5.0 Dieseling after 30 min run

[Sherminator]

We had out boat our yesterday just north of Bass Camp on the MIssissippi, we were running at around 4000 rpms and we came to a stop at the dam and i let it idle for a minute and then shut the key off, it caughed and sputtered for about 20 seconds then finally shut down, it restarted just fine but i didnt run it over 4000 rpms again for the rest of the evening. What could have caused this? too low of grade of fuel? i fiilled with 87, maybe i need 91-93?
Thanks

 

[Fishermark]

Re: 5.0 Dieseling after 30 min run

It is a common problem, and Mercruiser has even put out a tech bulletin on this issue I believe, (I don't know if you have a Mercruiser or not but this might apply). Basically they suggest letting it idle for a while before shutting down after prolonged use. I believe it has to do with the heat build up, etc. You can try the higher octane fuel, that would probably help, but I don't think it is necessary. Just letting it settle for a bit longer before shutting down. You might also want to make sure it is not idled up too high.

 

[180shabah]

Re: 5.0 Dieseling after 30 min run

didn't let it idle long enough for the combustion chamber to cool down.

 

[Sherminator]

Re: 5.0 Dieseling after 30 min run

Thats kinda where i was leaning towards too.. i have heard about gas car engines being run hard and turned off, that and a combination of low octane fuel were culprits. Just wanted to make sure!
thanks!

 

[John_S]

Re: 5.0 Dieseling after 30 min run

It may be bad fuel or not enough waiting before shutoff, but I'd check the base timing and idle speed, especially if wasn't done as part of your spring tune-up.

 

[tommays]

Re: 5.0 Dieseling after 30 min run

Running your bilge blower before you get ready to slow down can pull in a lot of cool air which can also be a big help


Many engine boxs are much hotter than the spec due to poor design that favors style over function


Tommays