Logo

Mercruiser 50L Alpha 1 Gen 2 Starboard Riser Hot

mikem

New member
"I have done just about everyt

"I have done just about everything I can think of to address this condition. I need help. My starboard riser is much hotter than the port riser. I can hold my hand on the starboard side about 3-4 seconds, port side is cool. T-stat housing discharging hot water out starboard side and cool water out port side. Some Facts:
1998 Mercruiser 5.0L carburated Alpha 1 Gen 2
brackish water use
RWC
Original Failure - mostly plugged starboard exhaust manifold resrticted water flow on starboard side manifold, spacer, riser. Melted/burned all rubber parts on/in the starboard exhaust components. Engine never overheated always runs 165-170F.
Actions Taken - replaced ex. manifolds, spacers, and risers as well as all melted/burned parts. Also replaced circulating pump (it was weeping out the seal hole) and T-stat. Upon testing the starboard riser did not burn or melt the rubber components but it was uncomfortably hot to the touch while the port side was cool.
Further actions - replace raw water pump (full kit including pump housing). Old impeller looked and felt in good condition but replaced anyway. Found metal backing plate from melted flappers in exhaust passage of outdrive upper housing. Upon testing same problem hot to touch starboard riser.
On muffs the water flow from exhaust are roughly equal port vs. starboard but the port exhaust water is cool and starboard is too hot to keep hand in stream. This can be traced back to the t-stat housing, it is hot on starboard side and cool on port side.
Further, Further Actions - replace t-stat housing old housing is rough with rust. Testing on muffs and later in water both result in uncomfortably hot (again to the touch) starboard riser. While on muffs the water flows are again equal but hot on starboard and cool on port.
I have since run the boat on the water for about 3-4 hours and at all rpms and boat speeds the riser remains consistenly hot. Engine temp always solid at just under 170.
T-stat housing is putting out hot water on one side and cool water on the other side. Housing is the open 4 hose type, no check valves/balls. part# 860256-C3. It appears that the hot engine water and the cool bypass water are not mixing prior to discharging out the respective sides of the housing.
What could cause this or is this temperature difference between port and starboard water discharge condsidered normal?
Thanks,
Mike"
 
"I am having the same the same

"I am having the same the same problem. Looking at the seloc book I have it says the system I have on my 1997 5.7LX is the one they show for the V6.
My tstat housing has 4 hoses. Twol large (about 2 inch) and two small (about 1 inch). The thing can only be installed and has no check valves or ball.
THe flow chart shows the raw water comming in on the port front, the stbd front to the engine driven water pump. That leave 2 ports left on the housing. They each go to the bottom of the ex manifold.
My seloc manual never shows a flapper valve although they mention it one time in the troubleshooting section.
Do I have to take off the rubber hose after the riser to check the flapper?"
 
"Thanks for the reply Guy. The

"Thanks for the reply Guy. The old housing and the new housing are both doing the same exact thing as far as cold water on port and hot water on starboard side.
Hose connectivity and functions (as I see it):
fore port - raw water inlet to housing from power steering cooler. In this chamber the water splits, some goes to chamber that feeds circulating pump and some goes to chamber that feeds the exhaust manifolds
fore starboard - circulating pump feed hose, this is fed from the chamber on the engine side of the thermostat
aft port - port exhaust manifold, this is fed by the thermostat (when open), and the raw water inlet
aft starboard - starboard exhaust manifold, this is fed by the thermostat (when open), and the raw water inlet.
Both aft ports are the same size and are coming from the same chamber, you can see through the housing at these ports.

The raw water inlet passage that leads to the discharge chamber of the housing is small and on the port side of the discharge chamber, I assume this is so that the incoming raw water can bypass the engine until it is up to temperature. Then once the thermostat opens most of the raw water enters the circulating pump to replace the hot water that has discharged through the thermostat, then any excess exits out through the bypass passage and into the discharge chamber where I would expect that it should mix with the hot water that has passsed through the thermostat.

There are 3 tapped holes in the housing
fore starboard - engine side of thermostat. not used (plugged)
aft port - engine side of thermostat. this is some probe, thermocouple for auto-choke?
aft starboard - engine side of thermostat. thermocouple to temperature gauge.


I also forgot to mention that I have replaced the thermostat 3 times to eliminate that possibility.
Thanks,
Mike"
 
"Im having the same &^$&#4

"Im having the same &^$(#&^ issue and can't figure it out! Replace and checked hoses, risers, thermostat, impleller. STBD is HOT, port riser is cool."
 
