Need advice on issues before purchasing a boat

LET ME BREAK IT DOWN FOR YOU:
Half the boat works & half doesn't.
You decide how much to want to spend fixing sh!t on a 20 year old boat!
That's all I want to say.

Not unusual to find issues like these on a 20 year old used boat.

lights and horn… minor cheap things.

air con for the flybridge, “doesn’t work” is vague and it could be a variety of causes ranging from cheap to real expensive. For instance if it doenst work because the breaker trips when the compressor tries to start, it may need a new compressor / condenser…. $2-4k. Or it could just be tripping on high pressure due to poor flow and just need a descaling.

Seized stern thruster… likely needs a new gear box and possibly motor. Not needed on a twin diesel, get a price adjustment for around $3k from seller and sont fix it.

overheating …. Likely needs a new impeller or raw water pump. Or could be more serious. Have seller repair before closing and do another sea trial

not unusual for temperatures to creep up at WOT.

Everything Pascal said is spot on. AC may need new compressor or something more simple. Stern thruster, just get a price reduction to cover a rebuild.

You did not say what kind of engines they were. I would absolutely have an engine surveyor on your team. My experience is they always pay for themselves. What kind of diesels? Maybe they need to have heat exchangers rebuilt or gear coolers? How were the engine oil samples, standard practice for an engine surveyor.

If all the fundamentals on the boat like any coring or below water running gear and bottom paint are good, thats important.

Did the engines make WOT recommended RPMs?

Strongly recommend you get bids for all repairs and factor that in to a price reduction. Would probably add 20% on top of bids. I almost always want a price reduction to cover repairs vs seller having items fixed. You want to go with someone you have faith in that will make repairs correctly

I agree with the above about getting a few reliable quotes to set your price reduction. You need to gauge the quality and state of the interior, wood, carpets etc. to judge future investments. Same with bottom condition, running gear etc. Are the electronics all operational and have they been replaced on a 20 year old boat.

Regarding the engines, what is their history? Do they have their 1000 hr services complete? Did they reach WOT RPMs? A temp creep at WOT is often an indication of a cooling system in need of service. Aftercoolers, heat exchanges and gear cooler service can be $20 or 30K on a boat like that. Most of these are addressed at a 1000 hr service, has that been done? A good engine survey will answer these questions.

You need to find a great VP tech.
Make him your best friend.
You are going to make him rich.
You are going to need to borrow some money back from time to time.

Folk gripe about the cost of keeping old Detroits up.
VP parts will suddenly put in the poor section of your hospitals cardiac ward.

I worked with a fellow in St Pete who spent $15,000 cleaning heat exchangers on a pair of D12's.

I cleaned all the heat exchangers on my Yanmar 6LP using acid that circulated for 2 hours in the system. Quick, painless and “only” $500 to the mobile service tech.
Any reason the same technique doesn’t work on D12s?

Yes

Keeping to a short line;
They are old D12s..

Brother incoming just replaced his HE case because of corrosion.
The last one in the country. I think one was still in Canada. That's EOL from VP.
When I visited his boat just before, those newer TAMD's looked brand new on the outside.

Like MTU, VP special parts and super special prices will cause heart failure.
OH, 6 - 8 months later, some VP customers are still waiting for new ECMs on even newer models.

It's going to be up to you to determine what the value of the boat is in comparison to what else is out there that's comparable. With that said, you should have a minimum of about $30K available to spend on the stuff that you are going to discover after owning the boat. You may not have to spend it, but if you don't go into it with that mind set, you are going to be disappointed. It can also get much worse than $30K. The 6 cylinder Cats in my boat were rebuilt at the tune of $65K each prior to my purchase. I don't know Volvos, but have heard parts are on the high end for diesels. Availabilty is also something to check out. Nothing worse than waiting months to get parts.