Low idle RPM at startup, then normal?

[George Kay]

Hello,

New member. Twin 6CTA8.3 450 diamonds on a 2001 Tiara 3800. Approx 1500 hours.

Purchased 2-3 months ago. Immediately updated the water pumps to SMX, pulled aftercoolers and hx exchangers, seemed the previous owner kept them clean. No maintenance records though, was just told “he kept them pristine, open checkbook etc.”

The RPMs via tach are different than when phototached but not too bad. The RPM on the tach shows lower.

Anyway!!! I digress.
I read that you can tell a lot about an engine on a cold startup. The only issue I’m having right now is that on a “cold” startup , weeks in between startups, 65 degree weather, the engines startup right away. BUT, the engines start up at a very low RPM ~500rpm. Then, when the engines warm up they creep back to ~650rpm.
This causes basically the engines to startup kinda like misfiring?? At the 500rpm, so I throttle up at the dock to about 750-800 until the engines warm up to about 100degrees. OR if my guests are late for fishing (most of the time, LOL) I just put it in gear and go. This lowers the RPMs more for about 5-10 seconds then Back to normal in gear.

Is this normal?? Sorry for the long question as my first question LOL. Thank you guys!!

Topic

[Tony Athens]

Cut and paste whre is says “suggested idle is 650 RPM”…………………………..One of us will be eating humble pie..

[Harry Karaoglanian]

Alternate user

Sorry, idk why my original post was under a different user. I must have logged in under my dads email.

[Harry Karaoglanian]

Follow ip

After starting, immediately bring the engines up 100-200 RPM to smooth them out

This^, if I’m up 100-200 rpm from the 500 at startup that makes me around 650-700rpm. Is it ok to shift into gear with the throttles up? I worry I might ruin the transmissions. I usually never shift while my throttles are not all the way backed off.

[Harry Karaoglanian]

Startup

Hey Tony. Thank you so much for the information.

Warming up engines at the dock- 9 times out of 10, no. I usually crank, untie the boat, And put into gear. But when I do this, especially right at startup, the RPMs are at ~500rpm. Then, after I’m done maneuvering my way out of the slip, I throttle up to about 750-800. As I make my way out the harbor, the engines warm up and when I back off completely from the throttle (still in gear) I am only then at the suggested 650idle.

Sounds ok? Sorry if it’s a really petty question.

[Tony Athens]

Are you attempting to warm up the engines at the dock? That is a 100% no-no

Raise the base idle RPM to something over 650-700 when the engine are warm–This engine rarely likes much below 700 when warm

After starting, immediately bring the engines up 100-200 RPM to smooth them out–Do your checks and get the boat out of the slip and at something above 700 to warm them up in gear

[donald roth]

Possibly air in fuel system?

[Author]

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