Any Perkins Mechanic's out there

On my previous boat. It had twin 453 N Detroit. When I had them rebuilt the mechanic told me after cruising for 3 or 4 hours I needed to put it wide open for 3 to 4 minutes to blow it out and then go back to cruising speed for fuel economy. Did that all the way from Keys to Pensacola and it ran great. Question is. Should I run the little Perkins 4.108 the same way.

Your little Perkins is old school diesel she would have served you and others very well till now just plodding along so why start playing with nature when something ain't broke

Our boat was originally powered by a Perkins 4-154 (58 hp). Your engine is around 48 hp as I recall. We re powered with a Perkins 4-236 (85 hp) This to establish that over the years of owning this boat and prior boat with 85 Hercules, there was never a time that I ran or run my engine wide open for any period of time. All of these engines ran or run at about max torque (load) therefore are not running 'light'. There is a consistant load on the engine.

Now, as a counter situation, were we to troll for salmon say, at 500-600 RPM for hours as many commercial fishing boats as well as pleasure boaters, the initial increase in speed following the ending of the days fishing to operating RPM, the expectation the engine has loaded up is true. However, I'd say it rare that a operator takes the RPM beyond his normal operating RPM range specifically to burn off the build up. It may be happening just not aware of discussing as a subject with operators.

The condition of the built up exaust smoke IS OFTEN a subject as the various hues of exaust can be indicators of engine condition. Black smoke,(Over fuel or pooling fuel unless you are turbo, that can be a expectation dumping excess fuel) Blue smoke( Ring wear, valve guide wear), White(Cooling system leak) smoke all are symbolic of potential clue to what is happening.
It would be suspect that you running your engine as the mechanic suggest, would yield one of these . As a habit? What ever turns your crank. If you are comfortable doing the occasional run up continue.

These comments are based on my personal observations and discussions. Open to counter comments to make the thread interesting

Al-Ketchikan

We have the big brother of the Perkins 4's, twin 6.354's. And like previous posters stated, while fishing, they do load up a bit when you're idling for extended periods. But it would be seldom that we don't bring the engines up to full cruise speed, 2400 rpm for us, for an extended period of time returning to the marina and before shutting them down. This pretty well cleans them out.

Unlike an engine in a land vehicle, Perkins engines in boats are supposed to be propped to not exceed the manufactures maximum operating RPM at full throttle, 2800 rpm for us. Running them up to max. Intermittent operating speed for a reasonable period of time, does not damage the engines, (according to the Perkins manual I think it's 1 hour). You're burning more fuel, but not going much faster.

I don't know that running them 400 rpm faster for a few minutes really does much more to clean them out. I do run mine up occasionally for maybe 20 minutes, just to see if they heat up. That's often the first indication that you have a pump/impeller issue or cooling system blockage.

But you aren't hurting them either way. So if it makes you feel good, DO IT !

PS: There is a Perkins Operation Manual in the Library that covers your engines. If you don't have it, it's there to download.

Thanks guys.

Edelweiss,
Your engine is supposed to turn a MINIMUM of 2800 rpm in gear WOT, not maximum.

kapnd said:

Edelweiss,
Your engine is supposed to turn a MINIMUM of 2800 rpm in gear WOT, not maximum.

Click to expand...

I understand what you're saying and I think we're saying the same thing, it's semantics.

However for clarity, the Perkins Operator and Shop Manuals only refer to "Maximum Intermittent Speed" and "Maximum Continuous Speed."

Page 33 and 34 Perkins Operation Manual: