Exhaust manifold bolts & gasket leaks
Been fighting the leak and manifold bolts coming loose for some time {years}, after changing bolts, new feltpro gaskets, searching this web sight and internet have finally fixed the problem and been doing good for 5 months now. What was done:
1. Go back to dealer for manifold gaskets, turns out the two are different unlike feltpro matching set. they are two different left & right.
2. The Bolts & studs found some Hi tempered ones at bolt supply house but the ones at dealer were cheaper.
Ran my F250 down interstate then checked manifold temp with therm o-gun my gun topped out at 650* F, all cylinders went over ranged for my gun. Out side air temp was 60*, {not a 100* summer heat stuck in traffic day} I found on internet 800* would be a normal. I have attached my findings on grade 5 & 8 bolts below.

What are the temperature limits of Grade 5 and Grade 8 bolts?
Grade 5 and Grade 8 bolts should not be exposed to temperatures above 450°F or below -50°F. Expect a reduction in yield strength at elevated temperatures

Can I replace a B7 bolt with a Grade 5 bolt? { B7 bolt is a High Temp Bolt}
It is never acceptable to make changes without notifying your customer or engineering department. Sometimes products may seem interchangeable, but certain applications may produce the circumstances that highlight the differences. While B7 and SAE Grade 5 fasteners have similar strengths, the B7 fasteners are intended for higher temperature applications. B7 fasteners are tempered at a higher temperature, 1100° F minimum, while Grade 5 bolts are tempered at 800° F minimum. This means that Grade 5 fasteners cannot be used in applications where the temperature can surpass about 450° F due to the re-tempering effects that they may encounter while the B7 fasteners can easily handle this temperature.

I hope this will help, I was fed up with dealing with this issue and wanted to share the fix with you all.

 

Thanks for the heads up. That is interesting.

Mods? Can we make this a sticky?