Over heating port engine

[Jay Fusaro]

Hi all - our new to us port engine ('98 445 with Cummins 6CTA 8.3L Diamond Series, 300 hrs) is overheating when it hits 2,000 rpm. It runs all day 1800 or below but once it hits 2k the temp climbs. Once you back off the throttles and go below 2,000 the temp drops down to 160-180. The prior owner did acknowledge that the impeller broke apart and both he and my mechanic have fished out pieces of it. (we did buy the boat knowing this issues and asked for and received a decent price concession as a result) There is the chance other pieces are lodged someplace and we're looking. Any other thoughts on a possible cause that we're not thinking about? Any and all suggestions are welcome.
Thanks in advance,
Jay

[km1125]

yea, definitely should tear some stuff apart to see if you can find all the pieces. If that engine has an intercooler (or aftercooler) you might want to have that popped open to see if the passages in there are clean too.

Do you know if the current impeller is still in good shape? I've seen new ones not last for very long, so it might be a simple fix.

[Tireless]

It almost seems like a flow issue. Engines are close cooled, however, sea water not able to keep the engines cool at higher RPMs. Sounds like you may have already figured out what the issue is. May have to start removing some things to check for the blockage.

Make sure you coolant levels are good, as well.

Just my thoughts, however, I guess there are other things that could cause the problem.

Greg

[Jay Fusaro]

QR_BBPOST yea, definitely should tear some stuff apart to see if you can find all the pieces. If that engine has an intercooler (or aftercooler) you might want to have that popped open to see if the passages in there are clean too.

Do you know if the current impeller is still in good shape? I've seen new ones not last for very long, so it might be a simple fix.

Thank you - yes it does have an aftercooler - as you can imagine it's a PIA to take the top off because the access to the engines is by lifting up the stairs from the dinette rather than the salon floor If we run out of places to look I see a new hatch in my future.

[Jay Fusaro]

QR_BBPOST It almost seems like a flow issue. Engines are close cooled, however, sea water not able to keep the engines cool at higher RPMs. Sounds like you may have already figured out what the issue is. May have to start removing some things to check for the blockage.

Make sure you coolant levels are good, as well.

Just my thoughts, however, I guess there are other things that could cause the problem.

Greg

Thanks Greg - that's what we're thinking (flow issue). Coolant level is good and the new impeller has been inspected. We really believe we missed a piece of the old impeller - I'm just trying to be sure that we're not missing another possibility.

[bud37]

Have your cooling system pressure tested if you can after looking for all the bits.......there can be all sorts in the heat exchanger tubes. (scale etc )

[Jay Fusaro]

QR_BBPOST Have your cooling system pressure tested if you can after looking for all the bits.......there can be all sorts in the heat exchanger tubes. (scale etc )

Good idea! I didn't think of that. Thank you.

[Phrancus]

When taking things apart, flush parts with a hose in both directions and check where it comes out. Easy if the boat is on land but in the water try to have an exit hose flush into a bucket/strainer. The first so you can dislodge a piece that is stuck in the usual direction of the flow and the latter to make sure that you know what did come out.

I've had this with my engines (with sterndrives) and you just keep worrying if you flush, solve the issue but are not sure you got it all out. In fact, the problem reoccurred some time later after a piece that was moved by the flushing relocated itself. Luckily it came out right at the first hose I disconnected but it was not a good experience.

It's a big design failure that a desintegrating impeller can move upflow in big enough pieces to block a heat exchanger.

[km1125]

I found that using a shop vac to find the pieces is easier than flushing. It's hard to get the volume high enough with flushing. You can also adapt a smaller hose to the shopvac that fits inside the water hoses, so it extends the shopvac suction all the way to the other end of a hose. Use something like the flexible bilge pump hoses and tape it to the shopvac hose, then slide the bilge pump hose into the water hose.

Had a friend just do that on his genset. The impeller was easy to change but the old one was missing pieces. It would have been quite a job to get down to where the heat exchanger was on the generator to get the hoses off there, but he could slide the bilge pump hose into the water hose starting at the water pump, and slide it all the way down to the heat exchanger and got all the missing pieces out.

[bud37]

This really could just be a case of the heat exchanger being scaled up. The impeller bits restrict flow then the temps go up causing scale to form.....you clean out the bits but the scale is now there impeding heat transfer, much like a bad rad on a vehicle overheating when put under stress.....we will see though....still need to cross some things off the list.