Logo
FULL SITE MENU

one riser hotter than the other

One manifold always runs warmer than the other but not hot to the touch. Rod's tet tells you how much water the impeller is pumping.

...have thoroughly inspected the thermostat housing, both the water lines running to the bottom side of both exhaust manifolds,
Click to expand...

Water flow to each manifold is controlled by the T'stat hsg. A second water flow test determines the volume of water going to the manifolds using clear plastic hoses while the outdrive is immersed in water and not connected to a garden hose with muffs. This method also tests the water pressure that the impeller puts out and the distribution of the water flow by the thermostat hsg.

If there are no bubbles in the water flow to the manifolds and the water flow is weak to one manifold then the T'stat hsg. is the likely culprit if the impeller output test (Rod's) is good. If there are air bubbles in the clear hoses, the air bubbles will not transfer manifold heat. The source of the bubbles is most likely the outdrive. There is a water pocket seal at the base of the upper half of the OD that the copper water tube is inserted. If the seal leaks exhaust/air can enter the water stream. The impeller housing can also allow air into the water stream especially if the plastic hsg. upper/lower halves are distorted from a prior overheat--they have to be replaced. Perfect seal on the base gaskets can stop air intrusion. JMO
 
To add one more thing about bubbles,

You say you did the impelklor allready?

If so there is a small odd shaped hat/seal that slides over the vertical drive shaft of the lower unit and sits on top of the stainless steel impeller housing.
If that is missing/not installed correctly it will allow exhaust gases to enter the water from the top of the housing.
 
Ok, well I think this "odd shaped hat/seal" is called the "face seal" which is included in my water pump kit however, I'm not sure about the "water pocket seal."Am I correct in these diagrams?

unit.jpg​




Thanks guys.
 

Attachments

  • upper housing.jpg
    upper housing.jpg
    72.6 KB · Views: 49
YOu are correct with the parts identification.
IMO the most likely culprit with air intrusion is the pump impeller/pump case.
Guy mentioned distorted plastic parts, but since yours is an Alpha Gen II this will not apply. The base plate and pump case can are all metal.
As was said, using a sealant around the base gasket will usually solve the air problem

Rod
 
The water pocket seal typically is not needed to be replaced. It does not wear out very often typically only if things get very hot in the water pump cavity. This occurs if you have thru prop exhaust and no or little water flow as the exhaust flows directly out and over the water pump impeller assemblyand it gets very hot and will dry out the pocket seal.

WHat does happen is the tube comes out and most will install it into the water pump housing and when installed can and will pinch the pocket seal. The tube should be installed into upper before lower installed.

If you seperate the two halfs you will have to physically look up and see what is going on. Typically if this is pinched it causes a over heat condition as the overall water flow is restricted..........

One other thing to consider, if the water pump housing base gaskets are torn they will allow exhaust gases to enter the water stream also.

Again if you had exhaust gases in the water stream then you would see an overheat condition espcially at high speeds................

One more thing, you said you had the thermostat housing apart, you said all looked good at the areas I pointed out in my first diagram.

When you said looked good, where the holes/output holes equal in diameter or could one have been corroded and scalling and smaller in diameter. This is easy to check, just remove the hoses and look. Also could there be an abstruction where the water flows into the bottom of the exhaust manifolds???
 
Thanks, non taken. If there are no bubbles then I'm leaning toward an oversized or narrowed diverter hole in the T'stat hsg. like Kghost mentioned. It just dawned on me that if the thermostat is installed w/o all of the seals or if they are in the wrong order or location then water distibution could be affected.
 
Has anyone noticed there have not been any posts lately from cheifalan? Must have gotton himself banned. Let's keep moving forward.:cool:
 
Well, I have all the parts to replace the water pump so maybe I'll try that this weekend. The thermostat housing was completely unobstructed and looked fine from all angles. Guyjg mentioned all the thermostat seals and locations? When I removed the old one there was only the one seal between the intake manifold and the thermostat housing, the plastic spacer that holds the thermostat, the thermostat and then a rubber round seal that goes in first between the thermostat and the top of the housing (all of which I replaced with new.) Is there supposed to be more?
 
Just a thought from racking my brain; can you post an overhead photo of the thermostat housing showing the position of it in relationship to the front of the engine. Include a few pics of the manifold hoses too. Let us know the clear hose test results.
 
One more item to look at,

the water hose that connects to the upper gear case and connects to the transom. Make sure this water hose is not kinked or collasped.
also look closely at the pick up gills on the lower and make sure there is no junk in there, if you do replace all the water pump components you should be able to look down and confirm it is clear.

One more note: it is not uncommon for one side to be 20+ degrees hotter than the other. The water flows the path of least resistance.......
 
I personally would not be to concerned with the heat/steam issue.

Due to your water flow configuration and the fact that the cold water flows thru the exhaust manifolds first (gets HOT) before the elbows and out the exhaust, I would say steam is going to be present.

Older/other water flow configurations had a second thermostat housing COLD water output hoses that went directly into the elbows which really cooled the exhaust....

My suspision is your cionfiguration is to blame for the steam. Maybe one of the current merc techs working in the business may be able to agree with this or disagree and why.

Thats my opinion.
 
The heat issue doesn't concern me as much as the steam issue.
Click to expand...

If there aren't any bubbles in the cooling water and you are concerned to the point that you want to balance the flow between manifolds then insert a 1/4 turn 1/2" brass water valve w/barbed fittings in-line of the high volume water line and adjust the flow to where each manifold runs at the same temp. Use a laser IR temp gun.
 