I have seen issues arising fro

I have seen issues arising from incorrect riser
gaskets being used. If memory serves me right
there are 3 or 4 different gaskets. One for full
flow and some partially blocked flow etc.
Did you pay attention to what the old gaskets
looked like? Check for exhaust flapper parts
lodged in y pipe
Kurt
}
 
"Thanks Kurt, I am using the o

"Thanks Kurt, I am using the original specification from Mercruiser, this is what the old gaskets were also. I am now aware that there is a tech bulletin from Mercuiser that says all gaskets should be open (4 slots) for my configuration and I will try that, I'm not overly optimistic that this will solve my problems though since I know the old gaskets were the same as they are now.
Current gasketing:
open gaskets (4 slots) on the manifold to 3" spacer surface and then restricted gaskets (2 open slots and 2 small holes on spacer to riser surface.

Earlier in my troubleshooting attempts I removed the shutter parts and confirmed clear passages with a boroscope in the ypipe and also from the outdrive (while changing the raw pump).

When I change the manifold/riser gaskets I'll check again in case the new shutters are getting damaged since I've run the boat like this for a few hours now.

One thing I'm not sure about (I never paid attention to it before so I don't know if it's always done this), is it ok that I see a small stream of water discharging through the prop while running on muffs? It's much less flow than what's coming out the exhaust ports?

Thanks,
Mike

John-with my configuration it is easier for me to loosen the lower rubber boot clamp that connects the elbow pipe to the ypipe then remove the riser, elbow pipe, and boots all in one in order to check the shutters. There may be a better way though.

"
 
"it ok that I see a small

"it ok that I see a small stream of water discharging through the prop while running on muffs? It's much less flow than what's coming out the exhaust ports?"

That is normal.

"Current gasketing: open gaskets (4 slots) on the manifold to 3" spacer surface and then restricted gaskets (2 open slots and 2 small holes on spacer to riser surface."

The top gaskets w/a hole and slot; could they be part of the restriction?
 
""The top gaskets w/a hole

""The top gaskets w/a hole and slot; could they be part of the restriction?"
It could be but it is the same way this engine has been set up since I bought it in 2006. I am going to change it to the wide open gaskets, I'm just not getting my hopes up too much since It ran fine like that for at least 2 seasons.
Thanks,
Mike"
 
"Installed the 4 slot gaskets

"Installed the 4 slot gaskets in all surfaces, no change.
Pulled the raw water hose that feeds the T-stat housing. Flow looks to be between 7-10 gpm at idle in the water.
When running on muffs I have equal flow out each exhaust port (hot on stbd and cool on port)

Heres where something seems strange to me, the t-stat housing is very hot where it feeds the circulating pump and relatively cooler where the hot water should be coming out of the engine and making it's way past the t-stat.
I am sure the hose configuration is correct and the new t-stat housing is identical to the old one, could the circulating pump be pumping backwards? I installed the flat pulley that came off the old pump (the back side of the serpentine belt drives it.)
Mike"
 
Mike:

The circ. pump hose s


Mike:

The circ. pump hose should be hot before the T'stat opens and adds cooler water to the flow. Don't take this wrong; is the T'stat hsg. installed w/the SS hose fitting connected to the raw water inlet hose? Is the thermostat pellet pointing down? Since we are running out of solutions I figured I'd ask. My apologies.
 
"Mike;
This is a long shot, a


"Mike;
This is a long shot, and I do not want to insult your intelligence; but are you sure the T'stat is installed correctly?

It should have the sping & pellet down, and the cone shaped end pointing upwards. It should be a 160 degree.

Also, there should be a flat gasket against the intake manifold, then a spacer sleeve piece (that has a partial cutout), then the T'stat, then a circular gasket where the t'stat sits in the housing. Is this all installed correctly?

The hoses to the manifolds get a mix of hot water passed by the T'stat, and excess cold incoming water. There is no way one should be hot and the other cold. Have you tried flushing these hoses out with a garden hose to assure they flow freely?

You changed the manifold and risers right?
The new circ pump should be OK, and direction of rotation does not matter.
If nothing else works you should maybe get another circ pump. It may be defective, as unlikely as that may seem.

Rod"
 
"Don't worry about my feel

"Don't worry about my feelings fellas I just want this right.
Raw water feeds the 1.5" nozzle (front port connection)
The 2" nozzle feeds the circulating pump (front stbd connection)
The two 1" aft nozzles feed the respective exhaust manifolds.

Yes, the t-stat is installed correctly, exactly as you describe.
Yes, manifolds, spacers, risers all new.

