1969ish Merc 500 Thunderbolt Water Pump?

[tredragon]

Okay, flame away search nazis... I've looked.

I have a 1968 Larson All American (Lapline) with a circa 1969 Mercury 50hp Thunderbolt 500 outboard. The guy I bought the boat from said he noticed no water jetting out below the head. I pulled the lower unit but was only looking at the impeller... which looked practically new.

My questions is... I've had it running in a trash can for over a minute and the two rectangular ports just below the head are spitting out almost exhaust-like air... that is... warm and pulsating with the motor. No water coming from the upper end of the unit. Is this cause for concern and if so... where to look? Water pump? Pickup Tube (maybe a spider or wasp made a nest??)?

Anyone with real experience with these older merc's please respond. I was hoping to take my family out this Sunday!!

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

If you really know anything about this older merc... please reply. I was hoping to take my family out later this weekend... need to know the motor isn't going to fry. I have young children!! Obviously I won't take them out until I know but they are all soooo excited to go out on a "real" boat!!

 

[jason1150]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

try sticking a piece of weedeater line into the pee hole to unblock it, I think those ports blowing hot air are the exhaust relief ports for when your not moving in the water, hope this helps, J

 

[emckelvy]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

If it's pumping water in the bucket, there should be water spray mixed in with the exhaust coming out the relief ports.

Feel the exhaust manifold cover with your hand while the motor's running. Idling in a bucket full of cold water with no load on the motor, the cover should be stone cold.

If it's not pumping water, the exhaust manifold will get Real Hot Real Fast!

Since the impeller looks good, if you're still having pumping problems you might try hooking a garden hose to the copper water supply tube (with the lower unit removed). Check for free-flow thru the powerhead. Watch water pressure if you've got lots of it; these motors never ever see more than 15 psi if anywhere close to that.

One other silly thing, make sure there's the impeller drive key is in place or she ain't gonna pump much!
HTH......ed

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

Stupid question maybe...

When you say exhaust manifold cover... do you mean the whole cover that wraps around the block/heads? Sorry, just give me an idea where to feel so I know I'm being thorough.

To the guy who said putting weed-eater line in... do you mean the exhaust relief ports where the water should be coming out as well? I'm guessing I'd be going up with the line?

 

[emckelvy]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

The exhaust manifold cover is the big flat plate on the Port side of the engine which covers the area over the exhaust ports. Water circulates through the cover and over the exhaust baffle underneath. This keeps the area cool, which is good because the exhaust dumps right onto these covers. Lotsa heat in the area.

So, if you're not getting good water pressure/flow thru the powerhead, the outer cover gets real hot real fast. Otherwise it'll be cool or just lukewarm.

BTW the cover over the back of the block is just that, a cover over the large area where water circulates around the cylinders. There is no cyl head on this model, the block is all one-piece casting. Where the spark plugs stick thru, the top of each cylinder is machined flat and that's what seals against that cover.

I think the weed-eater line reference would be sticking it up the telltale to try and clean it out. It's very common for the telltale to get plugged up then you get no indication of water flow.

Just look for a hose exiting the cowling on the aft Stbd side of the motor, and you'll see the hole in the outside of the lower cowl where you'll want to use line or wire to clean it out.

Blowing compressed air up the telltale hole is usually more effective, if you have access to an air compressor or other source of 'canned' air.

HTH........ed

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

Okay, but if I blow the air up the telltale... I'm guessing I want to disconnect the hose so I don't blow anything back down to the bottom end. Sorry, I've not looked at these parts yet so maybe I just can't conceptualize.

Thanks for being so helpful. Not only to me... you're all over the boards and I'm sure I speak for everyone you help when I say "THANKS!"

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

See pic (not my motor but close enough)...

This is where I'm getting the exhaust relief and should be expecting it to pee from... right?

 

[emckelvy]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

Yup, those are the exhaust relief ports. These come into play when the motor is in the water but the boat's not moving. The exhaust can't force it's way out the prop very well. To relieve some of the excess backpressure, the exhaust is allowed a path to get out via the ports.

Most of the water coming out of the motor is going down the middle of the center section (AKA "leg", "exhaust tower"). So, the water and exhaust will co-mingle a bit. Some of the water being dumped down the middle gets 'dragged' out the exhaust relief ports.

Thus the spray out there! And even underway you'll get some exhaust out the reliefs along with a good dose of water.

The "telltale" or "pee-hole" is a convenient way of being able to look back and see the motor's watering. Not by coincidence is the telltale on what's typically the driver's (stbd) side, so you can look over your shoulder and easily see it.

