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What's causing my engine to underperform?

2017 January 1

 What’s causing my engine to underperform?

Dear Boat Doctor,

I have a Yanmar 4JH2DTE in my boat and I don’t seem to be getting the power I am used to above 2,400 rpm. I checked the fuel filters and they seem OK. What else should I check?


Bill Cousins

Port St. Lucie, Florida

Dear Bill,


I have used that engine in quite a few boats and it’s normally a great engine. When dealing with diesel engine issues, fuel is always a good place to start. A clogged filter can supply enough fuel to run at low speed, but can choke off at higher rpm. It’s also a good idea to make sure that your stop cable is completely pushing back in, if the stop cable is pulled, even a little, it can disrupt fuel flow to the engine.

The symptoms you’re describing, however, sound like you may have a dirty turbo. In this engine, the turbo kicks in at about 2,200 rpm and really boosts the power. A turbo uses the flow of exhaust gas to spin a turbine that compresses the intake air and that dense intake air makes for more power. Over time, the turbo can get dirty and not run as efficiently.

There is a specific product designed to remedy this problem. Yanmar makes a product called Turbo Wash. This may seem a little odd, but it is water-based cleaner that you actually squirt into the air intake of your engine. It comes in a little tube and looks like spray cleaner or soapy water. You just snip off the end of the tube and squirt the contents into the turbo, followed with a little clean water. The cleaner gets the gunk off the turbo blades and allows it to work more efficiently. Yanmar recommends doing this every 200 hours or so, depending on engine usage and conditions.

Start by removing the air filter and housing, and running the engine under load at about 2,200 rpm. Squirt two shots of Turbo Wash into the air intake and let the engine run a minute or two. Speed up to 2,500 rpm and repeat, then speed up to 2,800 rpm and repeat again. Next you need to rinse. Slow down to 2,200 rpm and repeat the action above with clean water. Finally, let the engine run at 2,500 to 2,700 rpm for five to seven minutes to dry out. If your turbo is the culprit, you should notice an increase in power after the wash.

If this doesn’t solve your problem, you may have problems with your injection pump and you’ll need to enlist a qualified diesel mechanic.

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