Temperature Increase and Fluctuation at idle

"First off, let me tell you al

"First off, let me tell you all what I have already done. Replaced raw water pump impeller, replaced thermostat and gasket, checked Quickflush for blockage(none) and cleaned contact on water temp sender unit. The problem is that after running with temp straight up (170ish) for nearly 5 years, it now heats up to around 200 or so on the guage when idling and immediately cools to arounbd 155 or so with the slightest bit of throttle. What should I check next?"

did you ever change the impell

did you ever change the impeller's housing?

may help a bit if you can ID the beast with a bit more detail.

Did not change out the housing

Did not change out the housing as its condition was sound. The inside surfaces were smooth and free of pitting and extensive wear.

""may help a bit if you ca

""may help a bit if you can ID the beast with a bit more detail."

A kink in the water inlet hose, a partially blocked exhaust from rust, scale and mineral buildup.

No; Briggs-N-Stratton engines don't do that."

"For ID, I was thinking alpha

"For ID, I was thinking alpha styled pump in outdrive vs raw water pump mounted on engine like some of the bravos use."

"Sounds like bad incomming wat

"Sounds like bad incomming water issue.

The fact that is cools so quickly when a small amount of throtttle is added tells me incoming.

What is the temp when running full throttle?

What temp thermostat did you install?

I agree with guy on the condition of the inlet water hose at the outdrive, IF IT IS A OUTDRIVE boat??????????

Also just replacing the impeller is ok but it is also good to replace the entire assembly after a while including the base assembly.

The exhaust runs over the impeller housing(if it is an outdrive???) and over time tends to cook it a bit!

I will tell you that I onced chased a temp issue for 2 full days and it turned out to be the sending unit. I compared the change in ohms when put into hot hot water from a new one to the one in question. The one in question had a gradual change the jumped to a much differnt reading then the new one. The new one changed very gradaul until it peaked at the max for the water temp.

replaced it and the problem was solved even though I replaced all of the same things you have and then some.

(when I first started out in the industry) just so ya know..............."

It is an inboard engine with a

It is an inboard engine with a V-Drive. The temperature goes down to between 155 and 170 when running 3500 rpm or more. The new thermostat is a 160 degree just like the original. My water pump is a separate raw water unit that runs off the belt and the housing unit was ion very good shapre when I opened and replaced the impeller. Thanks for all of your feedback. B.O.A.T. Break Out Another Thousand....

"Oh also, it's a 2003 Merc

"Oh also, it's a 2003 Mercruiser 350 Mag MPI Tow Sports with 353 hours on it."

"Check the strainer cover - ga

"Check the strainer cover - gasket in good shape, not compressed, and the retainers evenly tightened. Also, check the hose clamps on all connections up to the raw water pump.

Did the wear plate have any grooving in it?

Is there a flush out system installed in the raw water line?"