New rings, blowby pushing oil out the dipstick tube...

[HallenTi]

I have a LOT of oil being pushed out the dipstick tube, due to new rings in one repaired cylinder that have not yet seated. They are moly rings, so I understand they may take longer than cast iron rings to seat. I have done the "accelerate from 30MPH to 50, then coast back to 30, then do it again 10-15 times" to help them seat initially. I am thinking of temporarily making or buying some sort of an "oil separator" to be used in place of the dipstick to catch the oil rather than having it squirt all over under the hood. I'd of course check the oil very often in this case after removing the unit from the dipstick tube. Any thoughts on how long it may take to seat the rings? Also, the engine had a small amount of oil from the dipstick tube before it was replaced with a new one (solved that problem at the time). I hesitate to plug the dipstick for fear that the internal pressure might blow out a seal, like the rear main seal, which I do NOT want to start giving me trouble! Thanks!

 

[Jeb]

I don't believe this is a normal condition that will fix itself over time.

 

[Aurora40]

does your PCV valve work?

 

[tnovot]

Moly rings can take several thousand miles to completely seat but it's hard to imagine that new moly rings in one cylinder - or even in an entire engine - would cause enough internal pressure to force a "LOT" of oil out the dipstick.
I agree with both Jeb and Aurora. Something (else?) is wrong. I'd also check the PCV.

 

[grapeknutz]

Moly rings can take several thousand miles to completely seat but it's hard to imagine that new moly rings in one cylinder - or even in an entire engine - would cause enough internal pressure to force a "LOT" of oil out the dipstick.
I agree with both Jeb and Aurora. Something (else?) is wrong. I'd also check the PCV.

Or the ring was broken when it was installed.

 

[Ken Anderson]

Moly rings can take several thousand miles to completely seat but it's hard to imagine that new moly rings in one cylinder - or even in an entire engine - would cause enough internal pressure to force a "LOT" of oil out the dipstick.
I agree with both Jeb and Aurora. Something (else?) is wrong. I'd also check the PCV.

Normal "seat time" on moly rings is 30 seconds or 30 feet-you may have installed them wrong.

 

[HallenTi]

PCV valve was replaced when the repairs were done (Chevrolet part). I checked it with the engine off for "clattering" when shaken, and there was clattering, and running there was a lot of suction on the valve as expected, so the tube between the valve and the plenum must be OK. I made a "catch can" to see just how much oil was coming out (I realize that saying "a lot" in my original post didn't mean much!). Over a 10-15 mile period, the catch can catches about 8oz of oil. Seemed VERY excessive to me when actually measured. I am afraid to just stop up the dip stick tube, as the pressure might (I assume) cause some other problems. I realize that on normal engines there is some pressure, and I expect if you left the dip stick out (or measured it as I have) there would be some oil and some positive pressure.

Removed all spark plugs and checked the repaired (driver's) side. #1 = 172, #3 (repaired) = 200, #5 = 180, #7 = 185. This was dry (no added oil). Didn't do with oil. I'd like some suggestions as to how to check the actual crankcase pressure, without buying some specialized equipment. I adapter my fuel pressure gauge to it, but got no reading (either I can't use it in that way, or the pressure is lower than I thought). If it is lower than I thought, then I am wondering if using the catch can to measure how much oil is lost is a bogus idea, as maybe in ANY engine, with oil flying all over in there it will fine the path of least resistance and would come out regardless of the condition of the engine. Any thoughts? Also, I plan to replace the dipstick again (have replaced it before) to see if that seals better, but in the mean time, would placing a restruction (ie: plug) in the tube with the stick removed prove detrimental to seals, etc. (guess that depends on whether there is "too much" pressure in the crankcase to begin with, which brings me back to a way to measure that...). Thanks for any more thoughts on this.

 

[C4Tom]

Wow... tough call. I'd say plugging it should not cause any problems. That said, if there are other problems... it could cause a problem. Since the crankcase evacuation sytem doesn't seem to be working properly, you need to find out why. If it's working, why isn't it able to keep up. Perhaps there is a windage tray wasn't reinstalled during assembly and that is causing too much splash near the tube, with blow-by pushing it out the tube. There shouldn't be enough pressure to blow the dipstick out of the tube. Are you breaking in the new rings with synthetic oil?

Just some thoughts of mine.

