dominics79

Recently had a marina change the inpeller and houseing on my 2005 496 mag because it would warm up at idle and then cool back down as soon as you gave it rpm's. now it warms up after you slow down from about 4000 rpm but runs at normal temp during idle. Any ideas

Knot 4 Me

Define "warm". I would start at backflushing the system to make sure they got out all the old chunks of impeller.

Raylar

On the 496's the larger broken rubber pieces of impellor if they get into the system after the raw water pump generally are caught in the inlet side of the oil cooler before the heat exchanger. Remove the hose on the inlet side of the cooler closest to the back of the engine and look in and you'll prbably find the larger pieces of impellor there.
Check you raw water pump pressures at higher rpms and make sure they are within the Mercury specs. If they are low for whatever reason the engine will not cool as well as it should and this will show up after running at higher rpms and then dropping to an idle.

As some one else said previously, what are the temps you are expierencing?

Best Regards,
Ray @ Raylar

Sydwayz

iTrader: (1)

I've seen more than one Baja have issues with that stupid T-fitting they put in for the fresh water flush. It get's all gummed up and the check-ball spring portion of it sticks and closes off the water flow. All you need is a T in the system; not that damn check balll spring loaded piece of chit.

Also, check your heat exchanger for clogs.
And, you have to change the antifreeze. It's only good for 5-6 years, max. It silts up and does not flow as well.

TWIN-SPINS

now that you mentioned it,,,didnt early 496 have those check ball spring valves on the bottom of the exhaust manifolds also

Sydwayz

iTrader: (1)

All 496s have an air system with a schraeder valve (valve stem) that you can pressurize which allows the water to drain out of the block and accessories; for extending the boating season.

Totally different system though.

When these fail, they fail open, to where the spring does not close all the way, and the FW side has a leak at one of the actuators.

Or, the air system can fail, and the actuator will not open when air pressure is applied.

Either way, this system should not effect cooling unless you have water leaking out due to a faulty spring. If this was happening, you would have a bilge filling with water.
Ask me how I know that.

Raylar

Those lovely ball check valves that Mercruiser put under the 496 exhaust manifolds can corrode , stick and break in two different posiitons. They are actually a check valve that is supposed to allow raw water to enter up into the exhaust manifold when the engine is running and fall back when the engine is off to keep water in the exhaust manifolds during short off persiods and allow them to drain slowly after longer off persiods. the problem comes in that they can stick closed up to prevent water flow into the manifolds , overheat the manifold and the engine quite quickly or they can stick open and allow most of the raw water when running to by-pass the manifold and overheat in the same ways. Not flushing the engine well after salt water usage and not running a strainer and pumping debris into the system hastens and causes a lot of this sticking and failures.

Best Regards,
Ray @ Raylar

dominics79

raises to about 185-190

TWIN-SPINS

iam not talking about the air system,,,but what raylar is talking about

Sydwayz

iTrader: (1)

Good call Raylar & T-S. I didn't know that was there.