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TOPIC: Riser-hot Cold

Riser-hot Cold 09 Jun 2009 05:59 #1

  • esealivin
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Hi, When Running My Engine--- Raw Water Cooled 5.0 L Carb B2, The Starboard Riser Gets Very Warm ( Hot ) Then Goes Very Cool ( Cold ) & It Does This On & Off While The Engine Is Running...is This Normal...i Had Some Problems With Overheating On This Engine, But I Thought I Corrected It...any Ideas...thanx

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Riser-hot Cold 09 Jun 2009 07:23 #2

  • Steelfist
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I am also curious to see the response to this question as i have an overheating problem with my 2651 with the 5.7 also. i was told it could be a clogged passage in the risers and to take them apart and give them a good scaling or whatever they do to them.....my temp also would climb to 180-190 them drop had a new thermostat in it and was idling on a hose so the impeller could not be the problem. but like i said curious to see.

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Dave
1990 Bayliner 2651 Merc 5.7 Alpha One leg
"she flies through the air with the greatest of ease"

Riser-hot Cold 09 Jun 2009 12:57 #3

  • Mocoondo
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esealivin;306721 wrote: Hi, When Running My Engine--- Raw Water Cooled 5.0 L Carb B2, The Starboard Riser Gets Very Warm ( Hot ) Then Goes Very Cool ( Cold ) & It Does This On & Off While The Engine Is Running...is This Normal...i Had Some Problems With Overheating On This Engine, But I Thought I Corrected It...any Ideas...thanx


Perfectly normal. Both risers will alternate between warm and cool while running. In fact, I've never seen a Mercruiser engine that didn't do this.

You should be able to keep your hand on the top of the riser without burning yourself. If you are able to do that, all is well.

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Mocoondo
2002 Bayliner 195 Capri "Sport"
Mercruiser 5.0L V8 / Alpha I Gen II
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Riser-hot Cold 09 Jun 2009 19:17 #4

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yea i put my hand on the top of the riser & it gets very warm but not enough to burn me & then it goes very cool..... but when i put my hand on the port riser it is cool all the time , ..like i said i had problems with overheating so i was somewhat concerned bout the hot & cold thing going on....hopefully mocoondo your right about the hot & cold..thank you

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Riser-hot Cold 09 Jun 2009 19:50 #5

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I just learned a lot about risers. I had the starboard riser smoke it was so hot. Required a tow and turns out I needed a complete exhaust rebuild on both port and starboard. Lots of $$$$$$ but she runs soooooo good now.

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Craig in Houston
1998 2655 Ciera

Riser-hot Cold 09 Jun 2009 20:14 #6

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i just had both engines manifolds & risers replaced with merc parts 2 seasons ago

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Riser-hot Cold 09 Jun 2009 20:14 #7

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I've never had a Mercruiser that didn't have the strange asymetric hot/cold riser issue. One riser will be warm to the touch; the other cool. Rev the engine up a couple times and it may switch around. The cold one will be hot and the hot one will be cold. In the end, one riser is always hotter than the other.

The rep. at Mercury whom I spoke with about this very issue stated that so long as you can keep the palm of your hand on the top of the riser, then you do not have a heat issue. On the other hand, if it is too hot to the touch then you need to be concerned. A riser that is too hot to touch is not getting cooling water through the passageways and probably is due to be changed out.

If you are really concerned about it, take some measurements with an infared thermometer and report back. I suspect that if you are able to keep the palm of your hand on the riser, it is not getting above 140° or so and that temperature would not bother me in the least bit.

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Mocoondo
2002 Bayliner 195 Capri "Sport"
Mercruiser 5.0L V8 / Alpha I Gen II
MMSI: 338091755

Riser-hot Cold 10 Jun 2009 04:44 #8

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i'll try that hand thing on the risers as soon as i can get back to the boat & i'll rev the engine alittle...as far as the infared thermoter i'll have to see if i can locate one..thanx & i'll get back & let you know what happened...thanx again

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Riser-hot Cold 10 Jun 2009 11:14 #9

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I have always wondered why Mercs have this issue with one side being hotter than the other...having only had the OMC...with the one piece batwing manifolds....both sides run at the same temp...and barely get warm....I usually check the temps every so often...from the top where the riser section is to to the bottom of the manifold...and even at the bottom it's only warm...never hot....unless you shut off the engine and let it sit for a while..

