Overheat hell. 2006 Volvo 5.7 i/o dp-s

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T

TRUE BLUE

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I have been fighting an overheat issue with this engine for two years. It's closed cooling, I/O dp-s drive. I've worked on it myself and with a Volvo certified mechanic. The risers are two years old and rechecked. The raw water pump replaced. The thermostat checked. The outdrive pulled, gaskets and one hose replaced. Last year it would overheat even at low rpm's. After the work performed now it does not overheat at the mooring, even running it at 2000 rpm. What's happening now is running a couple of miles at 3000rpm, it overheats severely and will not cool down even running at limp speed. When it cools all the way down and not moving at speed it runs fine. I'm at a loss here and really could use some help. Could it be a computer issue, maybe retarding the spark?
 
FWIW, I have a 5.7 inboard and just did cooling system work. My mechanic who's a whiz with Mercruisers pulled a vacuum with some fancy jig to fill the cooling system with new coolant. He said without that tool there would be lots of air in the system that's really difficult to get out and it would over-heat. Is this how yours was re-filled? If not, it might be worth a shot. good luck.
 
Mechanic put in a new raw water pump, checked the thermostat visually, said the codes would not help in this situation. Second mechanic said he thought a t-stat problem was unlikely.
 
Something I didn't mention. Launched the boat couple of days ago. Went from the yard to my mooring, about four miles, various speeds, mostly lower rpm's. One stretch I had it about 2500 rpms. All OK until the mooring. I left it idling while I hooked the boat up. When I got back to the wheel, the temp gauge was over 200. When I started it later, it ran OK. That's when I took it out for a fast run and had to get towed back.
 
I'm no I/O wiz, but from your descriptions of how she is overheating, I would suspect an airlock.
If the coolant in my collector car is not 'burped' properly, she can have the same issue. (1992 LT1)
Talk to your mechanic and suggest what TWOBOATER suggested with the re-fill tool and see if Volvo has something similar.

Not sure about that motor, but in the automotive world, if a thermostat fails, it generally does so in the open position.
You might also ask your mechanic about that as well.
 
Another thought, did impeller come out in one piece? If it (or an older one) was in pieces it could be plugging something up. You might pull the heat exchanger end caps and see if there's any debris in there.

Pull the intake hose and make sure you have good raw water flow.
 
Had a similar issue with my volvo diesel. Ran across the channel to Catalina (about a 30 mile run) at 3500 rpm with normal temps. When I arrived at the island and was idling waiting for a mooring assignment, temp gauge slowly rose til it maxxed out and alarm went off. Checked the raw water pump and it was cool, exhaust riser was only slightly warm, coolant overflow tank was half way point between min and max marks. Let the engine cool. Came home the next day. Temps fine all the way home until I get to the 5 mph zone coming back to the launch ramp. Same story. Temp slowly pegs to the max position. Took the boat to the mechanic. The only thing I did was add about 1 cup of coolant to bring the level in the overflow tank to the max line. Mechanic had the boat for 2 days but couldn't duplicate the issue. I put the boat back in the water and ran it hard for 12 miles and then back down to idle speed and couldn't duplicate it either. I'm stumped. Hard to imagine that adding a cup of coolant to the overflow could have made the difference....
 
Well, I quit gabbing and went to work. Two days with a Volvo certified mechanic last year failed to find the problem, so I figured if you need a hand, look to the end of your arm. To start, I hooked up a legnth of hose on the outlet of the raw water pump , with a clear section, to check volume. It pushed water over the end of the hose 1" when held at the height of the flame arrestor. However, I noticed lots of air in the water. So then I hooked up a section of clear hose in the intake of the pump. Still had the air. I then hooked up a 12v air pump to the intake line, figuring the head of water in the drive would give me a few pounds pressure. The was no pressure at all. Looked at the drive and found all the air coming out the very top of the drive. That seems to indicate failure of the hose or thru hull fitting in that area. I then clamped off the hose between the oil cooler and transom to pressurize the line itself, finding a small leak in the oil cooler. So, looks like a haul out for me and looking for a good mechanic (hard to find). It seems the mechanic I had was using water mainly in the water and muffs in the yard which did not make the leak location obvious. He also said the cooler was not an issue. He also had me replace the pump, which was a waste of money.
 
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