Exhaust manifolds and risers water line upgrade help

[hivoltg]

New to the forums and could use some expert advise.

I have a 1977 Wellcraft Suncruiser 2000 with a 351 Windsor engine. Mercruiser 888 setup. It had 35 year old log style exhaust manifolds and risers. Still working btw. I figured it was time to upgrade them. Yesterday was very fun getting them off. I have all the studs out but one, soaking it in pb blaster.

Anyways, I now have some nice new center style exhaust manifolds and risers ready to be bolted up.

Ok onto my question/help topic. My old log style setup had three water cooling hoses per manifold and riser. Two to the front and back of the manifold and one to the riser.

My new center style manifolds have a hole front and back but the new risers dont have an inlet for my "third" water hose. No capped holes on the risers to access.

Should I put a T inlet on the back of the manifolds, and allow water in both hoses to the back of the manifold or should I just cap one of them off up at the thermostat? I assume the riser hose is a bypass until the engine warms up. Im just worried the one of them is a water return line and I would hate to block off a return.

Im not too worried about a cold engine. I live in Texas and the lake is like bath water.
I appreciate any advise on this fun project. I'm sure one of you has upgraded an exhaust setup before.

 

[alldodge]

Re: Exhaust manifolds and risers water line upgrade help

Your new risers should have gaskets which allow water to folw from the manifold to the risers. If this is true, then block off the hoses leading to the risers because water will come up from the manifolds.

 

[hivoltg]

Re: Exhaust manifolds and risers water line upgrade help

Yep, they are pass thru gaskets from manifold to riser (no block off plates). I ordered some coolant hose deletes today. Thanks AllDodge.

 

[Bondo]

Re: Exhaust manifolds and risers water line upgrade help

Ayuh,... Welcome Aboard,.... Ya got any Pictures of what yer workin' on,..??

T-stat housin', 'n hose routin',..??

 

[hivoltg]

Re: Exhaust manifolds and risers water line upgrade help

Thanks Bond-o. Here are some pics of what im working on. 351 Ford. Two coolant lines above the thermostat per side. One below per side. Pics diagramed to where they go. Impeller water comes in below the thermo and block water pump line below also. Its pouring down rain right now or I would of taken better pics.

 

[hivoltg]

Re: Exhaust manifolds and risers water line upgrade help

Ok so alittle update on information. I removed the thermostat housing this weekend and cleaned it out. I figured out some internal water routing.

The top front existing coolant lines connecting the thermostat housing to the risers are passages after the thermostat opens which I found odd. So eliminating these two as suggested will make my thermostat non functional.

The rear thermostat housing top and bottom coolant lines that go to the front and rear of the exhaust manifold are before the thermostat and the water passages are connected inside the thermostat housing.

So based on this I think I should reroute the front hoses after the thermostat to the rear of the manifolds, and block off one of the rear passages instead keeping my thermostat working. Thoughts?

Pic of my old manifolds:

The cracks in the risers are from me beating them off with a hammer.

 

[alldodge]

Re: Exhaust manifolds and risers water line upgrade help

This is more of a puzzler then first thought and I'm glad you looked further into it. New exhaust circulation systems receive water into the top of Thermostat (TS) housing which passes through to the engin water pump and to exhaust manifolds. Exhaust manifold hoses are smaller then the water pump hose so water pump gets most the water. Water circulates through engine and comes out under the TS housing and small ports in housing allows water to pass to top of housing with TS closed.



The pic above is from page 588 of Merc manual No 2. It looks like to get this right you will need anorther TS housing, this is do if the top only are used the risers may have difficulity getting enough water when the TS is closed. If used just the bottom the risers will get water but it could reduce water going to engine due to restriction not being as great.

Going to need some additional help from the guru, Don, Bond-o, etc ??

 

[hivoltg]

Re: Exhaust manifolds and risers water line upgrade help

Thanks for the pic AllDodge. I think my system is exactly as you described but backwards.

My motor receives raw water to the bottom of the thermostat housing and the engine water pumps big hose connects to that chamber also. So does the two front and rear manifold hoses. The thermostat housing cover has a midsize hole thru it for water (from the engine?) to somewhat bypass the thermostat even when its closed. The thermostat housing cover chamber is where only my old riser hoses connected.

I am leaning towards capping off one of the lower thermostat hose chamber passages and having the old existing riser hose passages past the thermostat rerouted to the rear of the manifolds. This would allow cool raw water to the front of the manifolds before the thermostat and warmed engine water to exit/flow out the thermostat housing and into the rear of the manifolds. Then both dump out the risers into my y pipe.

