Mercury 90hp 1990 Leak

efine

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May 2, 2021
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Issues: I noticed water draining from the gear oil case, and gear oil leaking from the water weeping holes when the engine was tilted up. The high temp alarm also went off after running on idle with a water hose after about 2-3minutes.

Question:
Before I replace the drive shaft oil seals, and water impeller. I wanted to ask if I also need to replace the bearing carrier (#12 here: MOD EDIT - Competitor)???
Looking at space where the shaft rubs against the bearing carrier I see some gear oil, and possibly an o-ring. I'm wondering if that's cause to replace the carrier or if that's ok and the oil seals above it will keep the oil and water where they need to.

Details:
The water impeller looked fine, the inside had some gear oil so it had lubrication. I will be putting in a new one. I got a new face plate and gaskets for the face plate top and bottom, and a gasket for under the water pump base.
When I flipped the lower unit upside down, gear oil started pouring down the shaft. That's why I suspect the oil seals were busted.
I also replaced the thermostat and thermostat gasket. But I tested the old one and it did seem to function. So I'm still not sure what the overheating issue is if the water pump was pushing water, and the thermostat was working. When not on idle or in a body of water (not running off a hose) the high temp alarm doesnt go off.
 
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Chris1956

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Mar 25, 2004
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24,085
The driveshaft oil seal is installed in the waterpump base. It is generally easier to replace the pump base, rather than changing the seal. Make sure to use the correct O ring and base gasket, as well as the correct gaskets on both sides of the wearplate.
 

efine

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Thanks @Chris1956. I took the water base off and old oil seals. Will be replacing those today or tomorrow. What I'm concerned about is what is under the oil seal, which is the bearing carrier. Do you think that should be replaced too if there is a leak where it touches the shaft? Thanks
 

Chris1956

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Mar 25, 2004
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Under the waterpump base is the driveshaft bearing. I do not think there are any seals to replace, once the pump base is out.

Depending on the year of the gearcase, the driveshaft bearing has a taper. This taper faces either up or down to provide the correct clearance. They are hard for us laymen to check for looseness, however the driveshaft bearings seem to be quite robust, and I have never had to replace one.

Try pushing down on the driveshaft, when the pump base is out and see if the bearing has looseness. Repeat with pulling driveshaft up, to see which taper you have.

I also think some driveshaft bearings are without taper. Looseness on these would be easier to determine.
 
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