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3.8L Jeep Wrangler JK Engine Problems

Posted in How To: Engine on September 6, 2015
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Modern automobiles are supposed to be the best representation of what we can achieve and have learned over the 100-plus years of wheels on the road. While 100,000 miles used to be the break-over point for where people would grow weary of their vehicle, these days it’s not uncommon to see rigs still running the roadways with well over 250k on the clock. So, why is it that we keep hearing tales about 3.8L engine troubles on JK’s with less than 100,000 miles?

When the 3.8L V-6 was announced that it was being picked as the new power source for the Jeep Wrangler in 2007, few were singing its praise. The previous-generation Wrangler’s 4.0L inline-six engine wasn’t perfect but had many things going for it (most notably was its longevity). Conversely, there wasn’t anything for the 3.8L to hang its hat on. The 202 hp and 237 lb-ft of torque figures were more than the outgoing Wrangler, but it made these figures much higher in the rpm range. The result was a weak low-end power feel (something that was always a strong suit of the 4.0L).

The fact that the 3.8L was sourced from the Chrysler pool of mini-van engines only added to the ridicule. Now that the 3.8L JK has been out for some time, we are starting to see many nearing the 200,000-mile range. With years past, we are also noticing that the 3.8L has gained a reputation for not going the distance. By far the biggest complaint we are aware of is excessive oil consumption. Here at Jp, we’ve had two ’07 JKs with 3.8L engines die with just over 100,000 miles on the odometer. Both were consuming oil rapidly (in the end it was two-quarts to every 100 miles!) Sure, we might be harder than the average wheeler on our Jeeps, but a quick interweb search will reveal that we are not the only ones with 3.8L troubles.

The 3.8L engine isn’t all doom and gloom. In fact, for every person we’ve encountered with an oil-burning or chattering 3.8L, we encounter at least two with no issues. We’re no rocket doctors, but it’s pretty clear that the 3.8L won’t be taking the reliability title from the cherished 4.0L anytime soon. To get a better breakdown of what goes wrong with the 3.8L, we’ve put together a list of common trouble spots. Some spots are easy fixes, while others may have you looking for a new powerplant. Before you go off the deep end with your 3.8L, our list is definitely worth a look.

If you’ve ever had the lightning bolt of death flash at you on your dash and send your JK into limp-home mode, the fix may be easier than you realize. Below the drive-by-wire throttle body is a plug-in clip. This can actually become dislodged. When that happens, it will cause the JK’s engine management system to cut power, leaving you dead in the water. Typically, a trouble code will indicate that the throttle body is bad or not reading correctly. Before you drop a lot of money on a new throttle body, make sure that the plug is firmly in place.
If you’re noticing oil around the front of the intake manifold, there’s a good chance that the intake manifold gasket is bad. When we pulled our oil-burning 3.8L out, we saw that ours had been leaking from the back for some time. Obviously, this will be difficult to see with the engine still under the hood, but if your Jeep is experiencing a rough idle or burning oil, it is worth looking into.
Exhaust leaks are all too common on the 3.8L. The main culprit is typically a cracked exhaust manifold. Unfortunately, this isn’t a one side or another issue, so plan on replacing both. A cracked exhaust manifold can cause the Jeep to run poorly and eventually lead to trouble codes. It can also be misdiagnosed as an internal engine problem to the untrained ear. Before you go too far into the engine diagnostics, be sure to peel back the heat-shield covers and see if your manifolds are toast.
If you’re getting a 300-series trouble code, your Jeep likely has a bad spark plug or wire. Hopefully, your plugs have simply run their course and are ready to be replaced. You can purchase pre-gapped plugs from your local auto parts store, but we always recommend checking the gap to make sure it’s setup as the factory intended (0.050 is factory recommended for the 3.8L). However, if your plugs are coated with an excessive amount of oil, you could be dealing with ring failure or excessive bypass due to a number of internal issues.
Your Jeep’s 3.8L engine has plug wire guides from the factory, which are designed to keep the wires away from anything that could damage or melt the wires. Even in stock form, the wires could melt when resting against the stock manifold or aftermarket headers. Some preventative safety measures would be to sleeve the wires with a heat-resistant material or wrap the headers with a titanium heat-wrap, such as the ones offered from DEI (designengineering.com).
Smell coolant every now and again but can’t seem to source where it’s coming from? One of the most common sources is at the thermostat housing. It’s an inexpensive gasket that can cause plenty of headaches.
Is your engine burning excessive amounts of oil and making knocking noises? This was the case for both our ’07 JKs on staff. Pulling the engine’s oil pan revealed spun main bearings on Technical Editor Mansour’s JK, while the magazine-owned Red two-door had crystalized piston rings that came apart as soon as the pistons were removed.

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