I have an exhaust leak on the passenger side of my 98 F150 4x4. I cannot determine whether or not it is coming from the manifold at the block or the flange at the end of the manifold. I do not see any black soot at the flange and I cannot tell on the block since its painted black from the factory. The leak goes away after the truck has warmed up. I thought initially it was the flange since I did unbolt it when I was trying to install a new O2 sensor, but I check the bolts and tightened them all up. Are there any tricks for finding the leak?? I heard from somewhere about dripping trans fluid into the intake and looking for smoke. I also considered using Seafoam and hoping the smoke would leak through. I'd rather not use Seafoam since I have higher miles and last time I used it, the engine didn't respond too well.

 

Seafoam should 't hurt anything, you don't need to use the whole can. Just curious what happened last time?

I would check the manifold itself for cracks as they are prone to cracking.

 

Well after I put a whole can through a vac line and drove it, it had a high idle. The idle is still probably 100 rpm higher than it used to be. I'm not really worried since I rarely drive the truck (7k miles a year).

 

Get a couple of thick cotton rags and find yourself a buddy to help ya. Fold up the rags in one hand and press that hand over the end of the exhaust pipe for about 7-10 seconds or until your hand starts to get hot. While doing that, have your bud listen where you think the leak might be and you should be able to pinpoint it pretty quick if it's there. Just don't hold pressure over the end for to long. 7 seconds or so at a time usually will show you where the leak is...

 

I have a 2001 SuperCrew with a 5.4. Is this year & engine also prone to crackin manifolds? I have a small exhaust leak but only when it's cold. I'm having a hard time finding it & suspect somewhere's around the manifold.

 

I have two broken manifold bolts on the passenger side. The local dealer said this is fairly common. That may be where the leak is. Hope this helps.