![]() If your engine has been overheated, it might be a good idea to just go ahead and replace all the top hat seals – along with the timing chain tensioner which also doesn’t care for heat, and every O-ring you can get at. It might also depend on how hot the engine has gotten. Dielectric corrosion isn’t an issue because this pipe is electrically isolated by the top hat seals.įinally, note that the condition of rubber parts such as these isn’t simply a matter of age. I replaced my coolant manifold pipes with copper pipe others have gone with SS or brass, any of which mean you can forget about leaks there for decades. It’ll stay put until the top hat seal crumbles or the pipe itself rusts away. ![]() This is a more suitable application, though, because pressure is applied equally at both ends of the pipe so there’s no net force trying to push it out. The same “top hat” seal for the push-in fan switch is also used on the coolant manifold pipes. Almost nobody who knows the thing is there wants to drive around wondering when that rubber grommet will harden just enough to let the fan switch blow out and blow coolant all over the highway. Anyone with the earlier press-in switch can either tie some wire around the water pump inlet elbow or simply buy a new elbow with the threaded switch. That said, perhaps it’s worth noting that Jaguar did away with this push-in scheme for the fan control switch and went to a threaded fan control switch. I would hate to have been the engineer proposing the idea in the first place, but once established it was simply a matter of “how it’s always been done.” It was an established method of installing sensors and the like for many years. My experience has been they work just fine for many years. Not so for the rubber stoppers now in use. If you start to cork a bottle of wine, squeezing the cork, the part of the cork not yet inserted does not expand or lengthen. Interestingly, cork, unlike rubber, is one of few materials with zero Poisson effect. Seems like there’s not much force involved though, since the area is so small. But the drag on the inside of the grommet would cause, via the Poisson effect, an axial deformation that leads to a tightening of the grommet on the probe–like trying to pull a hose off a tube instead of pushing on its end, or Chinese handcuffs. Not to bore, but a third possibility is that axial force on the end of the probe itself would tend to push it outward. The Poisson effect from the external radial pressure would lengthen the bushing though, just like internal pressure in a pipe shortens the pipe. But perhaps the same pressure could make its way between the probe and the grommet, partially negating the effect? Regardless, that phenomenon doesn’t depend on the Poisson effect. OTOH, radial pressure applied to the outer cylindrical surface of the bushing (whose area is much larger than the area at the end available for axial force) would indeed squeeze the grommet onto the probe. With respect to the OP’s problem (ejection of the probe, not the bushing) it would seem that axial force from pressure would tend to expand the bushing radially (as Ed says), but that would make the hole bigger (as when expanding a nut by heating it). Yes, probably right, but I still can’t figure out exactly how. This is what holds the bushing in place when the coolant level probe is inserted into it. ![]() Ed Sowell already mentioned Poisson’s Effect in an earlier post in this thread.
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