Shah Mat

Seawater pump impeller came apart last Sunday. Changed the impeller and housing on river and headed back toward the marina. Ran about a 2 miles and the temp was normal, 150*. When I came off plane and idled for a minute the temp started rising. Got up to about 180*. Put it on the trailer and went home.
Yesterday I back flushed with a garden hose from the t-stat hose which flushes the power steering cooler and the oil cooler thinking I had some impeller junk stuck in the coolers. Didn't see anything come out.
Took it out on the river and idled through a 5 minute no-wake zone and the temp got up to 180*. Got up on plane and the temp dropped to 150*. Came off plane and after a few minutes it went back up to 180-190*. Turned around and headed back, ran it hard, 4000rpm, and it stayed at 150*. Got to the no wake (idle) zone and the temp went up to 220* and stayed there all the way back to the dock. I put in neutral and brought it up to 1500rpm, but it stayed at 220*.
Water flow in the sea stainer and out the exhaust appear to be normal.....WTF?

502 carb/bravo
It does have a pesky nose cone on the drive that has given me trouble in the past with seaweed and mud getting into the low water pick up hole but the symptoms are opposite: Temp normal 150*at idle and hot, 180* on plane.

Trippin

2 idea's.

Make sure that you have the inlet & outlet hoses connected to the correct orifices on the raw water pump, the pump dictates on the back which opening is for the rotation you have, unless you have the brass housing.

The CTS could have gone faulty (failed in range= no code) as a result of the initial overheat. Break out a hand held laser temp gauge or equivilent and verify that the motor is in fact overheating during operation, and replace the CTS if not, verify your hose connections anyway.

1BIGJIM

Try taking the hoses off at the coolers. After backflushing I have found parts still plugged in the cooler lines. I have used needle nosed pliers to pull them out.

You could have more pressure at higher RPMs forcing the water through. Idle lower water pressure and it is not circulating correctly.

Just more thougths

ezstriper

I agree that you still have some peices floating around in there...I always try count the peices to see if you get all the peices..Rob

MnFastBoat

I will say that after taking all hoses off this year I found that the stock 1998 Merc 502's have open Steering and fuel collers, meaning only large chunks could block them
However the OIL Cooler has small orifices for water passage
I found mine 98% plugged. Rubber impellar, pebbles, wood chunks, etc
I would take both the upper and lower hoses off the oil cooler and see what kind of 'light' your not getting through it

Takes about 5 minutes each to take off it you have excess to the front. And I do not have closed cooling in the way.
a 3/4" wrench on the oil lines and a 10 or 11m wrench for the mounting nut.
I took mine out and used a wire coat hanger to push and pry all the chunks of crap out. Took a lot of patience, but I unplugged all but one hole on each cooler.