I have installed a 355 with iron Vortec heads in my '77 Corvette. I am using an Edelbrock Performer Vortec manifold, with GM manifold gaskets, GM bolts, and black silicone on the ends (non-O2 sensor application). A week or so after I started running the car for the first time, the engine developed a coolant leak at the front of the engine on the passenger side. It weeps from under the gasket with the engine running. I have a few questions about what caused this and what can I do...

1. I installed the gaskets and torqued to 11 ft-lb (132 in-lb, correct?). I used the GM bolts without cleaning off the factory coating. Did I err here? Should I have cleaned off the threads and put something else on them?

2. At this point, it looks like I'm going to have to pull the manifold and start over... right?

3. What should I use on the threads? Do I need to use something suitable for wet threads like water pump bolts, or should I use blue threadlocker? Or should I use something else?

4. I used no sealant whatsoever on the intake gaskets and black silicone on the ends. I think this is the correct procedure.

5. What is the torque sequence of the bolts? Cross wise working from the center of the engine out?

Thanks in advance for any help! :confused:

 

I also have Vortec heads, but my leakage aways comes from the front and back of the manifold. I've changed gaskets a couple of times and used different sealers. I used sealant on the sides on top and bottom of the side gaskets and didn't worry about a torque spec. The sides held up fine. I've got new gaskets for the sides, but they are the blue o-ring type. I'd say that your major problem is that you didn't use sealant. Run a line of sealant around every hole, top and bottom of the gaskets.

 

Mike,

Where did you use sealant? Around the bolt holes only? The instructions for the GM gasket (blue O-ring type) say not to use sealant around the water and air passages.

 

This will be the first time I've tried the blue o-ring type, and based on what you've said, I may not install them. Up until this point, I've used the Felpro paper type and put sealant around every hole-coolant passages, valve passages. The torque specs should work fine, but I only torque stuff that I feel is absolutely critical. Anyway, I didn't torque anything and it all held up except for the ends. I guess I'll take the o-ring gaskets back and trade them for the paper type.