Beg to differ. Had terrible vacuum leak where passenger valve cover overlapped timing chain cover (mating surfaces not quite flush). Steady pin point stream of solvent would kill engine. If that isn't a vacuum leak don't know what is. Still have bad leak around timing cover crank seal. Most likely way that air is entering engine is via valve covers (vs block seal). Rich A just plugged vacuum leaks in his cam access plates, again under valve covers. Have you ever heard of anyone running PRV with valve covers removed? Martin G/Darren B know engine pretty well (in variety of marques). If valve cover vacuum leaks were bogus surely they would have said something by now. Bill Robertson #5939 >--- In dmcnews@xxxxxxxxxxxxxxx, "checksix3" <jetjock11@xxxx> wrote: > > And what is all this I keep reading about vacuum leaks caused by bad > valve cover gaskets? There is no negative pressure with regard to > ambient under the valve covers, on the contrary...measure it and > you'll see.