Opti 200, brief overheating problem...

[Paul E]

The Optimax 200 on the Boston Whaler I use has just started overheating, but only for a brief period before all is fine again.

It's just after you fire it up, and run it for a few minutes at idle or low revs in the harbour. The temp gauge rises quickly (to over 150-160F) then safe-mode kicks in, but only for a about 20 seconds before the temp falls very quickly down to 115F then settles at it's normal temp of 120-130.

I'm thinking it's a sticking thermostat? The water pressure is fine and the impeller was replaced at the start of the season. At high revs, or even at low revs after the initial overheat it's all fine

Any help appreciated, I take it the stat is a straightforward swap?

[Mollers]

I'd put my money on a sticky stat. For £20ish, you might aswell bung a new one in and see what happens.

[Paul E]

Yeah that's what all the symptoms point to, I'll give it a go. Cheers

[Searider]

If it's the same as a 150 opti there'll be two stats - one at the top of each cylinder head.

Might need to get the fuel / air rails off to access though.

[uncle al]

you do not have to take of the fuel rails it is an easy job

[HUMBER P4VWL]

We've just had exactly same problem on 175 opti. Sticking stat.