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gweaver
07-02-2012, 02:01 PM
88 Prostar with closed-loop cooling. I was having some cooling issues and coolant leaking in to bilge. Replaced the main hose that runs from the engine water pump to the front of the heat exchanger, and now the coolant level remains constant. No coolant loss!! :D The boat did overheat (temp alarm went off) several times while I was chasing this problem over the last few weeks.
Had the boat up at the lake over the weekend- as above, no coolant loss, boat runs great. Operating temp is about 175 degrees, but when idling for a while, temp climbs and the alarm goes off. (Trying to teach 5 year old to ski, lots of start/stop slow speed stuff.) Noted that if I shift in to neutral and increase rpms to about 1200, temp drops back down.
Raw water impeller is less than a year old. Most downtime the boat has had is about a 3 month stretch- is that enough to damage an impeller?

Is the rising temp at idle normal? Any ideas what I should be looking at for a solution? A friend suggested that the thermostat could have been damaged by overheating, which may have also damaged the temp alarm sensor, leading to false alarms. I know a new thermostat is cheap insurance, but what are my next steps here?

Cheers,
Greg

thatsmrmastercraft
07-02-2012, 02:09 PM
I see two possibilities:

1. Raw water pump impeller id bad and/or there are weeds in your oil cooler inlet restriction water flow.

2. You have air bubbles in the system, and consequently not enough coolant to get the job done.

gweaver
07-02-2012, 02:51 PM
I see two possibilities:

1. Raw water pump impeller id bad and/or there are weeds in your oil cooler inlet restriction water flow.

2. You have air bubbles in the system, and consequently not enough coolant to get the job done.

A few questions- is the 'oil cooler inlet' the same as the raw water inlet? If yes, then there are no weeds apparent in the intake, but I will double check.

Without pulling the impeller (just removing the impeller cover), what should I be looking for to see if the impeller is bad? Is it even possible to tell if it's bad without removing the impeller?

How do I check for/remove air bubbles? When I replaced the leaking hose, I squeezed both hoses on the coolant tank and got a few bubbles out then topped off to current level. Ran the boat for a while at speed with no drop in coolant level.

Thanks,
G

thatsmrmastercraft
07-02-2012, 05:30 PM
A few questions- is the 'oil cooler inlet' the same as the raw water inlet? If yes, then there are no weeds apparent in the intake, but I will double check.

Without pulling the impeller (just removing the impeller cover), what should I be looking for to see if the impeller is bad? Is it even possible to tell if it's bad without removing the impeller?

How do I check for/remove air bubbles? When I replaced the leaking hose, I squeezed both hoses on the coolant tank and got a few bubbles out then topped off to current level. Ran the boat for a while at speed with no drop in coolant level.

Thanks,
G

The oil cooler (see pic) is the first in line from where the water pick-up brings cooling water into the system. If you remove the hose at the inlet side, often times there is some amount of weeds in there. Two years ago on vacation I sucked a big glob of weeds and had to take a few minutes out to clean it out.

I have no actual experience with the fresh water cooled MC's, but as will all pressurized cooling systems, you may need to run it with the cap off for a while to work the air bubbles out of the system. There is no way to check for them, but at idle, you may see them slowly working their way out of the filler with the cap off.

Probably better off to wait until someone with some direct experience comes along with some solid answers on the air in the system.

Can't really tell if an impeller is bad util you remove it.

gweaver
07-03-2012, 12:32 AM
Mr. MC- no picture came through. As far as debris, I'll check, but I forgot to mention I have a raw water strainer on the boat. I'll start working on the problem this week and pull the oil cooler inlet.
G