Yanmar 3 overheating

[rods]

Hi I have the Yanmar 3 on a 2006 35 SO which overheats at over 2500 RPM. All regularly serviced and flushed cooling system with the acid at local dealers. Checked core on heat exchanger and it’s the defective 38 hole one. Can any one advise if Yanmar will still replace this free of charge if I pay for the Labour. I am being told I need a new core plus two new ends and seals

[Charlie-Bravo]

I would doubt that a free tube nest will be forth coming ....... but wish you luck with that.
The slightly under tubed nest will work but its tolerance for muck is less. Rather than pouring in acids to flush, pull the tube nest and clean it well, and if it is otherwise in good condition you should be fine unless going at 3000 rpm all afternoon, I find 2000-2500 gives a smooth 5 to 6 knots in average conditions which seems enough for me. 
A new heat exchanger is about £1200-1400 GBP plus gaskets and fitting ....... one day I will treat ours to one, but not whilst the aged one can still perform.
CB

[rods]

Thank you for all of the information. I think I may change the core myself now boat is out of the water. Local marine workshop have told me I only need the core and no need to change to ends on the heat exchanger. Can anyone please confirm if this is the case.

[Charlie-Bravo]

You could well be fine with just a new tube bundle, ends only really need replacing if they have been leaking and have corroded a lot ,  best to have new gaskets to hand though , and they may or may not come with the tubes.
Out of interest, was the tube bundle outrageously priced?
CB

[rods]

Hi there I have been quoted £281 plus vat