Tohatsu 18hp not pumping water when in gear

[adams.1986]

Gents.

Originally posted this in the wrong forum. take 2:

The motor is a mid 90s 18hp tohatsu

Here's my problem: in neutral my motor pumps plenty of water at idle and at higher revs.
When i drop her into gear she still pumps a reasonable amount of water at idle, however when i give her some juice and she comes under load the spray of water slows down to a trickle and the motor starts getting hot very quickly.

This is whils running at sea, so the intake is not being starved of water.

Impeller was still good however i have replaced anyway. thermostat is fine too. squirted water up the water tube and there was no blockage.

So where do i start looking? Head gasket?

Thanks

Adam

 

[pvanv]

Re: Tohatsu 18hp not pumping water when in gear

Check (again) for any blockages. Inspect the cup and plate in the pump... any discernable grooving, and you want a new wp kit -- not just the impeller. Was it a Factory impeller, or after-market? Is the motor rigged properly, or are you sucking air into the intake at speed?

 

[Sea Rider]

Re: Tohatsu 18hp not pumping water when in gear

How do you know thermo is good, probably good looking but not working properly. Have you done the thermo heat test to check it's working condition ?. Has engine overheated severely in any occasson ? If impeller is pumping ok, being an old horse surely will benefit performing a complete water path clean out with new head gasket and thermo change if proof defective as a preventive maintenance.

Is the round black grommet that seals water pulp against water pipe is in good condition ? Upper water pipe has a upper seal, is it ok too ? When you say water spray slows down to a trickle, are you reffering to the peing port or the rear water exhaust port ?

Happy Boating

 

[TOHATSU GURU]

Re: Tohatsu 18hp not pumping water when in gear

It could be a head gasket, but it is more likely that you still have a water pump issue. As Paul alluded to, you always kit the pump as the cup liner and wear plate can cause issues. It's also possible that some of the old impeller, if it tore up, went down rather than up. You could also have a corrosion issue somewhere between the pick up and the pump.

 

[adams.1986]

Re: Tohatsu 18hp not pumping water when in gear

gents,

Thermostat is only a year old and i function tested it. old impeller was only a year old and still in good shape - bothe the old and new are factory parts.
the motor pumps plenty of water whilst in neutral at any engine speed.

Sea Rider,
the motor has a "rear water exhaust port" i think (outlet that sprays water on the rear center of the upper mid leg - not a steady stream like modern outboards.

Wil reinspect the WP housing and maybe rip the head off, if only for learing purposes.

Thanks fellas

 

[Sea Rider]

Re: Tohatsu 18hp not pumping water when in gear

Are you testing engine with muffs, barrel or at sea ? Rear exhaust water port varies it's outing if house water pressure is low or using muffs that looses huge amounts of water sideways. If at sea, has the motor been correctly water flushed after each outing or once in a lifetime ? Probably with excessive salt accumulation giving very bad internal water flow throughout passages including poor refrigeration...

Happy Boating