Dry joint exhaust manifold cooling question

[Chased1]

Hey guys, i have a set of stainless marine dry joint exhaust manifolds on a 2000 merc 7.4 mpi. My issue is by the time my thermostat opens my exhaust manifolds are burning up. Is this how its supposed to be plumbed ?

 

[alldodge]

No

What is your engine serial number?

 

[Bt Doctur]

No, how are the cooling gaskets arranged?

 

[alldodge]

Post a pic of your hose routing

 

[tpenfield]

Probably all of your exhaust coupling (rubber) are burning up as well. As mentioned . . . let's see how your hoses are routed. I take it that these are replacement manifolds, and who ever put them on did not route the plumbing properly.

The exhaust manifold should get water directly from hoses that run from the thermostat housing.

I assume this is an open cooling system?

Water discharge from the engine itself would then go to the exhaust elbows/risers.

 

[HT32BSX115]

This sounds like a closed cooled system if the thermostat controlling flow to the exhaust manifolds.

 

[Bt Doctur]

a thermostat never controls how much water goes into the elbows

 

[Scott Danforth]

someone plumbed them wrong..... period

post a picture or two.

 

[Chased1]

You guys pretty much answered my question, i ll get some pictures today to see what you guys think about where i should get the cool water from. My super charger takes up a lot of room.

 

[happy hour iv]

I do not believe the 7.4 was ever available with dry joint. If you actually have a dry joint now I suspect you have a modified
8.1 system on the 7.4 engine. I do not believe the 8.1 system had closed cooling to the manifolds. Bottom line, to have closed cooling to the 8.1 manifolds the plumbing must be modified with a lot of thought. If the manifolds were open cooling before and the 8.1 manifolds are still open cooling then the thermostat is not in the system for the manifolds.
what was the system before the dry joint partial or full cooling?
what are the dry joint manifolds, 496/8.1 or something else ?

 

[HT32BSX115]

I do not believe the 7.4 was ever available with dry joint. If you actually have a dry joint now I suspect you have a modified

True statement! I wish someone did make "dry-joint" for the 454/502 engines!

The OP did say that he had Stainless Marine "Dry Joint" manifolds and risers.

I take that to mean he has the stainless tubing type risers since they can be set up that way.

Evidently Stainless Marine does build a "Dry Joint" 454 manifold. But they don't call it that. They say it HAS a dry joint between the riser and manifold.

Our manifolds are designed with two and one half to three times the thickness as the cooling jacket and we were the first company to build a manifold with a dry joint between the manifold and riser utilizing a v-band clamp method. We have been using this method for more than 27 years and in all this time we have not seen an internal failure on any of our manifolds. Our manufacturing process allows us to offer an industry leading 5 year limited warranty, unsurpassed in the industry.

They make nice stuff.....but bring your wallet!! (stuff it first!)

 

[happy hour iv]

Oops, I was thinking one stainless riser and oem manifold. Forgot about aftermarket custom.

 

[tpenfield]

http://www.stainlessmarine.com/

This is what I thought the OP was referring to . . . .

 

[Scott Danforth]

I do not believe the 7.4 was ever available with dry joint. If you actually have a dry joint now I suspect you have a modified
8.1 system on the 7.4 engine. I do not believe the 8.1 system had closed cooling to the manifolds. Bottom line, to have closed cooling to the 8.1 manifolds the plumbing must be modified with a lot of thought. If the manifolds were open cooling before and the 8.1 manifolds are still open cooling then the thermostat is not in the system for the manifolds.
what was the system before the dry joint partial or full cooling?
what are the dry joint manifolds, 496/8.1 or something else ?

you are correct, the factory never offered it. however the aftermarket performance market has offered "dry joint: for decades via companies like Gil and Stainless Marine, Dana, Lightning, etc. read the details of the posts

The OP is specifically calling out Stainless Marine as well..... because the OP specifically said.... I have Stainless Marine....

http://www.stainlessmarine.com/prod...big-block-exhaust-manifolds-risers-tailpipes/

however if plumbed the way the factory plumbed them in either open or closed cooling, they would work fine.



the OP also added or someone has added to his boat a supercharger. so my guess is the manifold feed plumbing was changed.

we are waiting for the pic of his plumbing to help him out.

 

[HT32BSX115]

Sure wish someone did make "Dry-Joint" manifold/riser kits for the 454 though........(like Barr, GLM, etc)

 

[wingless]

Sure wish someone did make "Dry-Joint" manifold/riser kits for the 454 though........(like Barr, GLM, etc)

Yes, the dry joint system affords many advantages, but my redesigned 454 MAG MPI Horizon raw water cooled wet joint exhaust was just disassembled for internal inspection after 3 years of salt water usage and the interior still looks brand new. My current guess / hope is that these parts will last the life of the boat.

Previously I would be hoping to squeeze another year at this point before discarding / replacing the entire system.

Part of my redesign permits me to drain bone dry and to flush after each usage.

 

[happy hour iv]

Someone does make a dry joint system for the 454. Mercruiser makes it. With a little plumbing and hardware modification for bolt on items like ignition module etc the 496 manifolds bolt right on to my genIV heads. I have 18 inch wet exhaust hoses that have just enough flex to take up the slight angle difference in the risers. I am actually running the 496 aluminum
manifolds in saltwater. I am however closed cooling the manifolds. The 496 manifolds were not initially designed for closed cooling so some plumbing modifications were needed. I assume the more recent 454 heads have the same layout, as std 454 mercruiser manifolds do not specify different applications based on vintage.