Ok, so I did check them and I'm glad I did. Several were about 1/2 to 1turn loose. So I re-torqued them all again and that is that.
Here are my thoughts on this, FWIW:
In most cases I don't believe the screws actually loosen themselve up by turning counter clockwise backing out of the holes as many seem to think. Whether it be caused by vibration, hot/cold cycling, or whatever, I just don't think this is the cause for these bolts coming loose.
My theory is this; there are 3 separate causes:
1) After initial installation of a new gasket, and after a hot/cold cycle or two, the seal will settle in and fully take the shape of the groove in the cover conforming completely into the groove. This process in itself would take some pressure off of the screws making them appear to have loosened. I think this is what happened in my case as I only brought the engine to full operating temp once before checking torque again the next morning. And just to clarify, when I torqued these the first time I didn't just go around once cranking them down. I started at 5 in/lb under and went around a couple of times until all were set and then went to full torque and went arount several times again until all bolts were solid with no further movement.
2) When first installed the seals have full resiliancy and provide constant push back pressure against the bolts. Over time, due to heat exposure and age, the resiliancy decreases as the seals get hard and the push back lessens, again making the bolts appear loose.
3) Same as above for the rubber washers on the bolts.
Thats my theory and I'm sticking to it!
And, as a matter of fact, if I get motivated today, I'll remove the intake plenum and mark the bolt heads on the passenger side to see if any rotation occurs over time.
So after this experiance would I recommend re-torquing these bolts?
ABSOLUTELY!
