6G74 - Valve seals leaking

[Spetz]

Hi guys,

I have a 6G74 Mitsubishi motor with about 115K miles and the valve stem seals are leaking.
Extended idle + throttle causes smoke.
Using about 1 quart of oil per 1,500 miles (around 400ml per 1,000km).

I've been researching some DIY seal replacement and it seems like a job I'd be willing to tackle.

My questions:

1. Does this cause any issues other than the inconvenience of filling up the oil periodically?
In terms of either worse fuel economy, damage to any part of the motor or any loss of power?

2. I was told that the valves are likely covered in varnish and replacing the seals without cleaning the valve stems is pointless. Is this true?
As I am only going to do this as a "heads left on" job.

3. From the service history of the car, Castrol Magnatec oil was used, and I've read this is likely the cause of the valve seal leak. Does this sound correct?

4. How fast will the valve seals deteriorate?

Help is appreciated

 

[bepperb]

I don't have any Mitsu specific advice, but:

1. Perhaps contamination of the O2 sensors and Catalytic converters, probably not an issue otherwise.

2. I think it's more likely the vitron/rubber/nylon/whatever seals hardened and no longer seal. I'd clean what you can but on Toyota's it is usually a heads on job with no valve cleanup/replacement.

3. I'm sorry, no Magnatec here, but no I would think it's more likely an engine production issue than an oil used issue.

4. Another 115,000 miles or a decade?

Will you hold the valves up with compressed air or rope?

 

[Kestas]

That's a common problem with the 3.0L Mitsubishi engines. I've read that though the seals wear out, the root of the problem lies with worn valve guides. The worn guides provide the slop that wears out the seals. People have reported replacing the seals only, only to have it leak 10-20K miles later.

With the mileage on your car, you may consider having the heads rebuilt. On my car I just let it go and lived with the puff of smoke every time I took off until I sold the car at 175K.

There is a lot of information about this problem on Allpar.com, a Chrysler enthusiast site. Chrysler sold a lot of vehicles with the Mitsubishi 3.0L engine.

 

[Donald]

Originally Posted By: Spetz
Hi guys,

I have a 6G74 Mitsubishi motor with about 115K miles and the valve stem seals are leaking.
Extended idle + throttle causes smoke.
Using about 1 quart of oil per 1,500 miles (around 400ml per 1,000km).

I've been researching some DIY seal replacement and it seems like a job I'd be willing to tackle.

My questions:

1. Does this cause any issues other than the inconvenience of filling up the oil periodically?
In terms of either worse fuel economy, damage to any part of the motor or any loss of power?

2. I was told that the valves are likely covered in varnish and replacing the seals without cleaning the valve stems is pointless. Is this true?
As I am only going to do this as a "heads left on" job.

3. From the service history of the car, Castrol Magnatec oil was used, and I've read this is likely the cause of the valve seal leak. Does this sound correct?

4. How fast will the valve seals deteriorate?

Help is appreciated


Valve stem seals normally show up as blue smoke at startup after sitting overnight.

Certainly popping the valve cover and having a look would be a good idea.

If they look to be failing, I think replacing them would be reasonable.

 

[Spazdog]

Very common problem although for some reason it seems more prevalent in Mitsubishi and Hyundai 6G7X motors than Chryslers.

....Not that Chryslers are immune. They are not. It happens on them as well. Just at a slightly lower frequency.

It is a common probem. Any oil would have this problem.

I would think that it would cause clogging of the catalyst(s) and contamination of the O2 sensors. But a lot of Mitsubishis run a long time with the cloud of smoke on startup.

 

[Spetz]

There is no puff of smoke after it's been sitting overnight.

Is there any other place the oil could be going?

As for getting heads rebuilt, it's not worth the money IMO.
I was thinking about a DIY project for the cost of the seals (some $100 or so).

 

[Doog]

I would do an engine flush. Then run a HM oil if you can get it where you are at. Clean the PCV system as well.

 

[Doog]

Originally Posted By: Spetz
There is no puff of smoke after it's been sitting overnight.

Is there any other place the oil could be going?

As for getting heads rebuilt, it's not worth the money IMO.
I was thinking about a DIY project for the cost of the seals (some $100 or so).


Yeah, past the rings.

 

[Donald]

The most likely cause is the oil control ring is gummed up or worn. The other rings may or may not be OK. So you could have good compression or bad compression and still have an issue with an oil control ring.

It can also be leaking past seals.

Kreen and/or HM oil and/or live with it until you dump it.

 

[CBR.worm]

Our '89 voyager started smoking w/ about 60k on it (in '91). We just lived with it, it got worse over time but ultimately it bothered other people more than us. That was the Mitsubishi 3.0 as well.

I believe that by 200k we were adding oil every couple fill ups which would have been about 1,000 miles between 1 quart additions. It's amazing how much smoke would come from so little oil...

More than a few times I had someone come up to me and tell me they thought my van was on fire while I was idling in traffic.

 

[bigt61]

I had an old Mitsu that I acquired about 10+ years ago that smoked horribly after idle at takeoff. No bugs within a 100yds and embarrassingly bad. I thought it was valve guide seals and put M1 5W-30 in it. At 1st, if anything, it was worse. But I drove it for a while and it started to get better. After 500-1000 miles the smoke was completely gone. You would have thought it was a new engine. The M1 brought the seals back to life all by itself, no other additives.

 

[Donald]

Originally Posted By: bigt61
I had an old Mitsu that I acquired about 10+ years ago that smoked horribly after idle at takeoff. No bugs within a 100yds and embarrassingly bad. I thought it was valve guide seals and put M1 5W-30 in it. At 1st, if anything, it was worse. But I drove it for a while and it started to get better. After 500-1000 miles the smoke was completely gone. You would have thought it was a new engine. The M1 brought the seals back to life all by itself, no other additives.


More than likely the M1 cleaned some of the crud around the oil control rings and that eliminated the smoke.

 

[Spetz]

So, from what I understand assuming that the oil is lost via the valve seals, anything short of a full head rebuild is wasted time?

Is it possible the oil is lost somewhere else?
The intake manifold is all black inside.
And the car idles poorly too in D.

 

[Doog]

Originally Posted By: Donald

Kreen and/or HM oil and/or live with it until you dump it.


+1 you might give it a "seafoam ultra treatment". One can in the gas tank, one can in the oil, one can in the intake manifold with an Italian tuneup.

 

[Spetz]

Guys I forgot to mention, and don't know if this has any bearing, but the motor is a 3.5L rather than the 3.0L and it is manufactured in Australia.

Does anyone know whether the valve guides are still soft and wear fast on these?