350 Mercruiser I/O exhaust risers are too hot

[lenny2113]

Past weekend I noticed exhaust risers are too hot to touch. Drop of water on the intake manifold boils and evaporates. With all these symptoms temerature gauge reads 140-150 operation temperature.<br />Anyone could comment on this?<br />Risers are 2 years old.<br /><br />Thank you !!!

 

[Don S]

Re: 350 Mercruiser I/O exhaust risers are too hot

You have a problem with the raw water flow. Impeller?, Plugged water passages, or hoses or ???? Manifolds could also be plugged up, especially if they are as old as the risers that were replaced.

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

Hi Don, <br />Thanks for reply. <br />Manifold and risers are 2 years old. I see a good stream of water coming out of thruhull exhaust. I channge impeller at the end of each season. <br />Should the intake manifold be so hot that water boils on it?

 

[Haut Medoc]

Re: 350 Mercruiser I/O exhaust risers are too hot

No way. That's way too hot!.....Did you check the 'check valve balls' that are located in the 'T' near the thermostat housing? You didn't say if you are raw water cooled or FWC. Pull the hoses off and inspect the check valves for free movement.......JK

 

[bryantjb3]

Re: 350 Mercruiser I/O exhaust risers are too hot

My intake manifold runs about 160* using a IR temp gun if I remember right. Engine temp 175*. Risers and elbows around 100*

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

That is raw water cooled setup. <br />I am not sure what are the "check valve balls" you're talking about, J.kopec.<br />If it is inside te T-housing, I will open it up this weekend and check. <br />If these things are stuck closed, I think I would not see cooling water coming out of exhaust... or am I wrong on that?<br />If they are stuck, I should replace the T-housing or are they just inserts of some kind?<br />Sorry, I never openned termostat housing on this engine.<br />Thanks!!!

 

[Haut Medoc]

Re: 350 Mercruiser I/O exhaust risers are too hot

You don't have to open up the t-stat housing......Just pull the hoses of at the 'T'and what I'm talking about should be apparent. All it takes is a nut drive with an 5/16 or a screwdriver. For the price of a gasket & removing two bolts, I would have a look at that thermostat though & replace it....Just because.....JK

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

JK,<br />Thank you!!! I will do some maintenance this weekend. Hope will fix it. Still not sure if the riser and intake manifold are mad hot, how is the temp gauge showing 150...

 

[Haut Medoc]

Re: 350 Mercruiser I/O exhaust risers are too hot

Because of water flow, I wish I could show you the diagram, it would be more clear then. When you get a good look at your engine it will become clearer.....JK

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

JK, <br />I opened top cover of t-stat housing. There are no check valve balls in there. I think it is a different style housing. <br />There is a T shape connector with hoses going to risers. <br />The riser itself gets too hot, but the hose adapter at riser's base stays cold. <br />I will be taking off riser sometime this week. I think there is a flow restriction. <br />Risers are only 2 years old.

 

[Haut Medoc]

Re: 350 Mercruiser I/O exhaust risers are too hot

The risers are only two years old, but how old is your block? Scale from the block itself or the manifolds can restrict flow at the water dumps in the risers, esp. in salt water operation. So they are probably O.K., but they need to be pulled and checked for scale......Pretty common. No check balls inside the "T"? Curious...What year is your model? At least you can do the risers in the water.....Let us know how you make out.....JK

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

JK, <br />This season is the block's 3rd year. Actually risers are same age as the block. So, risers and manifolds are 3 years old now, not 2. Sorry about that. Since the season is not over yet, I counted as 2 years. May very well be "wishfull thinking" . I have not flushed them with fresh water until just recently. I have installed flush system and use "salt terminator" every time I use the boat. <br />I will open and check risers next weekend or even during the week. I wanted to do it this past weekend, but the stripers were biting and I could not miss the action . <br /><br />Noticed another bad thing though. My upper shift cable was resting on the "silence choice" thruhull and the cable insulation started melting. If I saw that it would stop me from using the boat. Clogged riser waterflow did not stop me as I see no potential hazard caused to other parts.<br /><br />Thank you for your help!<br />Lenny

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

OK, Now I am confused and have no answer for my hot risers problem. <br />I dropped the riser this evening and was amased. It looks brand new after being used for the third season in salt water. I took pictures of the riser's water passage.<br />

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<br /><br />Exhaust manifold looks new as well with only some surface rust at the top. As I broke the riser from the manifold, the water came out from the riser. I do not see why it gets way too hot while running. I would suspect impeller, but I changed it at the begining of season. Oh, and another thing is - it still runs very hot while running on flush system, which is not dependant on impeller.<br />As I said before, engine operating temperature goes not go higher then 160. It is the risers and manifolds that are getting too hot. <br /><br />I also found the check valve balls in the t-stat housing. Please pardon me for saying my t-stat does not have them. I did not know...<br /> They are located at the tee conector of the t-stat housing where 2 hoses come out and are routed to the 2 risers. <br />Shown in this picture.<br />

<br />Those little plastic balls are moving freely.<br />Please, help me with what should be checked next...<br />Thank you!!!

 

[rbezdon]

Re: 350 Mercruiser I/O exhaust risers are too hot

when you say the risers are too hot, how do you know. If they are running around 160 to 175 like they should be they will feel quite warm to the touch. Some people can not touch it without feeling like it burned them but actually the temp is OK. Do you have an actual measurement of the over temp??

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

Ron, <br />No I do not have measurement of temperature at the riser. From the posts above, someone posted that riser should run at 100 degree temperature. If I can barely hold my hand on it, I say it is close to 180. As I said before, temp gauge is reading 160. <br />What could I use to measure temperature of riser accurately.

 

[malaki mama]

Re: 350 Mercruiser I/O exhaust risers are too hot

lenny.. people dig there IR temp gauges.. could pop for one of those.. can shot it at everything on the engine go nutty with it..

 

[rbezdon]

Re: 350 Mercruiser I/O exhaust risers are too hot

Lenny, that my not be as hot as you think. Mine run in the neighborhood oif the same temp as the engine. I have a 160 tstat and I run 170 to 175 running hard. You may be fine and chasing a phanthom problem. Get something and measure the temp and then decide of some thing is really wrong. I dont think 100 is realistic for the manifold/riser temp. It also depends heavily on the incoming water temp. The manifolds are cooleed by the water bypassing the thermostat. If the incoming water is 33, then the manifilds my be 100, if the water is over 80 (which it is here this time of year) then I doubt 100 is at realistic.

 

[lenny2113]

Re: 350 Mercruiser I/O exhaust risers are too hot

I am buying IR temperature gun. I have twin setup, so I really doubt that both temp gauges are wrong showing 160 top. For some reason I think that if I can barely touch manifold and riser they run at no less then 180. Water boils on top of intake manifold does not look right to me. In any case I am putting the riser back tomorrow and going for a ride with the temp gun ready.<br />Thanks for your input EVERYONE !!!