Aluminium oil cooler tube is a thin-wall flat or rectangular tube, usually high-frequency welded from brazing-clad strip, that carries engine oil, transmission fluid or hydraulic oil through a brazed cooler core. Its job is to hold pressure, transfer heat to the fins and braze reliably to headers and turbulators. This guide covers tube types, clad materials, typical sizes, tolerances, brazing and inspection, so you can specify the tube with confidence.
Oil coolers keep engine oil, automatic-transmission fluid, power-steering fluid and hydraulic oil within their working temperature range. Most modern coolers for vehicles and mobile machinery are all-aluminium brazed cores: rows of tubes carrying oil, separated by corrugated fins that carry air or coolant, joined to headers at each end in a single furnace brazing cycle.
The tube is the part that touches the oil, so it carries most of the engineering load. It must provide a defined flow path with an acceptable pressure drop for a viscous fluid; contain the operating pressure plus pressure spikes from cold starts, when thick oil can push pressure far above normal; transfer heat efficiently through a thin wall to the fins; and form a sealed, strong braze joint with fins, headers and any internal turbulator. It must also resist corrosion from the outside environment and keep enough strength after the brazing cycle, which anneals the metal.
Oil is far more viscous than water or refrigerant, and heat transfer on the oil side is usually the limiting factor in the cooler. That is why oil cooler tubes so often contain an inserted turbulator or a dimpled wall: both break up the slow, laminar oil flow near the wall and can raise heat transfer substantially, at the cost of a higher pressure drop.
| Tube type | Internal structure | Advantages | Best suited to | Points to confirm |
|---|---|---|---|---|
| HF welded flat tube | Single open channel | Simple, economical, flexible section sizes | Standard automotive, truck and machinery coolers | Wall, weld position, burst pressure, braze clearance |
| Tube with inserted turbulator | Stamped or roll-formed fin brazed inside the tube | Large heat-transfer gain; turbulator also stiffens the tube against pressure | Compact, high-duty coolers | Fin height and pitch, oil viscosity, allowable pressure drop, inner cladding |
| Dimpled tube | Regular dimples pressed into the wall, often touching opposite wall | Turbulence without a separate insert; dimples brazed together add pressure strength | Designs needing simpler assembly with better heat transfer | Dimple depth and pattern, flow area, burst strength |
| Rectangular heavy-wall tube | Single channel, thicker wall | Robust for high pressure and rough service | Hydraulic coolers on construction and agricultural machinery | Wall thickness, corner radii, weld seam quality |
| Extruded multi-port tube | Several channels formed in the extrusion | No weld seam; internal webs carry pressure | Some compact and high-pressure designs | Alloy, port shape, corrosion protection |
The choice is mainly a trade-off between heat transfer, pressure drop, pressure capacity and cost. Inserted turbulators give the highest performance but need tube strip clad on the inside as well as outside so the insert brazes to the wall. Dimpled tubes avoid the insert and the extra assembly step. Plain tubes remain the low-cost choice where the cooler has enough frontal area.
Welded oil cooler tube is roll-formed from brazing sheet: a core alloy carrying the strength, with a thin layer of low-melting aluminium-silicon alloy bonded to one or both faces. During brazing the clad layer melts, flows into the joints by capillary action and freezes to form fillets, while the core stays solid. The clad thickness is expressed as a percentage of total strip thickness, commonly around 5 – 15 % per side.
