High Mileage Oil = New Leak

My 89 4.0 has 125,000 miles and has seen only regular dino oil until recently. I decided to try Pennzoil High Mileage. Soon after my rear main started to leak. I don't know if it's a coincidence or not but it makes me wonder if I shouldn't just go back to regular oil. Any suggestions?

i thought that stuff was regular oil with additives to stop leaks

Yeah, that's kinda what I thought too. The label said it "conditions seals" to prevent leaks. Guess it conditioned them a little to well?

You probobly got yourself some Synthetic oil which has cleaning properties. It tends to remove the sludge that has been keeping your seals sealed over the years which creates the leaks. You may wana drain that stuff and put in some regular oil. 6 quarts 10W30.

Pennzoil is not something I'd use in a 2-stroke lawnmower, but that's just me. I've had to clean that crap out of too many engines, and I've seen a couple failures caused by it (the paraffin would collect in the oil galleys, giving the engine "arteriosclerosis" (sp?))

Also, the "high mileage" engine oils I don't bother with - I'm still running Chevron basic oil (in the absense of re-refined oils,) in my XJ's - with anywhere from 150K to 250K miles on each one, and none newer than 1989. No trouble here - and when a seal lets go, I just replace it. It's actually easier that way, I think.

Run something like Castrol, Valvoline, or Chevron (or any re-refined oil - when they "re-crack" oil, they blow all the paraffinoids out,) and change seals when they leak - you'll get great engine mileage. I just prefer to fix problems rather than cover them up - and there's no seal in an engine that can't be changed with an after-noon's work, tops.

5-90

The Hi-Mileage Oils that have additives that help condition seals, its usually esters that cause the seals to swell.

I guess its possibel to get a seal to swell to much and it gets torn up on the moving parts, or maybe the seal was bad to begin with and the swelling from the aditives just made it worse. I don't know, say a small tear in the seal, the swell caused the tear to open bigger?

I personally use Mobil1 Synthetic 10W30 in all my vehicles, its true Synthetic (PAO, engineered from building block chemicals), not phoney synthetic like Castrol Syntec (hydrocracked conventional oil that is ultra refined and passed off as PAO Synthetic oil). When I changed my cylinder head on my 2.0L Neon at 65k miles, the head only required washing with soap and water and it was spotless, looked brand new, not a single deposit, no residue, fresh clean metal. The cross-hatching still looked brand new on the cylinder wall. I've switched to Mobil1 in my '91 Caravan 3.0L mitsubushi at 180k miles, it ran smoother, qieter and eleminated the valve tick. No problems with leaks, the existing leaks in the motor were a little wetter with oil, but there was no increased oil consumption, nor dripping from the motor.

I was thinking of switching to Mobil 1 but not until I fix the rear main. I run it in my wife's van and believe it's highly superior to conventional oil.

Never understood someone switching oils on an engine that has been just fine for 100K miles.

Rev

That's the beauty of technology. People ran bias-ply tires for alot of years before radials. We also had standard headlights before halogens. Just trying to get the most life outa my jeep.

Rev Den said:

Never understood someone switching oils on an engine that has been just fine for 100K miles.

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With dino oil pushing $1.79 or so a quart... versus $4/qt for Mobil 1, I figured if I change synthetic every 6k miles, instead of dino every 3k, the costs are roughly the same, and I save the planet from half of my used oil...

I have no doubt that the Mobil1 could go longer than 6k (I also do a mid-term filter change), but I'm happy just getting double the life out of it.

Den

Do your self a big favor and not use penzoil or quaker state. These oils really suck and will eventaully cause your engine to sludge up.

As far as high mileage oils, they are a gimmick. When everything has been working fine with whatever you are using then why switch to a different formula oil. I would personally use good branded dino oils for an older engine or synthetics on a newer engine. I would stick to castrol, valvoline, chevron and mobile, along with a good filter. I personally have been using castrol gtx on many of my engines with no problems.

goodluck
pete