Loss of RPM then Overheating 7.4L

[Alegria]

Hi all,

Just thought I would put this out there for some feedback. Overall I think I was just lucky on my Birthday.

Friday we were headed down to the boat to enjoy my birthday. We headed over, fueled up, and then got on our way. We were planning a short cruise out to the bay.

We were running at around 3200 rpm and I was monitoring the gauges, oil and temp looked fine. About 15 minutes in the port engine lost RPM and the boat started to veer to port. RPM's dropped down to around 2000. I throttled down and immediatly got the hi temp alarm as the port engine was up at the 220 mark.

Shut her down and opened the hatch. Saw coolant all over the place as the pressure release worked on the cooler. Left the hatch open to cool things down and headed back. Checked the strainer looked clear.

Back at the marine had a mechanic come down to look at her, they purged the coolant, and found the thermostat was not fully open and mis-seated a bit. Placed it back in place, replaced the coolant. Ran the boat for 45 mins no issues. I ran it Sunday for about 2 hours no issues, actually ran a bit cooler then it did prior to the incident. Oil pressure stayed constant the whole time prior and after incident.

So I am thinking I hit a tree branch that was partially submerged and that got stuck under the boat blocking the thru hull and causing the RPM to drop.

On Sunday as I was playing around in the water with the kids I checked on the props and shafts they looked OK and found a branch wedged in behind the trim tabs...

Any other mechanical items I should look at?

 

[fc3]

Nah. The 7.4 is pretty tough. Cast iron block and heads are durable. No girly aluminum. Check that none of the rubber exhaust components overheated and melted or burned from high exhaust temps. Otherwise, it should be OK.

 

[Alegria]

Thanks! I felt around 4" exhaust lines and they were firm. Just replaced them this season. Also replaced the port muffler. I never get the same water flow out of the port as I do from the Starboard muffler. It seems to be just a bit off. The temps looked better then before on the port engine.

We shall see this weekend. On to the next project as I was leaving the boat Sunday I noticed that the back rest on the aft bench seat was lifted up from the transom. Realized that every screw had now backed out and left it unsecured. Screws are still there but not bitting into the wood anymore.

I am betting the wood rotted around the screws and off it went. I will redrill an inch or so on either side for good wood and seal up the old holes. May use a beefer screw the ones Sea Ray used, while SS, were a bit small for the load I think.. Now getting to the three that are behind the transom shower will be a treat. Oh well part of the ownership experience as my wife puts it!!!!