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Mercruiser 50L Alpha 1 Gen 2 Starboard Riser Hot

"Mike, I feel your pain. Wor

"Mike, I feel your pain. Word for word and step by step, was done on my boat for the past 3 weeks. Are you by chance at Mermaids? - same year engine, & 5.0L, same outdrive & boat -1990 Bayliner cierra 2455. (see earlier post). If not, I hope we can learn from each other, because I find it very strange. I will try removing the thermostat and see if the same response as you are seeing."
 
"Mike;
Is the flakey material

"Mike;
Is the flakey material some kind of metal? Are they shiney like they are freshly ground up? Or maybe just some sand that you picked up?

If its metal about the only place that could come from would be the circulation pump.
Save for the impeller, which is rubber, there are no other moving metal parts in the cooling system that I can think of.

Rod"
 
"Mike;
sorry I missed your e

"Mike;
sorry I missed your earlier email (on my post)otherwise I would not have asked the question above.
So must be a design flaw with this engine type and set up to be faced with the EXACT issues. Step by Step I have done exact as you have, including all the same parts(risers, manifolds circulating pump,raw water pump (2X), thermostat (2X)...every hose checked, flushed several times. Flow coming in is as you said good @ ~7 gal/min. We took the risers out again to check the gasket. The engine stays at 170 no matter what in brackish water ..so does not overheat. But the starboard riser continues to be hot and port cold.. The mechanic heard there might have been a recall on the thermostat housing , so he has ordered another ,which will be installed tomorrow. Current one does not have check valve /balls. Also will look into removing the thermostat as you did. Any thoughts whether the engine block itself is clogged.? As a last resort, we are contemplating flooding the block with acid to see if it helps. Will keep you posted...if I don't jump off a bridge."
 
"Ray,
I think for some reason

"Ray,
I think for some reason a partial blockage in the starboard riser/manifold causes an odd flow distribution in this style t-stat housing because the cool water bypass inside the housing is on the port side. When I remove both stbd and port hoses to the manifolds at the same time the water temps even out (coming out of the hoses). I think it works fine when all is right but if anything is wrong with the water flow the stbd side gets mostly hot engine water and the port side gets mostly cool bypass water.
I'm in Edgewood, MD just off the Chesapeake Bay.

Rod - I had all these symptoms for 2 weeks while in the work rack (never had the boat in the water since new components were installed)I finally decided to put it in the waters incase the water hose wasn't supplying enough water. After I put it in the water I never ran aground or went throug any muddy water and the symptoms stayed the same.
The material almost looks like something maybe left over from the casting process (tan in color, soft, thin, and flakey, and 1/2inch by down to small granules - partially fused casting sand maybe?), definitely not metallic. I never checked the water flow through these parts before installing them, I will certainly confirm flow in all passages on new exhaust parts from now on.

Once I get the passages all cleaned out I'll reinstall the T-stat (another new one) and see how it works.
Mike"
 
"Ray, keep us posted if the T-

"Ray, keep us posted if the T-stat housing did the trick. i have been through this same thing I don;t know how many times (replaced thermo x2, raw water pump, checked stbd riser, flushed lines, etc.) and still have a hot stbd riser and a cool port one. I can't explain it."
 
You can cross the hoses to the

You can cross the hoses to the risers from the T'stat hsg. to see if the hot and cool temps follows the hoses. If it does then it's a T'stat hsg. distribution issue.
 
"Guy,good idea I will try this

"Guy,good idea I will try this if the hoses are long enough next time.
Update after spending part of July 4th at the dock repairing the boat. I am encouraged but not totally out of the woods yet. First,I took the thermostat out as MikeM did and both risers stayed cool and engine gauge stays lower at 130 degrees. My engine is responding the same as Mike's. So at least its an option to not use the thermostat. I then put in a new thermostat but no improvement. Then proceeded, as planned, to clean out the Thermostat housing. By the way, the housing looked fine, some build up, but no blockage to harm water flow from a visual inspection or with a water hose. Took out the sensors first and then soaked the housing for 1 hour in Acid. Please be very careful if you try this( eye & skin protection please). Also I would recomend to block the 4 ports and pour acid in until full,rather than submerging the entire part as I did. (The acid takes the outer paint off as well). This made a dramatic improvement. Starboard riser (not port) will get hot to touch, but the thermostat would kick in and got very cool....even at 2100 rpms. This was a dramatic improvement,since before it never cooled at all. Took the boat out for test drive, but at higher 3000 - 4000 RPMs, strboard got hot and did not cool fast enough. Port riser stays ice cold throughout and Engine stayed at 170-175 degrees. I have ordered a new housing , to see if this helps, but I am not optimistic, since Mike also tried this. Mike. did you try Mercruiser original made housing..it should say ALPHA on top of it?? I want to try only original parts, not aftermarket, becuase I think this is the cause of the problem and would like to rule it out. My risers and manifold are AP(Aqua Performance) not Mercrusier OEMs. I think this engine type maybe very sensitive to changes as you and others have suggested. Even though after market parts are OK,there maybe cases where slight deviation cause flow problems.! Next steps: I am trying a lower range thermostat .. which seems to keep my engine cooler 165 degrees (not 170-175)at dock and also risers cooler...but have not had time to take it for a test spin at higher rpms. 2) rig up a set up to transfer a small amount of water directly from the incoming hose to strboard riser...with the rest going to housing as usual. 3)do as Guy suggested above."
 
