4.3L MerCruiser Alpha - Starboard Riser 100 degrees hotter than Port Riser

[RollinEEZZ]

4.3L Carb Alpha w/ TKS Serial #: 0W615760

all temps taken using a known to be accurate no contact IR thermometer

After engine is warmed up ...

• temp gauge hovering below 170
• both manifolds 150 - 160 F
• port riser through exhaust hose 70 - 80 F
• starboard riser through exhaust hose 140 - 170 F

While I'm not a tech and don't yet have tremendous experience w/ marine engines it seems off to me that the starboard riser was up to 100 F higher temp than the port riser.

Also noticed what I believe to be excessively abnormal exhaust smoke wafting through the air (it was a calm day at the ramp today). It did seem to go away after some time passed. (picture below)

Also alarming to me but maybe normal, there was a hot spot on both starboard and port where the manifold meets the riser. Temps were at 200 F at this spot. Maybe this is OK for a small hot spot like this, I don't know. (picture below)

My greatest concern is the starboard riser is 100 F higher temp than the port.

Does any of this sound like it needs to be addressed and what would I be looking for?

Thanks in advance for help.

 

[alldodge]

With the extra spacers which increased the height in the risers, I don't see an issue with the temps at idle. If you are getting 100 degree difference at mid range and higher rpm's then I might thing there was an issue

 

[bman440440]

No Title

to me it sounds like your starboard riser has a blockage in the water port... you have 2 choices... on order that I would do is... 1st take the starboard down pipe off and the upper coupler and check the water ports... see the attached pic red arrows show the water ports and the should be clear... 2nd is pull off the riser and check I the cooling ports for build up on the manifold and spacer as well as riser

 

[RollinEEZZ]

Drove the boat around the lake today at WOT & checked temps. Also checked temps at mid-range.

Both exhaust manifolds around same temps, getting up to 180 F.

Port spacer & riser through exhaust hose never gets above 90 F. Noticed the port manifold blue plastic drain plug was broken and has a drip. Not too concerned about this as there's an endless supply of lake cooling water.

Starboard spacer & riser through exhaust hose gets up to 180 - 190 F.

Boat runs good.

Not looking for a project but if these temps at operating speed indicate a problem would want to address it.

Does this need some disassembly and inspection or OK to run w/ it as is?

 

[bman440440]

Drove the boat around the lake today at WOT & checked temps. Also checked temps at mid-range.

Both exhaust manifolds around same temps, getting up to 180 F.

Port spacer & riser through exhaust hose never gets above 90 F. Noticed the port manifold blue plastic drain plug was broken and has a drip. Not too concerned about this as there's an endless supply of lake cooling water.

Starboard spacer & riser through exhaust hose gets up to 180 - 190 F.

Boat runs good.

Not looking for a project but if these temps at operating speed indicate a problem would want to address it.

Does this need some disassembly and inspection or OK to run w/ it as is?

yes you need to find the problem before it gets to the point of causing damage... such as causing a fire from a burned up starboard side exhaust coupler... is your boat a trailer boat? if so put it on flushing muffs and look at how much water is coming out the starboard side transom exhaust port... if there is a noticeable difference in the flow of water out that side its a pretty sure sign of a blockage and NEEDS to be fixed... is this a fresh water boat? when was the last time you replaced the manifolds?

 

[RollinEEZZ]

yes you need to find the problem before it gets to the point of causing damage... such as causing a fire from a burned up starboard side exhaust coupler... is your boat a trailer boat? if so put it on flushing muffs and look at how much water is coming out the starboard side transom exhaust port... if there is a noticeable difference in the flow of water out that side its a pretty sure sign of a blockage and NEEDS to be fixed... is this a fresh water boat? when was the last time you replaced the manifolds?

Thanks for response ...

yes it is 100% fresh water. closest brine is days away. Rarely hear of manifolds/risers being replaced here.

regarding hooking up to muffs and checking flow of water, is this possible considering it's a through-prop exhaust? There's really no way to tell which side the exhaust flow is coming from through the prop correct?

 

[bman440440]

No Title

Thanks for response ...

yes it is 100% fresh water. closest brine is days away. Rarely hear of manifolds/risers being replaced here.

regarding hooking up to muffs and checking flow of water, is this possible considering it's a through-prop exhaust? There's really no way to tell which side the exhaust flow is coming from through the prop correct?

if 100% fresh water a good rule is 6-8 years for replacement... just because its fresh doesn't meant they don't rust... just not nearly as fast... and there are exhaust ports on each side of the bottom of your transom plate (see attached pic) that flow a majority of the water when at idle and lower speeds.

 

[alldodge]

Does this need some disassembly and inspection or OK to run w/ it as is?

One side will always be hotter then the other, its just the way water flows, its always to the path of least resistance. If you didn't have the spacer in there I would lean a bit more to inspection of the manifold but right now I lean more to the Thermostat housing. The exhaust you have is the dry joint type. This means that no water passes thru gaskets around the manifold and into the riser. The water passes on the outside as shown by the arrow.




When the thermostat is closed most of the water should exit the boat from the Tee and the manifold passageway. The check balls are there to help keep everything full of water and to keep hot water from flowing backwards.



Here is your complete cooling system for a Alpha drive



I suggest looking close at the thermostat housing and not bother with the manifolds. A fresh water exhaust system will just about last the life of the boat before it needs replacing, and dry joint type even more so. Many bets are off if the boat was used in salt for some time, but yours looks like all fresh as you said

 

[RollinEEZZ]

Thanks for all suggestions ... we'll get into and report back what we find.

 

[alldodge]

BTW when was the last time the outdrive impeller was replaced?

 

[RollinEEZZ]

BTW when was the last time the outdrive impeller was replaced?

AllDodge, the seawater impeller was replaced two years ago ... we service it every three years.

 

[RollinEEZZ]

Update on this issue. We think the problem was a partially stuck starboard shutter valve.

Here's what we did on starboard side of cooling system about a month ago ...

• like AllDodge recommended, we removed hose at the thermostat going to riser, check ball looked & moved OK
• checked shutter valve, in good condition but not fully opening. Seemed to be stuck beyond fully closed position, manually freed-up
• removed hoses to flush riser cooling passages with garden hose

At this point we drained the block, risers & PS cooler & hooked the boat up to muffs. It was run on -100 burst antifreeze recirculated in a kiddie pool. Starboard riser temps seemed to be more in line w/ port riser temps. Temps all around were higher running on muffs w/ recirculating antifreeze than lake test running temps (the recirculated AF does heat up after a few minutes).

Bman recommended checking starboard & port exhaust ports at bottom of transom plate for equal water flow. The flow looked good on both sides.

Will update post again in spring after checking temps during lake testing.

 

[Bt Doctur]

Were the risers removed and gaskets replaced? you could have them reversed

 

[tank1949]

PULL HOSES TO RISERS AND SEE IF WATER IS GETTING TO RISER. BLOCKAGE COULD BE AT STAT HOUSING? COULD HEAT BE REFLECTING OFF SOMETHING BACK TO THE CONCERNED RISER? PULL RISER AND LOOK!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!