| Clad structure | Character | Typical use |
|---|---|---|
| 4343 / 3003 / 4343 | Double-sided clad; good formability and dependable brazing; inner clad lets turbulators braze to the wall | Automotive engine and transmission oil coolers |
| 4343 / 3003 (single side) | Outer clad only; used where nothing brazes inside the tube | Plain tubes brazed to fins and headers |
| 4045 / 3003 / 4045 | Higher-silicon clad gives more fluid filler and larger fillets | Designs needing more filler at joints |
| 4343 / 3005 or modified 3xxx core | Higher post-braze core strength | Heavy-duty truck and construction-machinery coolers |
| Long-life cores with zinc or interliner layers | Sacrificial layer guides corrosion sideways rather than through the wall | Coolers exposed to road salt or aggressive coolants |
| Alloy | Role | Key alloying elements (nominal) | Melting behaviour |
|---|---|---|---|
| 3003 | Core | Mn about 1.0 – 1.5 %, Cu 0.05 – 0.20 % | Melting range about 640 – 655 °C, stays solid during brazing |
| 3005 | Core | Mn about 1.0 – 1.5 %, Mg 0.20 – 0.6 % | Stronger than 3003; magnesium content must suit the brazing method |
| 4343 | Clad (filler) | Si about 6.8 – 8.2 % | Melts at about 577 – 613 °C, flows at brazing temperature |
| 4045 | Clad (filler) | Si about 9.0 – 11.0 % | Melts at about 577 – 591 °C, more fluid than 4343 |
Composition ranges follow the Aluminum Association registrations; melting ranges are typical published values. Magnesium above a few tenths of a percent interferes with flux (CAB) brazing, so magnesium-bearing cores are matched to vacuum brazing or to suitable fluxes.
Oil cooler tubes are produced in two broad families: thin-wall flat tubes for compact automotive cores and heavier rectangular tubes for hydraulic and industrial coolers. The tables list sections that are commonly requested. Other widths, heights and walls are made to drawing; a new size usually needs new forming rolls rather than a new die.
| Width (mm) | Height (mm) | Wall thickness (mm) |
|---|---|---|
| 16 | 4 | 0.32 / 0.40 / 0.50 |
| 19 | 3.2 | 0.40 |
| 27.66 | 3.19 | 0.50 |
| 30 | 4 | 0.45 |
| 32 | 2 | 0.30 / 0.50 |
| 34.7 | 3 | 0.50 |
| 43 | 4.3 | 0.40 / 0.50 |
| 65 | 4.3 | 0.40 |
Thin-wall flat oil cooler tube: typical sections.
| Width (mm) | Height (mm) | Wall thickness (mm) |
|---|---|---|
| 9.9 | 9.9 | 1.2 |
| 16 | 12 | 1.0 / 1.2 |
| 20 | 16 | 1.2 |
| 20 | 20 | 1.2 |
| 22 | 40.5 | 1.5 |
| 27 | 14 | 1.2 |
| 27 | 19 | 1.5 |
| 30 | 30 | 1.2 |
| 32 | 12 | 1.0 |
| 38 | 19 | 1.2 / 1.5 |
| 45 | 26 | 1.5 |
| 54.8 | 16 | 2.6 |
Rectangular oil cooler tube: typical sections for heavy-duty and hydraulic coolers.
Tube is supplied in cut lengths for core assembly, or in straight long lengths for the customer to cut. Specify cut length, end condition (square cut, deburred, sized ends) and whether ends must be free of internal burrs, because burrs restrict flow and can trap flux.
| Characteristic | Typical reference tolerance | Effect in production |
|---|---|---|
| Width | About ±0.05 mm | Fit in header slots; too tight jams, too loose leaves gaps the filler cannot bridge |
| Height | About ±0.05 – 0.06 mm | Core stack height and fin contact |
| Wall thickness | About ±0.02 mm for thin-wall tube | Pressure capacity, weight and post-braze strength |
| Crown (bulge of flat faces) | About ±0.10 mm | Contact between tube and fin along the full width |
| Corner radius / end dimensions | About ±0.05 mm | Header slot fit at the tube ends |
| Straightness, twist, cut length, burr height, weld position | Agreed on drawing | Automated tube insertion and core flatness |
Reference values frequently used for thin-wall welded oil cooler tube; final tolerances are agreed on the customer drawing.
Braze clearance is the most important reason for tight tolerances. Capillary flow of the molten clad works best in a narrow, even gap. If the tube varies in width or height, some joints are starved of filler while others pool it, which leads to leaks or blocked passages. Consistent tube geometry also keeps the core flat after brazing, which matters when the cooler is bolted into a tight space.
The most common method for automotive coolers. Non-corrosive fluoride flux is applied to the core, which is brazed in a nitrogen atmosphere at a peak of roughly 595 – 610 °C. Works well with 3003 cores and 4343 or 4045 clad.
No flux; magnesium in the clad or core helps break up oxide in vacuum. Common for stacked-plate and bar-and-plate coolers and for magnesium-bearing, higher-strength materials.
Low residual rolling oil and forming lubricant, so flux wets the surface and filler flows evenly. Excess oil leaves carbon and voids in joints.
The HF weld seam must be fully fused, with the inside bead controlled so it does not obstruct turbulator insertion or trap flux.
Tube, header slot and fin dimensions are chosen together so gaps stay small and uniform across the core.
Brazing anneals the tube, so pressure capacity is calculated from post-braze (O-temper) properties of the core alloy, not its as-supplied strength.
Ask for dimensional reports, burst test results and the mill test certificate (EN 10204 3.1) with each lot. For new programmes, a production part approval package agreed with your quality team avoids repeated qualification later.
| Factor | HF welded clad tube | Extruded tube | Folded tube |
|---|---|---|---|
| Source of braze filler | Built into the clad strip | None; filler from clad fins or added flux/filler | Built into the clad strip |
| Internal turbulator | Easy: insert brazes to inner clad | Not usual; channels formed in extrusion | Internal web formed by folding |
| Wall thickness range | Very thin to moderate | Moderate; thin webs possible in multi-port | Very thin |
| Weld seam | Yes, inspected by eddy current | No seam (or die weld lines) | No weld; brazed fold |
| New size cost | Forming rolls | Extrusion die | Forming rolls |
| Typical use | Most automotive and machinery oil coolers | Some compact or high-pressure designs | Radiators and condensers more than oil coolers |
For most oil coolers, welded clad tube wins because the cladding supplies filler for both the outer fins and the inner turbulator, and wall thickness can be chosen precisely for the pressure. Extruded tube is chosen when a seamless section or integral channels are preferred, and folded tube is more common in radiators and condensers. If you are unsure, send the operating conditions and core design and we will suggest the tube construction that fits.
A typical passenger-car transmission cooler might use 16 × 4 mm double-clad flat tube with a wall near 0.4 mm and an inserted turbulator, while a typical excavator hydraulic cooler uses rectangular tube of around 27 × 19 mm with a 1.5 mm wall, chosen for pressure capacity and resistance to rough service.
Tubes are packed in protective cartons or crates that keep thin walls from crushing and keep surfaces clean and dry, with labels for batch traceability.
Usually brazing sheet with a 3003 or modified 3xxx core and a 4343 or 4045 aluminium-silicon clad layer on one or both sides, roll-formed and high-frequency welded into a flat or rectangular tube.
Inner cladding provides filler metal to braze an inserted turbulator or touching dimples to the tube wall. Plain tubes with nothing inside need only outer cladding.
Inserted turbulators usually give higher heat transfer and add pressure strength but cost more and add an assembly step. Dimpled tubes are simpler and cheaper with a smaller heat-transfer gain. The best choice depends on oil viscosity, space and allowable pressure drop.
Yes. Width, height, wall, corner radii, weld position and internal structure can be made to drawing. New sizes usually need new forming rolls, so share the drawing early.
In-line eddy current testing of the wall and weld seam, burst tests on samples, dimensional measurement, cross-section examination and, for new programmes, brazing trials in the customer furnace.
Yes, with the right material. Vacuum brazing uses magnesium-bearing clad or core alloys; CAB uses flux and low-magnesium materials. Tell us your process so the clad structure is matched.
Send the section, clad structure, brazing method and volumes. We will reply with options, certification and delivered terms.
