Outboard Overheating

[cosmo]

G'day,
A few weekends ago I was out on the water with another boat. To give the kids a bit of thrill I opened the throttle on my early 90's 60hp Mariner to speed away from the other boat only to have the high temp alarm sound when the motor was revving above 5000rpm. I dropped revs to idle and the alarm stopped. The tell tail was working the whole time. I checked the engine and it was running hot. So I went home and dropped the leg off to check the water pump. The impeller was OK (only just over 12 months old) but the housing it runs in was a little worn. Not convinced that this was the problem I removed a few covers from the head to check out the cooling galleries. No problems there in fact it was better than expected. So my brother the outboard mechanic ordered in a complete new water pump kit (housing, seals, impeller plus the gaskets) plus the gaskets for the covers I had removed. I assembled it all yesterday and my brother ran it up on the outboard dyno to check the head temps. As soon as it started I noticed the higher flow than normal from the tell tail. We ran it up and down various rev ranges whilst checking all over the head with a laser thermometer. The motor didn't get hot at all.

The problem was a worn water pump housing that wasn't allowing enough water to be pumped through the engine. It goes to show you that just because the tell tail is working doesn't mean that all is well with the cooling system. Now I'm thinking that I might install a water pressure guage so that I can see if any decay in pressure occurs.

Get those water pumps checked!!!!!

[Roughasguts]

Your right mate the housing can let you down.

Water pressure gauge is good insurance.

Or if your motor is known good, run it at 1500 rpm and catch the tell tale water over a period of 30 seconds.

Mine when good is 500ml at 1500Rpm over 30 seconds,
(written that on the wall of me garage)

So I use this as me measure, as to when I should be looking at replacing the pump.

It's a lot harder to judge the flow accurately by looking at it after a few Beers, and several years of it slowly dropping in out put.
Or was it the other way around, several Beers.........an

Speaking of wich better go get some it's been 2 years since me last drink, but i'm digging outside and need the motivation.

[gutzy]

is this for all motors as mine is only 25hp , should I take the lef off and check?

[Kerry]

Water pumps should be replaced as a kit anyway as it is generally the case that is worn, not so much the impellor. Simply replacing the impellor (as most do including service dealers) doesn't fix the real issue of the worn case, which then continues to reduce the life of the new impellor.

[Barnacle Billy]

Check out Smelly's thread on overheating - One EPIC!

[cosmo]

Yeah I started reading that thread but lost interest after 15 pages!!!!!

[Roughasguts]

Yep The whole kit is only a few dollars more than the impellor alone.

How is Smelly anyway is he on the road to a full recovery?

[Barnacle Billy]

HI Guts.

That overheating thread was a monstor! We had fun though!!

Smelly is back at work - 90% - as he is still seeping...