What year is your Montero? I would first get a compression test done. If you've done your oil changes, the lower end will still be like new, and your problem will most likely be valve guides and seals.
You're welcome. Not sure if you will be tackling this yourself or not, but whilst you're at it I would recommend replacement of the following items:
- Timing belt and tensioner
- Water pump
- Crank and cam seals
- PCV valve
- Injector insulators
- Valve cover gaskets
- Engine mounts (easiest when the heads are off)
As for oil, I've found the best choice of oil for Mitsubishi engines tends to be 40 weights. Mobil 1 0W-40 or Delvac 1 5W-40 is a top choice.
The bottom-end of these and the 3.0L engines are bulletproof. Guide and seal problems go way back for some Mitsu powered rides. They are easily fixed. Mitsu came out with their way of fixing the guides on the 3.0 and several of my machinist buddies have done their mods on them to stop the guide drooping and wear problems.
I have built a number of them in my shop and the bore/cylinder wear is always minimal to non-existant. They did have wear issues in some of the 4cyl. Galant engines back in the 90s but since they went to all-aluminum blocks the problem has stopped.
The Montero is actually a good buy if you fix the smoking problem . The Asian Warner automatics in them are as solid as anything out there. Once the smoking problem is fixed correctly,it does not have anymore issues with consumption.
The bottom ends of the Mitsi V6 are pretty tough,but not bulletproof.With the waterpump being so prone to failure,overheating and headgasket failure is common.A sump full of water will destroy any crank....
Can't comment on the overheating, because I never had any issues - even in our 55-60 C (131-140 F) summers and I've got 282,000 km (176,250 miles) on mine to date.
Mokanic, I'm replacing my guides and seals, as well as a couple of other things with the head off. How do you go about modifying the guides to stop the wearing problem?
Speaking of which, Mitsubishi engine blocks have a massive amount of nickel in them, making them unbelievably hard. Unlike soft iron blocks, you can still see the original cross hatch pattern in the cylinder walls!
Well you won't have any overheating problems unless you have a cooling system failure.People over here have a tendency to run their vehicles into the ground - they are cheap enough,it's not worth repairing them...so they just step out and walk away.They will run with a blown headgasket so long as it will start,sump full of water,just keep topping up the radiator.By the time someone like me gets to pulling it apart it's all over for the engine.If it's worth more than $2,000 (not likely),we will drop in a used engine.
I agree with Falcon_LS, It is more then likely seals and guides these engines are well known for this! In spite of that they will normally go for close to forever even after this happens. The alternative to doing the proper repairs would be to use something like Lube Control and do a piston soak once a year to keep the deposits on the piston stops and int he ring area under control. Think of this as a band aid fix to allow you to save up a little each month so you can afford to get the parts you need to do the job properly.
I also agree with his choice of oils. A 40wt is the best way to go.Normally I would recommend Rotella-T 5W40 but since you live in S.Cal and you already have some oil burning I would instead go with a diesel oil like Delvac 1300 15W40. No sense tossing good synthetic out the tail pipe and 15W40 will work year round in California's climate even the rainy winter! Most OEMs like MB and BMW normally recommended 15W40 and 20W50 down to 20°F which is far colder then it ever gets in California!You can get Delvac 1300 15W40 at Walmart for about $9 a gallon and it is an excelent oil!