Hopefully not a hijack, but I suppose it could be related to smoke and head gasket.
It's been awhile and memories run together...Our '03 Sport with the 3.5L 6G74, lost the oem radiator to a crack in the upper tank. Quick trip to the local chain parts remedied the situation, but not too far down the road, I'm overheating occasionally again? Can't find the issue, exchange the radiator cap, (should have done that on the radiator swap) top off the coolant and back in business. But wait, several days go by and the temps creek up again, when sitting at idle or at the drive through for example.
Hmmm, something's not adding up. Coolant level is down in the radiator again, I pop open the overflow reservoir, and PANIC! The chocolate milkshake syndrome! I mean the coolant is brownish-milky, a few large bubbles, and all I can seem to think is "head gasket", and how big a job it's going to be and how much it will cost, and what if the block or a head is cracked? What's a cheap do-it yourself-er to do? Why get on the "interwebs" of course, see what the Australians in the pajero club think etc. BTW, there was never any evidence of coolant in the oil. I feel pretty foolish now, but at the time, I was sure of disaster.
I'd snooped enough DougC repsonses on justanswer.com to determine he was pretty sharp on Mitsubishi, so I prepared my questions, paid a small registration fee to JustAnswer.com and took my chances. After a little back and forth He really doubted my diagnosis, recommended I check for leaks on the coolant bypass pipe. (What bypass pipe? I'm thinking). So off to the races, and sure enough the pipe wall had corroded enough to leak only under full coolant, pressurized, and running. The coolant would work it's way down the back, and to the ground never leaving evidence, even on the garage floor.
I guess a few things happened all at once. The coolant level would drop slowly, allowing air into the system, the water pump would froth it up, and this would go on long enough to create the mixture which would float to the top of the radiator then out to the bottle in an attempt to self clean I guess. The leak was so slow that the truck would never dramatically overheat. I suppose there was enough coolant most of the time to protect the engine, except in hot and idle conditions where the temp would creep up. The bypass pipe is the highest point on the engine. I read more about common problems with the pipe, o-rings, and fittings which connected to the throttle body heating hoses etc. Ordered a new one from Mitsu, made the proper repairs, and back in action. I also did a complete system flush and refill using distilled water, and fresh coolant.
Compounding the issue was my shortcut on the original radiator swap. My truck has coolant piped to the console for the rear heat. The connections through the firewall are pretty high up, and I suspect I must have left some of the original tired red/orange coolant in the system, then when I drained and filled with the green, it must have added to the mess when the coolant leaked out. Keep in mind, there was never mist out the tailpipe, but I did get that hint of coolant smell while running from time to time which spooked me to head gasket issues even more.
I've never had to pull the head on either truck, and DougC was dead-on right, and as sharp as I thought I was, I was dead wrong, thankfully. He explained that these blocks had a very high nickel content and that they could take a fair amount of abuse before failure. Most of our issues are related to not taking care of the oil leak "gremlins" know to the brand, and lifter failure and valve seal issues that go with it.
If arb098's candidate truck isn't overheating, but is losing coolant, could he have a similar issue? Is the smoke really just the common valve stem seal smoke?
