What is Turbo Blow By and how bad is it that a machine would have it? Caterpillar has a used machine that is described as having blowby but is listed as normal ?
A turbo leaks oil and leaks at the housings.. neither one is "normal".. An engine has blow-by.. that's the engine compression going past the rings and into the oil pan.. There is a blow/by tube on an engine that releases the pressures & gases along side the engine.. [smoke] There is an acceptable amount of blow-by by industry standards.. an excessive amount of blow-by means, in most cases the engine is shot and in need of internal service.. rings/pistons.. Another quick telltale is, excessive smoke when you remove the oil fill cap while the engine is running. I hope this helps..
That's exactly right, but just a little more info: Turbo bearings are lubricated and cooled by pressurized oil from (and back to) the engine. The pressurized oil makes a circuit. There is a turbo bearing or bearings and seals on each side of the bearing (exhaust side and intake side) to keep the pressurized oil in. There is a minute, but allowable, amount of oil which normally gets past the seals, however if the seals leak an excessive amount ....which could be caused solely by just aged and leaky seals, or could be caused by excessive play from worn turbo bearings in a high-hour machine. In either case, if excessive oil is seeping past the seals it will coat the inside of the intake or exhaust side piping. If excessive oil leaks into the intake side, oil coats the inside of the turbo piping and gets into the intake and burns, looking like an engine burning oil. If excessive oil leakage seeps past the exhaust side seals, oil gets into and burns in the exhaust manifold or hot muffler. A lot of times when the engine is shut down and sits a while, then oil slowly leaks past the turbo seals and when it is started you might see a 'puff' or cloud of smoke. But sometimes it could be worse too, while it's running. Then you need to do something pretty quick. The cure is to remove the turbo and rebuild it with new bearings and seals (hopefully the shaft is in good condition) ...or replace it. Once you have the turbo off, if you have access to a press, the job usually isn't that hard. You can tell right away by wiggling the turbo shaft and see if there is a lot of play or not (some is normal). There might be a rebuild kit you can buy, I'm not sure for your unit. When finished, remove the intake pipes if they are heavily coated with oil and clean them and as much of the intake as you can get to with solvent. You're lucky it's just the turbo leaking oil (and not the engine).
And if excessive or catastrophic amount of oil leaks into turbo's intake side, you can have a runaway, where the engine starts eating its oil, and is damn near impossible to shut off...
I would be surprised if a Cat dealer listed "turbo blowby" as a parameter. I would expect that they would list "blowby" and as such that would be the amount of fumes coming from the crankcase/valve cover breather tube, as described above in post #2 An engine has blow-by.. that's the engine compression going past the rings and into the oil pan.. There is a blow/by tube on an engine that releases the pressures & gases along side the engine.. [smoke]
I agree. So what you should try to do if you are interested in this machine is to isolate weather the blowby is from the engine or turbo and how bad it is. Like the pumpguysc said, some engine blowby is normal, on cars/trucks, that's what the PCV system is for (to reclaim blowby gasses and re-burn them, rather than dump unburned hydro carbons into the atmosphere like they did up to the early 60's on cars), however, excessive engine blowby means bigger things: If it's minor, and the dealer is listing the condition to be fair and transparent, it might really be a non-issue, something you could potentially live with, with little concern for years if it isn't too significant ..depending on your use. I've had several engines that had excessive engine blowby that I used for years and eventually sold the car/truck or whatever it was and the other owner got a lot of use out of it. Really excessive blowby probably means new rings (and a whole engine rebuild mostlikely) to bring it back to spec. Could also be other things to like a leaking headgasket or cracked head/block, but usually worn rings is the culprit. Turbo blowby would be a LOT less work and expense if it can be proven that's what it is. Probably would be a great idea if you could personally talk to the tech who did the inspection and see what he remembers and what his take is. Or maybe ask the dealer to take it back to the service dept and dig into it a little more for answers ...assuming you are truly interested in buying it.