90hp merc 6 pack water flow prob? or not

[venom]

hi guys i have a 1986 90hp merc,I noticed on the weekend that at very low speeds just putting around that the water flow out of the engine hole is just dribbling, but if i gun it and keep it at full throutle its a steady stream engine didnt overheat or give any sighs of trouble .<br />Don't want to lose this motor she runs strong and pulls hard, only had the boat a couple weeks , should i be worried . help please

 

[timbo1963]

Re: 90hp merc 6 pack water flow prob? or not

sounds like you need a water pump impellar. It should be replaced everyother year at the least. If you just got it you probably have no idea when it was changed last. you know not to ever run it without being in the water or on the muffs. right?

 

[Chris1956]

Re: 90hp merc 6 pack water flow prob? or not

Venom, Those tell tale holes plug up easily. See if you can clean it out. The only real way to tell if she is pumping properly is to run it on the muffs and see if you have good flow out of the grating above the prop, and if the water flow is just lukewarm.

 

[venom]

Re: 90hp merc 6 pack water flow prob? or not

Thanxs guys for the replies, opened up the engine cover and took out the hose ,checked for blockage noticed that the plastic elbow that goes from the one end of the hose to the head was lose put a little tfelon tape on the treads and snugged it up put the muffs on and started it up, steady stream at idle good water flow out the vents above the prop and water is luke warm ran it for 10 min. Man i love this motor. thanxs

 

[andrewkafp]

Re: 90hp merc 6 pack water flow prob? or not

Do you have a pressure gauge connected ? Should be pushing around 14 at high revs and 4-5 at low.<br />It is just as important to remove the L/U as it it is to replace the impeller as the driveshaft can become corrosion stuck in the crankshaft end.<br />Do as the guys said.. Change the impeller and lightly grease the splines of the driveshaft. Also periodically remove and grease the prop shaft and replace with a new lock washer.<br />This site has many experienced members who can guide you through the preventative maintainence tasks and help keep that old Merc healthy.<br />BTW.. Not trying to scare you BUT... An impeller may seem OK , but may be beginning to delaminate from sitting around dry. The little pieces of rubber go through the cooling system and block things up.(Any change to flow may be a sign)<br />If you don't know when it was changed.. best to do it. It's a 1hr $30.00 job

 

[jimmbo]

Re: 90hp merc 6 pack water flow prob? or not

You will not get 14 psi out of an ilne six water pump 5 to 7 at WOT and about 2 - 3 at idle is the correct range for these engine. The V6s can do 14 at WOT and 4-5 at idle

 

[andrewkafp]

Re: 90hp merc 6 pack water flow prob? or not

Sorry.. Didn't know it was inline. They must have the high volume low pressure impellers. Still. I would change it anyway.

 

[jimmbo]

Re: 90hp merc 6 pack water flow prob? or not

Uni you might be right if it is a 3 cylinder job. I don't offhand recall exactly when Merc switched the 90 from a six to a three. Oh well the title did say 6 pack

 

[andrewkafp]

Re: 90hp merc 6 pack water flow prob? or not

No.. You are right.. 1986 was the last of the 90hp 6's. 1987 90hp was a 3 cylinder.And I did read somewhere on this site about a "Low pressure" "High volume" impellers used on some motors as opposed to some that squeeze out nearly 16 psi.