how to ? prevent exhaust man. overheating during engine warm-up

KEVIN D TOBIN

Member
Jun 12, 2018
69
Boat Info
1993 290 sundancer, 7.4L mercruiser repower 2018
Engines
7.4L Bravo ll drive
I am experimenting with a self engineered closed cooling system, problem is exhaust manifolds not getting enough coolant while thermostat is closed. I am using the old style thermostat housing,but have the screw on tee with the spring loaded check valve removed and plugged, the cap that feeds the exhaust manifolds is over top of the thermostat and does not get any flow until the thermostat opens, so that seems to be it, any thoughts ??? thank you
 
drill a hole in thermostat in my boat i did 3 to get antifreeze to circulate.
 
Well, see the bronze tee, that is not installed, I don't know if I will tee into the the line that feeds the bottom of the manifold or run a new line that will feed a different point on the manifold, but after doing some research I found out that that tee is what that is for, to help cool the exhaust during warm-up when the thermostat is closed
IMG_0274.JPG
 
Your trying to include the exhaust manifolds in the CC loop ? How big is the HE ? I converted my 502 to CC but the manifolds are raw water cooled and my T-stat housing looks completely different from Raw water one.
 
To engineer full FWC you need a adequate size HX and engine mounted pump. Exaust manifolds with FWC are plumbed in the bottom and out the top .The top port goes to the top cap of the therm housing.
waste water from the HX goes into the elbow and out the exaust.
 
all types of exaust systems need cooling water flowing to cool the rubber components, this has no bearing on the thermostat. With the T and the therm closed water forces the balls open to cool the exaust, once the therm is open, the balls close and flow goes in the bottom of the manifold up and out the elbow
 
Your trying to include the exhaust manifolds in the CC loop ? How big is the HE ? I converted my 502 to CC but the manifolds are raw water cooled and my T-stat housing looks completely different from Raw water one.
sorry it took awhile to get back, Well the HE is 6" dia x 24" long, one of the main problems I am having is I could not fit it where you see them over top of the front or back,this weights too much, I installed where the water heater was, I plumbed it in like I see them, but there is so much heat off those exh. mans., w/out them it would be no problem,but to me it is no sense in having a fwc w/o the exh. mans., I think the problem is not enough flow to the exh. mans.,my new inline coolant pump came today,so I'll let you know
 
To engineer full FWC you need a adequate size HX and engine mounted pump. Exaust manifolds with FWC are plumbed in the bottom and out the top .The top port goes to the top cap of the therm housing.
waste water from the HX goes into the elbow and out the exaust.
I'm not an engineer,I'm the guy they come out and see when they can't make something work,Pipe Fitter for 44 years,I build heat exchangers for a living.by the way exaust, is spelled with a "H",nice to meet you thou.
 
what I am going to try is to incorporate a bi-pass so that the exhaust mans. are always getting flow, using a inferred temp gauge I can tell just how hot they are
 
what I am going to try is to incorporate a bi-pass so that the exhaust mans. are always getting flow, using a inferred temp gauge I can tell just how hot they are

Did 7.4’s ever have the manifolds included in a closed cooling system?

Maybe you need 2 separate heat exchangers?

On a side note, I don’t think it’s a good idea to insult someone trying to help you.........
Pointing out a single misspelling in a post by a knowledgeable and very helpful member when no one here pointed out your grammatical errors is a quick way to cease any future assistance from others.
 
well maybe you should practice what you preach, yes most after market offer a full system which includes the exh. mans., when mercruiser made this boat mercruiser did not offer a full system for v-belt 7.4L engine, but crusader did, crusader is just better in every way , monitor does , orca does, to name a few. The dry joint would be a better type exhaust man. for fwc, or for any cooling system for that matter
 
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