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Manifold temps

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NJJim

New member
Just put my boat in the water today and I notices a pretty vast temp difference between the port and starboard manifolds. Motor is merc 5.7 260hp salt water cooled. Port side was cool to the touch just about everywhere on manifold and riser, starboard riser was a bit warmer but not hotter than 100-105 ( could keep hand on it indefinatly) but some spots on manifold were hot. Does anyone know how hot these manifolds can run without damage? Is it ok if manifolds are on the hot side as long as risers are cooler so as not to damage exhaust hose? I noticed some rust build-up in the raw water hose to starboard side which I will see if I can clean out, but my question is how can I tell if I'm running too hot. Is it time to replace or can I get the season out of them? Engine temp is approx 185@3,000 RPM. (gauge) Any info would be appreciated and thanks in advance,
 
mastertec Tech Mercury said:
Temp will be what your thermostat is, do you have 160 in, if so 185 is little high
Steve
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Steve, all due respect to you, but if you are referring to Jim's exhaust temps, I don't think that this is necessarily so... and allow me to explain why!

Whether an "open" or "raw water" system... or even for a "Closed Cooling" sytem......, most all sea water is by-passing the actual engine cooling demands.
IOW, the actual engine cooling demands typically require far less sea water than what is actually available if all is working correctly.

For an "open" system, the "thermostat" allows cooling water to "leave" the engine cooling system on an "on-demand" or "as-needed" basis as per thermostat temp setting.
The balance of the sea water is sent right on through to the exhaust system, and is expelled out the exhaust.
This is clearly demonstrated via a cut-a-way-view of a raw water T-stat housing and it's porting.
Would you agree?

I do agree that engine temp may have an effect on exhaust temps, but no where near the amount implied.
Again, this is because most all sea water provided by the sea water pump is by-passing the actual engine cooling demands.


My guess is that Jim's manifolds/risers are beginning to show signs of rust scale restriction, etc.
Being salt water cooled, it may be best to replace, rather than attempt to clean, etc.
Or a sea water pump that needs attention.

The other issue, Jim.... is the thermostat temp rating for a salt water cooled engine.
Salt begins Crystallizing at temps at/near 143* or so (depending on the info source).
Because of this, Stat Temp should not be at the higher end range... possibly best if around 140*!
Most OEM info will imply that a 140* stat be used for raw salt water cooling.

Once Crystallization begins, it's pretty darn hard to reverse the effects... and this will be in both the engine and the exhaust system.

Edit:
Jim, it may be worth your time to pull the risers, and take a good look at the transfer ports.
You're going to see that these are restricted with rust scale.
Often these can be cleaned, and we can temporarily renew some cooling ability.
Cost to do so would be two new gaskets.
Food for thought!


.
 
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Fyi merc used 143 degree tstat for many years and may still. Closed cooling (heat exchanger with antifreeze) typically used a 160 degree tstat.....
O
 
It is some what normal for one side to be "hotter" than the other. If you have the spring loaded poppet balls above the thermostat where the hoses that go to the elbows connect, it could be the ball is stuck close or just not opening propperly...
 
Ditto Rick and kghost. Manifolds in salt are chancy over 5 years. Port manifold typically runs hotter than strb. Engine running hot, I would say a raw water flow/volume issue. Before getting into your manifolds check the impeller and pump condition, and the t-stat. Alpha drive; pump in drive, Bravo and inboard; pump on engine.
 
By the way If you're engine is equipped with a tube that runs between the intake manifold and the starboard side exhaust manifold then it would be considered normal for the starboard side exhaust manifold to run a little bit hotter then the portside. It typically run almost 20ish degrees hotter at times because of that hot tube, water flow, And a number of other things mentioned above that effects the temp between the two sides. That tube will get upto around 220 + degrees, So be careful around that tube if your engine has one. That tube should be the only thing on this engine that will burn you quickly.:eek::(

If your interested, see number 4 for the tube that I'm talking about in the link below..
http://www.mercruiserparts.com/Show...7.png&inbr=8182&bnbr=90&bdesc=Intake+Manifold

Also make sure your engine temp is cooler than 185 degrees with something like a infrared temperature gun.
http://www.omega.com/toc_asp/subsectionsc.asp?subsection=J08&book=Temperature

To find out what your thermostat should be, What is your engine serial number?
 
