Smoke Coming Off The Exhaust Manifold

[NCdatsunZ]

Hi I've got a 72 240z. I recently changed the thermostat housing and used A LOT of penetrating oil to remove it and the fuel rail.

I put it back together today and cranked it up. It ran fine but I noticed a good bit of smoke coming from the engine. I shut it off and stood by with a fire extinguisher and tried to figure out why it was smoking. The smoke seemed to be coming off of the exhaust manifold.

Is this just penetrating oil burning off? What should I do to make it not smoke?

There doesn't appear to be any leaks in the valve cover gasket or the thermostat housing. Also I just put the air cleaner housing with a new air filter on.

Thanks

Will

Edited January 27, 2013 by NCdatsunZ

[Willoughby Z]

My guess is that it is the penetrating oil burning off. And probably some coolant. And some greasy grime (loosened by the oil and coolant) that dropped onto the manifold. Let it run -outside- until it stops smoking.

You should run it for awhile anyway, up to normal operating temp, to insure that you don't have any leaks at the thermostat housing

[NCdatsunZ]

When I was looking for smoke in the engine bay I noticed a bolt wobbling around in this spot. I tried to tighten it back down but it snapped leaving the stud buried inside the engine. Would I be able to limp it to my mechanic in this condition?

[Zed Head]

That was an exhaust manifold mounting stud. They break a lot. There are many Z's driving around right now with that stud broken. It shouldn't hurt to drive it a shop. Bummer, but it was probably already half-broken when you tried to tighten it. They crack and break from metal fatigue after a few tens of thousands of heat cycles.

[SteveJ]

You should be able to get it to your mechanic, but beware of exhaust gasses coming from the engine compartment. You don't have to drive far, do you?

[olzed]

Manifold bolts are very britle when hot. Don't tighten manifold bolts on a hot engine.

[ZCurves]

If it is not leaking, leave it ALONE! Is there any of old stud hanging out that you can see? This will be a good opportunity to learn in the future. If you take it to a mechanic - the only thing smoking might be your wallet! Consider repairing it yourself, there are plenty of us to help.

[rcb280z]

Soak it with some penetrating oil and drill it and "easy" it out. Then you can replace it with a new one.

[mjr45]

Its a pretty simple job even with the manifold on. I replaced the same bolt on mine long before I pulled the motor when I replaced all of them. I don't know about the 240 but on a 280 there is also an engine hoist hook on that bolt.

[NCdatsunZ]

There is absolutely no bolt showing and it's not leaking so I'm going to just leave it there for now. Later on down the road I will probably pull it out. At this point I'm in "get it on the road" mode so I'm not too worried about it right now.

[olzed]

That sounds like a good plan.

[FastWoman]

Dunno... I see carbon deposits on the head right above the #6 exhaust port. To me that says there's a leak, which is not all that uncommon on these engines. The hazard of having a slow exhaust leak, particularly on an aluminum head, is that the exhaust gasses can slowly erode away the metal, particularly if you also happen to have a lean fuel/air condition. Also carbon monoxide will be wafting around in your engine compartment, and that can make its way into the cabin. This may not be an URGENT repair, but it's probably one you should consider making soon. Until then, you should probably drive with your windows cracked.

Edited February 11, 2013 by FastWoman