Old Merc 150 pisser question

[Blue Agave]

The telltale (pisser) should have water coming out all the time.

I disagree,  no water will come out of the pisser until the motor reaches operating temp.  I have owned several Merc 200 EFIs and upon cold start they do not pee.

[Aquamaniac]

SeaBob......excellent point! Sure glad you pointed that out. SCARY.
Took me all of a trip to TrueValue to buy a $2 brass plug. Why wasn't it done right in the first place? I mean, really, it's just a motor run in salt water!!!  :banghead:


Capt. Bob.....ran wire into pisser with no obstruction noted. wide diameter tube from fitting on motor....but did not remove nylon fitting. Assume it is open behind it....although I suppose since an ell, the fitting itself might have some obstruction. Guess I will check that while I am at it.

Beginning to wonder about water pump...although when we added a 5" extension to make it a 25" motor, we did impeller, Tstats, and poppit.

Blue.....That is what goes on for me....nothing from pisser until you get going, although it does come from exhaust.

[Capt. Bob]

Capt. Bob.....ran wire into pisser with no obstruction noted. wide diameter tube from fitting on motor....but did not remove nylon fitting. Assume it is open behind it....although I suppose since an ell, the fitting itself might have some obstruction. Guess I will check that while I am at it.

My experience with the Rudes has always been, no clog felt but it peed great afterward.
Since it appears your tell tale doesn't flow until the T-stats open and no alarm is sounding, the "clog" may well have been your problem.
It never seemed to take much to block the flow on my Rudes so I have a habit of running a small wire up the "tale" on the Yamaha whenever I run it, pissin' or not.

[Aquamaniac]

Update on the pisser.....
Put in entire water pump (base, impeller,upper housing, etc.).....but still no stream.
Ended up pulling power head.
Found a gasket on the exhaust tuner was incorrect! Apparently did not allow proper flow.
Replaced gasket with correct one ...... now has a good stream!
Should note that even now, it has to warm up before it will piss.

[Capt. Bob]

Should note that even now, it has to warm up before it will piss.

This thread made me curious since I never owned or had experience with Mercury engines so I did a little searching around and found that indeed some Mercs will urinate before the T-stats open while others will not. Just a matter of the plumbing routing.
What year is your 150?

[Aquamaniac]

The FrankenMerc is a 1984 as best I can tell.

[GoneFission]

The image below shows the cooling water flow for your engine.  All V-6 Mercs of this timeframe were about the same - from 135HP to 275HP.

The water pump flow comes up to the cylinder/head water jackets, then exits through the t-stats at the top AND the outlets at the bottom that go to the pressure relief valve (poppet).  The water pump produces a good amount of pressure regardless of whether the t-stats are open, and that pressure needs to go somewhere.   When the engine is cold, water pressure opens the poppet and allows flow to cool the exhaust and water will also come out the telltale (pisser).  This allows some flow through the engine to prevent hot spots and also cools the exhaust before the t-stats open at around 140 degrees.  So if everything is working right, you should see water coming out the telltale fairly quickly after startup. 

A stuck or blocked poppet can also cause no water through the telltale until the t-stats open, but this could lead to no exhaust cooling and cracks on the exhaust outlets.  You may want to check or rebuild your poppet and see if what happens...     

[Capt. Bob]

Didn't I say this was interesting? ;D

On the Yamaha (and Johnyrudes) that "Water Discharge" exits through the vents/slots just above the ventilation plate and will begin flowing when the T-stats open. That's my visual indicator for their function since I currently have no temp gauge.

The poppet (high pressure relief) valve on mine (Yamaha) was sticking but I had tell tale water so I'm guessing it (tell tale) may be plumbed differently. I know the poppet was sticking because I would overheat (alarm sounded/rev limiter engaged) at speed.

As CJ stated, checking your poppet at this point is good procedure. Members will often include changing the poppet along with the T-stats/impeller as preventative maintenance.