 

[HallenTi]

I hadn't thought about the windage tray... I will have to look into it. The dipstick doesn't "pop" out of the tube, but is doesn't stay down tightly either (I have had to replace it before because of a bad seal between the stick and the tube, but the leak wasn't nearly as bad then as now). But, I do get a fair amount of oil out the tube now.

Plan "A" is to bring it to the local Chevrolet dealer and ask if they would just give me their opinion of the amont of blowby (I am far from an expert). If they say "Whew! That is WAY too much!" then I will have something more for the actual shop that did the repair. If they say it could be considered normal for one with 151,800 miles, then that's fine too - just need the information. I don't want to condem the repair place if this is normal.

In either case, I will order a new dipstick. I was mainly concerned that if this was excessive that plugging the dipstick tube (at least temporarily until I get a replacement) might blow something else out - I don't need any more trouble! I have had a LOT of trouble with the rear RTV seal on the intake manifold, and am wondering if there is excessive pressure, if that could be some of the cause. The car isn't worth (to me anyway) spending for a complete rebuild to solve the blowby problem (if it really is excessive). I do know that the PCV valve is working, and that the clean-air tube to the passenger side valve cover is OK (replaced it as well recently due to cracking).

I am not sure what type of oil was used after the rebuild of the single cylinder... something else to ask the shop.

 

[jmccloud]

Blow-by

I'm not familiar with the intake set up on your year, but in older year V8's there was a 'heat riser' passage from the center of each head that connected the exhaust to the depths of the intake manifold. This heated the intake and assured vaporization of the gas. There was even a 'heat riser' valve downstream of one of the exhaust manifolds that restricted flow (usually of the passenger side) until the car warmed up.
Is there such an intake 'heater system' in your manifold? If so, the intake gasket at that passage (at the center of each head between the intake passages) may be leaking and allowing exhaust to pressurize your oil plenum volume (under the intake, under the rocker covers, the crankcase, etc.)
I had this on a boat once and we were forever figuring it out. Once we pulled off the intake, the exhaust traces (soot) were visible where the gasket was broken.
My '95 LT-1 doesn't have this.
Hope this helps,

 

[rrubel]

FWIW, my mechanic (who's worked on Vettes longer than I've been alive) was telling me today that the older small blocks had a marginal PCV system to begin with and it didn't take much blow-by to get oil to come out the dipstick. Does yours do it all the time, or just at higher RPMs? Mine is doing it when I really get on it, and the whole shortblock was just rebuilt (pistons, rings, everything). I kept popping off the oil cap until I got a better one (I have a press-in on GMPP covers) and now the pressure is relieving itself via the oil tube. I'm going to try a couple things, including a 2nd PCV valve if I can find the right kind of oil cap.

He said that removing the dipstick and plugging the hole was one solution, but that it would probably start leaking under the valve covers or push out the breather if pressure got too high. You can also get a screw-in oil dipstick (the cap is threaded) and tube, designed for high-compression engines.
[RICHR]

 

[I_R_DA_ONE]

Hallen
there is a lot of things that could cause your problems...
1. to much oil....make sure you are putting in the correct amount of oil
2. the PCV valve sticking
3. blown head gasket..check all cylinders compression..should not vary more than 10% any more than this it will cause the motor to shake or vibrate
4. broken oil ring in one of the cylinders.....this will make it smoke [blue] look for oil on a plug .....may be fouled.. check all of the cylinders
5. a leak in the intake manifold gasket where the EGR valve is located
6. check for water in the oil....
I hope this helps
Mike R

 

[Jeb]

A quarter of a quart of oil in 10-15 miles is certainly excessive. You would empty the crankcase in about 300 miles....if the engine lasted that long, which it wouldn't.

May I ask why the ring was replaced in the first place?

You said there was "a lot" of suction at the PCV with the engine running. I don't know what you mean by "a lot" but generally there isn't a great deal of negative pressure there, just enough to evacuate the system.

You've got something going on in there that ain't right and replacing the dip stick with a catch can won't correct it, it will just hide it until whatever is happening finds another weak link in the system to prey on. Chances are, when that happens, something that is both very important and which rotates very quickly will be involved.

Get it to a good mechanic.

 

[vette-dude]

Individual Piston rings have a tapered side that has to be installed on the piston facing the right direction (per the instructions in your ring set). Also the end gaps must be staggered on the piston when installed in the cylinder. I feel that most likely you either have a broken ring or the taper of the individual ring was installed upside down or the last thing would be the staggering of the ring when installed. The other thing I could think of is that the dipstick is not reading correctly and you are overfilling the crankcase. How many quarts of oil does it take to raise the oil level to the fill mark? 5 qts with a filter change should read full.

