Perkins4108 funny idle at temp

[mainstreetmark]

After I let my Perkins 4108 idle for, say, 10 minutes, and it's up to temp, every so often there's a bit of a surge in idle, where it just revs for half a second and drops back to normal.

So, is that normal?

(I've replaced all the fuel lines, fuel-water separator, fuel filters, etc, so can't think of what's left to check in the fuel system)

A mechanic friend thinks water may be leaking into the combustion chamber, and the idle surge i hear is the engine compensating for steam. Say it ain't so?

 

[Stu Jackson]

It ain't so.

You asked for it.

The worst thing you can do is let the engine sit there and idle. Get the boat ready, then start the engine and LEAVE, and put a load on the engine. Idling is doing you NO good.

 

[larryw]

A ten minute idle won't warm up your engine, neither will a 30 minute idle. You have to get a load on it and run it for fifteen minutes at load, at cruising RPM. Every time you take the boat out, run the engine hard for ten or fifteen minutes. It will do wonders for it, and put some MMO in the fuel to the proper ratio.

 

[sailaway78]

Same situation

I can do the same thing with a 3GM Yanmar, and the explanation was so very simple, after that little light in my brain finally came on. The idle differences were the alternator pulling a load, whenever the fridge kicked on. Same when it went off. I have a 70 amp alternator which is small by the standards of many boats. I can assure you that if idling, an alternator will pull enough of a load to be noticable in engine sound.

 

[zeehag]

if the 4-108 is warming to temp in 10 min there is a problem--gooood luck!!! by saying isnt so just prolongs inevitable and makes repairs more expensive and complex!!!!

 

[RAD]

I have to agree with Zeehag and others cause my Westerbeke 30 (4-99) which is the little sister to the 108 takes forever to temp up and then only when there's load on it at the dock it never gets hot enough, you might have a cooling system issue going on