Good luck.

[Fletch170]

Interesting, this explains a lot on my merc.

If I'm reading this correctly here is what I gather:

1. At cold idle, the pressure isnt enough to open the poppet, thus the block drains into the exhaust, and the head water circulates back into the system.

2. The only water that would come from the telltale when the engine is cold would be if you rev engine, and the poppet opens to release pressure.

Good Stuff guys, learning a lot here.

[GoneFission]

Interesting, this explains a lot on my merc.

If I'm reading this correctly here is what I gather:

1. At cold idle, the pressure isnt enough to open the poppet, thus the block drains into the exhaust, and the head water circulates back into the system.

2. The only water that would come from the telltale when the engine is cold would be if you rev engine, and the poppet opens to release pressure.

Good Stuff guys, learning a lot here.

Here's a response:
1.  A good condition water pump generates plenty of pressure to open the poppet.  There is no recirculation into the system - there are 2 outlets - one through the stats, the other through the poppet. 

2.  The poppet should open at idle because a good performing water pump has enough pressure - otherwise the water pump would have to cavitate with no output until the stats open - remember what you see on the telltale is what is going to cool the exhaust - assuming everything is working properly. 

[Fletch170]

GoneFission,

According to that diagram, you are incorrect. If the poppet is open, water would come out of the tell-tale. The diagram shows all water draining into the exhaust until the poppet or tstat opens.

Sorry man, what you responded didnt really make any sense.

Interesting, this explains a lot on my merc.

If I'm reading this correctly here is what I gather:

1. At cold idle, the pressure isnt enough to open the poppet, thus the block drains into the exhaust, and the head water circulates back into the system.

2. The only water that would come from the telltale when the engine is cold would be if you rev engine, and the poppet opens to release pressure.

Good Stuff guys, learning a lot here.

Here's a response:
1.  A good condition water pump generates plenty of pressure to open the poppet.  There is no recirculation into the system - there are 2 outlets - one through the stats, the other through the poppet. 

2.  The poppet should open at idle because a good performing water pump has enough pressure - otherwise the water pump would have to cavitate with no output until the stats open - remember what you see on the telltale is what is going to cool the exhaust - assuming everything is working properly. 

1. There are constant outlets from the block and head into the exhaust tube.

2. See #1

Am I way off base here? At idle, the pressure wouldnt be enough to open the poppet. If this was the case.....it would render a poppet useless, right?

[fitz73222]

The true role of the poppet is to regulate water flow through the block and slow the flow rate down enough so the cooling water actually absorbs heat from combustion. A faulty poppet valve generally will manifest itself in an overheat condition from mid range into high speed when the water pump and thermostats are known to be operating normally. The water pump is capable at higher speeds to blow water right through the block and without regulation cause a situation of overheating because of the lack of absorption of block temperatures. The thermostats alone are unable to regulate water flow enough to maintain block temperature without water pressure regulation at higher speeds. At idle, the water pressure is low enough, 5-7 psi to maintain block temperature with the stats. The poppet should be closed at idle. The bleed off in the system at idle is adequate to allow the thermostats to regulate temperature. At higher speeds, 15-25 psi the poppet helps regulate the water flow to allow the thermostats to do their job and maintain cooling temperature. As far as peeing at idle, it can be anything from a small steady drip to steady pulsed discharge depending on thermostat opening. You can validate the temp by laser pointing each thermostat housing with a temp probe and comparing the reading to the rated temperature of the thermostat. I've also seen a bad warning module that tells the hot horn to sound when the there is no problem in the cooling system to give a false cooling issue.

[futch13]

^^^^^^^What Farley said, same on Johnrudes and Yamaha, they all have poppets of some design.  The only difference is the plumbing whether the tell-tale comes out at adapter plate, exhaust plate or behind tstats as in some of the merc v-6's.  Also of note, is the amount of water needed to fill the block and the hose pressure feeding the motor, before water will show at the tell-tale.