Fluid Leak Diagnosis

Systematic procedure to identify the source of fluid leaks on a 2015-2020 Ford F-150 3.5L EcoBoost through visual inspection, dye testing, and pressure testing methods.

Warnings

Tools required

Parts

• UV fluorescent dye kit (multi-fluid) × 1 — Use appropriate dye for suspected fluid type

Preparation

1. Park vehicle on level surface and apply parking brake
2. Place wheel chocks behind rear wheels
3. Allow engine and exhaust system to cool completely (minimum 30 minutes)
4. Prepare work area with adequate lighting for underbody inspection
5. Document existing fluid levels in all reservoirs for reference

Procedure

1. 1

   Initial visual inspection - engine bay
   Open hood and visually inspect engine bay for obvious fluid leaks. Check oil fill cap, dipstick tube, valve cover gaskets, oil filter housing, turbocharger oil feed and drain lines, coolant hoses, intercooler connections, and brake master cylinder. Look for wet spots, staining, or accumulation of dirt on fluid trails. The 3.5L EcoBoost is prone to turbo oil leaks and valve cover seepage.
2. 2

   Check fluid levels and identify fluid type
   Check engine oil, coolant, brake fluid, transmission fluid (via dipstick on some models), and windshield washer fluid levels. Note any low levels which indicate potential leak areas. Identify suspected fluid type by color and consistency: engine oil (amber to dark brown), coolant (orange), transmission fluid (red to brown), brake fluid (clear to amber), differential fluid (dark brown, gear oil smell).
3. 3

   Raise and secure vehicle
   Lift front of vehicle with floor jack at designated lift points on frame rails. Secure with jack stands at appropriate support points. Lift rear if rear differential leak is suspected. Ensure vehicle is stable before working underneath.
4. 4

   Inspect underbody - front section
   Inspect oil pan gasket, oil drain plug, oil filter, front crankshaft seal area, transmission pan and lines, power transfer unit (PTU) if AWD, and steering rack boots. Check for active drips or residue buildup. Pay special attention to turbocharger oil drain tubes which route down passenger side of engine - these are common failure points on EcoBoost engines.
5. 5

   Inspect underbody - rear section
   For RWD models, inspect rear differential cover, pinion seal, axle seals at wheel hubs, and vent tube. Check driveshaft slip yoke area for transmission output seal leakage. Inspect fuel tank and fuel lines for fuel seepage.
6. 6

   Clean suspected leak areas
   If leak source is not obvious, spray suspected areas with brake cleaner or degreaser and wipe clean with shop towels. This removes old fluid residue and allows fresh leaks to be identified. Focus on areas showing wetness or fluid trails. Allow to dry completely.
7. 7

   Add UV fluorescent dye if needed
   If leak source cannot be visually identified, add appropriate UV dye to suspected system. For engine oil leaks, add oil-specific dye through oil fill cap. For coolant leaks, add to coolant reservoir. For transmission leaks, add through dipstick tube. Follow dye manufacturer instructions for proper quantity based on system capacity.
8. 8

   Operate vehicle and allow dye circulation
   Lower vehicle from jack stands. Start engine and allow to reach normal operating temperature (approximately 10 minutes). Drive vehicle for 10-15 minutes or as recommended by dye manufacturer to allow dye to circulate and leak to manifest. Include varied engine loads and speeds.
9. 9

   Re-inspect with UV light
   After test drive, raise and secure vehicle again. Using UV light from leak detection kit, inspect all previously cleaned areas. Fluorescent dye will glow brightly under UV light, clearly identifying leak source. Use mechanics mirror to inspect hidden areas behind components. Photograph leak source for documentation.
10. 10

    Pressure test cooling system if applicable
    If coolant leak is suspected but not confirmed visually, attach cooling system pressure tester to radiator or coolant reservoir. Pump to specified pressure (typically 16-18 PSI for this vehicle). Observe for pressure drop and inspect for coolant seepage at hoses, water pump weep hole, radiator, heater core connections, and thermostat housing. EcoBoost models may leak at intercooler coolant lines.
11. 11

    Document findings
    Record leak location, fluid type, and severity (active drip, seepage, or residue only). Note any related component damage or corrosion. Document with photos showing leak source and surrounding area. This information determines repair procedure and parts needed.

Reassembly

1. Lower vehicle from jack stands and remove jack
2. Remove wheel chocks
3. Recheck all fluid levels and top off if needed for safe operation until repair
4. Clean any spilled fluids from chassis and driveway

Verification

• Confirm specific leak source has been positively identified before proceeding with repairs
• Verify fluid levels are safe for continued operation if repair will be delayed
• If UV dye was used, note that it will remain in system and continue to glow under UV light after repairs are completed - this is normal
• Multiple leaks may exist - ensure all leak sources have been identified before concluding diagnosis

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