"Ray,
While running without a

"Ray,
While running without a thermostat feel around your starboard exhaust manifold, spacer (if equipped),and riser and then do the same with the port ex manifold.
I was able to feel noticable hot spots and some cool spots on the starboard ex manifold while the port side was cool all the way around the ex manifold. This was only detectable with the thermostat out since cool water was going to both sides. After pulling the parts I did find some blockages in the new parts, still haven't cleaned them out yet but that's my next step.
Yes, I bought a new mercruiser part for the t-stat housing. Didn't make a noticible difference for me.
Mike"
 
"Sounds like a lot of work and

"Sounds like a lot of work and money being used up. I have the same problem with a 1998 rebuilt engine. Changed T-stat, removed and flushed riser and checkef flabber.
THen I called Mercrusier tech-support about the hot stbd riser.
Answer:
The port riser runs cool. The Stbd will be hot to touch but, you can not leave you have on it because it is HOT.
With a 160 t-stat and running the engine at 3500 the temp gauge should show about 170.


So my suggestion is to call mercrusier support and get there take on this issue."
 
"After all this work the starb

"After all this work the starboard riser still overheats. New thermostat housing and thermostat did not make a difference. Flushed block again and checked flow which is ok. I noticed a little sandish debris came out while flusing the block, but then flow was OK.
Question for the experts: suppose the engine block itself is blocked, can I pour acid in it without major damage.? what internal parts could be damaged in contact with acid? ex head gasket? This seems to be my last unchecked option. Thanks"
 
"Not sure I would give her an

"Not sure I would give her an acid job just yet.
Blockage in the block does not explain why one riser gets all the water and the other not enough.
If you are intereted in a little experiment, here is a long shot:

Why not put a C clamp on the hose to the port riser and see if you can restrict the water flow to it enough to divert more water to the stbd side and cool it down. Be careful you don't starve the port side.

If this somewhat unorthadox idea works at all, you could then insert a plumbing valve in the port hose and adjust it til you get a decent compromise.

I know this likely sounds pretty weird, but so far all the logical ideas have failed, so why not try it?

Rod"
 
"Having the same issue, I spok

"Having the same issue, I spoke to my marina mechanic today. He said that he belives it is normal for one side to run hotter. I do not have any check balls or diverter balls, so the natural way for the engine flow will make one riser hotter than the other. He said I could install the diverter balls to make it more equal."
 
"Sorry, I don't believe th

"Sorry, I don't believe that for a moment.
My 6.2 runs within 5 degrees of each other side to side.

Rod"
 
"Rod, I'm at a loss to why

"Rod, I'm at a loss to why my stbd riser is much hotter that my port. Port is cool. I've check all the lines, replaced seawater pump, thermostat and still hot...."
 
"SR75

I was reading about t

"SR75

I was reading about the type of T'stat hsg. you have w/o div. balls. There is a "by-pass hole" inside the housing. If it is narrowed it causes water hoses to expand when the thermostat is closed because the water can't get out fast enough.

If the hole (1/2" +/- 1/32") is over size, it can cause the engine to overheat at idle or low RPM because too much water is flowing out of the by-pass.

Early models have an inspection plug on the bottom of the hsg. If there isn't a plug, it must be drilled, 23/32" or 18.5 mm, and tapped for a plug, 1/2-14 NPT or M20X1.5 and A20 sealing washer. The hole needs to be drilled in a specific location from the bottom."
 
"Mike,
Check the hose that

"Mike,
Check the hose that is attached from the bell housing to the transom assembly( black hose) if there is a kink in that hose it may be possible that the flow is not ample and only one riser is cool while the other riser is hot."
 
"I had the same problem with m

"I had the same problem with mine, Three years ago I replaced the one peice log type manifolds with GLM manifolds/risers, in the process i had to clean out the remains of my flappers from the Y pipe, so I know their was no obstruction. After reading numerous posts and calling a couple dealers who told me it was normal because of the flow in the T stat housing I modified the plumbing to equalize the flow with PVC. BTW, I also replaced my bad fuel pump with a Holley marine fuel pump, they are about 1/2 the price of mercruiser and rebuildable. email for picture.... [email protected]"
 
"Hi Guys,

I'm having th

"Hi Guys,

I'm having the same problem. Hot STBD side. I've got a "74 Sea Ray with a 302 Ford (Please hold the commentary GM people)raw water cooled engine. I repowered in '05 and put 30 hrs on it that year. Replaced the T stat housing as well. I tried switching hoses going to the risers, and now the Port side is hot. Collin gave me an idea, re-do the plumbing...I restricted the port side with a piece of tubing , and now the STBD side is cool, and the port side is hot. I can experiment and get it to run "right" in the driveway, but what happens when I take it to the Bay and am in 5 ft following seas? I really don't want to re-design this thing, I'm not an engineer, and it ran with this design 30+ yrs ago. I'm open to suggestions.
Thanks for any help/thoughts
Ray A"
 
I have been following this discussion but then it ends. Was this overheating starboard side riser issue ever resolved? I am having the same problem. Nothing I seem to try works....
 
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