On May 12, 10:25 am, "jamesgangnc" wrote:
I can't get over the fact that you would spend that kind of money for a new
engine and then install welded, old exhaust manifolds. Let me guess, they
were the original 1988 manifolds too, right? So now it sat all winter with
water in the cylinders too? You're lucky it wasn't rusted solid.

You need to replace the manifolds and risers. I've never heard that the
vortec have reversion issues but it's possible. One of the primary
improvements in the vortec was flow related. Was that a marine vortec or an
auto one? The marine versions of just about all engines have a different
cam. I'd investigate 3rd party exhaust systems like stainless marine. You
can get good aftermarket exhaust for no more than merc wants for factory
stuff. They will be able to give you good advice too. You didn't mention
what the exhaust does after it leaves the manifolds? Goes thru the prop?
Or out the back? One easy thing to do is to run a higher idle. Go to 750
or 800rpm even. Most reversion due to cam happens at idle. Once the engine
is turning so rpms the exhaust flow will keep the water out.

"Jake S" wrote in message

oups.com...



The block and Starboard exhaust manifold on my 1988 4.3L OMC froze and
cracked a few winters ago. I purchaed a NEW 4.3 Vortec over the
internet to replace the block and had a reputable welder repair the
external crack on the manifold. Last fall, I started the engine (on a
stand with a cooling setup) and all seemed well. I drained the block
and then filled it and all manifolds with green prestone adntifreeze.
The spring, I installed the engine in the boat, hooked up the water
hose to the lower unit and went to start it. for "some" reason. The
motor was locked up - as if a rod was broke and blocking any rotation
fot he engine. I could not even turn it by hand wiht a socket on the
harmonic balancer. I went to pull the plugs (to make it easire to
turn) and clear water came out of several of the holes. I opened the
draincocks and GREEN prestone came out, Putting the plugs back in - it
started and after clearing the remaining water - A week later, I took
it to the lake - went to start it - and locked up again. I pulled the
plugs, cranked the engine and water came out, Put plugs back in - and
ran - went for ride on lake - ran very well.

I have people telling me the exhaust is cracked inside (also - outside
was welded earlier) but if that was the case - would not the green
antifreeze from winter storage gotten into the cylinders instead of
clear water. Found some new (later version) manifolds on eBay but
seller sad they woudl not work on vortech engines. He sent me to
manufacutrere when I inquired. Manufacturer claims that Vortech
engines have a long exhaust valve overlap and ti will actually suck
water back into the cylinder. and I woul dhave to use newer mercruiser
manaifolds (but no guarantee it will work) and modify them to mount to
OMC backend.

Has any one ever heard of this (vortech engine sucking exhaust water
back in due to its overlap) if so, how do you get around it? Vortechs
have been used in boats for several years,

How can I check if the manifold is cracked inside? My local boat
dealer says thie single piece exahust cannot be pressure checked?

Thanks in advance for any help!- Hide quoted text -

- Show quoted text -

Ouch - but guess I deserved it. It is a mercruiser vortec - the
exhaust ges through the prop (altho it seems to also come out right
below the sterndrive at the transom (always has) I have been searching
the internet for exhaust - like I wrote - Osco recommends theri
mercruisre one but ai will have to do some modifying to make it hook
up to the OMC Y exhaust pipe. If you or someone else can point me to
another aftermarket source for manifolds I'd apprecaite it. It appears
I can get factory ones for about $550 EACH