Plastic boost bypass valve leaks with age
Added · Updated
What causes "Plastic boost bypass valve leaks with age" on the Mitsubishi Lancer Evolution VIII (2003-2005), and how is it fixed?
One retailer says every VIII came with a plastic bypass valve that starts to leak after years of heat cycles. Fix: Replace it with the IX's metal bypass valve, which the retailer says is a direct swap (see F-evo-11).
Symptoms
Boost leak: lower or uneven boost.
Cause
One retailer says every VIII came with a plastic bypass valve that starts to leak after years of heat cycles.
Fix (summary)
Replace it with the IX's metal bypass valve, which the retailer says is a direct swap (see F-evo-11). Single retailer source.
Related parts
Related build entries
Other CT9A (Evolution VIII) problems
- Recall 04V-138: wrong weight ratings on the certification label (2003)
- Recall 05V-335: turbocharger coolant hose may leak (2005)
- Recall 16V-458: front crossmember corrosion can let the lower arms detach (salt states)
- 5-speed gearbox grinds as the brass synchro rings wear
- The MR's 6-speed is weaker than the 5-speed under high power
More for this car
- All Mitsubishi Lancer Evolution VIII (2003-2005) fitment answers · CT9A (Evolution VIII) common problems
- Newsletter archive: past issues with every new and corrected entry
Sources
- USDM EVO 8/9 Year To Year Changes — Wunderladen Racing (vendor article; read 2026-10-26; full page read)Plastic E8 bypass valve leaks and fails over heat cycles; E9 metal valve is a direct swap.
Summaries are in our own words. Not repair instructions; consult the factory service manual.
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