Volvo D4 260 overheat issue??

[GusC@AK]

Hi all. I have twin D4 260s with around 700-800 hours. Today my port engine threw an audible alarm and warning light (the triangle icon for general warning). Of course I killed power to the engine immediately, and inadvertently erased the fault code in the EVC. At the time of the alarm the temp gauge red normal (185F/85C) but I had coolant overflow boiling from the expansion hose.
Not knowing the code, I assumed a shredded impeller. So I checked. It was fine, but I replaced it anyway. Next, I checked the sea strainer. Nothing abnormal. Heat exchangers are relatively new and I fresh-water flush them regularly. I then ran the engine in neutral at 1500 RPM until it reached 185/85 degrees. I was unable to replicate the fault.
Any thoughts? Thermostat, temp sensor? Etc.?
Thanks!

 

[Momac]

Could be debris on the intake which fell off when you stopped the engine.

 

[GusC@AK]

Could be debris on the intake which fell off when you stopped the engine.

I like this theory! I will let you know ASAP when I take her out again.

 

[GrahamHR]

The plastic piece on the outdrive, looks like a small thermostat housing from the 1970s that connects the water supply from the inlet to the hose to the water pump. Earlier ones known to crack. Later ones modified with reinforcing ribs.

On our D4-300, the hose fell off that part ( not fitted correctly by a VP dealer during a warranty claim),. Result; no overheating when at slow speeds. Once on the plane, no water supply as the hose end was out of the water.

 

[ari]

You don't mention one vital part of information, did the alarm go off under high load or at low speed? There is a known issue with heat exchangers 'furring up' over time and restricting water flow so if it happened at WOT, it's quite possibly that (and it won't happen at low speed as it doesn't stop the water, only restricts it, so at low speed there's enough to keep the temperature down).

However if the alarm when off at low speed then it isn't that because you'd have been aware of it previously as it would have overheated at higher speeds.

Also worth checking the raw water 'basket', I've had that start to clog with weed and debris causing an issue. Very easy fix though.