Lack of Water Pressure 1983 70hp mercury

trevans

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Aug 17, 2010
Messages
7
Having trouble building water pressure on 70 hp mercury at full throttle I am getting 7psi and it is fluctuating on the guage. What pressure should I expect to see out of this motor? I have replaced the waterpump and when I slide lower unit back up I have trouble getting the water pipe into the waterpump. The water seal keeps getting hung up in the water pump and does not allow the pipe to slide in. Is there a trick that I am missing I am lubricating the pipe and seal. Thanks to everyone in advance.
 

ajgraz

Lieutenant Commander
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Mar 1, 2010
Messages
1,858
Re: Lack of Water Pressure 1983 70hp mercury

Have you gotten higher readings than that in the past?

These mid-70's to early-80's 3-cylinders have "high volume" rather than "high pressure" water pumps. I wouldn't worry much about the actual reading unless it was zero.

Are you getting a steady pee stream? If so, I wouldn't worry about it.
 

trevans

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Joined
Aug 17, 2010
Messages
7
Re: Lack of Water Pressure 1983 70hp mercury

I was getting 10psi before I changed the pump and I used to get 12-15psi a few years ago. The motor does have water coming from the telltale but it is not as strong as it used to be and takes longer to buildup than it used to. I have also tried putting the water hose directly to the water tube and get more pressure than with the muffs. I double checked the impeller and the insert is not spinning the only issue I see is were the water tube seals with the pump when putting the lower unit on. Is there any trick to getting the water seal to seal the water tube in the water pump.
 

Wingedwheel

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Jun 16, 2009
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1,071
Re: Lack of Water Pressure 1983 70hp mercury

Are you using the plastic guide-tube to put it together and did you replace the seal when you took it apart?
 

trevans

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Aug 17, 2010
Messages
7
Re: Lack of Water Pressure 1983 70hp mercury

I am using new water seal and nylon washer. I have the shop manual and it recommends using a screwdrive to push the seal down but I have been unable to get a screwdriver near the water pump during installation. Are you referring to the plastic tube part of the waterpump or an additional tool? I know the 75hp and larger motors come with a plastic tube to assist with installation of the water seal, is that what you are referring too?
 

Wingedwheel

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Re: Lack of Water Pressure 1983 70hp mercury

The actual seal is inside the top of the waterpump housing. When the tube fits in it slides into it. The plastic sleeve I'm referring to is a guide that assists in stabbing the tube. Thers should be plenty of room to get a screwdriver against the pick-up tube to let it be started into the guide. Try putting a little petroleum jelly on the end of the pick-up tube before installing the LU if your worried about it not seating. One of the things that can cause lower pressure is a worn face plate or cup inside the waterpump housing. A complete rebuild kit normally comes with those items. Did you replace the complete waterpump or just the impeller?
 

trevans

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Joined
Aug 17, 2010
Messages
7
Re: Lack of Water Pressure 1983 70hp mercury

Think i might have figured it out the merc dealer sold me a newer style complete waterpump (eventhough they had my serial number) and the waterseal for an older style waterpump. The diameter of the new style water pump tube is skinner by the slightest bit. Measured my old waterpump with a caliper when I figured out the problem. The dealer is ordering me the right complete pump should have it in 7-10 business days. Thanks for your help.
 
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