switched to synthetic... leaks already

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toneloc12345

Joined
Nov 25, 2005
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107
Location
Ohio
vehicle is a 1998 chevy k1500 4x4 5.7L vortec
172,000 miles.

I've had this truck for a while and it is a great truck. I drive used cars everyday at my job and I think this truck is in better shape than half of them. Anyway, I switched to supertech full synthetic about a thousand miles ago and I've already developed a small leak at the front of my oil pan. I never saw a spot of oil on the floor before hand.

Think this leak would have happened anyway? I wanted the synthetic for the cold starts up here in ohio, but I guess I might switch back to a high mileage oil. Recommendations?
 
I tend to believe that people should start the switch at 10k miles or less.

I switched to mobil 1 syn at 120,000 miles and it also started leaking. I sticked with it and the leak started to get bigger and bigger. I was told that switching back to dino will not do anything unless, you get a dino that would sludge up your engine... that's a different story.
 
the leak was prob always there. but beings the engine always ran dino. the crud built up around the seals and plugged the leak. when yo uput the syn it cleans the engine and prob broke the crud loose around the seals.

one prob on switching a engine to syn over 100,000 miles of running dino. yo urun the risk of producing a leak.

have heard Auto rx can cure some small seal oil leaks. so I would ask over in the fuel additives area.
 
That's pretty good oil so you should drain it into a clean container and save it for another car.

Search this forum for oil brands that folks claim slows or stops small leaks.
 
The problem you're experiencing is likely the bad initial synergy between high mileage deposits on seals and the improved cleaning abilities of many full synthetics.

At higher mileages, there are often enough deposits and dirt on the seals that a synthetic is now cleaning just enough off to create a leak.

Before switching over to a full synthetic on a high mileage engine used to dino, it is probably a good idea to first clean the crankcase with a more powerful dedicated formula like ARX (there are others, I'm sure).

Try a double ARX treatment, and then switch over to synthetic only after the seal is fully cleaned and the present leak stops.
 
I'd just switch back to dino, or a HM oil, or dino/syn mix with the syn. part being small.

When the same thing happened to my car, it took quite a while for the leaks started by the synthetic to stop...but you may be luckier...

switching to syn. at high mileage and it working is just luck, and it seems rare. most of the people who did this here got leaks/increased consumption.
 
Go back to what you were using. Historically, high mileage engines do not like synthetics and thus they end up with leaky gaskets and seals.

Engines should be "put on" synthetics when they are still fairly new-like under 20K miles. This ensures the seals and gaskets can "live with" the synthetic oil for the long haul.
 
I just don't buy into this 1970's theory that seals need to "live with" a synthetic early on or else. I don't believe these resulting seal leaks, in modern high mileage engines, have anything to do with the seal, and everything to do with dirt.

If this was pre 1990's engine sealing technology (like rope-style mains), the issue of materials composition and reaction to differing lubricants might carry more weight with me. But modern seals are synthetic materials themselves and do not deteriorate or react in that fashion.

I'm convinced that the leak issue on higher mileage modern seals is from deposit build ups on the seals combined with the suddenly altered detergency characteristics of using a full synthetic.

I've converted 100K+ dino engines over to full synthetic without any resulting leaks. But the seals need to be completely clean before the switch. The many leakers I've seen with others attempting it were always on engines that had less than perfect lubrication maintenance histories and where no effort was made to address the deposits.

Gaskets are different from seals. I've never seen a synthetic cause a gasket leak where there wasn't already a compromise such as weepage. But I've seen synthetic flow faster (better) than dino through a preexisting leak.

I don't know if LC is capable of this kind of seal cleaning on high mileage examples. Perhaps it is. But I've witnessed ARX do it repeatedly. I imagine there are other effective crankcase cleaners that can do it, too.

At 172K and with an unknown service history, I'll guarantee the seals on that 5.7 were heavily contaminated.
 
I'm in the "if it ain't broke, don't fix it" camp in regard to switching to synthetics in older cars. Unless you have a problem that requires a switch to synthetics, just leave it alone.
 
I switched my 350TBI in a '95 K1500 at around 160k miles and I have no leaks.

I did buy the truck with a leaking filter/oil line cooler adapter gasket.

I changed it and no leaks now.

Check the filter/cooler line adapter for leaks.
 
The leak is coming from the front of the oil pan. BTW my dad has a 350 TBI with the same oil leak. What oil did you switch too?

You guys think I should leave the ST in there for the rest of OCI or should I swap in some high mileage oil now?
 
With a high mileage vehicle, i'd use a thicker oil like 10w30 for better lubrication due to larger sized tolerances and a good dino oil like Schaeffer's, Castrol GTX, Havoline, or Chevron. Leave the dino in there for about 4000 miles, i believe the leak would slow down some while still providing good lubrication to all metal parts of an engine.
 
toneloc, I switched to Valvoline Maxlife Synthetic 5-30 API SL with AC Delco filter.

In another 500-1000 miles, I am going to do a filter change and run the oil for at least 5-6k miles minimum.

What oil were you running before?

How long have you owned the truck?
 
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