This Porsche Cayman 987 came to us after the owner had been through three transmission oil flushes at a previous workshop. The coolant was still there. Once coolant gets into a gearbox, flushing it out does not work. Here is how we traced the root cause, overhauled the gearbox, and got the car back running cleanly.
Job completed: August 2026
| Car | Porsche Cayman 987, Tiptronic automatic gearbox |
|---|---|
| Symptom | Milky, coolant-contaminated transmission fluid that kept returning after multiple flushes |
| Fault found | Failed transmission oil cooler letting engine coolant mix into the gearbox |
| Repair done | Full gearbox overhaul with new seals, gaskets, clutch pack and filter, plus reconditioned torque converter and OEM replacement transmission cooler |
| Parts | OEM-grade transmission cooler, quality overhaul parts, fresh fluid |
| Time taken | Timeline confirmed after strip-down |
| Cost | From $4,800 before GST for a full overhaul, we quote before work begins |
| Warranty | 2 years or 40,000km on the gearbox overhaul, whichever comes first |
The owner noticed the transmission fluid on his Porsche Cayman 987 had turned milky, a clear sign of coolant mixing in. He sent the car to a workshop which recommended flushing the transmission oil. After three separate flushes the fluid was still contaminated. Each time the colour came back wrong. He came to us having already spent money on a fix that was not working.
The Porsche Cayman 987 uses a Tiptronic automatic gearbox, a hydraulic unit that is sensitive to its own fluid quality. The gearbox has an internal transmission oil cooler that sits inside the cooling circuit. When that cooler develops a leak, engine coolant enters the gearbox oil passages under pressure. The cooler sits between two separate fluid systems, and once the seal goes, mixing starts immediately.
Coolant in a transmission is serious because water strips the lubrication properties from transmission fluid and causes rapid wear of internal seals and clutch pack materials. The longer it runs contaminated, the more damage builds up inside the unit.
Flushing a gearbox removes the fluid, but it does not seal the leak that is adding coolant in the first place. If the transmission oil cooler is still defective, new fluid picks up coolant from the same passage the moment you start the car. This is exactly what happened here, three times over.
We opened the gearbox to inspect the condition of the internals. The clutch pack and internal seals had absorbed contamination and were no longer serviceable. The milky residue inside the casing confirmed the extent of the damage. We also identified the failed transmission oil cooler as the source, an OEM-grade part that sits in the cooling circuit and had developed a leak between the two fluid channels.
The Porsche Cayman 987 Tiptronic gearbox has its transmission oil cooler built into the engine cooling circuit. It is a heat exchanger that keeps the transmission fluid at the right operating temperature by using engine coolant to manage heat. When the internal wall of this cooler develops a crack or a seal fails, the two fluids mix at the boundary.
Engine coolant runs at a slightly higher pressure than transmission fluid when the engine is warm. That pressure difference pushes coolant across the failed boundary and into the gearbox. Each time you flush the transmission oil and restart the car, fresh coolant enters again from the same source. The only way to stop the contamination is to replace the cooler, and the only way to restore the gearbox to a safe condition is to overhaul it properly.
We stripped the Tiptronic gearbox completely. The valve body, torque converter, clutch packs, seals, gaskets and the internal filter were all inspected, and the contaminated components were replaced with quality overhaul parts and fresh transmission fluid to the correct specification.
The failed transmission oil cooler was replaced with an OEM-grade replacement cooler to ensure the two fluid circuits stay separated properly. The torque converter was also replaced with a reconditioned unit, as the contamination had affected its internals.
After reassembly we ran the car to operating temperature, checked for any signs of continued mixing, and confirmed the fluid stayed clean. The car was road tested before handover.
On this Cayman the gearbox overhaul came to $4,800 before GST, with the reconditioned torque converter at $1,800. What another car costs depends on the condition of the internals and whether the torque converter also needs attention, so we quote after the strip-down. Coolant contamination cases usually fall at the higher end because more internal components are affected.
We quote before any work begins. Once we have opened the gearbox and assessed what is serviceable and what needs replacement, we give you the full cost breakdown so there are no surprises. The overhaul comes with 2 years or 40,000km warranty, whichever comes first.
Check your transmission fluid colour if you ever notice a sweet smell from the engine bay, unusual shifting behaviour, or overheating. Milky or discoloured fluid is a warning sign that coolant has entered the gearbox.
Do not keep flushing if the fluid keeps coming back contaminated. That is a sign the source of the leak has not been found. Acting early before the clutch pack absorbs too much coolant keeps the repair cost significantly lower than a full overhaul.
This Porsche Cayman 987 (Gearbox overhaul) was handled at 1 Car Service, an independent workshop in Sin Ming AutoCity, Singapore. For Porsche, we use dealer-level PIWIS diagnostics. The work is backed by our 2-year, 40,000km warranty. We hold a 4.9★ rating from 1,775+ Google reviews.
WhatsApp us your car model, mileage and the symptoms. We diagnose the root cause first, then quote before any work begins. Gearbox overhaul comes with 2 years or 40,000km warranty.
On this Cayman the full gearbox overhaul came to $4,800 before GST, plus $1,800 for a reconditioned torque converter. The figure for another car depends on what is found inside, so we strip and inspect first, then quote. Coolant contamination cases usually cost more because internal components are more extensively damaged. We quote before work begins and the overhaul comes with 2 years or 40,000km warranty.
No. Flushing changes the fluid but does not seal the source of the leak. If the transmission oil cooler has failed and is still in place, new fluid picks up coolant again as soon as the engine runs. On top of that, coolant damages internal seals and clutch pack materials over time, and flushing does not restore those components. A proper overhaul is needed once contamination has occurred.
The Tiptronic gearbox has an internal transmission oil cooler that shares the engine cooling circuit. When the cooler develops a leak or the internal seal fails, engine coolant passes across into the transmission fluid under pressure. Replacing the faulty cooler with an OEM-grade unit stops the mixing. The gearbox then needs to be overhauled to remove the damaged internal components.
A full overhaul typically takes 4 to 6 working days, depending on parts availability and the extent of internal damage found when the unit is opened. We keep the owner updated throughout and confirm the timeline once we have assessed the condition inside.
Yes. We use PIWIS, Porsche's own dealer-level diagnostic system, to read gearbox fault codes, run adaptation routines and verify correct operation after the overhaul. This is the same tooling used by Porsche authorised service centres.
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