95 Z28 6M, 56,800 miles. The car runs fine, with the exception of an occasional misfire at temperature. It doesn't run hot, and there's no white smoke coming from the exhaust.

I am noticing a drip of oil under the car after driving that I didn't notice when I bought the car. It's like a drop or two on the garage floor, hardly noticeable. It looks suspiciously close to where the trans meets the block. I am guessing rear main seal?

Also, something I should have seen before I bought it, but didn't. The engine was warm at the time so I didn't pop the radiator cap, but I did inspect the reservoir, and all seemed OK. After a couple of hundred miles and checking the fluids I am noticing some oil in the reservoir and in the radiator. It's not a milky foam, but it's definitely thicker and not clear, and feels a bit oily. Again, a guess is probably head gaskets. I did a look around the engine and I am not seeing anything leaking, but then again, I didn't tear anything out, just moved wires and hoses looking for trouble spots. The engine oil looks great and is at an appropriate level.

I wasn't prepared to drop the engine yet, so I would like some advice on how to proceed. I am confident that I can do the work myself if I take my time and have resigned myself to possibly needing to drop the transmission, but I planned on running some dye through the motor to be sure of the source of the drip before doing so.

Can I, or more importantly, should I, try to replace the head gaskets without dropping the engine? Should I have the heads checked once I have them out of the engine? It's not overheating, but I want to be sure that they aren't cracked. Is it worth doing other things while I am in there? The OptiSpark looks OEM, but the spark plug wires are definitely aftermarket.

Any advice from the LT1 gods is welcome and appreciated.

 

As far as the oil drip, three possibilities. Rear main seal, trans input shaft seal, intake manifold to block leak.

The T56 has an inspection plate/dust cover at the bottom. The starter nose pokes through it. Pull the plate and look for oil inside the bell housing. Motor oil from the RMS, red ATF from the T56.

Almost “normal” for the LT1 intake manifold to leak oil on the back of the block. The bottom of the intake is sealed to the rear wall of the block with RTV. Dries out from the heat of the EGR tube that connects the passenger side rear corner of the manifold to the #8 runner on the exhaust manifold. Take a clean paper towel, reach back in the area of the tube and wipe the back of the block. If it’s leaking there will be oil on the paper towel.

http://shbox.com/1/egr1.jpg

Could also be a leaking valve cover gasket at the back, or even the fittings and sensor for the oil pressure.

http://shbox.com/1/op_sensor.jpg

 

Thanks a million, Fred.

Any advice on the head gaskets?

 

Oil in reservoir (read not coolant in the oil pan) can be due to the internal radiator oil cooler leaking. You can buy test kit to test radiator fluid for oil contamination. If this is the case than a replacement radiator and complete coolant flush.

Rear oil leak can be as Fred describes. Most "common" is rear intake manifold leak. If so remove manifold and replace gasket and use new RTV. I always use Permatex black "ultra" RTV. I prefer the FelPro "Printo Seal" intake gaskets.

 

Awesome advice. I have to remember to look for the most obvious things first.

There is definitely coolant loss from the reservoir, and the radiator is full but contaminated which is why I was thinking that maybe it was burning some coolant. But, like I said, no white smoke or smell. I will try the test kit first before diving headfirst into a major repair (no pun intended). I would much rather pull an intake and reseal it and fix a radiator than drop a transmission or pull heads. Maybe I will get "lucky."

I read somewhere (and please, don't hate me for asking this) that LT1s with the T56 didn't all have oil coolers. Is that true?
I just answered my own question. I found the lines on the car and the original build sheet that came with the car confirms that this vehicle did come with the engine oil cooler. Hopefully, this is the source of my issue with the contaminated coolant.

I will try and keep you all posted.

Thanks again for helping a newbie!

 

http://shbox.com/1/oil_cooler.jpg

 

Thanks! This is perfect. I went out today based on your earlier message and bookmarked a bunch of stuff on the shoebox site. It's definitely my new bible.

 

Due to it's negligible performance and possible failure causing cross contamination, most people remove the oil cooler.

 

Unlike most people, the oil cooler was still in place and functional when I sold my Formula after 27+ years. The radiator had been upgraded to a Griffin aluminum unit in 2000, so maybe that avoided the issues. The shop that built the 800 HP LT1 engine felt it was worth keeping. Also worth noting that the design was changed in 1995 model year, and I think GM may have eliminated it completely in 1996. I don’t know if the Formula's buyer has kept it, I'll have to ask.

1993-94 design:

https://www.camaroz28.com/g/picture/8154201

 

IMHO an external oil cooler outside the radiator is ideal. No internal radiator tank issues on that type of setup

 

Thanks, everyone. If it is the oil cooler will I have to replace the radiator or just bypass, flush and fill? The radiator isn't leaking. I started researching new radiators last night just in case. I will certainly consider bypassing it as an option. I plan on doing some performance mods, but this is going to be a fun street car, not a strip or autocross car so the oil cooler probably isn't even necessary in my case.

 

The oil cooler system circulates coolant, not oil. The only way oil can get in the coolant is for the "cooler" unit bolted between the engine block and the oil filter to develop an internal leak. If that is the source of contamination, all you do is bypass the coolant flow from/to the radiator. Shoebox's coolant system hose diagrams show the bypass hose that was installed on cars without the oil cooler - see part #16:

http://shbox.com/1/95-97_hoses.jpg

 

My approach to minimizing concerns about oil temperature:

 

Excellent, that makes things clear. Thanks!

 

the oil cooler lines going to radiator go to a sealed tank inside the side tank of radiator. If that inside tank leaks, than engine oil gets into coolant....and conversely coolant could enter oil system. disconnecting the engine cooling lines from radiator would stop that but not fix the leaking oil tank inside the radiator then coolant would start leaking "out" the open fittings where oil cooler lines were on radiator "if" that tank is in fact leaking. If that was the case you will need a new radiator

your choice on whether to reinstall the external cooler or not and use a bypass hose instead.