Chrysler's mechanics were caught a bit off-guard when engineers delivered the company's first purpose-built, front-drive V-6 engine. Expecting a high-tech, dual-overhead-cam beast in the mold of the Ford Taurus SHO, they instead got an old-school pushrod engine like the standard Taurus. Still, the Chrysler 3.3-liter and its 3.8-liter derivative exceeded expectations, providing performance and economy belying their simple natures. But the 60-degree V-6 was still a fairly unsophisticated powerplant at heart, and even when new it wasn't exactly the quietest or smoothest engine out there. A decade of wear certainly hasn't improved that condition any.
Odds are good that your ticking problem is coming from the engine, but explore other options before tearing in. An engine ticking problem will typically manifest at idle, either getting better or worse as rpm or engine temperature goes up. If you only hear the ticking noise when the minivan is moving, then you might have any number of drivetrain or chassis issues. A medical-type stethoscope and an assistant are invaluable here. As you drive down the road, determine the conditions under which the ticking happens, duplicate them, and have your assistant press the stethoscope cup to the minivan's body, floorboards and wheel-wells as you go. Fortunately, a minivan is large enough that you can maneuver around inside easily, and get within inches of the suspension and drivetrain on the other side of the sheetmetal.
If the ticking gets louder or quieter as you go around a corner, then listen to the body as close to the wheels as possible. Odds are reasonable that you have a bad wheel bearing, or a cracked, loose or bent suspension or steering component. If you suspect a bad bearing, jack the minivan up and try to wiggle the wheels up and down by hand; if they move a noticeable amount, then you have a bad bearing. Check the steering and sway bar end links afterward. Loose lug nuts or wheel weights are also a possibility. If the vehicle knocks under acceleration or deceleration, but the noise isn't directly tied to engine rpm, then you may have one or more bad CV joints.
You can track down engine noises with a stethoscope, but a long screwdriver is safer and easier in a cramped engine bay like that on a minivan. Push the tip of the screwdriver against your target area -- the engine block, timing cover, valve covers, et cetera -- and nestle the end of the handle into your ear, or under your ear, against the jaw bone. Sound and vibrations will travel up through the screwdriver, and will enter your ear canal, or will transmit to your ear drum through your jaw bone. The ear is a better location for listening for deep, low-frequency knocks; the jaw is better for light, high-frequency taps.
This has been a known problem with 60-degree V-6 engines for some time now -- enough so that Chrysler issued a technical service bulletin on it in 1998. This sound, which might range from a light tap to a medium knock, depending on the engine, happens when the engine is fully warmed up and idling between 500 and 1,000 rpm. Place your screwdriver tip on one of the valve covers and listen; if the noise goes away over 1,000 rpm, then there's a good chance that you'll need to adjust the valve lash. This procedure might be best left to a professional. That's a somewhat expensive proposition, but it's not the worst case scenario.
Over time, using the wrong oil, consistently low oil levels, or using cheap aftermarket oil filters without the required anti-drainback valve will starve the lifters of oil for some time after the engine starts, resulting in valvetrain noise for the first minute of operation. You'll hear this tapping loudest when you listen around the base of the intake manifold. This is exacerbated by the fact that the lifter oil holes are very small and prone to clogging with oil sludge; combined with camshaft wear or low oil pressure, this will cause the lifters to remain collapsed and continue tapping long after the engine warms up. Consistent low oil pressures or levels will also cause cam bearing failure, starving the lifters of oil and causing tapping.
The worst case scenario for the valve train is a broken rocker shaft support, which will manifest as a deep tapping or knocking and a loss in engine power. The rocker supports on earlier 60-degree V-6 heads are fairly weak, and are known to crack and fail. The only "real" fix is to replace the cylinder head. However, drilling out the rocker shaft support hole in the head and inserting a "helicoil" will allow you to use a longer bolt, reattaching the rocker and getting the vehicle running.
The clearance between the timing chain and the timing chain cover on these engines is very narrow -- even normal amounts of timing chain stretch will send the chain rattling and scraping against the inside of the chain cover. This is very common on older engines, and not particularly dangerous except as a sign that the chain's slightly stretched. Noise from a malfunctioning oil pump is equally common, and generally results from following Chrysler's -- wildly optimistic -- 7,500-mile oil change interval recommendation. The oil pump is very close to the timing chain behind the front cover, so it can be very difficult to tell the difference between a bad pump and a bad chain. A bad pump will exhibit more of a pronounced tap or knock, though, compared to the chain's lighter, scraping tap.
Diagnosing a bad oil pump is critical, because oil pressure is critical on this engine. Engine-killing rod knock is very common on engines that experience very low, consistently low or fluctuating oil pressure. That's particularly true in this case, because the thrust bearings that keep the crankshaft in place are known to wear out before the rod and main bearings. Without a thick layer of pressurized oil to keep things in place, the rotating assembly winds up flopping around inside the block, causing lots of bad things to happen. Don't panic if you hear what sounds like rod knock, though; it might be a cracked flexplate. That's not a great deal better, but it is a bit. Rod knock will rise or fall in frequency linearly with rpm, and will generally get louder as rpm goes up. This may have as much to do with falling oil pressure as anything else. Rod knock is generally deep and hard enough that you can feel it when you put your hand on the intake manifold; cracked flexplates exhibit more of a loud, auditory tapping or popping.
You've probably noticed that a lot of this engine's issues come down to the oiling system. You might be inclined to completely flush the system to clean it out and rid it of any deposits, and that's not necessarily a bad idea if the knock is coming from your valvetrain. Aggressive oil flushes contain a lot of solvents, which will break down deposits in the engine and do a fine job of turning new oil into thick, black sludge in less than a hundred miles. In this case, though, the engine might already have experienced enough wear and damage from oiling issues that thinning it and sending sludge through the system may prove catastrophic. Instead, you should change the oil, add a 1/4-dose -- about 1.5 ounce for every four quarts of oil -- of "Seafoam" type cleaner, and change your oil again in 100 miles. Repeat this two or three times to gradually clean the sludge out of your system, while listening to hear if the knock worsens or gets better. Then switch to a high-quality 5W-20 synthetic oil.