One other factor is the cross hatch pattern on the cylinder walls for moly rings. It has to be super fine to get the rings to seat properly. If the cylinder walls were honed and left rough like you would do for cast iron rings the molys will never seat and you will have blowby and pressurize the crankcase. Just some things to consider.

Randy

 

[HallenTi]

I'll answer several of you in one post.

The reason for just one cylinder being redone was a nut dropped into the intake port of #3 when the intake manifold was removed/replaced due to the "usual" oil leak in the RTV at the rear of the intake (I dropped the nut I am very (VERY) sorry to say!). #3 had a new piston, rings, connecting rod, rod bearing, new valuves (for good measure), new valve guides, and a hone-job. All parts were GM (Chevrolet) and the work was done by a local shop that farms out engine work to an engine builder.

The oil level is correct. When I change the oil (and always the filter) I put in just under 5 quarts and the stick reads full. While I didn't add the oil myself this time (after the rebuild) the same dip stick was used, and I have checked the level and it is fine. Not overfilled as far as I am concerned.

The PCV valve is brand new GM part. By "a lot" of suction, I mean when the valve is removed from the gromet in the drivers side valve cover with the engine running and I place my thumb over the open end of the valve, there is a good deal of manifold vacuum there and it seems normal when compared to the various times I have done that in the past.

The drivers side head gasket was replaced, and I myself checked the compression on all four on the drivers side (did not have the facilities to do a leak-down test however). All were between 180 and 202 so I feel they are OK as far as compression is concerned. Did not (but will) check compression on the other 4 sometime soon just as a cross-check.

A ring could have been broken when installed I suppose, but I wold expect to see a lack of compression, and didn't. Don't know if ring(s) might be upside-down, but again would think hat the compression would be compromised and it doesn't appear to so.

I have not checked the EGR to manifold connection, but sure will! When I replaced the RTV on the intake, I did np remove te EGR valve (didn't need to, even thought the Chevrolet manual said I should) but I do not know if the shop that did the recent work might have. I will take a look.

I believe the oil is straight mineral oil, not a synthetic, but I haven't asked and will.

I did not see the hone-job but given the good compression on the rebuild cylinder, I assume it is OK given that is was (supposedly) an experienced builder. I did note some smoke for a few miles initially when accellerating/decellerating, but now I don't see any.

The engine seems to have about the same power as before, so the internals seems to be working fine as far as I am concerned.

I don't find signs of water in the oil. When I used the catch-can (which may not have been a good idea to indicate a problem, as I am sure oil/air will go out whenever there is an opening, and since I have never done that before on any car, can't tell if it is normal or not. Would like to try it on another similar car to compare it! There was no sign of water in the oil from what I could tell in the catch-can.

The exhaust "cross-over" on this engine isn't mid-manifold as in some of the previous years, but there is a steel pile that connects from the exhaust manifold to the passenger side, rear of the intake, and those connections appear to be tight. I do think there is an "exit" port in mid-intake into the block, but since I didn't do the intake reinstall, can't tell how that looks and assume they did it correctly. Hmmm....

Tim

 

[jr7221]

compression and oil rings have to off set to seal properly, if the gaps are lined up they will by pass....

 

[HallenTi]

I assume if you had a problem with the ring gaps aligned with each other, you'd see less than normal (less than expected anyway) in the suspect cylinder, correct? Also, if they were in upside down, would you see something similar (maybe not as pronounced as the gap alignment, but something noticable)?

 

[I_R_DA_ONE]

If you have a broken oil ring ,,,,it will smoke out the rear pipes in puffs and also out the intake PVC opening as well.... You say that it smoked a little when you frist started it up....then it cleared up....this is normal for a fresh rebuild of the engine...the only thig I can think of would be a cracked head....one that opens the crack when it gets hot...or a head bolt that is not torqued correctly....
Mike R

 

[HallenTi]

Mike,


Thanks for the ideas. I am returning it to the shop Thursday for a leak-down test, to see what we have. I did the compression check myself on the bank that was removed (drivers side) but the leak-down test will tell us more. The head had to be repaired (welded, then machined, then a $60 "pressure test" done to make sure it was OK before it was put back on). I will mention the oil rings and maybe the head bolts needing to be retorqued. Has anyone here had a leak-down test done on an engine similar to mine (L98, 1990, 151,000 miles, reasonable care). I will let you know...