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5.0 MPI exhaust manifold and riser temp

When running you should be able to touch with bare hand and not burn it. At idle one of the risers can get to hot to touch do to not enough water flow, but won't be an instant burn
 
AllDodge said:
When running you should be able to touch with bare hand and not burn it. At idle one of the risers can get to hot to touch do to not enough water flow, but won't be an instant burn
Click to expand...
Friend was out on his boat. Only just put new manifolds and risers on. All gaskets right and the flow restriction gasket in the right place. He was at idle for 15 mins and engine temp was 140ish on the gauge but he said the manifolds were really hot and the risers cold. I'm going out tomorrow with my laser thermometer but wanted to get an idea about the expected temps. It's a raw water cooler one.
 
Most likely either the wrong gaskets were used, or they were placed in wrong order
Would need the motor serial number to look up water should be there, also is it open or closed cooling
 
AllDodge said:
Most likely either the wrong gaskets were used, or they were placed in wrong order
Would need the motor serial number to look up water should be there, also is it open or closed cooling
Click to expand...
Open. Purely raw water cooled. Gaskets were identical to what came off. I've been trying to find a decent water flow diagram. It's a 2003 5.0 MPI. Am I right in thinking the thermostat housing recirculates until the temp opens it and then its diverted to the lower input hose of the manifold to allow more cold water in the engine. Just thinking that might be why the manifolds were hotter when he was just at idle on the mooring and the thermostat hasn't opened yet. Water temp here is still pretty cool at 11/12c
 
Raw water cooled

Most of the raw water coming in goes to the exhaust. When the thermostat opens some of the cool water goes into the block and some hot water mixes with cool water and exits out through the exhaust. The thermostat doesn't open for long before the cool water causes it to shut, and it will repeat

If motor has a single or 3 point drain system adds other complexity to it

If motor has dry joint exhaust this also has other gaskets and how they are installed
Example
Slide1.JPG
 
AllDodge said:
Raw water cooled

Most of the raw water coming in goes to the exhaust. When the thermostat opens some of the cool water goes into the block and some hot water mixes with cool water and exits out through the exhaust. The thermostat doesn't open for long before the cool water causes it to shut, and it will repeat

If motor has a single or 3 point drain system adds other complexity to it

If motor has dry joint exhaust this also has other gaskets and how they are installed
Example
View attachment 37003
Click to expand...
I was looking at this diagram and it seemed to me the thermostat closed allowed water to recirculate until engine reached proper temp then opened and allowed flow to the lower hose of the manifold.
 

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Anthonyexeter said:
I was looking at this diagram and it seemed to me the thermostat closed allowed water to recirculate until engine reached proper temp then opened and allowed flow to the lower hose of the manifold.
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Might look that way but no, the circulating water pump keeps water circulating around the block so there are no hot spots. Temp comes up and thermostat opens allowing hot to exit and cool to come in. There is always more being pumped than the motor will use

In your pics you have what is called warm risers
I this pic gasket C is full flow, so both round ports are full open holes

Gasket G is a restrictor so one side has a closed hole and is on the side of the exit exhaust. The other side has on small hole and is on the side where the hose connects to the elbow

1778015698196.png


This is the motor and agree with your color coding
The Blue lines gets full time cool water direct from the raw water pump.

When you said
he said the manifolds were really hot and the risers cold.
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The risers (correct term elbows) should be cold

The boat has warm risers/manifolds so the restrictor gasket will reduce the amount of water going thru them to reduce condensation. t idle the risers in most cases on one side will get hot enough to keep you from leaving your hand on it, but should not be an instant burn

It could be your ok, but need to see what the temps are

1778016333598.png


Was the impeller changed with the exhaust system?
 

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AllDodge said:
Might look that way but no, the circulating water pump keeps water circulating around the block so there are no hot spots. Temp comes up and thermostat opens allowing hot to exit and cool to come in. There is always more being pumped than the motor will use

In your pics you have what is called warm risers
I this pic gasket C is full flow, so both round ports are full open holes

Gasket G is a restrictor so one side has a closed hole and is on the side of the exit exhaust. The other side has on small hole and is on the side where the hose connects to the elbow

View attachment 37007

This is the motor and agree with your color coding
The Blue lines gets full time cool water direct from the raw water pump.

When you said

The risers (correct term elbows) should be cold

The boat has warm risers/manifolds so the restrictor gasket will reduce the amount of water going thru them to reduce condensation. t idle the risers in most cases on one side will get hot enough to keep you from leaving your hand on it, but should not be an instant burn

It could be your ok, but need to see what the temps are

View attachment 37009

Was the impeller changed with the exhaust system?
Click to expand...
Yeah, changed the impeller and also the back plate on the raw water pump.
 
"Might look that way but no, the circulating water pump keeps water circulating around the block so there are no hot spots. Temp comes up and thermostat opens allowing hot to exit and cool to come in."

That's what I meant. It looks like once the thermostat opens it allows flow into the top of the thermostat housing body and out to the bottom hose in the manifold, thus allowing more cold water into the block circuit. Using those hoses, the red ones I highlighted as a dump for hot water allowing the jabsco style pump to push more cold into the the block rather than just pushing it through the top entry in the elbow. I'm 40 years working on diesel workboats. Been doing this Mercruiser for a friend as a favour. I'll be out there tomorrow and getting some more accurate temps, more accurate than "it was too hot to keep my hand on it".
 
