The Mitsubishi 3.0L V6 Can Handle The Mileage If You Can Control The Leaks
Get the skinny on the oil leak problems that seem to plague this engine
In early 1987, Chrysler introduced a new engine option for the company's successful minivans. Up to this point, the most powerful engine option was the Mitsubishi-sourced 2.6L four-cylinder. The new engine option offered V6 power - a must for American consumers. It was also quiet running, due to the use of a timing belt compared to the chains and balance shafts of the earlier 2.6L.
This new V6 was, like the 2.6L, sourced from Chrysler's partner, Mitsubishi. Utilizing overhead cam construction, aluminum cylinder heads, cast iron block, and multiport fuel injection, this powertrain was a big step up from the old 2.6L four.
So, what does this engine have in store for the rebuilder? The lower end is pretty straightforward: cast iron block, cast crankshaft and a front-mounted, crank-driven oil pump. Cylinder heads are aluminum, of a single overhead camshaft design, with two valves per cylinder. The head castings themselves are interchangeable.
Rocker arms are mounted on shafts, with a lash adjuster in the tip riding on the tip of the valve. The distributor is driven from the left (or forward) camshaft. For the 1990 model year, the rocker arms were changed to a roller design.
The most often-heard complaint about this engine is not that it seems to fail, but that it leaks and/or consumes oil. Engine life seems to be good, with many of these motors reaching 200,000 to 300,000 miles. The oil leaks and consumption problems can be traced to several causes.
At the rear of each cylinder head is a black round plug. In the first year of production, the depth of the plug was minimal (1/4), and as a result, plugs tended to pop out in cold weather, leading to massive oil leaks. Chrysler had a recall to replace the thin plugs with a new, thicker style plug (p/n MD090761) which was approximately _ in depth.
If you encounter the thinner ones, do not use them. Even the new style plugs may leak, if improperly installed. Make sure the surface is clean, and apply a thin coating of RTV sealer on the exterior edge of the plug. Drive it into the head until it is positioned .020 below the edge of the cylinder head.
PCV system and valve covers
The valve covers on this engine are laminated with internal baffles that cannot be removed. Should these be sludged up, the oil drain hole may sludge shut, allowing excessive amounts of oil to be drawn into the PCV system.
If the valve covers appear to be sludged up, replace them. Make sure the correct PCV valve is installed and is working properly. Improper PCV valves or sludged covers will allow pressure to build in the crankcase, which will force oil to seep from the cam seals, crank seals, cam plugs or other places.
Probably one of the most notorious problems on this engine is slipping valve guides. The original valve guides did not have circlips to keep them from working down in the bores if they weren't tight. The exhaust valve guides tended to slide down slightly, causing the valve stem seal to act as an umbrella seal instead of a positive seal. Oil was drawn out through the exhaust guide, and out the exhaust. Chrysler did replace many cylinder heads or have dealers cut a groove in the guide and install circlips on the guide.
When preparing heads, check for slipped guides and replace with guides that have the circlip installed. Valve guides with the circlip installed are available from Chrysler/Mitsubishi (p/n MD185850 - exhaust guide) or the circlip only is also available (p/n MD 185547).
Aftermarket guides are also available, however, some valve guide manufacturers do not have the intake guides with the circlip installed. The exhaust guides were the ones with the problem. Oversized OD guides are also available from numerous manufacturers.
Ticking noises can occur if a gasket is used on the rear seal retainer. The retainer was originally installed with a small bead of RTV. The gasket may cause the seal retainer to have interference with the flexplate. Knocking can occur if the wrong oil filter is used. Always use an OEM or equivalent filter.
Other areas to watch
The water pump is mounted on the front of the engine and is driven by the timing belt. When replacing the motor, or even just the belt, check the water pump, and if in doubt, replace it. A tube mounts to the back side of the pump and runs down the valley between the cylinders. These tubes tend to corrode from the inside out. Check the tubes for corrosion, and if pitted severely, replace them. What may look like a cracked block leaking in the "V" may actually be just a corroded water tube.
Applications and interchangeability
For this article, we have focused on the SOHC version used in Chrysler FWD vehicles from 1987-'97. The connecting rods, crankshaft and blocks are the same for the entire 10-year span in FWD Chryslers. Cylinder heads are the same, with the exception of roller and non-roller cams. Certain valve cover differences require the use of a cylinder head with a taller threaded mount for the valve cover.
Either be aware of which valve cover the customer has, or supply the valve cover to fit. If supplying the alternator bracket, which is behind the cam gear on the right cylinder head, there are three different ones.
Engines from 1987-'89 use an 8 x 1.25 mm bolt; 1990 uses a 10 x 1.50 mm bolt; and 1991-'94 engines have a mounting pad for the tensioner used with the serpentine drive belt.
There are some RWD applications, as well as FWD Mitsubishi applications. These blocks are different and some cases have been reported of modifying the blocks to fit, but this is not recommended.
Other relevant Allpar pages:
- main 3.0 liter engine page
- 3 liter repair
- 3 liter turbo
- performance upgrades
- other engines