2002 cobalt 262 Volvo penta running 190 degrees

[Srush12]

Ok so here is my issue here. I have a 2002 cobalt 262 with Volvo 8.1 liter 502 I believe. While taking it out for the first time this year the impeller failed and boat got hot. Real hot. It melted the exhaust boots on the engine and burn the paint off exhaust pipes. I had my mechanic replace all parts of the cooling system. Took it back out and it ran about 180-185 on plane but when idle it got hot again and it shut it down. Took it back and he said prolly a blockage. He back flushed it all. Again and I took it back out and then it would climb to about 190 and stay there no matter on plane or idling. So I took it back to him and he took all hoses off and hooked it up to hose to make sure water is pumping and it was. So all aspects of cooling system are working however boat still gets up to 190 degrees when it should be and used to run 170-175. Next he is going to try a compression test but doesn’t think it’s in the engine because engine runs fine doesn’t miss a beat it just runs too hot all the time. Looking for suggestions on why this could be. Thanks

 

[Horigan]

If this is a closed cooling system with a heat exchanger, clean the raw water side of the changer. This involves taking off the end caps and running a rod down all the passages, then running a 50% solution of hydrochloric acid for a few minutes through just the heat exchanger raw water side. I used a bucket and spare bilge pump to do this. Google cleaning marine heat exchangers. I had a similar issue and after cleaning I have very stable temps at 160F.

 

[muc]

Freshwater or seawater cooling? Makes a big difference on what next. And a serial number always helps.

Did he replace the riser gaskets?

And Welcome to the forum.

 

[Scott Danforth]

fitting where the hose connects to the outdrive is also a place to look

 

[Srush12]

This is a freshwater cooling system. And I do not have serial number at the moment as the boat is in the shop. But I appreciate the welcome and the advice, I will make sure I try these things. And he has not replaced riser gaskets yet I don’t believe. Was going to do a compression test today and then dive into possible motor issues.

 

[muc]

We had a lot of issues with riser gaskets after bad overheats, especially if it was bad enough to burn the exhaust tubes. So I highly recommend that you have the newest version installed.

Replace the thermostat if that hasn’t been done yet, they can shift their temperature after a overheating.

While they are checking the heat exchanger, ask them to pay close attention to the gaskets on each end. They can deform and block flow or allow the water to bypass one of the passes.

 

[Horigan]

Those heat exchanger end cap gaskets are cheap. I'd replace if you open it up.

Agree with Scott to check the hose fitting. Easy to check with drive trimmed up, water on at muffs, with engine off.

 

[Srush12]

I appreciate your input guys. I will make sure these things get Checked! Hopefully we have a solution because this is getting frustrating

 

[QBhoy]

Hi
im likely going to get challenged on this but if you have an air lock in your internal circ pump (the main big centre driven one) but still your raw sea water driven pump is pumping water...you’ll still get some water out the rear but not a true reflection of the cooling at all.
Yours will obviously have a belt driven raw water pump on the front of the engine, drawing water from the drive...but also a larger circ pump in the centre too. This can get air locked and cause overheating. Not always obvious due to the fact that some water will end up coming out the rear just from the raw water primary pump.