You said the G gasket has a closed hole and a small hole. This is a picture of the one I took off. Open on the exhaust side and small hole on the water inlet/front side.
1000009704.jpg
 
The motor shows the Mans has Risers and Elbows
Gasket turbulators on Gasket face up

Gasket between Mans and Risers should be full flow, if pic above is the Man than it should be full flow. If pic is the Riser than gasket is correct
 
AllDodge said:
The motor shows the Mans has Risers and Elbows
Gasket turbulators on Gasket face up

Gasket between Mans and Risers should be full flow, if pic above is the Man than it should be full flow. If pic is the Riser than gasket is correct
Click to expand...
Yeah, it's the top of the riser. The manifold below it had 2 full flow gaskets and that's what went back with the new ones.
 
AllDodge said:
The motor shows the Mans has Risers and Elbows
Gasket turbulators on Gasket face up

Gasket between Mans and Risers should be full flow, if pic above is the Man than it should be full flow. If pic is the Riser than gasket is correct
Click to expand...
Popped out today to the mooring. Ran on idle and up to 1500 for about 20 mins. Didn't have time to go for a good run but the elbows were about 60-70f and the manifold ranged from 150-190f
 
If temp gun is accurate and with a 140* Stat I would say the Mans are a bit to hot

Item 20 in pic below is a reduced Tee fitting and should be slightly restricting the water flow to the elbows so the Mans get some.

The check ball above Item 24 should not pose an issue when running, and don't see both causing an issue at same time, if both Mans are about same temp

The one side restriction on the Elbow should not reduce the water thru the Mans a lot

1778185482153.png
 
AllDodge said:
If temp gun is accurate and with a 140* Stat I would say the Mans are a bit to hot

Item 20 in pic below is a reduced Tee fitting and should be slightly restricting the water flow to the elbows so the Mans get some.

The check ball above Item 24 should not pose an issue when running, and don't see both causing an issue at same time, if both Mans are about same temp

The one side restriction on the Elbow should not reduce the water thru the Mans a lot

View attachment 37014
Click to expand...



As I am not familiar with this newer style exhaust (which is way over engineered, if one would call it that).....

The combusted exhaust entering the manifold is around 1200* F.

Running in neutral at 1500 rpm for 20 minutes I would expect the elbows to be ice cold.

I have never temped a manifold (older style with no funky gaskets) to see what its operating temp would or should be. But I will say, Any I have worked on after running either on a hose or under load, The manifold were freaking hot. Not the elbows but the manifolds.

This design, The Elbows get raw cold water until thermostat opens Correct?

In this system does the manifold also get raw cold raw until thermostat opens?

Even so, I would think a cast iron manifold getting hit with 1200*f and has a no load running temp of 150*-190* F. I would say it would be just fine and the increase of 40 * F could be due to thermostat cycling.

If the cooling of the manifolds is controlled with engine water after thermostat opens, that is already at 150-160*F.

What are your thoughts on this?
 
This design, The Elbows get raw cold water until thermostat opens Correct?
Click to expand...
No, Elbows get cool water full time, it gets a bit less when thermostat opens but the thermostat doesn't stay open very long not in gear. Under heavy load the thermostat will stay open longer but not wide open unless the cooling system is not working correctly

In this system does the manifold also get raw cold raw until thermostat opens?
Click to expand...
Yes, but not as much as the Elbows.
The water from the water pump impeller pushes it to the single point drain and than divides up between the circulating water pump and the Tee (item 20). When the thermostat is closed the water goes in and out through the top of the thermostat housing and into the Mans. The Mans Riser gaskets are full open so water flows thru easy but gets slowed due to Elbow gasket with one side being restricted

The 180 to 190 is enough to burn someone at the touch. It can burn at one second at 160

If the cooling of the manifolds is controlled with engine water after thermostat opens, that is already at 150-160*F
Click to expand...
The Mans get water full time when the thermostat is open or closed, just a bit less when thermostat is open. With full open old style Mans you will see in most cases only the port side (if memory serves) gets real hot at idle. This is due because at idle the Elbow doesn't fill with water.
 
AllDodge said:
If temp gun is accurate and with a 140* Stat I would say the Mans are a bit to hot

Item 20 in pic below is a reduced Tee fitting and should be slightly restricting the water flow to the elbows so the Mans get some.

The check ball above Item 24 should not pose an issue when running, and don't see both causing an issue at same time, if both Mans are about same temp

The one side restriction on the Elbow should not reduce the water thru the Mans a lot

View attachment 37014
Click to expand...
The hoses are different on the one in working in. Hose 3 in your diagram goes to the drain manifold 9 on this engine. Also, at some time in the past the block drain hose has been removed from the block and drain plugs installed and the inlets on the 9 manifold blocked. I've only seen diagrams where the hose 3 is a drain direction. Does that also feed the manifold too? I'm guessing not as not as some engines just have a plug at the bottom of the tee on the manifold and not the extra no.3 hose
 
AllDodge said:
Yours is like this but with some drains blocked off

View attachment 37022
Click to expand...
Yeah. I'll take it for a run tomorrow out to sea. Engine temp comes up and never shifts. I think the owner is chasing a problem that might not be there. He's getting a thermostat kit , it's a cheap job and maybe the old one is a little sticky. Apart from that there can't be anything else wrong, unless there is a fault in the casting of the new manifold.
 
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