Guys I have a 7.3 IDI turbo motor in a boat and I recently had an issue with it while out at sea. I blew a hose and the motor got hot, or vice versa, I don't know... Alarm went off and I shut the boat down... just before shutting down I saw some black smoke. Not a lot, but I have never seen black smoke out of her before. No one on the boat noticed much steam until I opened the engine hatch. But sure enough the motor was 300 degrees and bone dry. I patched the hose and filled it with water but it blows white smoke when around 180 degrees. Starts and runs fine and doesn't blow white smoke until 180 degrees.

My question is... do you think I could get away with just replacing the head gaskets or is black smoke a really bad sign? I just rebuilt it 100 hours ago and it cost me almost 10 grand. I don't have a fraction of that money. The good news is it is a boat motor and I probably don't have to pull it out of the boat to fix.

Thanks

Dan

 

I would say the black smoke was probably from the increased friction from the high temps, making the motor work harder. Hopefull it didn't score a piston when this happened. Either way it looks as if the heads have to come off. Good luck!

 

I agree. Pull the heads. You can do a compression test to see where they are leaking. Surface and reinstall shoud be good.
Chet

 

Thanks for the advice... I think I will just pull the heads and replace the gaskets since they are only 33 dollars each. Will I be able to leave the motor in the boat to pull the heads? You only need access to the top of the motor right, you shouldn't need to get to the rear of the motor, right?

Thanks

Dan

 

Just the top, yes. You can leave it in the boat if you want, but the heads are HEAVY. You could very easily throw your back out lifting them. Plus, maneuvering them back into place will prove a challenge.

 

The bare head castings are about 95lbs each. You will need access to the side to remove the exhaust manifolds, but I'm not sure how cramped your engine bay is. Black smoke could also be from lost compression when the gasket failed.

I agree pulling the heads will be your first step no matter what you do. You can inspect the pistons and cylinder walls and then decide your course. You may also want to have the heads checked for warping or cracks.

Also, you must loosen the head bolts in the opposite sequence of torquing them down, or you may crack the head.

 

Really good advice there... I did not know you had to go opposite sequence. Can I reuse the bolts? I heard that most people get new ones. It would be nice if the black smoke was form lost compression. How would I be able to tell if the cylinders were scorched?

Dan

 

You can reuse the head bolts provided the outer ones are not pitted. Sometimes they get rusty and may not clamp well enough if reused. Also be sure to thoroughly clean the threads in the block and on the bolts to eliminate as much potential friction as possible. Any drag there will weaken the clamping force available at the rated torque.

Don't know about scorching of the cylinder walls, but I would take a good hard look at the head gaskets when you get them out. That will tell you the extent of the failure and it could be all that went wrong.

Other then that, what you want to see is a smooth cross hatch on the cylinder walls. Any deep, vertical gouges would not be a good sign.

 

Great advise Dave85. Just run a tape down the head bolt holes and on the bolts. If not pitted bolts should be okay.

Chet