Tohatsu/mercury Water pressure issues 25hp 4stroke

[wichi]

Mercury 25hp efi 4 stroke water pressure issues

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I have a Mercury 25hp efi fourstroke thats having water pressure issues. Replaced water pump, blew air in peehole and doesnt seem to have any obstruction. After replacing water pump psi started great went about 300 yards and same problems started occuring. The pressure just dropped to 0 with little water coming out. It seems to work off and on. Sometimes great pressure then for what seems like no reason just quits. It was running fine in idle yesterday after blowing compressed air through the pee hole, then i trimmed motor down and all of a sudden nothing. Water pressure dropped. Forced water through intake while lower housing was off and water came out fine. Removed houses last night and forced air through system, and again no obstruction. Could this be a thermestat issue? Local dealer said no, to replace pump. When I took it apart the old one was in good shape but went ahead and replaced with new. Any Help or ideas would be greatly appreciated. p.s. The motor is only two years old.
thanks

 

[pvanv]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

Typically this is a pump issue. However, I have seen cases where an impeller blew, and a chunk of rubber lodged up in the cooling system, intermittently plugging the cooling system. I would not expect this on a 2-yo motor. Has there ever been a bad/torn impeller replaced?

 

[wichi]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

Thanks, but I think I finally found the issue. After flushing the entire system including pulling the thermostat off, I went ahead and removed the lower unit again. I forced water through it and found that the water pump lower housing unit had a pin size hole in it. Under High pressure it shot a stream of water out. I can't imagine that its supposed to be there, so waiting on parts now to know for sure.

 

[wichi]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

P.S. Never replaced pump before on this motor, it was the first time. The old impeller was fine much to my suprise. Replaced it, since I had it apart and still had the same issues as before.

 

[Wee Hooker]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

Wow, i watched this one with interest. i have a new 30.
Hopefully you have it pegged. ( I was going to guess thermostat).
So how hard was it to replace the WP?

 

[Wee Hooker]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

Wow, I watched this one with interest. I have a new 30.
Hopefully you have it pegged. ( I was going to guess thermostat).
So how hard was it to replace the WP?

 

[TOHATSU GURU]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

By any chance did you grease the impeller when you put it in?

 

[wichi]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

By any chance did you grease the impeller when you put it in?

I did put some light grease on the impeller and contact surfaces when I put it together.
Right or wrong?

Also looking down on the top of the lower unit the fin tips of the impeller are pointed counterclockwise, is this also correct?

Thanks

 

[TOHATSU GURU]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

Normally it wouldn't matter what way you put in the impeller as the friction of the impeller against the liner would turn it the right way by itself. The grease introduces two potential problems. The first is that it keeps the impeller from correcting itself and the second is that it can disrupt the centrifugal pump action of the impeller. The impeller vanes should be pointed to the right, which I look at as the impeller turning clockwise. If the fins are pointing to the left then the impeller has not corrected itself.

When you replace the impeller you slide it onto the drive shaft, place the housing on top and while turning the drive shaft clockwise, push down on the housing so that the impeller fits.

 

[wichi]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

Thanks for the tip on the grease Tohatsu Guru!

It sounds like it did keep the impeller from correcting itself. So if I understand you correctly the final direction of the tips pointing is clockwise to the right towards the same clockwise direction as the rotation of the shaft?

And I still have not received the water pump base I ordered to replace the one I believe is defective that has the pin hole through the inside to the outside of the chamber in the compression/outlet side of the base. So I'm stuck on putting it back together to retest it.

Thanks again

 

[TOHATSU GURU]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

The tips would follow the clockwise rotation...IE the the outer edge of the vane would follow behind the base of the vane as it turns to the right(clockwise). A video presentation would make this easy

Mercury ships from regional warehouses, so it wouldn't take more than two days for the part to arrive. I think you need to ask the dealer the key question:

When did you really order it?

Dealers will often fib about order dates because they want to wait until they have "enough" to order.

 

[wichi]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

I ordered the parts on the Mercuryexpress part system, and it is a joke! The regional warehouses are not informed of the order. They have given me excuses and appologies for their system problems several times now in the last two weeks and still no parts. They did feel bad enough thou that they have refunded my expedited shipping charges, but still no parts.

Perhaps time to use JB weld on the pin hole?

And after your last explanation, the impeller fins have been in the correct direction, all water passages are clear , the thermostat opens at the correct temp so it must be the pin hole bleeding off the pressure?

 

[TOHATSU GURU]

Re: Tohatsu/mercury Water pressure issues 25hp 4stroke

The likelihood of you having a defective lower water pump case is very remote. Tohatsu does use a self cleaning water pump design on most models. I have never looked at the 25/30 4-stroke design to see if it has a bleed off port, but I suspect that is what you are seeing. Its an escape route for sand that reduces wear on the pump assembly. I'll have someone look at one tomorrow and see if is ported...MPE dumps the order to a "local MPE" dealer to fill...That really just puts you back at the normal dealer level that you would have been at to begin with or maybe a little worse, since that dealer may fail to see the urgency to fill it.