Worn valve seals

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Oct 3, 2008
My Mitsubishi truck has the infamous 12-valve 3.0L V6 (6G72) and although bullet proof, it's notorious for bad valve seals. I need to replace the valve seals about every 2 years or so, and that is being optimistic. Quite a shame considering it's an otherwise bulletproof engine with 259,000 trouble-free kilometres so far (162,000 miles). To clarify the problem, there's blue smoke at start up, more so when the engine is cold, and blue smoke at extended idle. Oil consumption at this point was a quart every 3,500 km (2,200 miles) with a 10W-30 grade oil.

So far, I've completed three Auto-Rx treatments, which have helped to some extent. The first two were with Motorcraft Synthetic Blend 10W-30, and apparently it wasn't working too well with the oil burning application. For the third, I switched to BP's Visco 2000 - an SJ rated GP II 20W-50. Before I go any further, my vehicle had a diet of 20W-50 for the first 125,000 miles of its life when it was serviced by the dealer. After the second treatment was over in January, the PCV valve was also replaced. As per Frank's recommendations, I ran a 3,000 mile clean and 3,500 mile rinse for the third application. There has been a reduction in the amount of blue smoke puffing out of the exhaust and at one point it seemed to have disappeared completely. Although at both stages, oil consumption was a quart every 2,500 kilometres (1,600 miles). However, the engine is now much more rev-happy, runs very smoothly and gets much better gas mileage so the treatments were worth it for those alone!

The instructions recommend sticking to a GP II or GP III oil following the application, and to use no additive once the rinse stage is over - until oil consumption reduces or disappears completely. As a result, I switched a GP Pennzoil Long Life Gold 15W-40 (which is Mitsubishi's recommended grade for this part of the world). The engine started running much smoother, and the amount of smoke being puffed out reduced - only to return last week. But it's an intermittent issue now and it doesn't always happen. Sometimes I could be at a traffic light for 5 minutes and there'd be no smoke, not even when you hit the gas. Next I could be at a light for 2 minutes and there's no visible smoke at idle, but it's blue smoke galore in the rearview once you hit the gas to move. At this point, oil consumption still remains a quart every 2,500 kilometres (1,600 miles). The amount of smoke puffing out of the pipe is extremely faint as well...until you rev the engine.

Being honest, I'm not too keen on replacing the valve seals once again in 2 years. It's not an easy job, the truck has to sit for at least a full day and it's kind of pushing me over the edge to get those dreaded seals replaced so frequently. Having said that, I posted on a Mitsubishi forum and a Mitsu technician said valve seals were a band aid fix. If the seals are gone, the guides should be replaced as well. That is something I'm considering, but for the time being getting those seals replaced is not a consideration unless the problem worsens considerably. However, I can hear the valve guides ticking at idle, so those are definitely worn if my assumption is correct.

I've posted about high mileage oils, and the only one I can get my hands on here is Quaker State High Mileage 10W-30 in a red bottle. But it isn't API certified and I'm not willing to use it for that reason. Somebody was telling me a cap full of brake fluid would give the same effect as a HM oil, but IMO brake fluid doesn't belong inside an engine and I wouldn't consider using it unless this is really true. After this treatment, I was considering a switch to Mobil 1 15W-50, but am unsure as to whether or not it would be a smart decision. I'd be running the M1 for a minimum of 16,000 km (10,000 miles) with a UOA at the 10,000 km (6,000 mile) mark with the filter change. If oil consumption continues at the same rate, adding oil would get rather expensive.

However, a recent post I read has made me rather curious. Apparently GP IV oils require more seal conditioners than comparable GP II and III oils. I'm wondering if those conditioners could help continue what ARX has done for me so far (with a maintenance dose to accompany it)? If somebody can shed some light on this, I would muchly appreciate it. It's quite a shame, because I did ARX treatments to switch to a synthetic initially with extended OCI's using a 90 ml maintenance dose of ARX. Thank you.
The more I hear about this, the stranger it sounds to me. Clearly it's a common problem with the 3.0, I just never experienced it. I have witnessed Caravans and Galants driving around as they fog mosquitos, but my '93 Sundance NEVER did this.

Perhaps Castrol has something to do with that? All that car EVER got was Castrol 10W-30 every 3000 - 3500 miles, with a Fram filter, and it ran flawlessly and with zero oil consumption for 75,000 miles before I traded it in. I did more than my fair share of stoplight drag races when smart-a**es in Camaros and Mustangs underestimated what was under the hood (and were caught very much by surprise). It stands as the only one of 17 cars I've owned that never visited a service department for ANYTHING. Can you tell I miss it? :)

Maybe there's something in Castrol that preserves the valve seals in this engine? Or I got really lucky....
ViragoBry, I only started to experience this problem after the 150,000 km (93,750 mile) mark. Up until then, I've never had any problems.

Billy, it's not expensive considering what it is - about $200 USD for parts and labour. It's just the inconvenience it causes.
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