A direct questions for you. When was the last time the manifolds and risers were changed? When was the last time the water pump was changed? What drive system does your boat have? year?
 
NJ Jim's engine is Salt Water cooled.

boat_tech said:
Also make sure your engine temp is cooler than 185 degrees with something like a infrared temperature gun.
To find out what your thermostat should be, What is your engine serial number?
Click to expand...
Again, Salt Water begins to chrystallize at temps nearing and above 143* F.
The double edge sword is that engines prefer the warmer operating temps..... Salt loves to chrystallize at these higher temps.

Docksidemarineservices said:
A direct questions for you. When was the last time the manifolds and risers were changed? When was the last time the water pump was changed? What drive system does your boat have? year?
Click to expand...
Ditto.... hence my suggestion of pulling the risers and taking a peek inside, and particularly at the transfer ports.
If this is the older Merc 260 (Jim mentioned 260 earlier) then he may have the log style manifolds, of which will also have the four end caps.

.
 
boat_tech said:
Also make sure your engine temp is cooler than 185 degrees with something like a infrared temperature gun.


To find out what your thermostat should be, What is your engine serial number?
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Good afternoon Rick, I hope your doing well today.:)
I just thought I had better mention that It appeared to me you forgot to highlight the important part of my post above "Also make sure your engine temp is" But to be honest I did forget to use the word "Much Cooler".:(

Rick as i know you are aware, The use of his engine serial number would be helpful to see exactly what engine/year we are dealing with here, (EFI/Carb, ect) so that we could make the attempt to explain to the O.P a much better suggestion of what temperature he should be using from both the engine manufacturers standpoint, As well as to see if "maybe" the engine he has might not so sensitive to engine temperature that maybe we could suggest using a lower thermostat temperature that could be used safely on his engine without compromising the engines runnability factor (To Much) if he's going to continue running in salt water. Of course if he does goes to a lower thermostat then someone may have to explain what he might be giving up in other maintenance items (Such as richer running spark plugs, ect) to help gain less crystallizing throughout the engine.;) And I would most definitely say you are pretty darn good at explaining all the differences here.;):cool: Keep up the good work.:) I do enjoy looking forward to all your post you do here, As well as all the other posters. You are all very well knowledged, And I myself learn something new everyday from all you guys. Thanks.

RicardoMarine said:
NJ Jim's engine is Salt Water cooled.

Again, Salt Water begins to chrystallize at temps nearing and above 143* F.
The double edge sword is that engines prefer the warmer operating temps..... Salt loves to chrystallize at these higher temps.

Ditto.... hence my suggestion of pulling the risers and taking a peek inside, and particularly at the transfer ports.
If this is the older Merc 260 (Jim mentioned 260 earlier) then he may have the log style manifolds, of which will also have the four end caps.

.
Click to expand...
Rick just curious to know, Do you take into consideration what style fuel system the engine has on it before just installing a 140ish style thermostat for your salt water guys? Or do you do it on a case by case basis, For example if they have a MPI engine, do you put in a 140ish if the boat stays in the salt water and you put in a 160ish if the boat is on the trailer and he runs 50% salt and 50% fresh? Not judging just learning. I work mostly inland SO-CAL area. Thanks.
 
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Hi all and thanks for all your replies. I will try to get ser. # over the weekend, and it's a 2 bbl carb and engine is a 1996. I am thinking of checking the thermostat and see what the temp rating is and then find a friend with a infered gun to check actual temps on engine. I'm going by gauge and I know they aren't know for being all that acurate. Both water pump and impeller were replaced 2 seasons and I've been known to stir up a little mud, but I don't know about manifolds and risers. I haven't replaced them and I bought boat 2 years ago. I'll keep everyone posted and thanks again for all the help.
 
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