8.2 MAG Running Hot

JasonA · May 2020

My 290 with 8.2 MAG starting overheating anytime it was above 1500rpm. Idled it to the service center a week ago and they found some stuff and repaired it. Picked up the boat today from service and its still running hot but not overheating any longer. The stuff that was serviced:

Bravo 3 pulled and cleaned has some build up which they cleaned

Raw water pump replaced (was leaking at pulley went from 21psi at cruise to 28psi)

Heat exchanger opened and cleaned look ok

Poppet values replaced tubes leading to them had some growth but were cleaned

One riser elbow removed to confirm condition of exhaust water passages (looked good only 2 years old)

Compression test done all cylinders in great shape

Idle is about the same 169-171 as prior to the problem (although today after getting back to the slip it sat at 174 for quite a bit). Boat used to run 174-178 max at 3800-4000rpm (cruise speed) and would build some temp at WOT. Now its running 183-185 at cruise and builds temp anywhere past 4200rpm. Any ideas on what to check next? Going to call the service center and talk to them tuesday when they are back in but it seems like they were MOL out of ideas.

YYZRC · May 2020

What temp thermostat? Possibly something lodged in the housing?

aero3113 · May 2020

Are you using Vessel View or the stock gauges?

Michael T · May 2020

Check thermostat and heat sensor. I had some problems with sensors (they're often made off-shore and cheap) on both my 2014 502 Magnums. Sensors replaced, no problem.

LaRea · May 2020

Could be corrosion at the fitting where cooling water from the outdrive passes through the transom. It's a well-known problem. You can inspect with the boat in the water, but it's a haul-out repair.

212rowboat · May 2020

how many hours on this engine? the engines circulation pump could be suspect.

JasonA · May 2020

Thermostat opens at 170 and the numbers are from a Vessel View unit. When the boat was in for service they pulled the outdrive and would have expected that they checked for blockage on the through transom. There are around 250 hours on the motor. Sounds like sensor and thermostat would be next things to check.

PickleRick · May 2020

You're closed loop. Losing any coolant that you can tell?

Aqua_Aura · May 2020

When you say it builds temperature past 4200 are you saying it continues to get hot and won't cool down or just heats up some more and then stops. Changing the thermostat would have been a good start. Also the numbers you posted seem so minimal that if you had analog gauges you probably wouldn't even notice. VV gives great info but then it also shows you such small variation it might make you worry about a non issue.