Vovlo Penta D1-20 B overheating

[Whiteoil]

2007' Bavaria cruiser with a Volvo Penta D1-20 B, changed out a plugged exhaust elbow preventatively (water inlet on the elbow was full of iron). Cleaned out the holes in the heat exchanger, and flushed the coolant and replaced with yellow (had green stuff before) stuff as advised by vovlo mechanic.

Ran for hour idling without problems, temp came up to 90c (operating temp) and water flow off stern looked better.

Went to motor out the harbor and as soon as I upped the revs to 2100 the engine temp gauge jumped way up, went down and then up again. Fluctuating slowly up and down based on revs.

What could cause this? The thermostat? Checked coolant, looks a bit yellow/ green now but no clumping. Dunno how to flush it all out as now I'm told I should have kept using the green stuff.

Now I've no clue what to do or check :/

Any recommendations??

[Engine man]

Originally Posted by Whiteoil

2007' Bavaria cruiser with a Volvo Penta D1-20 B, changed out a plugged exhaust elbow preventatively (water inlet on the elbow was full of iron). Cleaned out the holes in the heat exchanger, and flushed the coolant and replaced with yellow (had green stuff before) stuff as advised by vovlo mechanic.

Ran for hour idling without problems, temp came up to 90c (operating temp) and water flow off stern looked better.

Went to motor out the harbor and as soon as I upped the revs to 2100 the engine temp gauge jumped way up, went down and then up again. Fluctuating slowly up and down based on revs.

What could cause this? The thermostat? Checked coolant, looks a bit yellow/ green now but no clumping. Dunno how to flush it all out as now I'm told I should have kept using the green stuff.

Now I've no clue what to do or check :/

Any recommendations??

Is there a domestic water heater plumbed to the engine? Is it located higher than, lower than, or same level as the engine? Is there a coolant recovery bottle plumbed to the engine? Is there a raw water strainer installed on the intake hose?

Side note - idling any diesel engine for 1 hour accelerates engine wear. You should idle your engine for no more than 5 minutes, then either shut it down [if not getting underway] or put a load on the engine to bring it to operating temp quickly. Joe