I'll remove the belt, t-stat housing and some hoses and rotate the circ pump by hand to see if it's doing anything to the water in the block. Even by hand it should move some water through the block, right?
Mike"
 
""I am sure the hose confi

""I am sure the hose configuration is correct and the new t-stat housing is identical to the old one, could the circulating pump be pumping backwards? I installed the flat pulley that came off the old pump (the back side of the serpentine belt drives it.)"

For gm engines there are standard rotation and reverse rotation water pumps. Are you sure you have the correct one? Maybe you have the wrong one, witch would mean the impeller is not spinning the correct direction and not circulating water well enough.
Kurt"
 
"I checked on what circ pump I

"I checked on what circ pump I ordered, it is a bi-directional impeller.

I'll try to confirm that it is actually moving water."
 
Was this going on before you c

Was this going on before you changed the circ pump?
If not I would say the pump is your problem in some way.

Rod
 
"Before this problem:
I'v


"Before this problem:
I've always had warm-to-hot risers, but both were always a similar temperature. When on muffs the discharge water was the same temperature out each side and I could keep my hand in the stream.
The original failure event was the stbd riser heated up and melted/burned the rubber connecting hoses and shutter. Upon removal of the components I found that the stbd ex manifold allowed some water flow but it was restricted (it put back pressure on a garden hose) while the port side was free flowing."
 
Mike
I took mine apart last n


Mike
I took mine apart last night and my flapper was new and no resctriction in the riser
Water flow looked good on muffs and when garden hose hooked directly to the manifold hose.
I am begining to think mine is a lean running starbord head causing the heat.
Can I adjust that or not? Rod or Guy does this sound like a probability
 
John:

Perhaps two mixture s


John:

Perhaps two mixture screws would help; not sure. Sorry. On your T'stat assy. you don't have a "T" ball valves assy.?
 
"So it looks like the circ pum

"So it looks like the circ pump is moving water. Just before I jumped off a bridge I had one last thing to try...
I tried running without a t-stat to see what would happen.
Engine temp ran at 130, housing was cool and circ pump feed hoase was cool.
revved up to 1600RPM and temp drops to 120ish
I feel around the exhaust components and since all the water is now cooler I can detect hot and cool spots on my new stbd ex manifold and stbd riser. Could there be partial blockages in the new parts? Like I said on the muffs the flow was similar out the exhaust???"
 
------------------------------

--------------------------------------------------------------------------------
John:

Perhaps two mixture screws would help; not sure. Sorry. On your T'stat assy. you don't have a "T" ball valves assy.?

No T ball. <
 
John: I'm at a loss w/you

John: I'm at a loss w/your problem. It sounds like it's too lean but then it runs great. Perhaps the amplifier module is on its last leg and is acting up; just doesn't make sense. Most failing solid state devices act peculiar. You might try resetting the idle and mixtures when the engine is warm while in forward and tied to a dock. Good luck.
 
MikeM:

Anything is possible


MikeM:

Anything is possible with new parts. Are they Merc. parts or aftermarket? What brand is the port side? What riser gasket is on the starboard; 2 or 4 slot compared to the port?
 
"Idle mixture screws will have

"Idle mixture screws will have nothing to do with how hot or cold one side runs under power. You could have issues if one barrel's fuel venturi cluster is plugged off, but if ts running OK at power this is very unlikely.

Mike; if you have good water flow out both risers with the garden hose, your water flow is just fine. The water flow thru the manifolds and risers is not smooth or uniform and you will usually have some variations in temp.

The fact that things seem to work better with no T'stat seems to indicate maybe it is the problem. I would try another T'stat and if that doesn't help maybe just run without it. That is not generally recommended, but may be your best option in light of no other obvious solution. You are better off to have engine and riser too cool than too hot.

Rod"
 
"Guy - it's a 98 5.0L carb

"Guy - it's a 98 5.0L carburated.
Port and starboard exhaust components (risers, manifolds, & spacers) are all new and aftermarket, GLM. I originally used 4 open slots on the manifold and 2 open on the riser, then a couple days ago I switched to all open gaskets. No noticable change while running.

Thanks everyone for all the input throughout my ordeal, I'll pull the risers off and see if I can probe around in the manifold jackets near those hot spots, same with the riser. If I find anything I'll update.
Thanks,
Mike"
 
GLM are good AM products. 160

GLM are good AM products. 160 F. is the correct T'stat. Are you using a merc. brand T'stat? I would. Best of luck.

The GLM manifolds separate the exhaust outlets until they gather near the top of the manifold while Merc. allows them to enter a single chamber.
 
I do have some kind of flakey

I do have some kind of flakey material plugging up areas of the stbd riser (most of the top jacket) and ex manifold (forward 1/3 of the manifol side jacket). Didn't have time to dig it all out but it seems soft enough to get relatively easy.
 
Back
Top