Water Pump Question on a 1972 Mercury Thunderbolt 800 80 hp - Now Found Leaking Lube

[krizm200]

Hi everyone. I have been trying to figure out why my 1972 Mercury Thunderbolt 800 runs great for the first 1/2 hour, but then starts to bogg down, become hard to get into gear and not stall, and not get to WOT although the throttle is open full. I have noticed the flow of water coming from the pee hole is not very strong. Wondering if the water pump may be an issue. I did change fuel to a higher octane and it did help. Plugs are new. The engine was tuned up a few months ago at a marina. I'm about to drop the lower unit and check it out. I have never done this before, but the manual I have shows it as fairly simple. I woudl love to hear anyone's opinion on this. Also, I don't know what kit/impeller to order for a replacement. Anyone know? Thanks!

Mark Kriz

 

[EchoNovember]

It could be overheating. Take off the lower unit and inspect the water pump. My water pump was missing a top oil seal, and the plastic of the housing had melted a but. I have a new water pump kit on the way, as it's pretty easy to replace. The impeller on yours could be worn out, which can cause low water pressure in the cooling system which can, of course, cause it to overheat.

Check the waterpump, replace gaskets, O-rings, and the impeller while you're in there, and give the top and bottom halves of the housing a thorough inspection, looking for deformed plastic, cracks, signs of excess wear, etc.

Go look up the motor by serial number, and find what part to use. Of course, check to see if iBoats has the part first and take advantage of the forum discount.

 

[racerone]

Impeller should be changed at least every 5 years.---More often if running in near freezing water.----The stalling may mean that you have to open low speed mixture needles 1/4 turn.

 

[EchoNovember]

Everywhere I've read said change the impeller every 1-2 years. The rubber degrades, dries out, and become less flexible. When it does, it causes either lower water pressure or excess resistance on the driveshaft.

 

[krizm200]

Thanks everyone. The impeller was replaced 2 years ago, then the engine sat without usage. I bet the rubber has dried out, and causing the low water flow from the pee hole. Might even be causing resistance on the drive shaft. I may try opening the low speed mixture needles 1/4 turn after replacing the impeller and gaskets. I saw a kit for about $150. I bet it is the right one, though I will check with the engine serial number and search again to be sure. I'll let you know how it turns out!

 

[EchoNovember]

Ouch on that kit. I get most of my parts elsewhere as they seem to have more for my engine than iBoats, but what should I expect with a 30 year old motor? I got my new water pump on Amazon for $40. Learn from my mistake, though. Take it apart first to see if you need to replace the whole thing. I bought the impeller, gaskets, o-rings, etc., just to discover the pump housing was shot. So I spent $20-30 on all the parts separately after shipping, then ordered a full replace everything kit from Amazon for $40, just to get the housing. Your pump housing might be bad, or might be in good condition. You'll need new gaskets and o-rings for sure, though. But you may not need a full kit.

 

[krizm200]

OK, took the lower unit off, and there is lower unit oil all over the water pump! When I drained the oil, it was milky so I knew water was getting in. No metal flakes though (really lucky). I think I saw an oil bearing in the manual of the blow up. Is this bearing shot? What would cause oil to leak out into the water pump? I'm about to order parts, and a full new water pump. Let me know if there is anything I should look for. Thanks everyone!

 

[krizm200]

Mercury 1972 Thunderbolt 800 Lower Unit leaking Oil out of Water Pump!

Hi everyone, I need some help with my lower unit. I have done some auto mechanic work years ago, but never outboard engines. I pulled the lower unit off my 1972 Mercury Thunderbolt outboard, and the lower unit oil is leaking out the water pump (all over the inside and out). What should be holding the lower unit oil in? If I order a new water pump, would it have all the components I need? I see there are oil seals and O rings under the water pump. Should I replace those? Where can I find these components? Any help would be appreciated.

Just an FYI, there was water in the lower unit oil (no surprise) but no metal flakes, so I assume the gears are still ok.

Mark

 

[krizm200]

A bit more information, it turns out the oil is leaking from underneath the water pump base. I need to get the water pump base off, but the Filter screw does not want to move. Any ideas how I can remove the Filter screw so I can get the water base off? The screw is breaking the screw driver slit as I put pressure on it. Any ideas how I can get the water base off otherwise?

 

[GA_Boater]

Mark - Re-titled the thread and merged posts. Having two threads on the same problem leads to confusion.

