Blow by

[Frogman226]

There are several 5 tons on gov planet that state minor blowby, should this be a deal breaker? Some of these trucks only have a few thousand miles and you would think the engine isn't broken in yet. Anything would be helpful. Dumptruck is awesome, just looking for another one

 

[Suprman]

Alot of trucks have a little bit its not abnormal. GP usually has a vid of the vent tube. If the engine sounds funny and you see strong pulses blowing out it could indicate a ring or piston issue though.

 

[Frogman226]

Thanks, so minor that I can't make out on the video shouldn't be a problem, or at least I could consider the vehicle. I heard there was an issue with lmtv's that they over fill the oil which could cause vapor to be seen. Could that be the same issue?

 

[61sleepercab]

Blow by can be ok if engine has enough compression to start on its own without either. A single bad cylinder would cause a miss, or lazy cylinder. Also rings may be dry from storage and may be stuck on piston. Bottom line some blow by can be normal as long as engine will start and has power when running. Mark

 

[porkysplace]

There are several 5 tons on gov planet that state minor blowby, should this be a deal breaker? Some of these trucks only have a few thousand miles and you would think the engine isn't broken in yet. Anything would be helpful. Dumptruck is awesome, just looking for another one

Mileage and hours mean very little on military trucks as hour meters and odometers gets swapped out rather than repaired.

 

[WillWagner]

How do they know? Did they put a manometer on it and load it?

 

[todds112]

How do they know? Did they put a manometer on it and load it?

It's a "subjective visual" check. They take a video of the oil filler off and the truck running.

Personally, I think if a MV doesn't have some blow-by, it ain't running.

 

[gottaluvit]

I noticed some GP sites actually video the vent hose. I would trust that better so only one opening. If they take the cap off there is the vent hose plus the cap lovation open and you arent seeing it all. Just my $0.02 U.S.

 

[Rmtaunton]

It's a "subjective visual" check. They take a video of the oil filler off and the truck running.

Personally, I think if a MV doesn't have some blow-by, it ain't running.

No they don't take oil filter off

 

[todds112]

No they don't take oil filter off

"filler". Oil fill cap.

 

[M543A2]

Some blow-by is normal. In fact, it assures that moisture is getting vaporized and vented out of the engine.

 

[WillWagner]

Some blow-by is normal. In fact, it assures that moisture is getting vaporized and vented out of the engine.

No moisture involved, IF there is, there are bigger issues. You can't, in 99% of most cases, tell how much blow-by an engine has just by looking at the smoke out the breather, unless the tube is whipping around like an air hose with no end on it, whistling or has a very forceful stream of smoke pushing out the tube and covering the ground like fog, this is usually accompanied by a fair amount of oil on the ground and oil leaks on the engine. ALL engines are different when it comes to the vapor/smoke out the tube. The engine makes it's own wind and pressures and it needs to go somewhere or things happen. there can be two identical engines, new, consecutive s/n's right off the assembly line and the visible vapor will be different, same goes for a rebuild, two of the same engines, built with the exact same parts by the same person, and they will be not the same. The crankcase max spec for an 855 Cummins has been 18 inches of water column since forever, it is the same for the latest and greatest stuff from Mother Cummins with the exception of the 15l ISX having to use a .354 orificed fixture as opposed to the .302 used by all the other engines. The normal measured cc pressure is between 2 and maybe 5 inches. At that rate, there is a significant amount of vapor out the tube on some and on some, not so much. If the cc pressure gets above the 8 inch or so mark, that's where you start to see the above stated issues like the whistling, hose whipping around and toolie fog/oil on the ground on all engines, well Cummins stuff anyway. It is NORMAL to have drops of oil on the ground after flogging the engine and shutting it off. Idling/no load is the worst thing for an engine. This will cause excessive oil out the breather, not blow-by, and slobber out the exhaust.

In a nutshell i'm sayin' unless you are leaving a smoke screen behind you while driving or abating mosquitoes at an idle, don't hear loud banging from the engine, or have water/coolant out the tube, don't worry about what the smoke looks like down there, just drive the thing!

 

[WillWagner]

For your viewing pleasure.. This engine has a cracked piston. The CC pressure is very high, wouldn't want to even try hooking a monometer to it, it would blow the fluid out of it if it were a mechanical one and if a transducer type of tool was used, it would be beyond the measuring capabilities. This is a 505 cid C series engine....the same style as are in the A2 trucks.

 

[JohnnyBM931A2]

For your viewing pleasure.. This engine has a cracked piston. The CC pressure is very high, wouldn't want to even try hooking a monometer to it, it would blow the fluid out of it if it were a mechanical one and if a transducer type of tool was used, it would be beyond the measuring capabilities. This is a 505 cid C series engine....the same style as are in the A2 trucks.

View attachment 573456

That's brutal

 

[WillWagner]

This is normal CC pressure. This is from a 2009, 400 hp 15L ISX with 600k on it. I did not get a pic of the smoke coming out of the tool, kinda hard to get it when the truck is in motion, but I will try the next time I do a blow-by check. The smoke is visible and, since it is measured out of an orificed fitting, it is leaving the engine at a high rate of speed, but as you can see, it is not pressure, the measurement in in in of H2o.