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88 Four Winns 200 Horizon 4.3 OMC
98 Jeep Grand Cherokee 4.0/Selectrac
07 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

Long Island Sound Region

Riser-hot Cold 16 Jun 2009 05:20 #10

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hey again...soooo i did the hand on the riser thing & was able to keep my hand on it...the riser got hot, then went cold & did this for as long as the engine was running, but the other side stayed cool the whole time the engine was running, mmmmmm strange ???

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Riser-hot Cold 16 Jun 2009 09:05 #11

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esealivin;310264 wrote: hey again...soooo i did the hand on the riser thing & was able to keep my hand on it...the riser got hot, then went cold & did this for as long as the engine was running, but the other side stayed cool the whole time the engine was running, mmmmmm strange ???


Hi.

I had/have the same problem as you. Both my risers and spacers where clogged with rust. I have ordered new ones.

So, i have a teori about the warm/cold experience, if one of your raisers are clogged, the waterpreassure from the pump and heat will "open" a clogg then new cold water will come inn and then "close" the clogg.
Another teori use the same prinsip but this regards the ekshoust shutters, if one og the shutters is not working correct it might open when ekshoust and waterpreassure builds up and then close again when preassure drops.


Regards
--NORMARCO--

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Riser-hot Cold 16 Jun 2009 15:56 #12

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Hi

I've had same problems when i first purchased the boat, the risers got so hot they were burning the paint off.

The stardboard riser will always run hotter as i believe it is due to the amount of resistance within the engine and the flow with the Port side having an easier route back out.

Make sure that when you rebuild you use the more expensive Mercruiser gaskets, they are silver with a slightly sticky surface. I had internal leaks into the ports from using the cheaper paper based gaskets. (got away with it :D).

Regards

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1998 2452. 5.0l mercruiser with alpha one gen 2 and 2 bbl :)

Riser-hot Cold 16 Jun 2009 16:06 #13

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hi...i had the maniflods, risers, spacers & gaskets, replaced 2 seasons ago with genuine mercruiser parts, the boat ran great last season,, but this season every now & then the temp goes to 175 & then drops to 100 & then goes back up to 175, when it does this the starboard riser gets to hot to even touch

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Riser-hot Cold 16 Jun 2009 17:06 #14

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i have never heard of this. certainly, there are passages in the manifolds, risers and elbows that surround the exhaust gas passage and need to be rodded out and free flowing. the engine thermostat will open and close at the preset temp (160 - 180 i would think) to allow the block to be kept cool. the mainfolds, risers and elbows should have water going through them all the time.
i have a closed system now. my manifolds and risers have glychol in them and circulate with the engine block cooling. both my elbows are always cool.
before the engine change and closed system install, my elbows would be warm but never different or hot to the touch.

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"cullyJ" on 16 - 1997 2252 5.7L carb
alpha I/gen II 1.47:1 (?)
purchased by us in 1998 @ 50 hrs
new jasper long block, closed cooling,
psi hot water, deck shower
and privacy curtains - 2001
letas slant, bimini and glass - 2009
baltimore - norfolk, hydro race, 6 nights - 1999
baltimore - cape may,...

Riser-hot Cold 16 Jun 2009 17:35 #15

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yea i think maybe there is a block some where , but its kinda strange that its happening all of a sudden, like i said everything was changed 2 seasons ago & the boat ran beautiful the last 2 seasons, but this season its acting up...i'm thinking that maybe one of the flappers in the dump broke loose & is getting stuck every once in awhile

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Riser-hot Cold 16 Jun 2009 17:41 #16

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i found a flapper hung up at the bottom of the Y at the exit boot to the leg but it didn't effect temp.

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"cullyJ" on 16 - 1997 2252 5.7L carb
alpha I/gen II 1.47:1 (?)
purchased by us in 1998 @ 50 hrs
new jasper long block, closed cooling,
psi hot water, deck shower
and privacy curtains - 2001
letas slant, bimini and glass - 2009
baltimore - norfolk, hydro race, 6 nights - 1999
baltimore - cape may,...

