tracing blowby

[DeepRoots]

found a local 7.3 w/ turbo
tons of blowby, looks like the engine is on fire
low power too.... alot slower than my truck, and similar setups (turbo'd w/c6).

to find if it's the valves/rings/turbo related, I assume:
1. compression test
2. leak down test
3. pull the turbo off and see if the problem persists

any other suggestions?

seems like a nice old truck, and the price is right (I'm looking for a extra work vehicle, but don't want a moneypit).

thanks
drew

 

[Mr_Roboto]

Where are you seeing the blowby? With the oil cap off or does the engine have a road draft tube? Or is it coming by the gaskets?

 

[Diesel JD]

Sounds like it is smoot worn out, they can have a lot of blowby before the compression and power goes, but when it's low on power too....... That having been said, if it's cheap, and you are a good home mechanic, you can get yourself a set of rings, and the pistons may still be useable.... if it just needs rings, and you do your own work, figure about $350, figure more if you bore it, which may be knocking on cavitations door, still more if you do it right and sleeve. The truck may be worth it fo rteh turbo and parts alone, or if you want a project. You could check compression, but I feel comfortable saying with that much blowbyits rings, unless it does have a road draft tube, in that case, you're going to see a lot of blowby even on a relatively healthy engine.

 

[towcat]

Hang on for a second here guys....
blow-by is a fact of life when you are dealing with high compression motors. Blow-by at idle is perfectly normal. My usual way of testing to see if a motor is washed up or not is to open up the oil filler cap and fire up a WARM motor. It is perfectly normal to see a thin to moderate trail of smoke coming out of the oil cap. Bring the motor off idle to 1k rpm and then observe the smoke output. If none, you are in good shape. If you do still see smoke, you have a problem. Before you start stressing out, do a little basic PM. change out the CDR valve( do not clean it) If you have a RDT installed, then it is perfectly normal to see smoke or "the engine looks like its on fire" Also, if you are leaking oild profusely, and you have a RDT already, its a really good indication your rings are done.

 

[DeepRoots]

back to the turbo.
I've seen on smaller motors, where a turbo has an oil/exhaust seal leak and it pressurizes the crankcase... is this ever a problem on these?

I'd feel really stupid if I re-ring'd this motor only to find out the problem still exists. Since this is to be a spare truck, I wouldn't mind re-ringing/redoing head gaskets etc as time isn't an issue.

Is there anyone in Ga area that has a good running 7.3? all the ones I've driven were a little beat up (my own included) I'd like to see what the average mark feels like.

 

[Exekiel69]

Also, if you are leaking oild profusely, and you have a RDT already, its a really good indication your rings are done.

Calvin I have a jasper with 21k and rtd that does drip oil (one or two) everywhere I park it, also I noticed some oil consume lately. Does this apply to what you said or is it just marking it's territory :Sly

 

[zigg]

Don't forget the heads. A lot of blow-by is associated with worn valve guides/seals. Although the intake on these engines has way less vacuum than a gasser, oil can still be pulled into the cylinders on intake stroke when the seals and guides are worn.

If the engine has bad blowby, is low on power etc, and it consumes quantities of oil, then it is a pretty positive indication that the overall condition of the engine is poor, and it will not only need rings(and most likely bored to fix out of round and taper in the cylinders) but also heads gone over.

Zigg

 

[towcat]

Don't forget the heads. A lot of blow-by is associated with worn valve guides/seals. Although the intake on these engines has way less vacuum than a gasser, oil can still be pulled into the cylinders on intake stroke when the seals and guides are worn.

If the engine has bad blowby, is low on power etc, and it consumes quantities of oil, then it is a pretty positive indication that the overall condition of the engine is poor, and it will not only need rings(and most likely bored to fix out of round and taper in the cylinders) but also heads gone over.

Zigg

zigg-
i agree with you on the valve guides/seals. problem is, when you are looking at the vehicle the first time, you are going to have to forgo the long term tracking stuff. Now if you do hear woofing from the intake and woofing from the tailpipe, those are clear indicators of valve/guide issues.

ez-
i've seen a few of the RDT conversions where oil started leaking out of all the seal and gasket areas. "JPR" had a good idea of using the RACOR rdt filter assy where it helps to remove some of the oil in the blowby.