Fine...I know this is a question which is simply ripe with variables. But, as a general rule, how many miles do you guys get out of your original factory installed piston rings (those which it came with from the factory) before a compression test yields pressures below the "wear limit" (which is right at 412 psi on the Mark II's I run)
?
My 2nd VW diesel was an '82 Jetta with the darned automatic trans. I never checked the compression on it for all of those years, but I had an honest 435,000 miles on it when it finally failed to start. I realize many of these will start and run once they are "out of spec" on the compression values. As a side note, I used to drop the ATF pan on that trans about every 5K miles and do a fluid change. When that car quit, reverse was only beginning to get slightly weak!!!!
I have never had another engine which hung in there like that one. My area is quite sandy and I do spend time in rural areas. But, I do not consider it overly dusty.
So, how many miles do you guys get and keep spec. (above minimal) compression???
i'd say around 300'000km's would be it for these engines... after that it seems like the engine develops a bit of piston slop, and at that point even new rings don't really do the trick.
not everyone uses the best oil for the engine, and that is the main reason for the "low" mileage. i'd like to see a gasser with 300'000km's run like my engine with almost 400'000km's :lol: i think i have a valve guide seal issue though.. either that or my compression is totally whacked out. because i'm getting white smoke under hard acceleration. when the engine is fully warmed up though i can get some black... :cry:
i'll be checking my compression within a few weeks, but my money is on a valve sealing issue more than rings.
Well, you have opened the door for what I was kind of getting at. I wasn't going to talk about this as it is about "gasser" engines (as you once called to my attention in an earlier post :roll: .
But, yes, I do have two of the VW (same era Mark II's) GX code, 1.8 mech. inj. gas engines in a Golf and a Jetta. The Golf has well over 300,000 miles on it. A few years ago, I replaced the head gasket and found something I wasn't expecting.........the cylinder walls all still had their very obvious and extremely fresh looking cross-hatch pattern. Now, this engine has really never been pampered. Yes, it has always had very good maintainence. But, there WERE many times when I got behind the wheel....ahh...kind of angry and aggressive.....OK, LOTS of times!
When I studied metallurgical engineering, I once asked a seasoned PhD. instructor why my VW engines lasted so much longer than most of everything else on the road. He casually stated that the Germans put 2 tenths of one percent (by weight volume) MORE nickel in their engine block cast iron. Hence, the improved wear characteristics.
I later went through the local machine tool program (vo-tech school) and found that machining materials like stainless steel did indeed pose problems (higher nickel content) regarding tool wear and heat generation. So, the professor's view was rather substantiated.
Lately though, 3 of my diesels have gotten very sloppy (bore/ring) wear and I was just expecting much better overall wear characteristics. I am looking at a lot of repair in such a short amount of time......and money is tight. And yes, I did elect to go with a set of Prothe pistons in the first rebuild.
Cut to the chase: I was just expecting longer life in these engines....that's all.
what oil are you running though??? it is the soot content in the oil that really wears down these engines. Total (formerly Elf) is a really good oil for these engines. some guys even use a product called molyslip or even lubro-moly oil.
check out amsoil's bypass filter or even
www.fs2500.com (for big trucks, but can be fitted to your motor)
some big trucks running the fs2500 filter have over a million miles, with little to no wear on the engine. true its highway miles, but still :wink:
i'll be fitting my fs2500 when i get my mTDI engine done.
I run Rotella about 2/3 of the time. But, now I am about to get paddled...as I used Walmart 15/40 other times in order to cut my expense. My change intervals were certainly not excessive.
What spurred me to talk about this, was I checked my compression on the '92 Eco this weekend. I used two different very good compression testers. A Mac Tool (I scored in pawn shop years ago) and a V.O.A. trained mechanic's Snap-On tester. I found this pristine Eco about 5 years ago. And I never really drove it as my "clunkers" just kept running and it was too nice to drive (I'm kind of wierd that way...). I have stored it in a dry barn at the farm and I usually would take it out and drive it every couple of months. I would change oil in it about once a year. When I exercised it on those outings, I would get it good and warm for at least half an hour and run it pretty hard.
Do you think the periods of time "sitting" tended to stick the rings a bit? It looks very much like showroom condition with an engine with 390 to 410 psi across the board. The original owner may have tended to "rod it" when it was new and didn't do an intelligent ring break-in.
It certainly starts right up after sitting and runs as good as an Eco can. I was actually saving this car for when I move off the family farm. So, it appears more investigation is in order. It will have to wait until engine #2 gets whatever it needs. AND, I rob a liquor store for more bread!!!!
Oh, the mileage on this one is 144,000 miles. And this compression with THIS mileage chaps my bottom!!!!
seals etc might tend to dry up. especially stuff in the head. store it with a good synthetic oil for sure...