How do I tell if I have a leaky manifold?

[mnypitboat]

I keep hearing people saying they blew the manifold gaskets, but how do you know?? I just replaced my 350 Mercruiser and then I had a problem keeping timing steady. I solved that problem with a new distributor, but now I have a chirping noise, but cannot pinpoint where it is coming from. It runs perfect, but that noise is driving me nutz. Anybody have any ideas? Will a leaky manifold leak into the cylinders? Will it cause a ping/chirp? It goes away if I get over 2200rpm and only occurs when in gear, it does not do it on the muffs.

A little background on the engine. It has 60 over pistons and was completely rebuilt, including valve job. It is an 01 Vortec 350 with a 2bbl. Mercruiser Alpha.

 

[cr2k]

Re: How do I tell if I have a leaky manifold?

Intake or exhaust???

If intake spray some carb spray around the manifold keeping it away from the carb intake, if it changes there is a leak where you sprayed it and made it change. Also check the carb gasket.

 

[HT32BSX115]

Re: How do I tell if I have a leaky manifold?

How do I tell if I have a leaky manifold?

If it was leaking, you would get water into the exhaust area and possibly into open exhaust valves after shut down. If it was enough, you would experience a "hydro-lock" when you tried to restart.

Will a leaky manifold leak into the cylinders?

Only when the engine is shut down......not when running.

Will it cause a ping/chirp?

Probably not since it's jacketed. (maybe, if it's a "dry-joint" manifold)

If it was leaking, you wouldn't hear the chirp because the leak would be into the water jacket.

You rebuilt the engine?

How old are the manifolds and risers?

 

[artificialreef]

Re: How do I tell if I have a leaky manifold?

If the carb spray you are using says flamible on the back of the can. You shouldnt be spraying it around the base of a hot intake manifold.

 

[mnypitboat]

Re: How do I tell if I have a leaky manifold?

I was thinking exhaust. Intake is not leaking, I sprayed carb cleaner around it and no change. I bought a short block and remanned heads and put it together. I used Mercruiser gaskets. Manifolds are origional, but I had them inspected when it was apart and they are like new.

OK so only leaking into cylinders when shut off. That is what I figured, but someone told me otherwise so I figured I would ask. I wonder if the alternator could make this noise? No way to run it without the belt on plane. OK so what to check next?

 

[NHGuy]

Re: How do I tell if I have a leaky manifold?

You say the squeak is at lower rpms. Did you try the carb cleaner spray around the edges of the intake manifold? There is more manifold vacuum at lower rpms.
If you suspect a belt noise get a look along the belt(s?) from the side. Look for any pulley a little out of the plane of the belt. All it would take is a washer or shim on the wrong side of a mount to put the pulley out of position. Is your belt system serpentine or vee? With V belts you need the right tension. Too much causes bearing loads & wear. Too little causes slipping. If it's serpentine the tension is managed by the belt tensioner.
If the boat is in a stable place like on the trailer, you could take a long screwdriver or socket extension and use it as a stethoscope. Carefully put the metal piece on each pulley drive's housing and listen at the other end. Just be careful that it doesn't have any chance of slipping into the path of the pulley or belt, that would get you a trip to the hospital, or worse.
You check the alternator, power steering pump, water pump and idler if there is one. You can also take the belt off and feel the pulleys for play, and spin them by hand. While the belts are off check the crank pulley/harmonic balancer too.

Good luck, it's got to be some stupid thing.

 

[NHGuy]

Re: How do I tell if I have a leaky manifold?

You could also get a cheap mechanics stethoscope at the auto parts and check all over the motor with it.

 

[mnypitboat]

Re: How do I tell if I have a leaky manifold?

I cant use a stethescope, or whatever method, because it only does it when I am in gear and at lower RPMS on plane. It doesnt do it at idle, or without any load. So I would have to have the engine hatch open up on plane, and that is not an option. I havent done anything to the engine while it is actually making the noise because of this issue.

It is a Serp belt and they are all lined up. It wasnt making the noise when we first got the new engine in. It just started last time we took it out. It has a new belt on it.

I am hoping it didnt blow another head gasket. I suppose I will check the obvious like compression next. I would hate to buy an alternator or power steering pump only to find out it is not the problem. I guess if its one of the pulleys, it will let me know when it goes out completely. LOL. Thank goodness for Boat Tow.

 

[mnypitboat]

Re: How do I tell if I have a leaky manifold?

Oh and I did spray carb cleaner around the intake, but not when it was making the noise. The RPMs stayed steady and there was no change in anything at idle and slightly above. But there again, no load.

 

[GLENN M]

Re: How do I tell if I have a leaky manifold?

chirping sound usally your belts.try your old one

 

[mnypitboat]

Re: How do I tell if I have a leaky manifold?

Old belt is trashed because I didnt get the balancer, crank pulley tight when I first put it back together. I put the boat up for a while, covered and ready to sit. I will get back to this next time I take it out.

I am not getting email notifications when someone posts. I am not ignoring people. Thanks for the suggestions.

 

[Gary H NC]

Re: How do I tell if I have a leaky manifold?

The 5.7 in my truck had a chirping noise.Replaced the belt and problem solved.
It may be worth a try plus you will have an extra serpentine belt to keep on the boat.

 

[mnypitboat]

Re: How do I tell if I have a leaky manifold?

I was planning to pick up a spare belt anyway. The problem is that the noise is only under load. I dont think a belt squeeking would do that. We will find out soon enough.