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I have completed a full engine rebuild, down to the bare block, of my Tacoma. Replaced all the gaskets, cleaned and lapped all the valves tight, tuned the valve lashes to spec, cleaned everything, replaced the starter, torqued to spec etc. It was a 3 month effort working on it a couple of nights a week.

Last night was the turn key night. I must admit I was nervous, as it was the biggest automotive repair I had ever done. The engine started fine but then I notices something like smoke coming out of the catalytic converter and around both the exhaust manifolds. I thought it may be the excess engine assembly lube I used to put everything back together but soon I realized it wasn't smoke -- it was steam. When I went to the tail pipe, it was confirmed, the vapor coming out was definitely steam and there was some condensation inside the pipe as well.

I wonder if this is normal for a major rebuild that perhaps some moisture condensed inside the cylinders and it had to find its way out.

I ran it idle for about one hour, steaming had stopped, then drove it about 20 min and everything was fine.

amphibient
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3 Answers3

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This is a non-issue. HC (hydrocarbons) and CO (carbon monoxide) in the exahust combine with oxygen to become Carbon Dioxide (CO2) and Water (H2O). When the exhaust is cold the water can condense enough to show as water vapor or even as dripping water from the tailpipe. The water is always in the exhaust, but when the engine and exhaust system is hot enough it 'boils off' the water vapor into steam, which you can't see with the naked eye.

This process is easy to see in action in the sky behind jet-powered airplanes; because the atmosphere is so cold where the plane is (~30,000ft), the water vapor in the exhaust condenses back into a 'trail' that we can usually see.

Nick G
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What kind of climate are you in? It's quite common to see steam coming out of the exhaust of a cold car if you're in a damp climate - water condenses on the cold metal all the way through the system, then evaporates off as it heats up. It usually stops after a few minutes as the car gets up to temperature.

Nick C
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If it isn't condensed water inside the engine, which by the way accumulates if you drive your vehicle on short distances and not allow it to reach operating temperature, it's probably related with the coolant cycle and some gasket faulty cylinder gasket.

If it persist (I strongly hope not) and you want to be 100% sure, you could do:

  1. Pressure check on your coolant system for leak.
  2. C02 test on your coolant system for cylinder leak, i.e. faulty gasket.
Ziezi
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