PBO reader Simon Mitchell is worried there might be something wrong with his Volvo Penta engine. Our expert Stu Davies has this advice…


Simon Mitchell from Essex writes: “I have a Volvo Penta 2003T with 950 hours running time. It starts perfectly and runs smoothly. There is no oil or water consumption and both fluids are clean.

“The normal top speed revs would be 3,200rpm. When propelling the boat, the engine has recently started to top out at 2,100rpm.

“Opening the throttle any further produces black smoke from the exhaust but no increase in speed. In neutral, the engine still revs freely to 4,000+ rpm with a clean exhaust.

“The boat was ashore recently while the hull was cleaned and new antifouling applied – but even before cleaning, there was far less fouling than usual.

“The shaft was checked, turning freely by hand, and the prop is perfect. I’ve changed the air filter, but to no avail.

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“What could be causing the low revs? I’m wondering about injectors or turbo problems, but don’t want to just change things for the sake of it. Are there any tests I can make to determine where the problem lies?

PBO engine expert Stu Davies replies: “It sounds like a classic case of blocked exhaust elbow or turbo. More likely the turbo.

“It’s easy to check: remove the air filter, the turbo blades should be visible. Gently spin them with your finger. They should turn really easily.

“If they are stiff then it’s probable that the blades are carboned up. I have cleaned them before now with a brass wire brush.

“If that proves OK, check the turbo overpressure valve isn’t stuck open, which could cause lack of pressure.

“If all is OK with the turbo then check the exhaust elbow isn’t blocked with salts and carbon.”

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This feature appeared in the May 2022 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.

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