There's Water Flow 101 !

Now, don't worry about blowing air up the telltale hose. You're not gonna hurt anything. Just keep the air turned down to a reasonable pressure (not 150 psi if you know what I mean!).

All it's going to do is blow thru the block, mostly out the discharge ports at the bottom. It'll blow a bit back down the water tube, but the discharge side of the cooling system is so much larger that most of the pressure will be relieved thru that side.

If you hear air flowing very freely you know that the passages are clear. There should be plenty of water flowing out the telltale with the motor running.

Just remember that the telltale is NOT the exhaust relief ports but a separate hose, connected to a portion of the block that sees full water pressure.

If you're not sure what this is, look inside the lower cowling on the stbd aft side and you'll see the hose connected to a fitting at the cowling. This hose runs around to the other side and connects to another fitting screwed into the block. It's rather hard to see where, but if you look under the end of the bracket that the throttle & shift cables sit on, you'll see it at the bottom of the exhaust manifold.

This is the hose you blow out. Either blow thru the telltale fitting from outside the cowling, or disconnect the hose inside and blow thru.

BTW, it won't do any good to blow air up the exhaust relief ports if that's what you meant (just to make sure there's no misunderstanding).

That oughta do 'er & thanks for the kind words!.......ed

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

I'm going to post some pics after I take a further look. I found a hose that runs from the top of the block to just above the exhaust relief ports, but on the stbd side, not centered above them. Edit: (The former was the right one, the telltale.) Then I found a plugged hose on the stbd side that runs to the port side and becomes almost invisible under the linkage(s) over there. My guess is that the plugged one was the water pressure gauge hookup...

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

Edit: Nevermind. The first pic, that hose going from top of block goes down the stbd side and then into a fitting at a perpendicular angle to the ground. Tracing a straight line from there and then looking up from beneath... I found the actual pee hole... where some sort of hymenopteron had made itself a home.

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

i"m an idiot... or so I feel. All this time I was looking for the exhaust relief ports to be the exact same place that the water should be peeing out of. Only after I traced the hose from the top of the block down to where it met another fitting and seemed to go no further... did I notice a little grayish brown "smudge" just under that. I picked at it a little and realized it was mud, more than likely a wasp/bee nest. I used a small screwdriver, then a 12" piece of trailer light wiring I had laying around and tons of sediment came out of the hole. I was then convinced that was the actual pee hole and (although I had to jump start the boat) got it to start and immediately... PEE!!

Thanks Ed and everyone! Fiberglass repair just got done today (aint pretty but for $200 and it's sturdy as hell....)... so I think the boat my see her maiden voyage tomorrow!!

 

[emckelvy]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

Yay! Feels good!

Now for a shameless pun on Tom Petty, "yeah I'm Free, Free-Flowin'!!!!

 

[tredragon]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

last question... my battery was nearly dead... these motors do have alternators though, right?

 

[MIKEY*2007]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

yes but you should always top up on charger now and then keeps battery healthy and stators don,t charge as quick as cars

 

[emckelvy]

Re: 1969ish Merc 500 Thunderbolt Water Pump?

I smell another thread coming!!!!

Your Merc has a set of charging coils (aka stator) under the flywheel which act as the alternator. You'll find a harness with 2 yellow wires coming out of it, coming from the stator. These go to the rectifier which has (3) connections on it.

(2) for the AC component coming from the stator (yellow wires), and (1) for a battery (+12V) red wire.

If you have a voltmeter (digital or analog), measure the voltage at the battery terminals at idle. Then rev the engine up a bit (not too fast in neutral now!) with the fast idle lever and voltage should go up. If it doesn't, the most common cause of that is the rectifier. Easily replaced and not that expensive retail. And if you do a search on the forum for "rectifier", you'll find some recommendations for a very very cheap aftermarket replacement that probably does a better job than the original.

There's also a possibility that the stator is bad but that's very rare. To test the stator, disconnect one or both of the yellow stator wires at the rectifier. With your meter on Ohms x 1 or whatever low-range scale it has, the stator should "ohm" out at a very low value, usually less than 1 ohm. With the meter on a hi-ohms scale, measure the resistance between one lead and a good ground (anywhere on the block). This value must be very high, in other words the stator mustn't be shorted to ground.

But if you're not charging I'd bet money the rectifier is shot. If you don't have a meter, I'd also bet Sears is having a hot 4th of July sale on them right now!

One last possibility, maybe the batt just ran dead 'cause you were doing a lot of starting while you were troubleshooting? Give it a good charge and see what happens!

Cheers......ed