Mercury 1.5L Optimax Water Pump Replacement

[TritonTRXV8]

Heres the how to thread I promised for my 1.5L optimax engines. These steps will be the same for the 3.0L optimax engines as well as the 50-60 Bigfoot and 75-115 4 stroke engines. My dad was here to lend a hand which helps alot for handling the gearcase and re installing. Gotta thank Don Weed for giving me a few pointers and answering my questions as well.

I recommend performing this with the engine in NEUTRAL and have a helper turn the flywheel slightly to line up the splines on the shaft for re assembly.

I trim the engine up to about the same angle as the engine sits on the transom saver. You need room for the shaft to clear the bottom of the mid section during removal.

First there are 5 15mm nuts to remove. 2 visible on each side and one that is recessed just in front of the trim tab. This pic has an arrow pointing to it. (On 3.0L models the rear fastener under the cav plate is a bolt instead of a nut)
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Break all the nuts loose. I completely remove the one near the trim tab them thread the last 4 down until the nuts are flush with the ends of the bolts. Then give a few firm pulls and side to side movements and the gearcase slips loose and rests against the nuts. This way the gearcase will not fall. You do not want it to hit the ground.
While supporting the gearcase remove the 4 remaining nuts and slide the gearcase out. In this case the seal from the pickup tube stayed in place in the midsection. If it comes off onto the pump housing simply remove it and place it back on the pickup tube. The arrow points to the seal and tube. Sorry the pic is sort of dark.
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Once removed place the gearcase in a holding device of some sort whether it be a vise or bars clamped to a bench a milk crate just something to support it. I use an adjustable stand that I made for holding the gearcase.
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[TritonTRXV8]

Lets get started. First make sure the shaft is nice and clean so the seal will slide easier. Remove the 4 6mm bolts from the housing and them remove the seal above the housing on the shaft. Its a VERY snug fit and it takes some work getting it slid up the shaft.
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Then remove the housing. The impeller should stay inside.
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Then remove the base plate and the gasket. Now its time to clean the surfaces and remove the old silicone from the exhaust bridge to the water pump housing. On the rag is all the new parts that will be used from the kit.
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[TritonTRXV8]

For ease of aligning the parts I recommend alignment pins. They can be purchased or what I did was take two 3" long 6mm bolts and cut the heads off and radius the ends. Thread these into the same holes that the bolts for the housing would thread into so as you add the gaskets and install the housing over the impeller everything stays in place.
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First install the base gasket then the plate then the housing gasket.
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After that install the new impeller key from the kit. Its just rests against the flat recess in the shaft.
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Now time for the impeller. VERY IMPORTANT. DO NOT USE GREASE OR ANY OTHER PETROLEUM PRODUCT ON THE IMPELLER. Use DAWN dish soap on all the fingers of the impeller. Then slide it down the shaft and align the slot in the impeller with the key on the shaft.
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This is where those studs really come in handy. Slide the housing over the impeller then while turning the shaft CLOCKWISE with one hand and pressing down on the housing with the other the housing slips right down from the soap.

[TritonTRXV8]

Remove the studs and re install the housing bolts. I add a dab of blue loctite for good measure. Torque the bolts to 40 lbs/in. Yes POUNDS PER INCH. (Torque values will vary by model)
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Next add a bead of silicone to the exhaust bridge between the bolt holes approx 5/16-3/8" (thanks for this tip Don). I used RTV black. Thr exhaust is water cooled and will not damage the silicone. Allow this to stand for 10 min before installation. This will give you time for the final touches.
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Now its time to install the drive shaft face seal. The tool is on the left and the seal on the right. Slip the seal over the shaft with the tool over it and push it down the shaft to the housing. Again its snug. The tool will make sure the seal is not pressed down too far so it meets the sealing surface properly.
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[TritonTRXV8]

This is something I do and it really helped with the disassembly the next time compared to the first. I add a dab of 2-4-C grease to the alignment dowels at the front and rear of gearcase and on the shift shaft and splines of the main shaft. NOTE: when greasing dowel pins be sure to wipe grease off of the ends so the grease will not hinder the gearcase seating fully to the mid section.
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Now time to reassemble. This is where a helper comes in handy to turn the flywheel slightly to align the splines of the shaft. Just feed it in slowly and when it stops turn the flywheel and as long as you did not move the shift shaft at all it will slide right back together. Make sure the gearcase and midsection fully mate together by hand do not force with the nuts when tightening. Install the 5 washers ans nuts and torque down to 40 ft/lbs. re install the prop and check that it rotates freely indicating that the gearcase is still in neutral. I allowed the silicone for cure for about 45 min before running the engine on the muffs. First start up will have some foam from the soap but it quickly clears out. Check your pressure which will likely be a tad higher with the new impeller. Thats it your set. Hope this helps out.

[bassassin]

Another great write up! Wish I was as handy as you. My first thought when reading this was - how much does a mechanic charge for this?

[Nova Kaw 650]

"Next add a bead of silicone to the exhaust bridge between the bolt holes approx 5/16-3/8" (thanks for this tip Don). I used RTV black."
Is the silicone directly exposed to the exhaust? Hopefully the exhaust is cooled enough to not burn the silicone off.

[rocket man]

I always thought the bolts were torqued to 60in.#. Maybe my motor is different.

[TritonTRXV8]

I edited some of the wording to answer the 2 above posts. The exhaust is water cooled so exhaust heat will not damage the silicone.

Also torque values will vary engine to engine.

[gatorglenn]

Great post!! curious How did your oil seal look, with the hours you have on the motor?

[spinningreel]

Dumb question, but why do Marine water pumps need replaced so often? Can't manufacturers build them to last for years like those in automotive use?

[Nova Kaw 650]

Automotive pumps have metal vanes. Outboards have rubber impellers, probably to allow dirt and crap to go through without plugging or jamming. Plus outboards don't have a closed cooling system.

[Nova Kaw 650]

I used your write up today, and put a new impeller in. Thanks!

[TritonTRXV8]

Hope it helped you out.

[Nova Kaw 650]

It helped a ton.
As I get older, my short-term memory is getting poor, so it was great to have something for a reference that is clearer than the manual.

[TritonTRXV8]

[SoonerFan]

This is awesome. If it's not a sticky on the Merc forum, then it ought to be.

I did my 50 horse merc without having a clue...just take it apart and try to get it back together right by the third try. I was too skittish to plunge into my 150 Opti so I've been paying Johnny's boys to do it for the last 10 years. With this, I can do it no problem.

[SilverFox579]

Roy, saw your post referenced on the Merc forum and thought I'd share a tip I used when servicing my 2.5L Opti in Oct. Wipe the housing clean with some brake clean or lacquer thinner. After removing the seal, pick a spot on the driveshaft above the housing and do the same. Now make index marks on the driveshaft and housing. No need for a helper to turn the engine to line up splines, they line up perfectly. Was a light bulb moment for me in Oct and it worked perfectly.

[Champ2005]

I followed Sherm's directions and he did not say to create a gasket with permatex on the exhaust bridge, is that because our motors are different? One other question, how do you get a torque wrench on the four bolts (2 on each side)? I couldn't get either of my torque wrenches on them, because there wasn't enough room.

[TritonTRXV8]

I followed Sherm's directions and he did not say to create a gasket with permatex on the exhaust bridge, is that because our motors are different? One other question, how do you get a torque wrench on the four bolts (2 on each side)? I couldn't get either of my torque wrenches on them, because there wasn't enough room.

The sealant on the exhaust bridge was recommended by Don weed on the merc board. Your 225 3.0l opti should be the same. Mine had sealant there from the factory i scraped it off and used the black rtv. To get the torque wrench on there you need a torque adapter socket.