350 mag mpi manifold/elbow temp

[alldodge]

EC motor but I removed the cats and added the 02 sensor bypass kit.

Still have the same water flow W or W/O

 

[Mhorn0817]

Makes me feel a little better and it ran good with no problems. The little bit I've seen online says it should be cooler but there wasn't enough talk and evidence to support that. I have the Merc manual and it does not give a specified temp it should be.

 

[Lou C]

If you're starting out with everything new that may be what it's going to be.

 

[alldodge]

While 150 is very hot and 190 will give instant 3rd degree burns, so we might want to do something. These temps will not hurt the motor

With removing the CAT and bypassing sensors, you could reroute the hoses so all water goes thru the Mans and out. Loose the 3 point and install a 7 point

 

[Mhorn0817]

How would I go about doing that? Manifolds have a fitting at the bottom that 2 hoses run to. Elbow has 1 big hose running to them.

 

[alldodge]

This is simplistic and showing a V6 but its basically the same



With that in mind, the issue doing it this way with your Mans might be the Man to elbow gasket. Don't know if the 2 holes are enough to pass all, probably will but have not been tested

If I knew you were going to use O2 bypass I would have mentioned to get the cheaper non-CAT Mans

 

[Mhorn0817]

Yeah I was just trying to do what the manual called for, parts wise. Again it rubs great, I just thought/assumed it should be cooler.

I reused the ball valve T fitting on the bottom of manifold. I cleaned them out before installing but could they be bad or restrictive some how?

 

[alldodge]

Just guessing, but I think by removing the CAT it changed how the water flows. The 150* while hot and can burn its not that bad. So one is at 150 and other at 190, so the 190 is not getting enough flow.

The port side drain fixture if not clean may also cause some issue. I just don't know enough

 

[Mhorn0817]

150 is the motor temp. Manifold/elbow temps are 170 starboard and 190 port. That's after coming off plane riding around for a hour at 3800 rpms.

 

[Lou C]

Since for cats to work they can’t be too cold it might be that these manifolds are designed to maintain a higher temp.

 

[Mhorn0817]

I've read it's normal for each side to have a different temp reading so the difference in temps side to side don't bother me too much. But the 190 makes me wonder. Wonder if I could get ahold of anyone at mercruiser to answer the question.

 

[Mhorn0817]

Spoke to Mercury today. They said they do not have a temperature spec for manifold and elbow. Basically said if there are no alarms or codes then it's within range.

 

[alldodge]

Spoke to Mercury today. They said they do not have a temperature spec for manifold and elbow. Basically said if there are no alarms or codes then it's within range.

That would be good news if it wasn't so sad

 

[Mhorn0817]

Exactly. You would think there would be some type of number or range.

 

[alldodge]

There is, Merc is not divulging

 

[Lou C]

So then can they tell you at what temp an alarm is set? Sounds like a silly guessing game here. Certainly that info must be in their shop manual!

 

[tpenfield]

Sounds like you have CAT's with raw water cooling. The exhaust manifolds will be the one of the last stops of the raw water on its way through the engine. Therefore it should be the hottest of the major parts of the engine. Raw water does directly flow to the riser portion of the exhaust, so they may be a bit cooler.

If it ain't broke, don't fix it. But you may want to get an IR temperature 'gun' and take some readings at various parts of the engine after it has been run for a while. This record will help ID any cooling issues that may arise.

When you say 'brackish' water, does that mean you are near the ocean, but not quite in the ocean?

 

[Mhorn0817]

I talked to Mercury again, different person. They said every engine calibration is different but a general number to set the alarm off is 215 degrees. Im not close but I'm also not far away either, atleast on the port side.

I did use a IR temperature gun to get my readings. From what I've read and been told, the elbows should be cooler then the manifolds and they are not. They are the same temperature.

Brackish water meaning rivers and bay, not ocean. So not fresh water but not fully salt water either.

 

[Lou C]

One last thing, the thermostat housing is basically a distribution valve, that takes in cool water & feeds the exhaust system, make sure the nipples that the manifold & elbow hoses connect to are clean and open.
Have you ever tested the output of the impeller with the boat in the water? Might be good idea, even if its new, to make sure you're getting the volume of water you should.

 

[Mhorn0817]

I'll take the housing off and double check. Is there a gasket there that needs to be replaced or sealant? Or can I just take it off and put it back on?

What would be the best way to check the impeller output in the water?