Riser-hot Cold 16 Jun 2009 18:59 #17

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ohhhh i was hoping it was gonna be something that easy, like the flapper, ohh well , like i said it only happens 1 out of every 10 times i start the boat & when i give it throttle, its goes back to normal

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Riser-hot Cold 16 Jun 2009 19:08 #18

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Go here- http://www.boatfix.com/merc/Techbk/94/94hg6a.pdf and to section 6A-14.
In the thermostat housing feeding the risers there should be a rod with spring loaded balls attached. These balls, when adjusted properly balance the water flow between the riser and internally to the exhaust manifold. If one of the balls is getting hung up or not adjusted properly, might make a difference in your riser temps. Doesn't explain your engine temp. difference on the gauge.
I know on my 7.4L/ B2 when I replaced the thermostat housing and manifolds/risers, I was told by a reputable Merc. mechanic to leave the ball checks out of the system as the engine driven raw water pump has enough capacity to feed and balance the system with out them.
Just a thought.
John

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Riser-hot Cold 16 Jun 2009 20:10 #19

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yea i had the thermo housing off & i did'nt see any rods with the balls, my boat is a 2000 3055 with the 5.0 carbs b2 drive...i don't no if its not equiped with these rods & balls or someone before me took it out, i'm thr third owner....i'll check again tho...thanx

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Riser-hot Cold 18 Jun 2009 04:41 #20

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t

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Riser-hot Cold 18 Jun 2009 07:08 #21

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esealivin;310554 wrote: yea i had the thermo housing off & i did'nt see any rods with the balls, my boat is a 2000 3055 with the 5.0 carbs b2 drive...i don't no if its not equiped with these rods & balls or someone before me took it out, i'm thr third owner....i'll check again tho...thanx


Hi Easyliving.

There are thre types of gaskets between the manifolds/risers and spacers. "closed flow" this is for a fresh water colling system, "restrickted flow" you dont want these gaskets, you can recognise this by them having just two tiny holes where the water is going, these holes can easely get bloced. I had these gaskets and they cost me a lot of cash.
"full flow" gaskets are completely open, and lets water pass without restriction. These are the gaskets i now will put on my new risers and spacers. Had to change both sides, the manifolds will be changed during winter.
If i am not mistaken, the risers/spacers and mainfold have to be inspected ones a year, and changed between 3 to 5 years. I bet you have a block in your system. Hope you will figure this one out, and let us know.

Regards
Normarco

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Riser-hot Cold 18 Jun 2009 19:01 #22

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Are you running on hose or in the water? I know on my 7.4L I will get fluctuations sitting dock side not under load. When I take her out and run her temp. settles out. On hose is not an accurate indication at all.
If you have Harbor Freight around, you can pick up a temp. gun at a very reasonable price. I have one and it works great.
John

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Riser-hot Cold 19 Jun 2009 04:55 #23

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hey guy...the manifolds & risers are only 2 seasons old & the boat ran beautiful all last season i put 85 hours on it last season...the boat is in the water & when the problem occours i notice if i bring it up to bout 3000 rpms the temp levels out & the riser gets cool...

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Riser-hot Cold 19 Jun 2009 08:29 #24

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esealivin;311905 wrote: hey guy...the manifolds & risers are only 2 seasons old & the boat ran beautiful all last season i put 85 hours on it last season...the boat is in the water & when the problem occours i notice if i bring it up to bout 3000 rpms the temp levels out & the riser gets cool...


Hi.

Do you run in freshwater or saltwater? I know that you have changed the risers and manifolds, but they need inspection every so often.

Have a look at the link http://marinesurvey.com/yacht/exhaust_risers_1.htm

It makes sence that the engine and risers get colder at highet rpm, you press more water through the system. I am no expert, just an humble mechanic that learn somthing new every dag. I dont know if you have a restrainer on your inntake, if you do, clean it. Try to take of the hose from the thermostat housing and blow through it(the one that goes to the riser/manifold), and the other one, any difference in the resistance?
Remember, when the thermostat opens, the raisers will be a bit warmer due to the hot water from the engine that goes through them, BUT if there is some sort of restriction in the flow the water will not circulate fast enough to cool the engine and raisers when idling.
Hope you figure this out, and share it with us.
By the way, i got my new risers today (friday) and will mount them with OPEN gaskets this evening.

Best of luck.
Have a nice weekend.

Regards
Normarco

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Riser-hot Cold 20 Jun 2009 05:13 #25

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hi, thanx for the info..i'm trying everything....the mechanic at the marina thinks its the flapper

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