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by Keith Vickers
The Mitsubishi 3.0 liter engine used in many Chrysler vehicles, from the Shadow to the Caravan, is prone to oil burning in later years. An otherwise reliable engine, the early 3.0s almost invariably burned oil after a few years. Keith Vickers’ guide is posted here, with his permission, to help you to save money in repairing this defect.
This is a pretty serious job, and if you don’t have a lot of experience working on cars, I’d leave it to another mechanic. Most of the procedures I will discuss are covered in the Haynes Shop manual for your vehicle, and I highly recommend you purchase that manual and read the related sections. I’m not going to cover all of the gritty details, only the parts that none of the manuals cover. READ THIS ENTIRE PROCEDURE AND THE RELATED SECTIONS IN THE HAYNES MANUAL BEFORE YOU BEGIN.
1.1 There are a few tools that you MUST have to do this job, in addition to the standard stuff.
1.2 You have to have an “on the car” valve spring compressor that requires very little clearance (about 2 inches above the spring). I made my own tool, which basically looks similar to an itty-bitty strut spring compressor. If you can get the correct tool from Snap-On, do it, because it would save you much time. You will have a clearance problem between the intake plenium and the intake valves. Frankly, the job would be a lot easier if you remove the intake plenium, but that removal is not easy or trivial, so I skipped it.
1.3 To get to the valve seals, you must remove the valve springs and the “keepers” that are on top of the valves. Now, STOP AND THINK WHAT CAN HAPPEN - THE VALVE CAN AND WILL DROP INTO THE CYLINDER IF YOU DON’T TAKE THE NECESSARY STEPS TO KEEP IT FROM FALLING IN!!!!!!
1.4 For this, you should have an air compressor and the necessary hose/fittings to put compressed air into the cylinder and this will hold the valve up. Use at least 100 psi. As an added precaution, I recommend putting the cylinder at top dead center prior to working on the valves for that cylinder.
1.5 Don’t forget, you will need to purchase a new set of valve guide seals and I recommend replacing the valve cover gaskets and cam end-caps while you are there. You should get some of the silicone-gasket maker material for the sharp corners on the valve cover (I use the orange stuff - be sure the stuff you buy is oxygen-sensor safe!) Also, one of those little mirrors on a telescoping handle is very handy for inspecting hard to get to places.
2.0 Start this job with the engine cool, lots of time, and a spare vehicle. The front bank of cylinders is very easy to work on, but the rear is a pain in the butt, so start with the front. I don’t remember exactly, but I think that these are the 2, 4, and 6 cylinders. Remove all 6 spark plugs from the engine to make it easier to rotate by hand. Remove the front valve cover (you’ll have to get the plug wires out of the way, and be careful to note the cylinder that they go to-the factory wires have the number on them).
2.1 Before going any further, I would use that mirror to inspect the seal and guides through the springs. There is a "side-view" picture of a valve guide/valve seal assembly in the Haynes manual. Your valve guide should extend out of the head the same relative distance. In some cases, the guides will slip in so far that the seal cannot be attached to the guide, and this is when the really bad oil burning takes place.
If it looks as though your seal is no longer attached to the guide and the guide has slipped into the head, you are out of luck, and the heads will have to come off to really fix the problem. If the guides on this bank are okay, I recommend you inspect the rear bank before proceeding. There are general guidelines for removing the rear valve cover in Paragraph 2.6 below.
2.2 Assuming that you don’t have this problem, you can proceede. Prior to removing the rocker arm assembly, you must first do something to keep the hydraulic tappets in place in the rocker arms. I used twist ties - they worked very well. With these in place, remove the rocker assembly, following the guidelines in your shop manual. Remove the cam bearing/cap that is located on the end away from the timing belt and put it back on the head in its original position This MUST be done to hold the cam in place and keep the timing belt from coming off its gear on the cam. If you let the timing belt get out of position, you are into another 3 or so hour job to re-establish the proper timing.
