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one riser hotter than the other

R

rjkj

New member
Hello,

can anyone ofer any suggestions, having some trouble with a 2002 5.0L efi engine. low power under load, and i just noticed today that the left side riser was considerably hotter than the right. also, under heavy load you can hear something ticking in the back left corner. the left side was so hot that the rubber coupler was swelling up and changed color.
 
Possibly a blockage in the cooling system on that side? That's weird for sure. I would wait for kghost, chief, Ricardo, or one of the more experienced guys to chime in.
 
I experienced the same issue, what I found was the internal exhaust flapper that prevents water ingress into the engine when launching or the stern is facing waves or a heavy sea had broken off from were its located above the "V" tube that is attached to the transon plate, and had caused a restriction for that side of the exhaust.

In my case I had to pull the engine to fix it, when I re-powered several years ago I had the mercruiser installer leave them out on the new engine.
I'm new to this forum and I'm sure there are folks with much more experience then me on here that may have a better solution but it don't sound good.

Fred
 
I'm assuming this is a stern drive application. The loss of power and excessive heat does suggest a blocked exhaust as a possibility. You should be able to unclamp the rubber exhaust coupler at the top of the exhaust horn and pull it up. Look into the horn and see if the shutter is still there or that it moves freely. If it's missing, it could be lower in down in the horn causing a block. You can get to the bottom of the horn by removing the drive and looking through the exhaust bellows. If you find a melted chunk of plastic, it's most likely a shutter and you need to find the cause of the meltdown; probably an overheat at one time or restricted water flow or volume.

Not a good idea to do away with the shutters.
 
Had the "hot port riser" problem also, but mine was the plastic check ball in thermostat housing, leading to the port riser was stuck closed. Pulled off the hose at the thermostat housing, leading to the riser, cleaned the ball seat and problem went away. Have noticed the Port riser is always "a little warmer" than th stbd after a full throttle run, but not bad.
 
His boat a 2002 does not have the old ball and spring Tee like us older boat owners......that is the boat not us........lol

They use a fixed oriface Tee now. It may be blocked on the left side.......pull the hoses of the Tee and make sure both sides are equally open.

If your motor cooling system only has two hoses going to the exhaust manifolds (to the bottom of them) then one would have to assume either exhaust manifold or elbow blockage. need more info on your system as there are several different ones. A picture would be good.


The difference between left and right can be as much as 20 + degrees difference........need to know what that temps actually are before any diagnoses can be made. A temp probe or infa red temp gun will work.

I believe someone just posted that they did away with the metal/rubber coated flappers and went to a composite type long ago.

The flapper could be an issue or elbow/riser blockage.....

Also need more info on boat usage.......salt water? yes or no? if salt then exhaust manifolds and or elbow/risers are suspect.....
 
Last edited:
Wow thanks everyone for all of the responses. i sould have offered more info.
2002 5.0L efi - stern side is noticbly hotter (could not hold my hand on it) - this is while driving - boat is solely used in salt water - the risers and manifolds have 4 yrs. on them - they are after market ceramic coated (because they were supposed to last longer....ha) -
 
i took the rubber couplers off and looked at the flapper, it appears to be working properly, so from there i removed the riser. not really sure what to look for as far as damage from salt water is concerned. should i just replace the manifolds and risers since the one side was too hot to touch while driving?
 
One important thing that you said was felt when running............Redo your touch test after running and idleing for at least 5 minutes to allow the motor to cool off...............
Also getting a actual temperature reading will help a lot also.

You need to answer some of the questions posted.

how is your cooling hoses routed? is there one to the riser/elbow and one to the bottom of the exhaust manifold? or only to the bottom of the exhaust manifold? VERY important...

Basically you either have a incomming water flow issue or a outgoing water restriction.

When was the water impellor replaced last? Is this a I/O or an inboard? What are the conditions of the incomming water hoses?

We still neeeeeeedddddd more INFORMATION
 
i have one hose to the bottom of each manifold. i took the riser off and all of the ports look clear. hate to spend $1000 on the manifold and riser parts if thats not the problem.
 
also the impellar was replaced last season, this is the first year i did not replace it at the beginning of the season.
 
Is this a INBOARD/OUTBOARD OR A INBOARD SKI BOAT.....??

If an I/O is it thru prop exhaust or thru transom?

STILL NEED EVERY PIECE OF INFO YOU CAN SUPPLY.............
 
I'm still stuck on the "low power under load" Can you be more specific? I'm still thinking exhaust blockage re low power and heating up.
 
is it possible the impeller self destructed and the debris scattered somewhere, clogging a port in cooling jackets, water pump, manifolds? I always wondered what happens to those fins on the impeller when they self destruct.
 
If you really want to know what happens to all thoses pieces, spend a couple of years at a morina fixing them and it will become very clear....they get everywhere!!
 
WoodieMan said:
I'm still stuck on the "low power under load" Can you be more specific? I'm still thinking exhaust blockage re low power and heating up.
Click to expand...

I wonder if the efi systems have a over temp limp mode when temps reach a certain level?? That would explain it but I personally do not know enough about the efi to know for sure..........
 
Good point kg. If equipped with Guardian, it will definately drop available power by an amount proportional to the type of problem the computer detects. Should be hearing a beep if Guardian is active. Doubt there is exhaust temp probes on this app but there may be a monitored system causing Gaurdian to kick in. There may be more than one issue at play here and just coincidental that it's all being noticed now (heat, reduced power, ticking noise). Ticking noise is probably the shutter on that side. Heat is lack of water volume or flow restriction or exhaust restriction. Reduced power; numurous reasons for that.