I am going to be using restricted riser gaskets to mitigate lose of water cooling the engine. If I find these arn't flowing enough I will switch to open style riser gaskets.

I know im kind of reinventing the wheel on this old boat to modernize it. I appreciate you guy's help on this.

 

[Bondo]

Re: Exhaust manifolds and risers water line upgrade help

Thanks for the pic AllDodge. I think my system is exactly as you described but backwards.

My motor receives raw water to the bottom of the thermostat housing and the engine water pumps big hose connects to that chamber also. So does the two front and rear manifold hoses. The thermostat housing cover has a midsize hole thru it for water (from the engine?) to somewhat bypass the thermostat even when its closed. The thermostat housing cover chamber is where only my old riser hoses connected.

I am leaning towards capping off one of the lower thermostat hose chamber passages and having the old existing riser hose passages past the thermostat rerouted to the rear of the manifolds. This would allow cool raw water to the front of the manifolds before the thermostat and warmed engine water to exit/flow out the thermostat housing and into the rear of the manifolds. Then both dump out the risers into my y pipe.

I am going to be using restricted riser gaskets to mitigate lose of water cooling the engine. If I find these arn't flowing enough I will switch to open style riser gaskets.

I know im kind of reinventing the wheel on this old boat to modernize it. I appreciate you guy's help on this.

Ayuh,.... You sure are,.... I donno if yer plans gonna work, or Not,...

I'd suggest ya study how Volvo, or even OMC dealt with the issue,...
I'm thinkin' yer gonna need a Different t-stat housin',....
Donno whether a Chevy housin' would fit or not, never tried,...

Keep Us posted, yer kinda breakin' fresh ground,...
I can't recalec anybody reportin' back whether it worked or not,...

 

[RCAnderson]

Re: Exhaust manifolds and risers water line upgrade help

Why not drill and tap a hole in the outer water jacket of your new risers ? Then leave the plumbing the same. I found what appears to be your system on page 7D-2 of Service Manual #1. I would not really advise using the old riser ports of your T-stat housing going to the rear of the manifolds, as this is a restricted passage (originally so that the risers still got some cold raw water even with the t-stat closed, presumably for outdrive cooling) The other end of your exhaust manifold is open to the same port as your water pump inlet. So you might create a situation where there is actually suction (from the engine recirc pump) pulling the raw water out of the front of your manifolds, without any going through the risers, thus potentially overheating the outdrive. This would only happen with the t-stat closed. I may be out to lunch though.

 

[hivoltg]

Re: Exhaust manifolds and risers water line upgrade help

I mounted the new center style exhaust manifolds today. I capped a set of the rear tstat housing hose ports and ran the old riser hoses to the rear of the manifolds. It worked fine. I ran the motor for 20mins in this configuration. I had plenty of water coming out the risers. After 20mins I could place my hand on the risers and leave them there as long as I wanted. Granted this is on the muffs and at fast idle (real world lake use may change this). I let the engine warm up till the thermostat opened. I had a small water drip at the thermostat housing seal. All the rest was good. Its always one more thing to redo.

I agree with what you said Bond-o i'm doing this setup very similar to how pleasurecraft marine is routing their water cooling. I did some research. They use the same 351 motor in a lot of their ski boats.

One issue: Im not happy with the exhaust boots angle of attack to the y pipe coming off the new risers. Its too extreme/close/restrictive and Im concerned it may become a leaking or collapsed exhaust boot issue. (Thru hull exhaust project to come or riser extensions?)

I will post some pics soon. I worked on this thing until it was dark out.

 

[hivoltg]

Re: Exhaust manifolds and risers water line upgrade help

I ordered some Osco 90 degree exhaust pipes and they worked great for the extreme angles off the risers to the y pipe.

I took the boat out to the lake today and ran it all day. The hottest the motor ever got was 160 after a short stop and restart. It was 120-140 all day long and I am very happy with the outcome. In the past I had to really fight to keep the boat at 160-170. The boat also has a noticeable horsepower increase and the motors exhaust sounds better too (I also ported/matched the heads exhaust ports to the manifolds during the switch).

I adjusted the waterline setup, and I now have the after thermostat line to the front of the manifolds. I have the top rear line capped and the bottom rear going to the rear of the manifolds. Both risers are staying cool and equal temp. I hope this thread helps someone else upgrade their old log style exhaust to a newer center style. I want to also thank all of you for your help on this project and its successful outcome.

 

[alldodge]

Re: Exhaust manifolds and risers water line upgrade help

Sounds great, looks like you will be the go to dude when soneone else try's it. :thumb: