Mechanics

OIL BLOWING OUT OF DIPSTICK TUBE

Chevrolet Corvette

1993 Corvette manual transmission with new GM Goodwrench 350 cu in LT4 engine, LT4 Hotcam, Canton roadrace oil pan, and headers. Approx 1200 miles on the engine. Oil pressures are 40psi at idle and 60-65 psi at WOT. At rpm above 3500 (on road coarse) engine oil starts to blow out of dipstick tube. As the engine warms up and the higher the rpm the more oil is blown out. New working PCV valve. Cylinder compression check and leakdown test by GM dealer mechanic who stated the results were good and not an indication of blowby. Leakdown of between 12 and 15 psi for all cylinders (done dry, no oil added to cylinders during the test and the engine was warm but not at operating temps). This is a track car only. What do you suggest I do to alleviate the problem? Aside from this, the engine runs strong. Thanks, in advance for any help! --Ralph
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Akcelr8
November 26, 2007.



Might sound crazy, but RTV the cup in the dipstick. Worked for me once!

Merlin2021
Nov 26, 2007.
I'm concerned that if it's excessive crankcase pressure, that if I block that escape I'll only end up blowing seals somewhere else. There's enough pressure to blow the oring-sealed dipstick up a half inch to allow the oil out! I was thinking that maybe the existing PVC system isn't adequate at sustained higher rpm (3800 - redline) and maybe I should vent both valve covers (in stock form, only the right side is vented to the throttle body) to a breatherd catchcan. Does that make sense?

Tiny
Akcelr8
Nov 26, 2007.
Yes it does. Would definatly help, mine did not have 40 psi at idle. But was not built to either, must be a high volume.

Merlin2021
Nov 26, 2007.
Thanks Merlin, for the quick response. It's always good to get some confirmation when trouble shooting a problem. It's a standard volume/pressure Melling oil pump but those oil pressures are normal for this application. I'm still concerned as to where the crankcase pressure is coming from. Is 15psi leakdown within a " good" range? Some have said that it shouldn't be greater than 5-8 psi. It is a new engine and maybe the compression rings haven't completely seated yet but I thought with 1200 miles that shouldn't be the case. If the pressure is " normal" then is this all due to a windage problem? Any thoughts? By the way, the engine doesn't smoke or burn oil. Thanks again!

Tiny
Akcelr8
Nov 26, 2007.
What's the vacuum reading on this motor?

Merlin2021
Nov 27, 2007.
Good question! I haven't done a vacuum test. I just did some quick research about vacuum testing and see where this might be very helpful. I'll do it (or have it done). It might be a few weeks before I can get to it but I'll let you know what I find out. Thanks again and stay tuned!
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Tiny
Akcelr8
Nov 27, 2007.
OK, I did some further research and found that if I had any manifold vacuum problems I'd have a variety of indicators such as reduced vacuum assist in the brake pedal, check engine light, ruff idle or the MAP sensor would through a code. None of those things are occuring. Also, how would poor manifold vacuum affect high crankcase pressure? I'm not trying to be argumentative, just trying to understand. Thanks again.

Tiny
Akcelr8
Nov 30, 2007.
Low vacuum could also indicate rings or valves. Did you install a deep sump oil pan? Did it have a baffle in it?

Merlin2021
Nov 30, 2007.
I have a 7 quart Canton Road Race Pan that has wings (not deep pan) with baffles to keep oil under the pickup under lateral, braking and acceleration forces. As for the rings and valves; wouldn't that show up in my leakdown and compression checks? That's why I thought the vacuum test was redundant to what I've already done. Could high oil pressure from the oil pump be causing my problem? I'm running 40psi at idle and 60-65psi at WOT. I thought this was within a normal range but know I'm not sure. What do you think?

Tiny
Akcelr8
Dec 3, 2007.
It's high at all ranges, race engines top out like yours but are a short life engine! You may need to replace this oil pump! I was thinking baffles, but if it has em, the pump must be too tight!

Merlin2021
Dec 4, 2007.
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