2.3 Now its time to get your cylinder of choice on top dead center (TDC). I started with number 2 (the one on the left). Put a No. 2 phillips screwdriver into the spark plug hole and SLOWLY rotate the engine clockwise (in the same direction that the wheels turn when going forward) with a ratchet/socket on the crankshaft pulley bolt. You should feel the top of the piston with the screwdriver. Continue to turn the engine until you begin to barely feel the piston start to move down. This is just past TDC (at this point I positioned the ratched on a floor jack so that the engine could not turn any more when I pressurized the cylinder). Then put pressure in that cylinder. You may now remove the valve springs for that cylinder.
2.4 Follow the instructions that came with your new valve seals for installing the new seals. There should be a little "slip cover" that allows installation of the new seals over the "keeper cutouts" on the valves - use this cover to prevent damage to the new seals. Put the springs back on, being careful to get the keepers in properly. Depressurize the cylinder, and go to the next cylinder. Don’t forget - TDC on this cylinder and air pressure! If you do forget and drop a valve, don’t blame me!
2.5 When you finish those 3 cylinders, take the cam bearing off and reinstall it on the rocker assembly. Follow the Haynes directions for re-installing the rocker arm assembly, being careful to tighten the cam bearing bolts slowly and evenly! And don’t forget to remove those twisties from the tappets! Replace the cam bearing end-caps and the valve cover gasket, put the valve cover back on and go have a beer.
2.6 The rear bank is similar, except that you have to remove the alternator and the air filter assembly First the battery should be disconnected. I always remove the negative cable so that I don’t get sparks in case my wrench hits the vehicle body or any grounded metal.
2.7 The procedure for this cylinder bank is the same as the front, but this one is more difficult due to having to get around the intake plenium.
2.8 Before you try to start it, don’t forget to put the spark plugs back in and the wires back on the plug. And be sure to get that ratchet or pull bar off the crankshaft pulley!
3.1 I’ve heard that even if the valve guides haven’t slipped into the head and the seals are replaced, the problem may return within 20,000 miles. I can only assume that the guide/valve interface is wearing out, allowing the valve to ’wobble’ and wear out the new seals prematurely. You might want to consider this prior to embarking on this mechanical journey.
3.2 When I did this job, my little valve spring compressor worked only so-so. On some springs it kept popping off. One spring would take 5 minutes to remove/reinstall, and the next would take 45 due to the tool not staying in place. If you can find that mystery tool at Snap On, buy it, because it will save you much grief. As a result, the entire job on all 6 cylinders took me over 8 hours. This time would have been cut in half by the proper tool.
3.3 It’s not absolutely necessary to replace the valve cover gaskets and the end caps, but I recommend it because these get hard and brittle about the same time the valve seals go bad.
4.0 GOOD LUCK!!!!
I was able to buy the on engine valve compressor and the hose (air compressor to spark plug hole) at the local Pep Boys. The valve compressor worked okay. It did the job but I wasn’t overly impressed. The one I bought included a bolt that replaced the handle if there wasn’t enough clearance. I had to remove the handle and use the bolt for all the valves.
I didn’t bother with setting each piston at TDC. The air pressure pushes the piston all the way down. I replaced all the spark plugs, the valve cover gaskets and the valve cover end caps. I did the forward bank of valves (1-3-5) on Friday night and it took me 4-5 hours. I worked at a leisurely pace and I’m a novice. A real mechanic would take an hour or two.
I did the rear bank (2-4-6) on Saturday. It took me all day. Again, I went slow and took lots of breaks. I highly recommend removing the alternator and the mounting bracket for more clearance. I was happy to find no valve guides sunken down into the head. Also, my back screamed at me for a couple of weeks after due to leaning over that engine for so long.
Dave (David J. Allen)
Jim Thatcher reports that the smoking from his 3.0 liter engine was coming from the PCV housing. The mechanics ordered a new valve cover, with a redesigned PCV housing, which is supposed to handle the oil properly. Details from Keith Vickers: inside the front valve cover, the PCV housing does not always drain oil properly. Drilling holes in this may cure the problem - we have no experience with that.
We also have a guide to other issues which may cause 3-liter V6 oil leaks at the end of our timing belt replacement guide.
Follow this link to view Ellsworth Chou’s step by step instructions on the same subject. We advise printing out both pages before doing the work.
- Want to get more performance out of your newly repaired V6? Click here!
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