8.1 manifolds replacement question

[liv2ryde100]

I know it’s ridiculous, was hoping to run it today and make sure everything is all good

 

[KevinC]

Two stainless steel elbows out of 4 (one on each motor) are leaking water into the exhaust manifolds. This causes rust in the manifold, rust on any of the exhaust valves and valves seats that the sea water gets to, salt buildup on the spark plug and maybe a slight hunting of 20 - 40 rpms in the engine when running (which you will probably not see with an analog tach), and maybe some evidence of seepage around the "dry joint" turbolator gasket, provided you catch it early enough.
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Never gave it much thought but when down at the boat today I noticed a slight hunting at idle on smartcraft guages. Never noticed it before or gave it any though until reading this post. I guess I am cracking open my elbows to inspect whats going on. Hard to tell if there is any seeping from the gaskets since it is not easy to see behind the manifolds and the fronts look somewhat normal but everything looks disastrous with a paranoid eye.

If this is the problem can it be related to a failed turbolator gasket or it pretty much always the elbow and just exhibited at the gasket? Also what is the best way to test the elbow or is pretty much just swap it out or is it just time to pull manifolds and elbows?

-Kevin

 

[mnm99]

Never gave it much thought but when down at the boat today I noticed a slight hunting at idle on smartcraft guages. Never noticed it before or gave it any though until reading this post. I guess I am cracking open my elbows to inspect whats going on. Hard to tell if there is any seeping from the gaskets since it is not easy to see behind the manifolds and the fronts look somewhat normal but everything looks disastrous with a paranoid eye.

If this is the problem can it be related to a failed turbolator gasket or it pretty much always the elbow and just exhibited at the gasket? Also what is the best way to test the elbow or is pretty much just swap it out or is it just time to pull manifolds and elbows?

-Kevin

Take the elbow off. Put it on the counter, plug the 2 water inlet ports and fill it with water through exhaust outlet. You'll see the 2 chambers, till it's full. Let it sit for a while and pick it up. If there is no water coming out of the welds or on the table on the mounting point I say there good.

 

[liv2ryde100]

weather has been out of control. i was on paternity leave last week since we had a baby boy, and i spent every second of it sandwiched between those 8.1's in the bilge. wife not too thrilled but happy i saved a ton of money by doing the job myself.

 

[LG111]

Mistercomputerman I owe you a HUGE thank you for your post and the detailed description on the rpm hunting!!!!! About 6 weeks ago my starboard engine started hunting 10 to 20 RPM around 650 rpm. You could not hear it nor did it show on my analog gauge. But my Vessel View mobile pick it right up!! I thought it was the IAC. Or the new crank shaft sensor.

Several weeks back I noticed a white line on the back side manifold. Figured it was condensation leaking from a failing tubilator since the humidity had been so high with the change in season. I didnt think twice since most of the moisture was gone over the past few weeks. I read your post and thought that's It! I pulled the riser today and brought it home. Filled it with water to the hoses. Sat it on a paper towel for three hours. When I checked it, the towel had a quarter size wet spot. And there it was a very fine crack on the inside rim weld.
Ordered a new riser today. Spoke to a mechanic about the hunting. He said Yup, the hunting is due to moisture getting on the spark plug and interruting the spark. Once the few drops are burned off the hunting stops. That was mine. After a high rpm and going to 650 rpm, the tubilator over flowed until the small amount of water burned down and the pressure was low enough that the crack only weeped.
Also the tubilator was not as bad looking as the pictures above but mine did have rust on both sides of the cone. I did a spot check on one suspicious riser on the other engine. All good on that one!

Thank you again!!

Mark

UPDATE!
Confirmed! No more low rpm hunting with new riser!!!!! lesson to be learned on 496 8.1. If the digital rpm hunts 10 to 15 RPM over under 650 idle, the riser is most likely leaking water at the weld.

I love this form! thank you! probably just saved a $20k disaster if I ignored the hunt and didnt read the forms religiously!