Outboard cooling?

Dobieman · 12 April 2010, 20:00

Hi All
I have a 1998 Mariner 50hp 4 stroke which gets hot when ticking over for more than a few minites ( once fully warm )

I was told that the water pump is 'low velocity' or something like that, and was not designed for ticking over for long periods.

The engine can be run at 2000rpm or higher all day with no problems.

Does anyone know if this is true?

Jizm · 12 April 2010, 21:08

Quote:

Originally Posted by Dobieman

Hi All
I have a 1998 Mariner 50hp 4 stroke which gets hot when ticking over for more than a few minites ( once fully warm )

I was told that the water pump is 'low velocity' or something like that, and was not designed for ticking over for long periods.

The engine can be run at 2000rpm or higher all day with no problems.

Does anyone know if this is true?

Never heard of that....Thermostat stuck closed?

spartacus · 12 April 2010, 21:24

Quote:

Originally Posted by Dobieman

Hi All
I have a 1998 Mariner 50hp 4 stroke which gets hot when ticking over for more than a few minites ( once fully warm )

I was told that the water pump is 'low velocity' or something like that, and was not designed for ticking over for long periods.

The engine can be run at 2000rpm or higher all day with no problems.

Does anyone know if this is true?

On the contrary, a 4-stroke will endure tick over more than its 2-stroke counterpart. As Jizm pointed out, check the thermostat and the cooling recess itself. Fairly cheap fix. Do you know when the impeller was last changed?

Dobieman · 12 April 2010, 21:32

This is the first outing since the impellor was changed,the engine did the same thing on the old impellor too....

Is changing the thermostat an easy job? i see in my workshop manual the thermostat housing is easily accesable on the side of the block just above the ignition coils.

thanks

outboardtech · 12 April 2010, 21:41

pull the powerhead off and check the water grommet on the adaptor plate . THIS IS A VERY COMMON problem on the earlier fourstroke engine's . Salt water attacks the seal were the water pumps up thru and causes the seal to close restricting flow at low rpm . As you can see in the picture's . did this 3 week's ago on a 50 Mariner fourstroke

Jizm · 12 April 2010, 21:42

Quote:

Originally Posted by Dobieman

Is changing the thermostat an easy job?

Providing the bolts come out and don't shear off, then yes...

outboardtech · 12 April 2010, 21:44

NEVER heard of an ISSUE with the waterpump's . They are BULLET PROOF and work well . My earlier post is your problem . cheers Barry

Dobieman · 12 April 2010, 21:54

Thanks for the advise guys.

I'm not confident i could remove the powerhead muself - too big a job for me.

Outboardtech -what do you charge for this job? I'm fairly local to you...

reply by PM if you wish,

cheers....

9D280 · 13 April 2010, 11:45

Quote:

Originally Posted by Dobieman

I was told that the water pump is 'low velocity' or something like that,

I believe that the older (like pre 1908s) Merc/ Mariners had two "flavours" of pump - one was high flow low pressure, the other was (relatively) low flow, high pressure. I don't believe they were cross - compatible (i.e certain HPs had the flow pump, others had the pressure type).

I sussed this out by accident whilst piecing a few pages of Clymer together, so don't read it as gospel! (Outboardtech might be able to confirm?)