Volvo Penta V6-260-C-J overheating diagnosis - steady temp climb, raw water flow to heat exchanger inlet seems OK
Diacom - https://drive.google.com/file/d/1zvtvDllIaYzeMZ28uzKVNoeZ9hbRQcX8/view?usp=drive_link
Overheat condition - https://drive.google.com/file/d/1NynhiYQn4jv1GAIhyt3mpP8uliMWEqZW/view?usp=sharing
I’m diagnosing an overheating issue on a Volvo Penta V6-260-C-J and would appreciate a second opinion on where to focus next. With Diacom hooked up, ECT steadily climbs from about 150°F to 168-169°F over roughly 1.5 minutes of video / 2.6 minutes engine run time. RPM is basically idle, around 650-660 RPM. Oil pressure stays OK around 38-39 PSI. No MIL, buzzer, derate, or low rev limit is showing during that clip.
I also have a separate video of the actual overheat condition without Diacom hooked up. The tech shut the engine down early because temp was continuing to rise and we didn’t want to trip the sensor or cause damage.
Troubleshooting done so far:
- Checked raw-water flow directly after the impeller housing: flow looked OK. - Reconnected tube to the heat exchanger and checked flow into the heat exchanger: flow looked OK. - Opened the bottom of the heat exchanger housing and inspected up to the grate: no obvious obstruction before the grate. - Did not yet remove the heat exchanger assembly/tube stack because we didn’t have the correct tool/nut at the time. Current next step is to remove the heat exchanger assembly and inspect/clean the tube stack internally.
Remaining suspects I’m considering:
- Fouled/restricted heat exchanger tube stack - Thermostat stuck partially closed - Impeller still weak under load even though static flow looked OK - Raw-water pump cam plate / wear plate issue - Possibly fuel pump issue, because the tech noticed it sounded loud/angry, but he didn’t think that would directly cause this overheating issue
Question: given that flow from the impeller to the heat exchanger inlet appears OK, does the steady ECT climb point most strongly to internal heat exchanger restriction, thermostat, or raw-water pump performance under load? Anything else I should check before/while pulling the heat exchanger?