in a corrosive environment.  The electrical conduit is not good for passing water all the time- and it's not what it's made for.

the steel conduit would probably rust through from the outside in.

OK, I've got a 2' section of 3/4" Type M copper pipe. Aside from the sand trick mentioned above, any tips for bending copper? Propane or MAPP? What should I be looking for as it heats?

Even with sand (which I agree is helpful), I'm wondering whether that type will bend. It's the "mechanical" style copper pipe not the soft, bendy stuff. At a minimum I think you will need the sand, some type of mandrel system and enough leverage.