from what i have seen when one of these engines gets some hours on them the blow-by in the valve cover gets high and oil contaminates the pcv valve in the valve cover. Even though the valve cover does have a baffle in it the oil still vaporizes and gets past the baffle.
During Pm's cleaning that pcv valve is imperative. If that pcv valve sticks open it will allow oil vapor (which builds up over time) to go through the hose to the mixer/governor and that's where the smoke comes in.
At least that's my take on what i think is causing the smoke.
Using the wrong engine oil or not servicing the engine 'on time' consistently will contribute to premature piston ring and valve guide wear creating the blow-by.
and of course i could be totally wrong about this too, it just seems more logical than anything else i can think of after seeing it quite a few times myself too :o)
If this is a common problem (and it is for us), I would expect more people to chime in on it.
I noticed that the 4G52, 4G54 and 4G63 engines use an "oil separator. What is its function?
The truck we are working on now has a 4G52 with 5500 hours and has the same compression as a new engine. The is a small hose that goes from the valve cover to the governor. When we disconnect the hose the engine stops smoking. Any ideas.
Seen this happen many times. I have a friend that is a in house tech for a company and he had a fleet of lifts with the Mitsu engines. Seemed his woes came on about the 2000 hr mark. They also smoked on idle. He used one of the units to try and trouble shoot why they were smoking. He had the head reworked, new fuel system and ignition system. He even tried that restore for engine stuff. Never got worse and never got better. Some visibly smoked and some smelled as though they were burning oil It is possible that the cylinders are egg shaping and ring grooves are aligning as they are getting wear on them but thats just a thought. BTW my friend never found the cause.
Well we've got another one. It's a 4G54 but it usually doesn't make a difference what model engine it is. Same exact problem no smoke when working the truck, only smokes after idling. I checked the internet and it seems that Mitsubishi car engines have had the same issue. Some say that the OEM valve seals are crappy and they change them to high performance racing ones. Other sites say to use only 15W40 oil in these engines. I can't be the only one with this issue.
Any thoughts?......
We've already replaced the valve seals.
The compression ranged from 115 to 125 PSI dry and 125 to 130 wet.
We also took out the spark plugs and put some Marvel mystery oil in each cylinder and let it sit for 5 days thinking that the rings were stuck. This did clear up the smoke for a couple of days but it came back. I really feel that there is something that happens to these engines if they don't get a lot of usage and sit for a while.
I pity the people that own the little Clark (G127) with the Mitsubishi motor. There is a oil galley that comes up through the head gasket on the left side by #4 cylinder. I've fixed 2 of them that had the oil pouring right out of the head gasket next to that galley. I suppose oil could leak the other way into the cylinder. Maybe check the spark plugs to see if they are all uniform. I have one customer that has had this head gasket problem, cracked both tilt cylinders, lift cylinder leak, brake overhaul needed (who designed that master/inching cylinder set up?), starter and alternator gone bad, and fuel system failure. One problem after another. After putting on a perfect reconditioned head it still puffs a little smoke when started and when you floor it after idling a while. But this machine has a lot more than 2000 hours. I wouldn't rule out the valve seals. If it ever got overheated, I think it hurts the seals.
Yet another Mitsubishi engine with the same symptoms. This one is in a Clark that has just over 2000 original hours.
1. Engine does not smoke when first starting which indicates that the valve seals are good
2. Engine does not smoke when using the truck in a normal driving situation.
3. Engine does not smoke when running it hard.
4. As in all of these cases, the only time the engine smokes is when is sits idling for five minutes or more. It will blow smoke for a minute and then clear up.
As always, any help or insight will be greatly appreciated.
Have you changed the PCV valve? I cant remember the exact intervals on these but I think they should be changed every 1000 hours to stop to much positive crankcase pressure.
Check the valve seals, is this oke the motor needs nwe oil scrape springs i think.
Does the smoke not smell like oil than the engine have to much LPG for combustion
If it is condensation then I guess that I should just run the truck really hard to get rid of it? New trucks create so much condensation that the almost leave a trail of water droplets behind them as you drive.
I really don't think that is the problem though. It absolutely only happens once the truck has idled for about 10 minutes and it smokes. Once you start using the truck and taxing the engine it goes away. It seems to happen on every Mitsu engine I've seen.
I had some issues with a Cat GC25K - (Same as Mitsi) - Check to see if i just condinsation built up in the Muffler - White smoke - Stop/start application????
I have bought yet one more truck that does the same thing and it only has 1300 hours on it. Any ideas??