Steam coming out of the exaust (outdrive)

[mochosla]

Hi everybody,

I just put a new engine on my boat (350 5.7 Vortec). Before I did this, my mechanic mentioned that the motor (the old motor that is) was creating a lot of vapor out the back and that I should look into that. Since I was replacing the motor I did not want to do anything. Well, like I said, I just put the new engine and got it running today. After the motor warmed up, the steam came back. The exhaust manifolds looked just fine as they were replaced not to long ago.

Any ideas where the problem may be coming from? Like I said, I put a BRAND NEW complete engine (carb, dist, water pump, intake manifold etc. The only thing I put from my old engine was the exhaust manifolds, wiring harness, alternator, brackets etc.)

Thanks.

 

[Gary H NC]

Re: Steam coming out of the exaust (outdrive)

Have you pulled the risers and replaced gaskets.I wouldn't run it untill you find the problem. It still sounds like a manifold problem. Bad way to break in a new engine...

 

[1730V]

Re: Steam coming out of the exaust (outdrive)

You do not say what kind of outdrive you have. That is a big question.
Did you replace the impeller in the outdrive? If not, you will turn that brand new engine intom scrap quickly.
Using old manifolds on a new engine is not a great idea.

 

[Haut Medoc]

Re: Steam coming out of the exaust (outdrive)

I would pull the risers & check the condition of the mating surfaces between the riser & manifolds......

 

[I/O WALDO]

Re: Steam coming out of the exaust (outdrive)

Did it get hotter than it should? U will see steam with cold outside / water temps.

 

[mochosla]

Re: Steam coming out of the exaust (outdrive)

Hi. I have a OMC stringer 800. I only run the motor on my driveway (no load at all). An the impeller was replaced 2 months ago. I will pull the raisers and see how the gaskets are. Any tips on what to look for?

THanks.

 

[flashback]

Re: Steam coming out of the exaust (outdrive)

Don't know about a stringer, but I have a pre-alpha merc that has been steaming for years with no aparent ill effects.. I think they all put out some steam you have hot exhaust gases mixing with cold water.. it's gona make a little steam IMHO.......

 

[mochosla]

Re: Steam coming out of the exaust (outdrive)

I pulled the exaust manifolds yesterday and took the raiser off. It all seems fine. no rust or missing metal. I can see that the water is not leaking back into the manifold (exept where it is supposed to). I pulled all the spark plugs out to see if there was any water going into the pistons and nothing. I'm confused and don't know what else to do. Like I said, it is a brand new engine and the only used part that could cause this is the exaust manifolds. I'm having my mechanic look at them today.

I'll let you know what he thinks.

Thanks.

 

[Zackman]

Re: Steam coming out of the exaust (outdrive)

I thought some water vapor was normal?

As the hot water exits the exhaust, some flashing of the water to vapor is normal. The colder the outside temperature the more vapor will be visible. Also, the higher the relative humidity, the more the vapor will be visible.

 

[sabastianunf]

Re: Steam coming out of the exaust (outdrive)

^ I agree - mine has some vapor and more when it is cold and humid out. I just put new exhaust manifold, riser and seals in mine last year and have flushed and drained it everytime I have run it.

 

[mochosla]

Re: Steam coming out of the exaust (outdrive)

Thank you all. Just to be safe, I ended up buying new manifolds and raisers. I'd hate to kill my brand new 4K motor. I will install them on Monday when I get them.

 

[Zackman]

Re: Steam coming out of the exaust (outdrive)

Sometimes, it's better to safe than sorry. Let us know if the change made any difference

 

[mochosla]

Re: Steam coming out of the exaust (outdrive)

I have a question for you guys. I got the new manifolds and raisers and will install them ASAP. My question is, before I put them together, should scrape off the paint between the manifold and raiser (not the one where the manifolds seal with the motor) so that the gaskets seats on clean metal or should I leave the paint on?

Thoughts?

 

[180shabah]

Re: Steam coming out of the exaust (outdrive)

Mating surfaces should be flat, smooth and shiny metal, no paint for best sealing.

 

[Reel Poor]

Re: Steam coming out of the exaust (outdrive)

When you replaced the water pump impeller was there any parts of the old one missing? If it had missing parts they could be hung up in the water inlet line somewhere causing a restriction, not letting enough fresh water into the engine.

 

[mochosla]

Re: Steam coming out of the exaust (outdrive)

Nope. The "old" water impeller looked like new. I will, however, run a water circulation test. That is a good point you mention. My manual tells me how much water should be circulating.

Thanks.

 

[mochosla]

Re: Steam coming out of the exaust (outdrive)

Okay all, after changing the manifolds, the problem went away. The motor's temperature stays in the 160 degrees.

Thank you all for your help.

 

[Gary H NC]

Re: Steam coming out of the exaust (outdrive)

Thats great! Better than ruining that new engine.You should be good to go for many boating seasons..

 

[Zackman]

Re: Steam coming out of the exaust (outdrive)

Good news, but I'm curious how much vapor your seeing now compared to before replacement.

 

[mochosla]

Re: Steam coming out of the exaust (outdrive)

Barely any. It was a hotter day when I tested it though. The water comes out pretty cool.