[kahunamax]

Hey Guys,
Im struggling to fix a lingering problem getting worse.  I have a 1988 Tiara with twin Crusader 270 engines.  The starboard engine overheats when I go slow.  Its definitely getting worse too.   I checked sea strainer, replaced impeller, replaced thermostat and still not resolved.  Brand new heat exchangers were installed in 2019 and there is no coolant leaking.  Is there any other things I can check before I start stalking a boat mechanic.    Thank you!

[MC1600]

A slow overheat will always make me look to HEX and any other cooler. It’s no unheard of to need to clean them again after three years (depending on where you are). I might start with a Barnacle Buster flush first and see where that leaves you, but start preparing to pull stuff none the less.

[Misdirection]

A heat gun is your friend here. It will help you locate possible (aka hotter) areas to inspect further.

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[RMS]

How old are the exhaust elbows and risers? Crusader OEM parts should have the date code cast on the part.
Elbows and risers are raw water cooled and need replacement every five to ten years depending on how salty your raw water is. Have you tried backflushing the raw water side? Have the fluid coolers been changed or acid washed? Years ago I had a small piece of cellophane wrap clog the fluid (oil or tranny?) cooler on a 270 Crusader. As the fluid cooler was the first place raw water flowed after the pump, everything downstream was running hot. And get an IR temp gun as previously suggested. Bob