Why would one exhaust manifold be hot and the other not?

[aneal000]

ok, the strange ones always happen to me. take your standard issue marine GM block. I started it up and ran it in the water for a good 10-15 minutes at idle to get it warm for an oil change this last weekend. Everything seemed fine, oil pressure, temp, etc... but after turning it off and playing around to drain the oil I noticed one exhaust manifold was extremely hot, like you don't want to touch it hot and you could start to smell a nice burning smell. I went to check the other side and it was normal warm, but not hot to the touch.

This really makes no sense to me and I'll explain why. I pulled the hose from the top of the thermostat housing that goes to the manifold - I could easily blow through it. Dumped a gallon of water down the hose and blew though it again, you could hear the water going thru to the exhaust. Nothing seemed clogged. I then pulled the hose off to the other side/exhaust and you could see straight through the top of the thermostat manifold, could see the thermostat as well, nothing clogged or in there to impede water flow. Went ahead with the oil change and put everything back together. Started it up later and everything ran fine. Nothing got hot. Ran it for a while at varying RPM's and everthing seemed fine the rest of the weekend. I also pulled one of the exhaust manifold drains and water shot out while running so I knew it was good at that point.

So my question is what could of caused that? Could an air pocket of been in there? Could running at idle for 10-15 minutes limit the water flow enough, but even so why only one side?

[BlastRlxi]

Did you use a fake-a-lake? I have heard of them slipping off part way and not allowing enough water into the pump intake. Could there have been a kink in the garden hose? It sounds like you had some water going into the engine, but maybe it wasn't quite enough. I am assuming that your thermostat wasn't stuck and that everything else in the engine was okay. If you had no water going into the engine for 10 to 15 minutes, you would have done some good damage.

Whenever you run the engine on a garden hose, never leave it unattended!!

[John I.]

BlastRlxi Posted Today, 12:52 PM

Did you use a fake-a-lake?

I'm going to say no.

I started it up and ran it in the water for a good 10-15 minutes at idle to get it warm

plus

Boat: Silverton 352

[BlastRlxi]

Oops, missed that. Sorry.

[Baddog]

Some kind of debris blocking the outlet on one side, then self cleared after the motor shut down???

[aneal000]

BlastRlxi Posted Today, 12:52 PM

Did you use a fake-a-lake?

I'm going to say no.

I started it up and ran it in the water for a good 10-15 minutes at idle to get it warm

plus

Boat: Silverton 352

....uh, yeah that would be a negative on the fake a lake.

[aneal000]

Some kind of debris blocking the outlet on one side, then self cleared after the motor shut down???

That's the closest thing I can come up with. That or a funky air pocket. I have a nice sea strainer on the intake hose that filters out debris, so unless it was debris flaking off the inside of the hoses/motor then I really don't know how it got there. It just seems extremely odd and obviously I don't want to have it happen again if I can prevent it.

[M3Fan]

I believe there is a general bias in waterflow out of the Tstat housing on most boats. On my boat (and all boats, I'd imagine) the water comes in on the same side of the T-stat housing as the output for one of the manifolds. I'd imagine the pressure of the water coming from the RW pump would probably naturally fill the side opposite the input first, before then getting back-pressure to fill the same side as the incoming water. Unless the input came in from the front of the T-stat housing, into a dead Y split, you will probably always have a bias until both mani's fill up with water, which would even things out a bit. You can see in the pic below just how uneven the feed path is to each manfold relative to the source.

[aneal000]

I believe there is a general bias in waterflow out of the Tstat housing on most boats. On my boat (and all boats, I'd imagine) the water comes in on the same side of the T-stat housing as the output for one of the manifolds. I'd imagine the pressure of the water coming from the RW pump would probably naturally fill the side opposite the input first, before then getting back-pressure to fill the same side as the incoming water. Unless the input came in from the front of the T-stat housing, into a dead Y split, you will probably always have a bias until both mani's fill up with water, which would even things out a bit. You can see in the pic below just how uneven the feed path is to each manfold relative to the source.

Interesting...

...but, I've actually got two identical motors and they were both running same lenght of time, etc... and the other motor, both manifolds were cool to the touch... just like the other side of the hot one. So 3 out of 4 were cool - one hot.

Super wierd, imho.

[Lakenut]

Maybe one of your four muffler bearings is going out. When those things go, they do cause a lot of heat.

[aneal000]

Maybe one of your four muffler bearings is going out. When those things go, they do cause a lot of heat.

The one thing I didn't check, what would I do without this board! You guys are the best!!!