Newer Mercruiser Cooling System Questions . . .

[tpenfield]

Greetings,

Pre-season prep work is just around the corner and I am reviewing the closed cooling systems on my new-fangled Mercruiser engines. (2016 6.2 SeaCore models S/N' in my signature)

1) These engines have a 'poppet' valve, which are a new 'thing' to me. I believe poppet valves are more common with large outboard engines. Anyway, my understanding is that the valve releases at higher engine speeds (based on raw water pressure) allowing more raw water to go directly to the exhaust. At idle speeds the valve is closed and the exhaust gets raw water after it has gone through the raw water side of the cooling system.

Is my understanding correct? My previous boat had the old-school big blocks and the cooling system was more basic. . . . water flow to the exhaust was not regulated.

Another question/issue . . .
2) There was (and is) some coolant lost on the port engine . . . I noticed it last year after a 6 hour run and then again over the winter. It is loosing about 12 oz of coolant, and needs to be topped off. My plan is to check for leaks and do a pressure test if nothing obvious is found. The cooling systems on the new engines seems to be a lot more complex than the older engines. There is a 'crossover' assembly and I'm not sure what that does ??? It seems like a new 'thing' as well.

TIA

 

[tpenfield]

@Scott Danforth Any help on my crossover question. What does it do? Sort of looks like a junction box for cooling

I assume that this is a new(er) thing for I/O engines ?

 

[Scott Danforth]

Let me check with some folks

however you nailed it here:

The cooling systems on the new engines seems to be a lot more complex than the older engines.

 

[tpenfield]

Let me check with some folks

however you nailed it here:

Thank you

Here is the illustration . . .
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Merc P/N = 8M0107035

I think it is on the front of the engine under the Heat Exchanger (somewhere)

 

[alldodge]

Best guy to answer the question is @muc

My thinking is the crossover is something that helps keep the entire motor more the same temp all over. With pre-cross types the thermostat did all the work, with cross types the circulation pump keeps all coolant moving between pump and block until more cooling is needed.

From MUC 7/24/19

The poppet valve and spring are color coded for what engine, drive and cooling system your engine has.

 

[Scott06]

@Scott Danforth Any help on my crossover question. What does it do? Sort of looks like a junction box for cooling

I assume that this is a new(er) thing for I/O engines ?

What this looks to be is a bigger version of the thermostat housing that would be on top of the intake on an older chevy based V engine. I suspect there is no water crossover in your intake. This collects hot coolant out of both banks of heads and from exhaust manifolds. Thermostat is in top feeding hot coolant up to heat exchanger. Also has cooled coolant coming in and being delivered to block and exhaust manifolds, maybe through hose 18. These are the merc designed 6.2 not GM based correct?

 

[tpenfield]

What this looks to be is a bigger version of the thermostat housing that would be on top of the intake on an older chevy based V engine. . . . .. These are the merc designed 6.2 not GM based correct?

Correct.

 

[muc]

The poppet valves serve a different purpose on outboards then on your engine. On outboards they release excess block pressure. On a catalyst engine they are one of the methods used to control catalyst temperature.
Yes the crossover serves the the purpose that the intake manifold used to. But your engines don’t have them. The heat exchanger is what combine’s the coolant flow from the heads so a single thermostat can control engine temperature. You are looking at the wrong parts breakdown.

 

[tpenfield]

The poppet valves serve a different purpose on outboards then on your engine. On outboards they release excess block pressure. On a catalyst engine they are one of the methods used to control catalyst temperature.
Yes the crossover serves the the purpose that the intake manifold used to. But your engines don’t have them. The heat exchanger is what combine’s the coolant flow from the heads so a single thermostat can control engine temperature. You are looking at the wrong parts breakdown.

I’ll certainly double check and take a look at the engines- I got the cross over parts list from the Mercury website based on the engine serial number. There seemed to be 2 parts lists - one for raw water cooled and another for closed cooling.

 

[alldodge]

There seemed to be 2 parts lists - one for raw water cooled and another for closed cooling.

