Question on Manifold and Riser temps

[Fishermark]

I have a question about what is "normal" for the temps on both the manifold and riser on a Mercruiser, 5.7 liter. (It is a 2003 engine and manifolds and risers of the same year. DonS mentioned that I have the dry joint exhaust system).

Anyway, here's my question. On the port side, the riser is hot to the touch - as is the y pipe on that side. Too hot to keep my hand on it. But the manifold on the port side is cool to the touch.

On the starboard side the situation is reversed. The riser is cool to the touch, while the manifold is hot.

Is that normal? If not, which one is indicative of a problem?

 

[Don S]

Re: Question on Manifold and Riser temps

Need some info.
Is this raw water cooled? You say I mentioned you HAVE or MAY Have dry joint exhaust. Did you post pictures or how did I know? ? ? ? ? ? ?
What outdrive do you have?
Do you have a raw water pump in your drive or belt driven on the engine?

 

[Fishermark]

Re: Question on Manifold and Riser temps

Sorry Don, when I posted the original question I was going to add a link to the discussion from last month, but couldn't find it. (You know how well our "search" feature works!)

Anyway, here's a quick description of what I have: I have a 2003 5.7 Mercruiser with a raw water pump attached to the engine with a 1.25" thru hull pick up. This is the main cooling for the engine. The impeller in the outdrive merely goes up through the outdrive, through the transom assembly and is then routed back through the stern. The only purpose this serves is to cool the outdrive. (The outdrive is an Alpha 1 clone from Sterndrive Engineering and is only one year old).

I did find the post from last month where you mentioned I have the dry joint system. Here's the link: http://forums.iboats.com/bbBoard.cgi?a=viewthread;fid=24;gtid=1216454;gpid=1216454#gpid1216454

 

[bjcsc]

Re: Question on Manifold and Riser temps

When does this happen? My engine has one side warmer (not hot by any means) when flushing. Underway they are the same. If they are getting hot, you must have a restriction or flow problem. From reading your other post, could be the same problem.

 

[Fishermark]

Re: Question on Manifold and Riser temps

"From reading your other post, could be the same problem."


I'm thinking along the same lines. I don't know if this is the case when underway, (I'm busy "driving" at the time d ) I will take the time to check next time I'm out however. We are going out to look at the Christmas lights tonight by the water, (one of the advantages of Florida this time of the year ), and I will be sure to check then.

When I'm flushing the engine, even though I have water to both inlets, it is perhaps the case of not enough water to the main engine pump due to low water pressure.

Back to the main question - does anyone have a schematic or web page showing the flow of water through the engine?

 

[Don S]

Re: Question on Manifold and Riser temps

When I'm flushing the engine, even though I have water to both inlets, it is perhaps the case of not enough water to the main engine pump due to low water pressure.

Does this heating problem happen in the water or only when flushing on the hose? If it's only when flushing, yea, it's probably low water pressure. Especially if you have a splitter, 2 hoses and using water on the drive also. Might try turning the water down a little on the drive hose. you don't need full flow on it for test runs, just enough to protect the pump impeller.

 

[Fishermark]

Re: Question on Manifold and Riser temps

Hi Don,
Thanks a bunch for the picture - you can delete it as I saved it on my hard drive.

Does this heating problem happen in the water or only when flushing on the hose?

I'm not sure - I will find out tonight when I take the boat out - I will make sure to check. I will be taking it out either tonight or tomorrow night, but when I do, I will let you know what I find.

Especially if you have a splitter, 2 hoses and using water on the drive also.

That's exactly what I'm doing. I will try adjusting the flow as you suggest - otherwise, forget the splitter and use two hose bibs.


Again, thanks for the picture and help. It is greatly appreciated.

If you ever get tired of the winter in Alaska, look me up here in Pt Charlotte - I have a few houses you can buy! You can be one of our snowbirds. 8)

 

[Fishermark]

Re: Question on Manifold and Riser temps

Took the boat out again this evening and checked the temps. Same thing.

The port riser is hot to the touch, (not hot enough to burn you, but hot enough it would be very uncomfortable to leave it there long), while the port manifold is cool as a cucumber.

The situation is reversed on the starboard side. The starboard riser is cool, while the starboard manifold is hot. (Again, not so hot to burn the hand - about as hot as the port riser).

Having said all that, the engine is running fine and is not running hot at all. It stayed about 120 - 130 degrees all evening.

Is this normal? Am I being concerned for nothing?

 

[bjcsc]

Re: Question on Manifold and Riser temps

Well I don't know if it is, but I suspect it is not normal. Yes you should be concerned because if in fact it is not normal and whatever is making the riser/mani hot gets worse it could be a fire hazard. Something's funny...from my limited understanding they should be the same temp. underway - maybe a slight variation measurable by an instrument from port to star., but certainly the riser and mani should be the same - but then again you've got the dry joint so maybe not. I think it's time to back all the way up when you get time. Check all your hoses, make sure you've got good flow everywhere. Pull hoses, watch it come out, etc.. Sounds like you're starving for water to me...but I'm no pro...

Is 120-130 normal operating temp. for that engine?

