Merc Outboard Overheating
 

I have a '97 Pro-Line with a 150 HP Merc that has recently experienced
overheating problems. It idles at about 150F, and gets up to over 180F
at higher speeds before I idle back down. I am guessing it has both a
water pressure and a water temperature alarm, because sometimes the
alarm goes off right away when the motor is started cold, sometimes not
until the temp gets over 180F.

I replaced the impeller, which made no difference. The pee stream seems
hot and not as strong as usual. Is there anything else I can check?

Thanks,
Jim

It's an outboard, not a I/O!


wrote in message
...
On 6 Jul 2005 08:03:30 -0700, "mjb920" wrote:

I have a '97 Pro-Line with a 150 HP Merc that has recently experienced
overheating problems. It idles at about 150F, and gets up to over 180F
at higher speeds before I idle back down. I am guessing it has both a
water pressure and a water temperature alarm, because sometimes the
alarm goes off right away when the motor is started cold, sometimes not
until the temp gets over 180F.

I replaced the impeller, which made no difference. The pee stream seems
hot and not as strong as usual. Is there anything else I can check?

Thanks,
Jim


My guess is a stuck check valve in there somewhere. It may just be
gummed up with 35 year old oil. I would start with a complete oil
change and do it a couple times, Oil is cheap.
Change it, operate the system for a while and change it.
Maybe a little dose of automatic transmission "revuvenator" and use
ATF on the first pass.

BTW "hydraulic fluid" is just light machine oil. I would avoid
multiviscosity motor oil. I would use ATF or power steering fluid. It
is more appropriate to the application than motor oil.

You really need to install a water PSI gauge to check things out. Could be
thermostats, passageway restriction, headgasket. Go to www.screamandfly.com
as there are many OB guru's there

"mjb920" wrote in message
oups.com...
I have a '97 Pro-Line with a 150 HP Merc that has recently experienced
overheating problems. It idles at about 150F, and gets up to over 180F
at higher speeds before I idle back down. I am guessing it has both a
water pressure and a water temperature alarm, because sometimes the
alarm goes off right away when the motor is started cold, sometimes not
until the temp gets over 180F.

I replaced the impeller, which made no difference. The pee stream seems
hot and not as strong as usual. Is there anything else I can check?

Thanks,
Jim

Remove the thermostats from the heads and see what happens. Not the sensors
but the actual thermostats. If this cures the problem then chances are one
was partially closed up.
You can either replace them if your in a cold climate or just run without
which is what most do in the south.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com

-
"mjb920" wrote in message
oups.com...
I have a '97 Pro-Line with a 150 HP Merc that has recently experienced
overheating problems. It idles at about 150F, and gets up to over 180F
at higher speeds before I idle back down. I am guessing it has both a
water pressure and a water temperature alarm, because sometimes the
alarm goes off right away when the motor is started cold, sometimes not
until the temp gets over 180F.

I replaced the impeller, which made no difference. The pee stream seems
hot and not as strong as usual. Is there anything else I can check?

Thanks,
Jim