Sorry Ted but this is one of the DAH moments , right

 

[tpenfield]

The poppet valves serve a different purpose on outboards then on your engine. On outboards they release excess block pressure. On a catalyst engine they are one of the methods used to control catalyst temperature.
Yes the crossover serves the the purpose that the intake manifold used to. But your engines don’t have them. The heat exchanger is what combine’s the coolant flow from the heads so a single thermostat can control engine temperature. You are looking at the wrong parts breakdown.

Here is the 'crossover assembly' on the engine. Looks like it serves the purpose of collecting the coolant from each side of the engine and sending it to/from the recirc. pump & heat exchanger. Correct?


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In the old school GM blocks this was done at/by the front of the intake manifold.

So, it looks like my engines HAVE the crossover and it does as explained. Correct?

the thing sure looks complicated

 

[tpenfield]

Here is to poppet (Popeye ) valve (I believe). I recall reading somewhere about it being gray in color.
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[Scott06]

Here is the 'crossover assembly' on the engine. Looks like it serves the purpose of collecting the coolant from each side of the engine and sending it to/from the recirc. pump & heat exchanger. Correct?

View attachment 357613
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In the old school GM blocks this was done at/by the front of the intake manifold.

So, it looks like my engines HAVE the crossover and it does as explained. Correct?

the thing sure looks complicated

That would be my take as well. When you look at the modern V engines (bot these merc and automotive) none have an intake water crossover like back in the day. Yes 10 lbs of stuf in a 5 lb box...

 

[muc]

Here is the 'crossover assembly' on the engine. Looks like it serves the purpose of collecting the coolant from each side of the engine and sending it to/from the recirc. pump & heat exchanger. Correct?

View attachment 357613
.
In the old school GM blocks this was done at/by the front of the intake manifold.

So, it looks like my engines HAVE the crossover and it does as explained. Correct?

the thing sure looks complicated

Yes, you are correct your engines do have the crossover and the parts breakdown you posted is the right one.. I was wrong.
Note that when you pressure test this system, MerCruiser recommends testing with an almost full system at 20 psi.
The service manual --- p/n 8M0099748 --- has a good discription on testing.

Your engines were built August 2015 and put in service July 2016. If you haven't changed the coolent yet, now might be a good time.

 

[tpenfield]

Thanks for the clarification. I have the service manual, so I will check out the testing procedure.

It looks like the thermostat is located in the heat exchanger for the closed cooling models (i.e. SeaCore) and in the crossover for the raw water cooled models (red labels).

I assume that the coolant flow is from the recirculating pump into the engine block, up through the cylinder heads and out to the crossover (?) . From the crossover, the coolant either goes to the H.E. or directly back to the recirc. pump, depending on the amount to t-stat opening.

So, I'm assuming the crossover fastens at the cylinder heads (?), but it also looks like there may be an attachment point in between.

 

[muc]

I assume that the coolant flow is from the recirculating pump into the engine block, up through the cylinder heads and out to the crossover (?) . From the crossover, the coolant either goes to the H.E. or directly back to the recirc. pump, depending on the amount to t-stat opening.

So, I'm assuming the crossover fastens at the cylinder heads (?), but it also looks like there may be an attachment point in between.

Yes, I believe that pretty much sums up coolant flow for the engine. The exhaust manifolds will have constant flow from the crossover to the manifolds to the heat exchanger And back to the crossover.
I think there is only seals between the crossover and heads.

 

[tpenfield]

FWIW - Here are the cooling system flows for the engines.

Raw Water Side . . .
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Closed Cooling Side . . .
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[alldodge]

Thanks for posting

 

[Lou C]

Interesting, I wonder if you’ll see more consistent temps in all parts of the engine & exhaust system?
The only engine I ever saw with a crossover like that was a horizontally opposed Subaru flat four

 

[tpenfield]

It is interesting . . . Sort of a different twist from the GM block approach.

The t-stat is up at the heat exchanger so the flow gets a little interesting. The raw water cooled version have the t-stat in the crossover itself.

I know with my GM 454's and closed cooling the exhaust manifolds would get very hot before the t-stat began to open. I fabricated in a little bit of bypass to address that issue. I'll have to see how these engines go through the warm-up cycle, but it looks like the crossover has an extra input hose from the H.E. that might keep coolant flow through the exhaust manifolds even if the t-stat is closed.

As long as it works . . .