Full Closed Cooling?

ASDF

Member
Sep 18, 2017
63
Boat Info
Boatless
Engines
Boatless
Does anyone know if the 7.4 mercs in the 1992 400 Express Cruiser are full closed cooling include the exhaust manifolds or are they just the blocks? A boat I'm buying has closed cooling and I'm told stainless steel risers. Yet I see rust at the riser/manifold gasket area. I wouldn't think the risers would be rusting like this and if it's complete closed cooling it wouldn't be from the exhaust manifolds.. is it possible to have rust like this from a leaky gasket even with full closed cooling and stainless steel risers?
Survey 1992 Sea Ray 400 Merritt.jpg
 
From the fittings I see , there are 2 on the manifold, That would mean the manifolds contain A/F. The rust stains you see are from a leaking gasket .
To correctly repair it, drain the A/F from the manifolds, drain the riser/elbow if equipped, remove it and examine the gaskets. I say plural because I prefer the gasket below the SS blockoff plate and the gasket above the blockoff plate
 
There is an aftermarket Full Closed System that includes the exhaust manifold but that does not look like it. From the factory the Closed System would not include the exhaust manifold, only the engine block. Mercury states that the big block creates too much exhaust manifold heat to be included in the Closed System.

Can /do you have a pic showing the top of the manifold and complete elbow/riser? Then we could tell for certain.

From the pic the manifold and riser are cast iron.
 
Thanks BT Doctur.. so here is where my ignorance will show through... if there is a block off plate, what is the risk associated with water leaking out of the gasket at the riser/manifold connection if the raw water won't get into the manifold anyway? I'm not debating that the gaskets need replaced but can you still get water in the engine from a failed gasket if it's full closed cooling?
 
Thanks Kap, here are the only other pics I have
Survey 1992 Sea Ray 400 Merritt6.jpg
Survey 1992 Sea Ray 400 Merritt5.jpg
Survey 1992 Sea Ray 400 Merritt3.jpg
Survey 1992 Sea Ray 400 Merritt2.jpg
5850326_20160714173801482_1_XLARGE.jpg
Survey 1992 Sea Ray 400 Merritt6.jpg
Survey 1992 Sea Ray 400 Merritt6.jpg
Survey 1992 Sea Ray 400 Merritt6.jpg
Survey 1992 Sea Ray 400 Merritt5.jpg
Survey 1992 Sea Ray 400 Merritt3.jpg
Survey 1992 Sea Ray 400 Merritt2.jpg
5850326_20160714173801482_1_XLARGE.jpg
 
sorry for the duplicate pics. Most of these are from the survey. Really only main issue during survey was white steam coming from starboard exhaust starting around 1500 rpm, then when we got to WOT a lot of steam came out both exhausts (starboard and port). The water was cool (it was last week on upper chesapeake) so it could make sense, but I also had coolant overflowing the tank while it was getting up to normal operating temp. Once it got up to normal temp it subsided. Other than that it ran great, got up to 4300rpm at WOT, engine temps were steady at 170 each, no overheating and surveyor said he saw no bubbles in the coolant and no water leaks at risers.
 
Based on our boat you have a leak at the gaskets. It is probably both AF and raw water. The only real solution to corrected the problem is to replace the manifolds and risers. If the engines are in good condition and their is no water in the engine oil and you want the boat get the present owner to replace the manifolds and risers or reduce your price by 5,000. White smoke at high RPM is normal. White smoke at low RPM and no AF smell is raw water riser problem.
 
The system looks like the manifolds ARE in the closed cool system. If the gasket between the elbow and manifold fails it can allow sea water to leak into the exhaust gas area of the manifold and ultimately into the engine.
 
great news, thanks guys. Sounds like I'll hopefully only need to budget for the gasket replacement then.. assuming the SS risers aren't rusted. I would hope not on the Upper Chesapeake.
 
you think the risers will need replaced too?
 
you think the risers will need replaced too?

Manifolds, bolts, exhaust gaskets to start with and then whatever else you find once you get in there. Plus complete system flush and refill. How about hoses? Belts? Oil coolers? Transmission coolers?

If the risers are stainless then they maybe OK, provided they aren't plugged up or the mating surface doesn't need resurfacing.
 
The hoses and belts are all good. Survey noted all that in good condition and no evidence of leaks other than riser/manifold gasket. If it's a complete closed system hopefully the manifolds will be ok unless there is complete failure at the gasket.
 
The hoses and belts are all good. Survey noted all that in good condition and no evidence of leaks other than riser/manifold gasket. If it's a complete closed system hopefully the manifolds will be ok unless there is complete failure at the gasket.

By looking at all of that corrosion I would have to wonder. And I guarantee you the exhaust gaskets are shot, and once you take the manifolds off to change those you need to replace the hardware, and the gaskets, etc.

I would have to wonder what the inside of the transmission cooler and oil coolers look like.
 
The cast stainless elbows were known to leak due to the uneven heating properties of the different metals.
Change them to cast iron and live with a 5 year throw away part.
That fiberglass exhaust can (muffler) appears to be leaking but, can be easily fixed.

Not even looking, I’d plan on replacing heat exchangers, oil and tranny coolers and elbows just to set a zero point on those wear parts.
 
+1 on replacing elbows, manifolds, gaskets and hardware along with heat exchangers, oil and tranny coolers - unless the seller has receipts showing any of those parts have been replaced within the last 5 years. Replacing these parts is part of typical maintenance on this age vessel.

Good luck with the purchase!
 
I agree with replacing most off the mentioned components except the heat exchangers. Have them cleaned and pressure tested at a good radiator shop. They will rarely fail catastrophically and are very expensive as we all know to well. My 1986 Crusaders have the original heat exchangers and I have them checked every 3 years.
 
Thanks for all the input guys, I'm having a marine mechanic replace the gaskets and inspect the risers manifolds and make suggestions on what he sees. I'll ask him about the trans and oil coolers too.
 
Thanks, that may be one of my first diy projects when I get her home and settled.
 

Forum statistics

Threads
112,950
Messages
1,422,880
Members
60,933
Latest member
juliediane
Back
Top