Valve Seals & Engine Oil

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Jul 29, 2002
I was wondering, do you think some engine oils are better suited to maintaining good “valve seal health,” or is that type of engine wear more a function of engine design and engineering? (Assuming proper viscosity and OCI.) I had a 1992 Plymouth equipped with a 3.0 liter Mitsubishi-made V-6. I always suspected that those engines were prone to “premature” valve seal damage/failure/leakage/premature wear, often resulting in the all-too-familiar puff of blue smoke at start up and initial acceleration from a stop - in engines with sometimes as few as 50,000 miles. Yet, I never had that problem through the 145,000 miles I owned the vehicle. I attributed that to the very strict oil change regimen I maintained using nothing but Mobil 1. (I’m very certain my OCI were far shorter than necessary.) I wonder if any decent quality oil would have prevented the type valve seal “failure,” the evidence of which (puff of blue smoke) I’ve seen countless times in 90's model Chrysler products with that V-6? [Patriot]
This is an interesting question. I'd like to know what opinions and experience people have regarding this, both for this particular engine and in general. There are at least a few Mitsubishi 3.0 V-6 owners hanging out here. Let's hope that M Smith sees the resurrection of this thread and lets us know the viscosity of Mobil 1 used as well as the length of the OCI.
In general valve seals last a lot longer these days on most engines than they did 20, 30, or 40 years ago. I attribute this to the great improvements in synthetic elastomers. The big killer of valve seals is heat, and letting a car overheat, or a design that keeps the cylinder head at the high end of the acceptable temperature range, greatly reduces valve seal life. In my own cars, beginning with Pennzoil Turbo 5W-30 right through the current Mobil 1 synthetics, I have never experienced a valve seal failure - using a regime of 3,000 mile oil changes (now 4,500) with vehicles driven to 200,000+ miles.
Valve seals generally are not much of a problem like they were before the mid 80s Material and design have come along ways since than. Overheating, excessive valve stem to valve guide clearance, and sludge are not friendly to valve seals.
I know the 3.0 had bad exhaust guides. Oil was being drawn into the exhaust from the outside of the guide. The friction/press fit of the guides became loose (some actually dislodged and fell into the port). Also the valve guides were "soft" wearing out fast. I think Chrysler fixed all those problems 93-94ish??? Also the hydraulic lifters would completely drain (car/van sat awhile)lots of valve train ticking.
If you are worried about it, buy group IV or V synthetics & change oils & filters at/under 8K. Drive only 4-7K every year - in congested cities? Change once a year. The main thing here is that synthetics keep engine cleaner than dinos - when matching mile-per-mile. The only dinos that come close are high moly dinos like Chevron & Havoline... maybe the new high sodium ones like Mobil Drive Clean 5000.... I dunno. I am just an amateur poster here... only pass along info the gurus mention here. I use this oil change regimen & have no issues. Mobil-1, Pennzoil Platinum & German Castrol 0W-30 are good synthetic choices - with sales ranging a few times each year. Otherwise... I would use Havoline or Drive Clean 5000 dinos to help keep your engine/seals clean. [ April 03, 2006, 01:29 PM: Message edited by: Triple_Se7en ]
we had a 92 acclaim with a 3.0l. it got dealer bulk oil until about 60000 and supertech 5w30 from 60000 to 185000 miles. it never gave us problems, ran great. no smoke, only used a half a qt in 3000 miles. it just had proper maintenance.
The SuperTech product line on the East Coast is blended & bottled by ExxonMobil at a Paulsboro, New Jersey lube plant. So this backs-up what I'm saying about buying Mobil Drive Clean 5000 or Havoline when choosing a dino to keep engines/seals clean.
I've got a 1990 Diamante here at the moment that fills up my workshop with smoke after idling for 5 minutes.It's the exact same model as my own Diamante,with the 3.0 DOHC 6G72.I don't know the history of my own motor as it was a transplant,but I know the heads had been off and it had new valves all through,so expect it has new seals smoke in my one of course,and it's always been on good oil since I've had it. I was given this other one as payment for a $200 repair,and am not sure if I'll strip it for parts to keep mine going,or turn it into a runner...depends on that other Mitsi problem,the auto...but I'll see if I can reduce the smoke without doing the seals,it's a bit of a mission on the DOHC.
I think long oil drain intervals like 8,000 + miles will kill contact seals. The seals run at zero clearence on an extreamly thin layer of lubracant. We know that particules in the oil of less than 5m are not the wear culpret for bearings. I am convinced that the oil seals trap 5m and smaller particules that become imbeded in the seal and continue to wear at an accelerated rate. Look at the shaft the oil seal rides on after many thousands of miles and there is a grove where the seal contacts the shaft.
I have a '95 Mitsu 3L engine. All "older" mitsu V6 engines are known to have weak valve seals. Many people actually replace the valve seals without removing the head and their oil consumption is nearly eliminated with that fix. I have 160k miles on my 3L. It burns some oil, but does not smoke at all. The oil consumption varies between 1qt per 2k to 1qt per 3k miles. I did an ARX on it (single dose) and it might have helped a bit, but it still uses oil. Even so, my engine is better than most Mitsu's when it comes to oil consumption. OTOH, when the truck was new it did not require any make-up oil for my 7500 mile OCI. I used synthetic oil only for the first 120k miles. However, I did OCI's of 7500 to 8500 miles. I believe that the synthetic oil helped with the "health" of my valve seals. I need to add one more thing. This 100% made and assembled in Japan Montero has been an incredibly reliable nearly maintenance free vehicle.
depends on that other Mitsi problem,the auto
I did not think that Mitsu A/Ts (Aisen) were known to be problematic?
Mitsubishi's are notorious for this. I had a '90 2 litre 4 banger in a Plym Laser, made by Mitsubishi, and everytime I would startup from a short idle it blew out more smoke than a hippie at a rock concert. [crushedcar]
I had a '91 Plymouth with the 3.0 Mitsu V6. Left a ghost at every stoplight. I replaced all the valve seals at around 115,000 miles (just pulled the intake & valve covers). It was moderately sludged (I didn't know BITOG then), but I just buttoned it back up and ran it. It still ran fine with no smoking at 126,000 when I sold it. The person I sold it to ran it until 180,000+ and sold it. He said it didn't smoke then either...and he changed the oil every 3000.
I had a 90 Ply Laser w/ a 2.0L Turbo. It smoked after idling. I put M1 in it and that cured the problem. I droved it another 2 years like that with no more smoke.
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