Mercury 500 50 hp Thunder bolt ?

[fancy1]

We have recently purchased a boat with a Mercury 500 50 HP Thunderbolt engine, we think its a early to mid 70's model. The engine does not "pee" while idling only when you rev the engine and then it is extremely hot (you can not put your finger in the stream). We are not sure if this is normal for this type of engine, if anyone can help that would be great. We have not been able to put this boat in the water yet and have only tried it with the muffs and the water hose. Other than this issue the engine seems to run great. If any more info is needed let me know. Thank you all in advance for any help you can give.


P.S. This is a project boat we purchased, we have another we fish with but really want to get her in the water soon.

 

[FLATHEAD MAC]

Re: Mercury 500 50 hp Thunder bolt ?

good chance of bad impeller . just replaced one for my buddys '74 mercury 500.

 

[MacDaddy21]

Re: Mercury 500 50 hp Thunder bolt ?

Impeller replacement and the thermostat could be bad. If its pumping hot water, it needs a thermostat too.

 

[Gomer50]

Re: Mercury 500 50 hp Thunder bolt ?

If its a 70's merc. 50hp they didnt have thermostats.First thing usually when purchasing a used boat I would suggest replacing the water pump impellar and gaskets just on the safe side.The water when peeing on muffs will get warm but not hot.It is possible that when running on muffs there is not enough water pressure to fully cool the engine (maybe).When submerged in water (the lower unit) the water pump can do its job like its suppose too.

 

[MacDaddy21]

Re: Mercury 500 50 hp Thunder bolt ?

I assumed it would have a thermostat because my 1979 402 40 hp does.

You could do something similar to what Gomer suggested and run it in a big tub of water to simulate submerging the lower unit in a lake

 

[Gomer50]

Re: Mercury 500 50 hp Thunder bolt ?

You are right most that I am aware of are 1976 and older so to tell for sure a serial number would tell all.

 

[MacDaddy21]

Re: Mercury 500 50 hp Thunder bolt ?

Yeah, the Mods should put a huge note at the end of registration that tells all new forum users to always post year, model, and serial number in the first post when posting in any of the outboard forums.

So, can we get a serial number?

 

[scoyt]

Re: Mercury 500 50 hp Thunder bolt ?

I have a 1974 Mercury 500 that "pees" at idle. Replace the water pump and you will probably be good to go. Happy boating!

 

[tbagger]

Re: Mercury 500 50 hp Thunder bolt ?

Not wanting to hijack but I have the same motor, same problem and just replaced the water pump but can't get it to shift when I put it back together.I've taken it apart and put back several times still the same, I know it's the shift splines but can't seem to get them to line up, any suggestions. Thanks, Tom

 

[MacDaddy21]

Re: Mercury 500 50 hp Thunder bolt ?

pull the lower unit, shift the control box into F, N, or R (whichever you choose), then grip the splined shift rod with pliers where it comes out of the lower unit, and turn it so the prop spins the correct way for the position of the shift lever on the control box. Then put it back together.

 

[scoyt]

Re: Mercury 500 50 hp Thunder bolt ?

X2 on macdaddys comment. Thats what i had to do when I changed my pump one time.

 

[Faztbullet]

Re: Mercury 500 50 hp Thunder bolt ?

The only 50 hp with a t-stat is the 3 cylinder.. the 4 cylinders do not have one.

 

[MacDaddy21]

Re: Mercury 500 50 hp Thunder bolt ?

The only 50 hp with a t-stat is the 3 cylinder.. the 4 cylinders do not have one.

thanks for the clarification, good to know.

 

[fancy1]

Re: Mercury 500 50 hp Thunder bolt ?

Yeah, the Mods should put a huge note at the end of registration that tells all new forum users to always post year, model, and serial number in the first post when posting in any of the outboard forums.

So, can we get a serial number?

I'll get the serial # and post it as soon as I can

 

[tbagger]

Re: Mercury 500 50 hp Thunder bolt ?

Thank you MacDaddy, it worked in nuetral like a charm, life is good again. I had to tap down the upper shift shaft from above to get it down to mate with the lower but it clicked right in. Now have to wait until this torrential rain stops to see if the water pump works.

 

[fancy1]

Re: Mercury 500 50 hp Thunder bolt ?

Thank you all that have responded, sorry it took me so long to get back with the serial # but here it is Serial # 4806224, and more info will always be helpful

 

[Buzz Killington]

Re: Mercury 500 50 hp Thunder bolt ?

Look at some of the videos on Youtube to get an idea of what to do. Just type in "mercury impeller change" or variations on that. I JUST did this job this weekend on my '68 1400 - I bought a new impeller and water pump housing. Iboats may even carry it, I can't recall now. It's straightforward. You can't really mess up the gasket replacement because they are all indexed so that you can't install them unless they are lined up right (at least on mine).

The first time I had it apart and back together it didn't work - one of the "vanes" on the impeller was twisted backwards.

The second time it didn't work - I forgot to re-install the "slinger" (a little rubber o-ring that sits on the shaft above the water pump housing). I also took this opportunity to blast the water line out with my garden hose to make sure no junk was in there.

Third time it worked like a CHAMP! Very satisfying.

 

[MacDaddy21]

Re: Mercury 500 50 hp Thunder bolt ?

Okay fancy, your motor is a 1977, as shown here:

http://www.iboats.com/basics/mercury.html

Here is the parts schematic for your motor:

http://www.crowleymarine.com/mercury-outboard/474.cfm

I'm see no thermostat on this motor. I'm going to call a friend of mine who is a former Mercury mechanic, and see if he has any ideas. I'll try to get back to you tonight or tomorrow morning.

 

[fancy1]

Re: Mercury 500 50 hp Thunder bolt ?

Thanks MacDaddy, I appreciate it.

 

[MacDaddy21]

Re: Mercury 500 50 hp Thunder bolt ?

I wasn't able to get a hold of my buddy today, but I thought about it for awhile today, and I was going to ask you if the water coming out of the hose is pretty hot. I don't know where you are located, but I'm in Central Texas, and in this summer heat, the water that comes out of the hose can be really hot, even after running for 5 or 10 minutes.

I also wanted to ask you to check the condition of your impeller housing. Check for cracks, wear, or any imperfections around the base of the housing, and around the 2 holes in the housing (where the driveshaft and water feed tube go). It may not be getting enough water through the system fast enough, so the little amount that exits is hotter.

I found this video on youtube. The motor is one year younger, but is all the same. Watch the tell tale at idle. There is a steady stream coming out. Yours should do this. I think you need to pull the lower unit, and try to force some compressed air up the the tell tale and see if you can get anything to come out that may be blocking the flow. For now, that is going to be your best bet.