Battery Tray Leaks/Repairs

Overview

This guide explains how to fix a leaking battery tray on your Porsche 944 with its 16v engine. A leak can cause serious trouble, especially since the DME (engine control unit) sits in the passenger footwell. Water from a clogged or damaged tray can drip onto the DME wiring and ruin it. Regular maintenance—like cleaning the tray and checking the drain—can prevent this, but if damage occurs, this procedure offers two repair methods depending on how bad it is. Keeping your battery tray in good shape protects your car’s electronics and saves you from costly repairs.

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Tools Required

• 10mm (3/8 inch) wrench
• Metal scraper
• Brush (for rust converter and seam sealer)
• Gloves, mask, and eye protection
• Cup (for testing drain)
• Cutoff tool, cutting torch, or plasma cutter (Method 2 only)
• Permanent marker, paint, or scratch awl (Method 2 only)
• Hand grinder (Method 2 only)
• Welding equipment (for galvanized or stainless steel, Method 2 only)

Parts Required

• Mild soap
• Rust converter (e.g., Mar-Hyde or equivalent)
• Brushable seam sealer (e.g., 3M or equivalent)
• Primer (for bare metal, optional)
• Paint (to match car’s color)
• Battery cover, 944 611 021 00 (if missing)
• Metal plate (galvanized or stainless steel, Method 2 only)
• Paper (for template, Method 2 only)

Step-by-Step Procedure

Step 1: Assess the Damage

1. Remove the battery using a 10mm (3/8 inch) wrench to loosen the clamp.
2. Inspect the battery tray bottom. Look for holes or weak spots (areas that flex when you push them).
3. Decide your repair method: Use Method 1 for no holes or small ones; use Method 2 for large holes or a weak tray.

Step 2: Remove the DME Control Unit (Method 1 or 2)

4. In the passenger footwell, locate the DME control unit under the carpet or panel.
5. Disconnect its wiring harness and remove it to avoid water damage during repairs. Follow this link to ensure this step—DME Control Unit Removal—is followed accurately.

Step 3: Clean and Test the Tray (Method 1)

6. Stuff rags under the tray to catch leaks.
7. Pour a cup of water into the tray to check the drain. If it doesn’t flow out, clear any clogs with a small tool or wire.
8. Mix mild soap with water, then scrub the tray to remove dirt and debris. Rinse it well.
9. Remove any large debris (like leaves) by hand if it won’t flush out.

Step 4: Prepare the Surface (Method 1)

10. Scrape the tray bottom with a metal scraper to remove loose paint.
11. Look for rust (discoloration or exposed metal). On light-colored cars, it’s easier to spot; on darker ones, scrape off most paint to be sure.
12. Wear gloves, mask, and eye protection. Brush rust converter onto any rusted areas. Let it dry completely (follow the product’s instructions).

Step 5: Seal and Paint (Method 1)

13. If you scraped down to bare metal, apply primer first and let it dry.
14. Brush on a layer of seam sealer across the tray bottom. Match the brush strokes to other factory-sealed areas under the hood if you want it to look original.
15. Let the seam sealer dry fully, then paint the tray to match your car’s color.

Step 6: Cut Out Damaged Section (Method 2)

16. Mark the damaged tray bottom with a marker, paint, or scratch awl.
17. Use a cutoff tool, cutting torch, or plasma cutter to remove the marked area.

Step 7: Replace the Tray Bottom (Method 2)

18. Have someone hold paper against the tray bottom and trace the cutout shape for a template.
19. Transfer the template onto a metal plate (galvanized or stainless steel recommended).
20. Cut the new bottom from the plate using your cutting tool.
21. Tack weld the new piece into the tray to hold it, then fully weld it in place.
22. Grind the welds smooth on the tray’s top side with a hand grinder.

Step 8: Seal and Paint (Method 2)

23. Apply primer to the bare metal if desired, then let it dry.
24. Brush seam sealer over the new bottom, matching factory brush strokes if you care about looks.
25. Once dry, paint it to match your car.

Step 9: Final Steps (Method 1 or 2)

26. Reinstall the DME control unit and reconnect its wiring harness.
27. Install the battery with a cover (944 611 021 00) if it’s missing.
28. Secure the battery with the clamp, tightening it to 20 Nm (15 ft-lbs) using a 10mm (3/8 inch) wrench.

Post Procedure Checklist

• Check for leaks by pouring water into the tray and ensuring it drains properly.
• Confirm the DME control unit works (car starts and runs normally).
• Inspect the tray for unsealed spots or paint flaws.
• Verify the battery cover is in place.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manual, Volume 1
• Youtube