The cheapest jet ski we ever bought was a 2017 Yamaha VX-C with 290 hours on the engine. The seller wanted ฿165,000. We talked him to ฿140,000 and felt clever for a week. Within 90 days the impeller had failed twice and we'd spent ฿42,000 on a new pump assembly.
The reason: the previous owner had ridden it into shallow sand off Patong, twice, and never mentioned it. We hadn't asked. We hadn't checked.
This is the test we use now, before any second-hand purchase. It takes 30 minutes if you know what you're doing. It takes longer if you don't, but the seller is usually patient because they want to sell.
Before you arrive
- Ask the seller for the VIN/HIN (hull identification number) before you make the appointment. Run it past the Marine Department to confirm registration status.
- Ask for the service log. If they don't have one, that's not automatically bad — most Thai owners don't keep formal logs — but it's a yellow flag.
- Ask for the last service receipt. Any receipt from a marine workshop tells you they've serviced the ski at least once.
- Ask if it's ever been registered and where. The blue book is non-negotiable for ownership transfer.
The 30-minute test — in order
Minutes 0–5: Cold-start engine inspection. Ask them to start the ski cold (not pre-warmed). It should fire on the second crank, idle smoothly within 30 seconds, no white smoke. Blue smoke = burning oil. Black smoke = fuel mixture problem. White after 30 seconds in a cold morning = head gasket starting to fail. None of these are deal-breakers but they're all price-negotiators.
Minutes 5–10: Engine bay inspection while it idles. Open the engine bay. Look at the fuel hoses (cracking?), spark plug wires (clean?), engine bay floor (oil/fuel pooling?). The biggest tell: water in the engine bay. Salt-water + electrical = corrosion you can see. If the bay is dry and the floor looks like the inside of a new fridge, the ski's been kept covered. If it's mossy, run.
Minutes 10–15: Pump and impeller. Engine off. Get under the back. Look at the impeller — the steel blade inside the pump. Pitting on the leading edges means it's been through sand, repeatedly. New impeller costs ฿4,500. New pump assembly with wear ring is ฿32,000. Know which one you're walking into.
Minutes 15–20: Hull walk-around with phone camera. Photograph every panel from three angles. Watch for: repairs to the gel coat (a different shade of white), epoxy fills on the side rails, cracks anywhere on the front rub strake. A repaired hull isn't a deal-breaker but a hidden one is.
If the seller objects to your phone photographs, walk away. Nothing about a clean ski needs to stay off-camera.
Minutes 20–28: The water test. Most sellers will agree to a 5-minute on-water test if you can get to a marina. Ride it. Wide-open throttle, hold for 5 seconds, release. The ski should pull smoothly to top speed without hesitation. Watch the engine temp gauge. If it rises sharply over 5 seconds at full throttle, the cooling intake is partially blocked — a clean is ฿3,000, a pump rebuild is ฿18,000.
Minute 28–30: Compression test (optional but recommended). If you can get the seller to a workshop or you have a compression gauge, take the spark plug out and crank the engine. A healthy Yamaha VX-C 1,100 reads 130–150 psi on each cylinder. A healthy Sea-Doo 1,630 reads 110–130 psi. More than 10% variance between cylinders is bad news. Compression below 100 psi means a top-end rebuild — ฿80,000+.
When to walk away
- No paperwork at all — no blue book, no service receipts, no VIN match. Walk.
- White smoke that doesn't clear after 60 seconds. Walk or budget ฿100,000 for a rebuild.
- Impeller pitting deep enough to feel with a fingernail. Negotiate ฿30,000 off or walk.
- Compression below 100 psi on either cylinder. Walk.
- Seller won't let you photograph the hull from underneath. Walk.
The Yamaha VX-C we bought without doing any of this? We sold it 14 months later for ฿100,000, having spent another ฿60,000 keeping it running. Net loss on that ski: ฿100,000. Not the worst tuition fee, but tuition all the same.
Buying through a workshop instead? They do this test as a standard PDI (pre-delivery inspection). Pongphat in Bangkok and Mongkol in Phuket both offer this on second-hand sales. The ฿15,000 premium is a bargain.
