Originally Posted by 19bonnie95
I head something about spraying soapy water on the intake and another one was spray wd-40 on the intake and if the rpms go up its leaky...... are those safe to do or would that not work?
OK two things here.
1. The intake manifold seals an area of the engine that is under negative pressure - vacuum. So, the traditional way to find a VACUUM leak to the outside of the engine is to spray around the edges of the manifold with something that the engine can burn, light oil like WD-40, Carb Cleaner (lacquer thinner), or the like. The idea is if you spray on a spot that is leaking from the inside vacuum to atmosphere, the vacuum will suck the additional combustible material in and you will hear an increase in the speed of the engine. Spraying soapy solutions is good for finding leaks on stuff that is under positive pressure, like an exhaust manifold or a tire. Spraying soapy water on an intake manifold with a leak would not reveal the leak by an increase in rpm. And, unless it was a big leak, probably you would notice no change.
2. Our intake manifolds most commonly fail when the seal is lost between coolant passages and the interior or exterior of the intake manifold. In these cases, coolant can be sucked into the combustion chambers from leaking gaskets on the lower aluminum intake manifold seal against the cylinder heads, or from a heat- induced perforation or distortion in the plastic upper intake manifold where hot EGR gasses pass through near the throttle body. Coolant leaks may also occur where the seal is lost from the coolant passage to the outside of the manifold. In this case, coolant usually is seen running down the transaxle. Coolant leaks can be confirmed with a pressure test of your cooling system. The leaks to the outside are not nearly as important as the leaks that allow coolant to trickle into a combustion chamber where hydrostatic lock can bend a connecting rod, or as others have pointed out, into the oil in the crankcase, where it will mix to form a milky acidic brew that will attack the bearings in your engine. Internal coolant leaks can quickly and effectively destroy your engine.