Do you by chance have your engine serial number handy?:)

Ace111799 said:
Guyjg mentioned all the thermostat seals and locations? When I removed the old one there was only the one seal between the intake manifold and the thermostat housing, the plastic spacer that holds the thermostat, the thermostat and then a "rubber round seal" that goes in first between the thermostat and the top of the housing (all of which I replaced with new.) Is there supposed to be more?
Click to expand...
When you say "Rubber" seal, Is the seal that you're using a Black rubber O'Ring or is it more of a tan clored cork type material?:confused:

kghost said:
One more note: it is not uncommon for one side to be 20+ degrees hotter than the other.

I personally would not be to concerned with the heat/steam issue
Click to expand...
This is what i'm used to seeing especially on the non dry joint exhaust manifolds. Normally it's on the starboard side. Another reason this style engine would run hotter on the starboard side is because i believe he should have a tube that get's very hot going between his intake manifold and starboard exhaust manifold. See item # 4 below for an example. Your engine serial should help confirm this theory.
http://www.mercruiserparts.com/Show...697&bnbr=180&bdesc=Water+Pump+And+Front+Cover

Your right is not all that uncommon to see some steam coming out at times.


guyjg said:
Use a laser IR temp gun.
Click to expand...
I couldn't agree more, The infrared thermometer reader gun is the best tool to use so you know exactly what temperatures you are dealing with.:)
 
Just for a reference point, my 6.2 MAG MPI is RWC with a 170 F t'stat. The 170 F T'stat water goes to the bottom of the manifolds, and cool inlet bypass water goes to the base of each riser.
The temp gauge is rock solid at all times, and the manifolds run 180-190; the risers 80-90F. All taken with an IR temp gun. The risers are never hot to the touch. The lake water runs 65 to 75 F.
I often get several seconds of steam from the exhaust just after starting up after a shut down of a few minutes to a 1/2 hour or so. Then it stops.
I have side exhausts above the waterline, so its easy to see whats coming out.

Rod
 
My engine S/N is 0L614081.

I do have part#4 in the digram (the tube from the intake manifold to to starboard exhaust manifold.) What is that?

When I put the thermostat in there was a flat rubber seal that fit in the housing above the thermostat, I replaced it with the same one in the kit. Then the cork gasket that has these rivet looking things embedded in it went between
the housing and the manifold.
 
Ace111799 said:
My engine S/N is 0L614081.

I do have part#4 in the digram (the tube from the intake manifold to to starboard exhaust manifold.) What is that?

When I put the thermostat in there was a flat rubber seal that fit in the housing above the thermostat, I replaced it with the same one in the kit. Then the cork gasket that has these rivet looking things embedded in it went between
the housing and the manifold.
Click to expand...
The tube I believe is to help control engine emissions. it gets well over 200 degrees so be careful around it.

In case you would like them, The below link is the engine parts to you're engine serial number for you.
http://www.mercruiserparts.com/selectSerailRange.asp?doc_nbr=5.0L+(2+BBL.)+GM+305+V-8++1998-2001

Was the flat rubber seal Tan in color? It looks like it was, Just as long as it was not a black O'ring your good.
It should look like item number 3 in this link below, Click on the part number 27-806871 for a photo.
http://www.mercruiserparts.com/Show...r=2697&bnbr=110&bdesc=Standard+Cooling+System
 
Yeah it looks like that one but it was rubber. It was just like the one that I took out which had been in there for who knows how long. Seems like it's working as it should. Except for the original problem that I was trying to fix. My plan tomorrow is to pull the drive and change/align the gimbal bearing. I will put in my new water pump while I'm at it. If it's still doing it after that I may try the clear hose test and go from there. Or just not worry about it.

Thanks for all the input.
 
Well I didn't find anything obviously wrong with my old water pump but I went ahead and replaced everything. I winterized the boat over the weekend also so I guess I won't know if I accomplished anything until next spring. Thanks for all the input from everyone.
 
You should have not spent all that money and replaced everything . I hade the same issue but lucky for me I am a marine mechanic so I diagnosed the problem in seconds . I own 4 boats and all of then hade the same problem . I know the 100% guaranteed solution to your problem . Let me know if you still want to know and I will tell you . In curiosity sake .
 
Okay So If You Checked Everything The Thread Said And What People Suggested To Do Did Not Work For You And You Still Have The Problem. Follow These Steps Carefully. (1/3) Remove Your Riser & Take It Apart Making Sure It Has Not Build Up Any Rust Inside That May Be Restricting A Good Water Flow. If You Wanna Make Sure For Sure Then Take Off The Water Housing Thermostat And Check Water Color The Water Is Inside The Thermostat. If It's A little On The Rusty Color Side Then Definitely Remove The Riser. Pressure Wash Or Air Compress The Inside Of It And Put A Dab Of Oil Inside. (2/3) Check The Wide Rubber Hose That Comes Down From The Riser To The Drive And See If Its Not A Purple Color. If It Is Definitely Replace That IS A MUST. (3/3) Last But Not Least Once You Have Done And Checked Everything I Said And It Still Does Not Work Then The Best Thing To Do Is Just To Buy A New Riser And Hose. And You Will For Sure Not Have The Problem. Hope This Helped. Capt. D.J. From Venice Marina Good Luck
 
Well considering I replaced both risers & manifolds with no change I'm pretty sure I can rule that out. Its been doing this since I have owned it (4 years) and has not seemed to have any other adverse effects so I'm not really worried. Best I can figure is I'm not getting enough pressure from the raw water pump which may indicate it has some kind of seal issue. I may revisit that theory when I pull the drive next time. Not really planning on that till next summer. Thanks for the input though.
 
Back
Top