Rednels

I race a C4 vette. I just got done putting a new engine in it because I threw a rod at Road Atlanta in March.

So I put a new engine in, dynoed and tuned it and it was fine. Packed it up and headed to Road Atlanta for the NASA event in June. I did 2 laps in test and tune on Friday and was black flagged for smoke.

Turns out oil was leaking badly from the back of the motor and being slung on everything including the header. It does not leak when idling or sitting, only when its turning 3-4k rpm or higher.

I know its either the rear main seal or oil pan leaking. Problem is, I have dropped the tranny and flywheel off and I can not tell where its coming from.

With a C4, the motor relies on the tranny and C-beam to hold up the back of the motor. Would it be safe for me to put a block of wood under the oil pan with a jack to hold up the back of the motor and start it without the tranny or exhaust on?

Is there a better way to find this leak?

Thanks,
Eddie

rbl

Can't answer the question but are you real sure it is the rear main or pan? You would have to pressurized the case to cause that.

Mine did a similar trick ... (different car) and it actually turned out to be the valve cover in the back. Seemed at high RPM there was enough oil up there to cause it and to the extent that it actually got on my rear tire and I spun the car in a low speed corner! (at the track).

To your question ... wonder if you can get a hook on the engine top and pick on it to hold it up in addition to the block on the pan???

ScaryFast

Eddie, I don't know if I would try running the car like that, but thinking about it logically it may be OK at low RPM. Not sure I'd want to try opening the throttle, but I'm guessing that's what you're trying to do. I do like the idea of having a cherry picker holding it up as well, it seems it could easily vibrate the jack and fall which would cause more damage.

That said, I am sadly something of an expert when it comes to C4's leaking oil, so if you haven't already tried, look in these places:

1) Rear of the valve covers (already mentioned), specifically passenger side. It's often hard to get the covers to seat well.

2) Oil pressure attachment to the head. I've seen these leak on LT1's.

3) Front and rear corners of the pan. Did you silicone them? Lots of guys have seen them leak there, although I personally have not on my car

4) is the motor bored out? This is the trickiest one. If you have done internal work, sometimes the rear 3 bolt holes (oil pan to block) can get nicked. they are blind holes, so if you nick one the oil will weep THROuGH the bolt threads and run down the block, spraying everywhere at speed.

5) Dipstick hole in the block if you have excessive crankcase pressure

I've even had oil leak from my pan drain hole. And of course only when hot.

You can also buy some dye ($8 a bottle) that you put in the oil. Run the car and turn out the lights, shine a black light on the block and you can see where it's coming from.

Hope this helps.

jaa1992

In addition to Scary's list check where the dipstick goes in the block. Ooops, just re-read his post he covered it

Sometimes it can be a front oil leak as well.
Good luck with it!

rbl

Yes ... definitely the dye. We use that on the AC engines and it will pin point the leak for sure. Need a black light.

The local Caterpillar dealer will have one ... probably can borrow or get one of the mechanics to come over in the eve with it. Works slick and takes all the guessing out.

BrianCunningham

Don't put a block under the oil pan, you'll crush it

You can safely pull the c-beam trans and clutch off w/o further bracing it.

I've done it more than once.

also check the back of the intake, it's notorious for leaking.

Rednels

Thanks for all of the advice. I will try to rig up something with the engine hoist instead of a jack.

Are you sure? If I don't jack mine up and support it, it will first crush the distributor, once that's removed, it will lean far enough to put the valve covers into the firewall.

I do know that its coming from either the rear main or oil pan. I can see the back of the intake, valve covers, and heads and its all dry up there.

One way or another, I will get to the bottom of this.