400DB not getting enough power

[mjmason1]

I am hoping Frank Webster chimes in here.
I have 20 year old 3116ta 350hp diesels. The specs say I should get 2800rpm's. I did two years ago when I bought the boat. It also topped out around 25kts.
Now I am only getting 2600 rpm and topping out at 20kts. I cleaned out my Racor's and changed the secondary filters. There was a huge chunk of algae stuck in the vanes of one of the Racor's. I scraped my bottom and cleaned all my running gear. The boat runs great, it just doesn't get the speed or rpm's.
What do I check next?
We are taking a long trip starting this weekend. Is it ok to run wide open and do 20kts for a long period of time?

 

[CliffA]

I am hoping Frank Webster chimes in here.

well now that is a little insulting to members that have knowledge about diesel engines.....if you believe Frank is the only one that can help you should just send him a private message....Frank has a wealth of knowledge but I bet he will agree others on the forum can also offer help with questions about diesel engines....

cliff

 

[ZZ13]

Mike, any chance your tabs are set or stuck on the full down position?


Sent from my iPhone using Tapatalk

 

[fwebster]

I am thinking that the bottom and running gear isn't clean enough or that the load in the boat has changed. Here is my reasoning:

If your boat once hit 2800 rpm, then the props are correct for the loading at that time. However, what has happened to the weight on the boat since then? Didn't you tell me you and Pam were now live aboards?

The 400DB always has been very sensitive to loading whether it be from weight on board or resistance from slime and hard growth. Scraping the bottom with a blade removes hard growth like worms and barnacles, but there may still be some slime (saltwater algae) on the running surfaces. A 3M scrub pad is about the only way to remove that without a haul out and pressure wash. Slime is horrible in Florida in the late summer and it can easily add up to a 200 rpm loss at WOT.

A diesel engine will suck air into a spot where fuel won't leak out of so fuel starvation usually presents itself with the engine gulping a slug of air then stopping dead untile the system is purged and fuel flow restored, however, Sea Ray uses swedged end fuel lines on their boats so air almost can't enter the system until you open it somewhere. A fuel delivery problem will show up with the engines gradually slowing down to below idle speed and dying because there is no fuel passed on to the engine. If your problem was the junk in the Racor, then the engine would have continued to slow down, not stabilize at 2600 RPM. The other eliminating factor is the fact apparently, you have the 2600 rpm problem with both engines. If it were a clogged filter, then it would affect the engine with the clogged filter, not both engines. You may have dirty fuel tanks and your filters may have needed service, but I don't think that is the issue you are addressing here.

As far as running Cat diesels at WOT goes, these are pleasure or recreational rated engines and Cat says you can run them at 2800 rpm up to 8% of the time. However, your engines are overloaded if you can only get 2600rpm at WOT. To be safe, figure your adjusted cruise speed like this: 2600 wot rpm/2800 wot rpm X 2400rpm cruise = 2230 adjusted cruise rpms. But, I would not run the engines at WOT in an overloaded condition.

 

[fwebster]

well now that is a little insulting to members that have knowledge about diesel engines.....if you believe Frank is the only one that can help you should just send him a private message....Frank has a wealth of knowledge but I bet he will agree others on the forum can also offer help with questions about diesel engines....

cliff

You shouldn't take Mike's comment that way. He just said he hoped I saw his question and responded. I certainly don't have all the answers and since Mike has both my email address and cell phone number, I feel certain he would have called or written a note had he felt he just wanted one opinion.

 

[CliffA]

You shouldn't take Mike's comment that way. He just said he hoped I saw his question and responded. I certainly don't have all the answers and since Mike has both my email address and cell phone number, I feel certain he would have called or written a note had he felt he just wanted one opinion.

you are probably right Frank....sometimes the intent of a message gets lost or misunderstood when interpreting the written word.....

cliff

 

[mjmason1]

well now that is a little insulting to members that have knowledge about diesel engines.....if you believe Frank is the only one that can help you should just send him a private message....Frank has a wealth of knowledge but I bet he will agree others on the forum can also offer help with questions about diesel engines....

cliff

Wow. I didn't expect this. I posted it, instead of a private message, just in case someone else has or had the same problem. After all, that is what the forum is for. It's good to share. So, don't be insulted.

 

[CliffA]

Wow. I didn't expect this. I posted it, instead of a private message, just in case someone else has or had the same problem. After all, that is what the forum is for. It's good to share. So, don't be insulted.

I'm not insulted Mike.....I don't know anything about diesel engines so i could not help you with your question anyway.....when I first read your post it sounded like you are putting more faith in a reply that Frank would make than replies from others.....I am sure that is not what you intended but I did read it that way and others may have also....there are lots of very knowledgeable folks on this forum that go out of their way to help others when they have questions....if members are made to feel their posts are not as important as others they may stop making the effort to help and that would be a very bad thing....as you said that is the primary reason for forums such as this....a sharing of information....

i'll get off my soap box now and stop making something out of nothing.....

cliff

 

[carterchapman]

well now that is a little insulting to members that have knowledge about diesel engines.....if you believe Frank is the only one that can help you should just send him a private message....Frank has a wealth of knowledge but I bet he will agree others on the forum can also offer help with questions about diesel engines....

cliff

I don't know Cliff...I have the same problem with my 3126 diesels, and FrankW has always given me perfect advice on every subject - esp pertaining to 3116/3126 engines. I, too, would reach out to him on this site - as others may have had the same problem.

Who is your "go to guy" for "6.2 strokers"?

 

[my3sons]

What do I check next?

High Idle RPM with the engines at operating temp and gears in neutral.
If not ok, most likely fuel delivery issues or adjustments may be needed.
Post results to help narrow things down. Good luck

 

[CliffA]

I don't know Cliff...I have the same problem with my 3126 diesels, and FrankW has always given me perfect advice on every subject - esp pertaining to 3116/3126 engines. I, too, would reach out to him on this site - as others may have had the same problem.

Who is your "go to guy" for "6.2 strokers"?

Carter, I would absolutely agree that if I had diesels i would want Frank to be involved....my only 'slight' issue was the way the quesion was posted....it seemed like Mike was going to value Frank's opinion over everyone else.....I know that is not what he meant....it was just the way I read and interpreted it.....

I don't really have a 'go to' person for my engines or for any other part of my boat.....I respect the opinions of everyone that takes time to read my post and reply...I now enough about things to be able to sort through the replies and make a decision on the ones I think have merit in that particular instance.....

I apologize for dragging this out....I read the post at a point in the day where I was not happy with things at work so it just hit me a little wrong....so my frame of mind was not the best...this was something that I should have just kept quiet about....

cliff