8.1 overheated and aborted trip (for now)

8.1 overheated - aborted trip. I broke down for the first time ever yesterday and came back to port on one engine because my Stb engine overheated.

I was about 25 miles into a 70 mile trip and cruising along nicely. All of a sudden, the RPM’s dropped and my exhaust hose temp and engine alarms went off. I stopped, opened the hatch and coolant was spraying out of the coolant recovery tank vent hole. The temp shot up to 250 after running at 175/180.

My first thought was RWP. No big deal, I have a spare pump and impeller onboard but the raw water flow was fine. I popped the cover off of the RWP just to make sure all of the vanes were there. I thought (wishful thinking) that maybe a bag got caught on the intake and caused the overheat but after cooling down and running again, the temp started going up right away. I replaced the thermostat and circulating pump when I went through both engines two years ago. The heat exchanger was rodded out at the same time.

This was a pretty quick spike in temperature so I feel like something failed. It was running at 175/180 minutes before this happened. The thermostat seems unlikely since temps were good already run for over an hour. I only replaced it because I had the engine home and was replacing the short hose proactively. Ironically, I didn’t do the same on the port engine. I have about 70 hours on the new thermo and circulating pump. (AC Delco).

The circulating pump seems like a suspect only because of how quickly the temp jumped. I removed the belt and it feels fine when I rotate it. Has anyone ever had the shaft break internally? Meaning the bearings are fine but the impeller isn’t moving any coolant. What’s the easiest way to rule that in or out?

Coolant level was good in the h/e, I checked that yesterday after it cooled down.

What else should I be checking? The oil is clean and at the right level.

Thanks
Bob

I think due to the quick spike that you have a blockage somewhere. Pull all the hoses and check each one.

Yes, I will check that today. One other detail which someone else pointed out to me. I have a separate exhaust hose temp alarm and that went off along with the temp light on the crusader gauge cluster. I think that should have also set off the engine buzzer for temp (light was on) but I don’t remember if I was hearing two alarms at the same time.

If I had good raw water flow but the engine was overheating, would you expect the exhaust hoses to stay within a relatively normal temp, meaning not set off the alarm? Now I’m wondering if I had good raw water flow at idle but NOT at higher RPM’s again using the exhaust alarm as a clue.

Bob

Here’s an update, it WAS the impeller after all and a first for me. It was bugging me that all things pointed to the closed side of the system and with a new circulating pump and thermostat that had run for over a year, it just didn’t seem like either would be the smoking gun. But, I had raw water flow and this event happened fast. It wasn’t a case of, “it’s been running a little hotter than normal lately” scenarios.

Once I dug in, I decided to check the impeller again and noticed tiny rubber bits on the cover. In the heat of battle, I was only checking to make sure all the
vanes were there. I pulled it out and the center bushing was separated from the impeller rubber. So, it must have grabbed just enough so I had flow at idle but nothing as I powered up.

Exhaust temp alarm saved the day again. I am changing these every year like clockwork. This is the second time I tried to stretch another season and it’s burned me both times.

Bob

bob: bummer on the overheat. Glad you got it fixed.

FWIW, it could have well been a bag on the pickup scoop...depending on how well the impeller was made and how long it ran dry, it could have cause the hub joint to 'soften up...

Mark, yeah you might be correct about that. Somewhat related, I've been running these P110 pumps which don't have a great reputation buy they are an easy rebuild. The same pump which had the impeller failure is leaking and bearing are shot.

I'll create a separate post on that topic.