Overheating at WOT/Max RPM

[Toucan]

The overheating problem at WOT/Max RPM on our 220 HP D3 engine was first noticed when the boat was fairly new. The Volvo gauge warns of overheating that will soon cause an automatic power cutback. We do not have an overheating alarm at lower RPM settings. The speed scoop screen is relatively clear (thin layer of bottom paint on most of it). The problem manifested both before and after replacement of the impeller. No pieces of the impeller have ever separated from the hub. The coolant overflow tank is near full.

With great difficulty, I have removed most of the old plumbing so far - ball valve, street elbow and tailpiece. First step was to remove the bilge pump hose to get it out of the way. Then unscrew the strainer housing from the hull and pull back, pulling the hose off the tail piece attached to the street elbow. To remove the tailpiece, what worked was to go to the local auto parts store and borrow a kit with a 36 mm deep socket. One screw held the muffler in place. The ball valve and elbow came out together using an adjustable wrench. The elbow contacts the snout on the muffler in the process of rotating it and with effort the muffler will barely move out of the way as the hoses keep the muffler from moving more than a smidgen. Only the screws on the outside are holding the speed scoop in place at this time.

The only chance to get the 1 1/4" plumbing in place will be to move the hole in the hull outward and a bit forward, as all the new plumbing pieces are longer and wider in diameter. The neck on the speed scoop will need to be shortened as much as possible. If this is not enough, the next thing is to either fill in the hole in the hull and start over with a new hole farther away from the muffler or to modify the muffler for more clearance.

Stay tuned for further developments.

Barry Thompson
TOUCAN, R-27 Classic

 

[Red Raven]

Barry,

Did you check/backflush the oil cooler? I do this annually and have found stuff in there every time. The 1 1/4” intake mod is good in any case but won’t help if you have a blockage downstream.

Curt

 

[Glen]

Barry, I agree with Curt, eel grass collects in the trans/reverse gear fluid heat exchanger, I backflush mine every 50 hours or whenever the engine coolant temp increases above normal. Very simple, just take the raw water hoses off the heat exchanger, put a garden hose nozzle in the starboard side of the heat exchanger, and spray the grass out the port side. I use a kitchen colander / strainer to catch the grass and keep it out of the bilge.