My truck (12-valve 6G72) is in the shop for a cylinder head job. This is to resolve the dreaded valve guide/seal problem, and whilst I'm at it I'm getting a lot of things replaced; intake/exhaust valves and guides, all gaskets/seals that come with the full kit (including head gasket, cam seals, etc.), timing belt and tensioner, PCV valve, spark plugs, etc.

I trust the mechanic who's working on the truck, and have known him for years. However, one of his colleagues spoke to me and said I should consider overhauling the engine...or at the very least replacing the piston rings.

I've been told the bottom ends of these engines are extremely reliable, provided they are not abused. I've had my truck since new, always done lubricant/fluid changes at the manufacturer's recommended intervals and recently even switched to synthetic. I've basically babied this truck as much as I could, but the guides and seals going bad was inevitable on the 12-valve.

His colleague told me the chances of 'killing' the engine would be high if I just do the cylinder head, because compression will be higher up top and lower in the bottom end, eventually leading to oil shooting out of the engine and resulting in a complete overhaul.

My mechanic said there was no need to overhaul the engine at all, seeing how everything is clean and the compression test yielded rather decent results. In his view, I'm already going over the top by replacing more things than necessary. Is his colleague trying to sell me something I do not need, or should I seriously consider what he has said? Thanks for any input.

 

your mechanic is right. there is NO reason to take apart the lower end. if you've done your oil changes, the lower end will still be like new. His buddy is an idiot that knows nothing of engines. You will NOT wreck an engine by repairing the oil leak. Dont ever talk to him again, because hes a dolt.

mitsubishi blocks are NOT like crappy american iron. the iron has a massive amount of nickle in it, making it unbelievably hard. It is not a soft iron block like the domestics use. You would no doubt still be able to see the original cross hatch pattern in the cylinder walls!
if you have no problem with the lower end (and you shouldnt unless you ever ran it out of oil or neglected it), leave it alone. fix only whats needed.

 

Manybrews, thanks once again for sharing your knowledge and expertise with these engines - muchly appreciated!

Up until recently, the truck has always had 3,000 mile oil changes with dual-rated HDEO. Oil has always been checked at least once every few days, and topped up as necessary. Never has this engine had less than 4 litres out of required 5 in the slump. Only recently have I switched to synthetic and extended oil changes to 10,000 miles. I'm quite obsessive about proper maintenance, and this has been my service schedule for years:

- Tire pressures checked/adjusted at every fill up
- Air filter replaced every 3,000 mile (extremely dusty conditions, don't like blowing it with compressed air)
- Tire rotation/balancing every 6,000 miles
- Lube undercarriage every 6,000 miles
- Oil/filter with GP IV synthetic every 10,000 miles (previously 3,000 miles with HDEO)
- Clean throttle body/IAC/MAF every 12,500 miles
- OE copper NGK plugs every 15,000 miles
- Coolant, transfer case oil, brake fluid, power steering fluid, differential and fuel filter every 25,000 miles
- ATF flush through cooler lines every 25,000 miles (with filter/gasket replacement)
- Timing belt/tensioner every 55,000 miles,alongside cam seals, PCV valve, radiator hoses/cap (water pump replacement every second change with distributor rotor/cap and plug wires)

Wear and tear items (pad, rotors, CV boots, etc.) were replaced as necessary and lasted quite long. The Galant's not going to be treated any different, except replacing all lubricants with synthetic right from the start. I'm looking to get the cylinder head sorted, and get many more trouble-free miles out of this truck (daily driver). It's been the most reliable vehicle I've ever had, despite the oil burning issue, which is why I went and bought another Mitsubishi.

 

my diamante (essentially the same block) has 235000 MILES on it. Completely original.

all thats been done is oil changes and timing belts every 100k. Thats it. (a set of plugs and wires was done at 141k).