 

[Don S]

Re: Question on Manifold and Riser temps

No it's not normal, and running at 120 to 130° is also not normal.
I still think you have an air leak in your system somewhere. You need to put a piece of clear hose between the pump and the hose that goes to the strainer and check for air bubbles. Do the same on the output side. Could be a bad pump that is sucking air.
Have you changed the impeller? I think you said you did, did the problem exist before you changed it or start after?
You have a problem, time to find out what that problem is before you use the boat again.

 

[bruceb58]

Re: Question on Manifold and Riser temps

I would suggest getting an IR temp gun and taking the measurements. Maybe the temp difference is not as much as you think. Also, you can take the measurement of the hose leading to the manifolds to see if the water being sent to the manifolds is hotter on one side than the other. On my Volvo, one side is over 10 degrees warmer.

 

[Fishermark]

Re: Question on Manifold and Riser temps

I will take the time to pull the hoses off everywhere and see "what's what." Don - I replaced the impeller in the outdrive last month.

I don't know how long this has been an issue as I haven't felt the need to feel the temps on the two sides. After the tube melted last month, and I replaced things I started paying a little closer attention to see if I could determine what the problem was.

Here's a little more background which may shed some light on things: Last year the main engine mounted raw water pump gave out on me and when I pulled the thermostat housing, pieces of the impeller were inside.
(Here's the link to last year's post: http://forums.iboats.com/bbBoard.cgi?a=viewthread;fid=24;gtid=491259;gpid=491262#gpid491262

As I mentioned, I will do a little more intense searching, it is possible that I didn't get all the pieces of the impeller out of the system which is causing a restriction somewhere.

Don - on the schematic you sent, I notice the water flows from the raw water pump back through the power steering cooler and then through a fuel cooler before it reaches the thermostat housing. Are you familiar with the actual inside water passages in these cooling units - is it fairly straight through, or is it likely a piece could hang up in there and still be there after a year? I have never even seen the fuel cooler - it is evidently under the manifold and not readily visible.

And Bruce - While an IR gun would be helpful in giving specific temps, trust me, there is a quite a difference in temps.

I will post what I find. Stay tuned! :^

 

[Fishermark]

Re: Question on Manifold and Riser temps

:$:$:$:$

Well, a lesser man would say he couldn't find the problem and it just went away on its own.... being a glutton for punishment, I will admit I goofed up!

When I replaced the thermostat last year I apparently switched the hoses incorrectly. I didn't notice till I looked at the schematic Don posted and noted that my hoses were not routed as indicated in the diagram. I then looked closer at the picture I took last year, (before the thermostat replacement), and compared it to my current set up. Yep. The hoses are not in the correct alignment. Here's a picture of the "before":

Note that both top hoses go to the risers.


Here's a picture of the "after":

Note that now the top hoses go to the starboard riser and the port manifold. Both of those run cool. (Amazing coincidence huh?)

Anyway, I will swap them back as they are supposed to be and take it from there. I will let you know the final outcome!

(Before anyone notices, the clamps are not on the one hose because I had already removed it to check for obstructions).

Also, I note that I do not have a fuel cooler. The main cooling hose goes from the pump to the back of the engine, through the power steering cooler, then up on top of the engine on the port side and directly to the thermostat housing.

 

[Fishermark]

Re: Question on Manifold and Riser temps

One more note... I put everything back together as it should be, with the hoses routed correctly. After running the engine for awhile on the muffs and through the strainer, both risers are now very cool, while both manifolds are hot.

I'm curious as to the purpose of the spring loaded balls (like check valves) in the theromstat housing. These are in the outlets going to the risers, while the outlets going to the manifolds have no such thing. What purpose does that serve?

I can take the hoses off of the thermostat housing and flush water into them, through the manifolds, and it comes out the back of the transom housing - just like it is supposed to, so there are no blockages there.

Do the manifolds just run hotter than the risers?

 

[bjcsc]

Re: Question on Manifold and Riser temps

OK. so backtracking the hoses found a problem. I still think there is someting else going on - but again I don't know what normal is with the dry joint systems. Seems to me that something could be going on in the thermostat housing. Did it run at a low temp. again (120&deg -130&deg) ? It's almost as if you have too much flow in some areas at the expense of the others. The thermostat and/or the housing and whatever those other components are you found could be the problem. I still think that the manifolds and risers should both be warm at most. That's about all I have, I'll defer to the techs from here on out...

 

[Don S]

Re: Question on Manifold and Riser temps

Those hoses on the port side of the engine being crossed is what caused the hot manifold on one side.
Those "Check Balls" are actually like a poppet valve on an outboard. They basicly stop the flow of water to the risers and use only the water coming up from the manifolds, until there is enough water pressure (Higher rpm of the engine and water pump) to open the poppet valves for extra cooling of the riser. With the one hose from the poppet valve going to the manifold, would basically stop any cooling water from going into the manifold untill the engine speeded up.
But, it has nothing to do with the engine running so cold, that is a thermostat problem, and it needs to be checked out a probably replaced.

 

[Fishermark]

Re: Question on Manifold and Riser temps

I will check the engine temp again next time I'm out and post the results. Thanks again!