Cooling System Question(s)

J

jere1972

Petty Officer 2nd Class
Joined
Nov 1, 2011
Messages
183
Have a couple ? that I'm hoping someone with more experienced then me can help with regarding the cooling system, have a mercruiser 7.4 Bravo 1 (carbed)not 100% now on the age...but believe it to be a 1990/91 Mark IV... I have new manifolds and risers (cast iron),and a brand new GM Cast Iron intake, and would like to also replace cooling systems hoses, along with a new thermo housing...my ? is the new risers (GLM) to not have the 1" water nipple only a removable plug (guessing I would have to install a nipple), my old risers were OEM Stainless with casted inlet...how important is the hose that came from the old thermo housing popet ends to the riser?? can I do away with that...it seems newer engines don't use that?? I would like to use a stainless housing that states for BB chevy I have attached a pick of my old stye and a pic of the stainless one I would like to use..
old therm.jpg
new thermo.jpg
another question I have is because the old risers were the Stainless ones...the remote oil filter adapter bolted at the base of the riser....the new risers are cast iron and have long bolts that go through the top of the riser...any issue with the remote oil adapter being inverted with the filter inverted aswell....so I can bolt the adapter to the top of the riser...not sure if you guys may know what I mean on that subject???
 
Tail_Gunner

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
Re: Cooling System Question(s)

Good thread im in the same boat and have found little concise info on the subject. The new lower style is the one i am choosing to go with and if that does not distribute enough water supply well then i have a new water pump planned that will supply enough....that might be the answer here it get the feeling the older water pump's were not quite up to the job.
 
J

jere1972

Petty Officer 2nd Class
Joined
Nov 1, 2011
Messages
183
Re: Cooling System Question(s)

the dude that rebuilt my engine told me to just cap off the thermo nipples, and leave the thermostat out, the hoses were not needed...me being me...I question everything....they had to be there for a reason if not needed what were they for....I'm thinking there may have been to much water pressure and those hoses were for relief??? and the popet things prevented backflow from the risers...Maybe?? and to leave out the thermostat???? his reasoning was less restriction and if she starts to heat up you know its not from the thermostat??

also don't know what to do with the remote oil filter....I have seen on other engines it was inverted....don't know if thats a different part...or system design or I can just flip mine to better mount it to my riser...but something about the filter being upside down seems like it could defeat its purpose (allowing stuff to flow back istead of being trapped)
 
Tail_Gunner

Tail_Gunner

Admiral
Joined
Jan 13, 2006
Messages
6,237
Re: Cooling System Question(s)

The old thermostat housing did redirect water now as to the riser's that i do not know. I do know that the big blocks do have heating issue's and merc's history with water pumps on them is cloudy...Personally i will be installing a Johnson crank mounted pump and use the newer housing you've posted along with a freshwater pickup. There people who do run without thermostat's and the conversation seems to evolve around oil temp's i just dont have enough exposure to a big block yet to really know.

There are a few guy's on the board who do know the 454/7.4 well they may respond and illuminate what's going on.
 
achris

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Cooling System Question(s)

Leaving the thermostat out is probably the WORST advise anyone can give. Your engine will never reach proper operating temperature and that will increase wear and not allow the oil to get warm enough to boil off the lighter contaminates...

What you have is the older style 'warm manifold' system... The 'excess' water from the pump goes through the elbows (what you're calling risers) and the water that flows though manifolds has passed through the engine first. When the 'stat is closed the water in the manifolds is static. The new style 'stat housing is designed for 'cold' manifolds. The 'excess' water from the pump flows into the bottom of the manifolds and out through the elbows. The manifolds have water flowing through them regardless of the 'stats condition (open or closed).

You can change one system to the other, but it helps to understand how each system works in order to make the change. One important change that a lot of people miss when doing the conversion, the gasket between the manifolds and the elbows... Warm system requires a restrictor gasket, cold system requires 'full flow'...

To make the change, obviously change the 'stat housing. The existing hose that come from the water supply pump remains, as does the large hose that goes to the engine circulation pump. The other 2 outlets on the housing go to the bottom of the manifolds. That's it....

One more thing. If the stainless elbows are in good condition, reuse them! Just put a plug on the nipples.

Inverting the oil filter is fine. The new filter cartridges have an anti-drainback valve in them. Merc have been using inverter filters for almost a decade. Personally, I HATE them.... When you go to change the filter, oil everywhere. I'd like to find the first-class moron that came up with that idea... I'd kick his backside from here to Antarctica and back! JMHO :) But if you reuse the SS elbows, you can use the filter housing as designed.... :D

Chris......
 
Last edited:
achris

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Cooling System Question(s)

Tail_Gunner said:
Thank you Achris by chance is there a tutorial avaible for such a conversion...i have a real mess going with a 87 454 low rpm good temps 3000rpm and here come's .....Ill start a new thread me bad,

Upon further review The Difference Between Warm Vs Cold Marine Exhaust Manifolds | Performance Product Technologies

Again thank you achris
Click to expand...

A while back I wrote just about exactly what is on that website (I have never seen it before BTW)... 84EdH may remember where it is... Ed?

Chris......

EDIT: Found it... http://forums.iboats.com/mercruiser...outdrives/overheating-633114.html#post4432663
 
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