Please stop adding your email address. This forum only works with open exchanges

 

[krizm200]

OK, sorry about the email address. Thanks for combining the threads.

 

[GA_Boater]

What's the serial number of the motor. With that we can ID the parts to stop the lube leaking from below the water pump base. One, possibly two seals on the driveshaft and one O-ring on the base.

What causes the lube to rise out of the housing is water is heavier than the lube, so the water displaces the lube and it leaks out where ever it can. The shift shaft is also another place, as well as the prop shaft seal(s). Have you pressure tested the lower unit?

 

[krizm200]

The serial number for the mercury is 3189892. It's the Mercury Thunderbolt 800 80 hp 4 cyl engine, assuming 1972. I don't have a way to pressure test the lower unit, but I can see all the lower unit oil on and around the water pump, I don't see anything around the shift shaft. I would like to replace the water pump base, oil seal and O ring. The gaskets broke just under the water pump cover, so I will need a water pump repair kit as well.

Main issue now is the Filter screw is really stuck. I may need to cut it out. I had read that new versions of this engine did not have the Filter screw. Wondering if I can do without it.

Mark

 

[krizm200]

Correction, the Flush screw is really stuck. If newer versions of the engine do not use it, I assume I can cut through the threads to pull out the water pump base. If I need to I could drill out a hole through the frozen screw and get a tap and die kit. Or maybe skip the Flush screw completely?

 

[EchoNovember]

No Title

Here you, parts diagrams for the lower unit.

 

[krizm200]

Hi EchoNovember, I actually have these diagrams in my SELOC manual, and I have seen them on various websites as well (including Iboats). My biggest challenge is in trying to figure out which parts to order as I find multiple water pump selections every time I do a search. Also trying to find out if the base assembly has the oil seal rings and O ring. Already have sent an email to iboats to see if what I think is correct is!

My greatest challenge is with the Flush screw, it holds the water pump base in place in the lower unit. The screw is frozen and the slit is cracking particles off as I try to turn it. My SELOC manual says later motors did not have this screw, so I am wondering if it will be a problem if I do not have one to hold the base in place.

It is definitely been interesting pulling the lower unit. I have never gone this deep into an outboard repair before. I have the idea on the issue (I think it oil seals are shot) and how to fix it, just need to get the correct parts!

 

[Mercurylips]

Having just gone back into my lower unit to repair a water leak, I can tell you to make sure that all the parts and gaskets that are needed are installed. I completely missed a gasket under the pump base because the original was nearly non existent so I didn't put one on. It is on now! I did get a pump that was not OEM and it was a problem for me so I ended up rebuilding my old pump and my pressure test was a bit harsh (60psi) but the unit passed. I'll test in the lake next.

 

[EchoNovember]

Hi EchoNovember, I actually have these diagrams in my SELOC manual, and I have seen them on various websites as well (including Iboats). My biggest challenge is in trying to figure out which parts to order as I find multiple water pump selections every time I do a search. Also trying to find out if the base assembly has the oil seal rings and O ring. Already have sent an email to iboats to see if what I think is correct is!

My greatest challenge is with the Flush screw, it holds the water pump base in place in the lower unit. The screw is frozen and the slit is cracking particles off as I try to turn it. My SELOC manual says later motors did not have this screw, so I am wondering if it will be a problem if I do not have one to hold the base in place.

It is definitely been interesting pulling the lower unit. I have never gone this deep into an outboard repair before. I have the idea on the issue (I think it oil seals are shot) and how to fix it, just need to get the correct parts!

When iBoats doesn't have the parts I need, which for my old motor is pretty much all the time, I go to Marine Engine. If they don't have it, I can at least get the part numbers for the OEM and for Sierra Marine, then sometimes I have to hit Amazon or eBay or good old fashioned Google to find the dang part.

 

[krizm200]

I found another site, oldmercs.com out of PA that looks like it has what I am looking for. Easy to use their engine search and part locator. They even have the Flushing screw that I need to replace.

 

[EchoNovember]

I found another site, oldmercs.com out of PA that looks like it has what I am looking for. Easy to use their engine search and part locator. They even have the Flushing screw that I need to replace.

I just discovered a Mercury Service shop a couple miles from my house that either has everything in stock or can order it in. I can't believe how much I spent on shipping over a few orders that I could have saved by driving there. Oh well, live and learn.