Impeller pieces typically get stuck in the cooler but can go futher. If in the cooler though, it would restrict flow to the entire cooling system not just one side.
 
this is an I/O with prop on alpha one gen II outdrive. i took the starboard side (the side that got really hot, more than just the norm of a little hotter than the otherside) exhaust apart, the flapper is flapping just fine, does not show any signs of wear and is operating fine. i almost ordered new manifolds and risers but the passages look clear. took it out of the water today to have the impellar changed. kinda sucks since we only get 12 weeks of summer here. for the past three years i changed the impellar every year and it did not look that bad so i figured let it slide a year like everyone else. we will see tomorrow.
 
What kind of shutter did you see in the exhaust horn; metal or plastic? If metal, it should have had a rubber rim around the edge, if that was missing due to heat, that would at least explain the ticking noise on that side.
 
The alpha 1 Gen II impellors should last for several years with no issues........this is a soft, low pressure high volume style impeller in a stainless steel housing, used in Johnson/Evenrude outboards for a million years........should not be the problem unless you sucked up a ton of sand and ruined it that way. Also if you did not get a good seal with the gaskets at the water pump housing and are sucking in exhaust gasses then this could be an issue.

If you take the outdrive apart look closely at the water pump components. If they are melted or disfigured replace.......also look close at the water hose from the bell housing to the transom assembly, is it kinked or show signs of being kinked, is it rotted or looks bad?

Look at the lower unit where the water gets sucked in, is that area clear of debree?

I will repeat my self again.

you either have a incomming water flow issue or a out going water flow issue.

If your manifolds are clean and free of rust and scale and debree then work backwards towards the thermostat housing. The incomming water flow gets split at the thermostat, those parts are typically cast iron and are suseptable to rust, You may need to take the thermostat housing appart to inspect, at the very least remove the hoses and look at the ports and see if they are restricted.
 
Sorry for the time lapse, had trouble logging onto forum site and was waiting on info from mechanic. he told me that the impellar was warped, most likely from the extreme cold weather we had here in NY last winter. this is the first time that i have not removed the drive and changed the water pump at the end of the season. still waiting for a bay test to see what is going on.

is it possible that the lack of water flow would contribute to the lack of power issue?
 
rjkj said:
Sorry for the time lapse, had trouble logging onto forum site and was waiting on info from mechanic. he told me that the impellar was warped, most likely from the extreme cold weather we had here in NY last winter. this is the first time that i have not removed the drive and changed the water pump at the end of the season. still waiting for a bay test to see what is going on.
Click to expand...


Sorry Not buying that a one year old impeller gen II type is bad.........Now if it got damaged from sand or something then yes.....

I run a gen I with the older hard impellor, I live in mass so same basic weather and mine has been fine for 5 + years with no issues and limited boat usage.......

Again not buying the "mechanics answer".

Just my opinion
 
now i cant wait to see the old one. he was running some diags on the engine we will see. hopefully sooner rather than later.
 
so far two weeks into it and they have changed the impellar because when they took it out the vanes stayed curled up and would not relax and open. be it whatit is it's changed now i will move on. still dealing with the lack of power issue. the mechanic said that when he bay tested the pump the engine back fired through the TBI unit. i never had that, just no power under load.
 
So I am having a similar issue and was wondering if the above issue was ever resolved.

I have a 2000 Crownline 182 runabout. 5.0 mercruiser 2 bbl carb 160ish hours. Alpha 1 Gen II. Raw water cooled, freshwater use only.

Starboard side elbow/manifold gets hot enough that I can't hold my hand on it more than a few seconds. Port side elbow/manifold is luke warm at best. I also have a fair amount of steam from starboard exhaust. I also have captains call exhaust. Steam emits from the through hull exhaust when the captains call is on and from the standard through drive exhaust when captains call is off. Both on starboard side. Port side operates as normal and never steams.

I have recently replaced, both exhaust manifolds and elbows as well as the thermostat. No change in steaming/temperature.

I have thoroughly inspected the thermostat housing, both the water lines running to the bottom side of both exhaust manifolds, and the exhaust flappers. All seem fine.

I replaced the drive impellar only Spring of 2009. No fins were missing from the old impellar.

I have had no cooling issues with the boat according to the gauge. Temperature always right where I want it. Water pressure/flow seems adequate.

I notice most of the water output coming from the port side so it seems there is less pressure or some sort of blockage on the starboard side. If I restrict the water flow to the port side (clamping hose with vise grips) the water output to the starboard side increases and seems to operate normally.

I do plan on replacing the entire drive water pump assembly in the next few weeks.

I can't seem to locate any sort of blockage anywhere in this system.

If replacing the drive water pump does not fix this what else could it possibly be? Engine circulating pump?

On a side note: I noticed in the old maintenance records that the previous owner had compalined about this problem but it could not be replicated in the shop. This has been an issue in the three years I have owned the boat. It wasn't noticable enough to worry me until this season it seems to be getting worse so I was prompted to take some action.

Any theories welcome.

Thanks.
 
That was the first thing I looked at too. I removed it from the engine, looked in all the holes, ran water through it in every possible direction. There are no blockages in the housing. This is when I went ahead and replaced the thermostat.
 
I would try an inlet water flow test at the T'stat housing by briefly removing the inlet hose at the housing and run the water into a bucket.
A V-8 should flow 5 GPM at 1000 rpm; so it should fill a standard 2 gallon bucket in 15-20 seconds. This will settle the water flow question.

Rod
 
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