Mobil 1 15W50, 1.3k mi OCI, 7k mi, C7 Corvette Z06

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So, I had the LT4 rebuilt last year after it lost compression in one cylinder due to a bad tune from what I thought was a good shop. I spent most of last year dealing with the excessive blowby of the new engine due to the larger than normal ring gaps. So we tried different catch cans but they still filled up too quickly. We ended up installing an engine air oil separator that drains the contaminants back into the oil pan rather than have to drain it. That could mean needing to do more frequent oil changes.

Here's the oil samples going from earliest to latest (right to left in the image). The earliest is UOA is from the engine break-in oil on the dyno. The second sample is from changing the oil after picking it up from the engine builder and driving it home. Finally, the most recent UOA was after a track event (2-3 track hours and the rest are street).

I'm now looking to see why the fuel dilution is higher. It could be due to: (1) short trip driving before oil sample, (2) HPFP gasket is leaking, (3) larger amount blowby of the engine since the ring gaps used were larger than a typical street engine. On recommendation of engine builder, for the next OCI I went to a different oil: Valvoline VR1 20W-50 full synthetic. I will post those UOAs shortly.

Screenshot 2022-08-14 084515.gif
 
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2.5% doesn't seem like a huge amount of fuel dilution, but for the miles on the sample, it is.
Viscosity hasn't dropped to a range dangerous to LS/LT engines. It's only about 5% down from the virgin viscosity.
The oxidation number has gone from 8.8 to 27.7. That's not good.
How hot does the oil get while you are on track?
What have you done with the cooling system to keep intercooler heat soak to a minimum? The C7 Z06 is notorious for flooding in A LOT of fuel once the intake manifold temperature goes above ~140F.
 
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FZ1

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So, I had the LT4 rebuilt last year after it lost compression in one cylinder due to a bad tune from what I thought was a good shop. I spent most of last year dealing with the excessive blowby of the new engine due to the larger than normal ring gaps. So we tried different catch cans but they still filled up too quickly. We ended up installing an engine air oil separator that drains the contaminants back into the oil pan rather than have to drain it. That could mean needing to do more frequent oil changes.

Here's the oil samples going from earliest to latest (right to left in the image). The earliest is UOA is from the engine break-in oil on the dyno. The second sample is from changing the oil after picking it up from the engine builder and driving it home. Finally, the most recent UOA was after a track event (2-3 track hours and the rest are street).

I'm now looking to see why the fuel dilution is higher. It could be due to: (1) short trip driving before oil sample, (2) HPFP gasket is leaking, (3) larger amount blowby of the engine since the ring gaps used were larger than a typical street engine. On recommendation of engine builder, for the next OCI I went to a different oil: Valvoline VR1 20W-50 full synthetic. I will post those UOAs shortly.

View attachment 112458
When in Doubt; Change it out! Go down to 5k oci. Probably, just break in noise.
 

Emperors6

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I'll post the newer UOAs showing it's not just break-in noise. The oil temperature goes up to 300F. I've upgraded the oil cooling system with a separate air to oil cooler and gotten rid of the OEM oil to water cooler. Upgraded the main radiator and fan to a DeWitts 70mm thick radiator (up from like 35mm thick OEM one). Also, replaced center heat exchanger for the supercharger charge air cooler (CAC) loop with two cheek radiators as well as changed the layout of the flow to the pump to reduce the chance of cavitation. Also, made sure the CAC loop is bled properly, which is pretty difficult. We also added additional cooling for the transmission and differential in the rear.
 
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So with the upgrades to the oil cooling system, the oil still goes to 300F? Are there obstructions to airflow to the new air-oil cooler? Things that seem to be small obstructions can make a big difference. Can a dedicated duct be added to force ambient air to go directly to the cooler? I'm keyed into the increased oxidation number being a result of the high oil temperature.

Do you have a performance data recorder on the car? It would be nice to see the history of intake manifold temperature as you go lap after lap. I have never been a fan of GM's practice of putting air-water intercoolers on cars intended for road course use. Air-air is safer for engines that operate under boost for more than a couple of minutes. And monitoring other parameters such as lambda number and spark timing might show that the engine is entering thermal protection mode. As I recall, the catalyst over-temperature protection algorithm greatly richens the mixture. That may be a source of fuel dilution. Do you notice the engine performance dropping off in the later laps of a session?
 

Emperors6

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Yes, it still goes to 300F, but it needs much hotter ambient conditions and more aggressive driving. The new airflow air-oil cooler is off the crash impact bar at an angle. The air is forced to go through it, as before we added it the oil got even hotter faster. Next track event I'll bring my thermal imaging camera and verify the cooler is getting nice and hot as well as the other coolers.

Yes, I have a PDR. I haven't looked at the IAT in the PDR, but my top speed on the straight stays consistent and I don't feel any derating. The performance of the engine is pretty consistent throughout the 30-40 min sessions. I've actually found a hack during the last few events to lower the oil temperature 20-30F. If I run the HVAC system on heat high it provides more cooling to the engine as when I pit in the oil temperature is cooler. I don't mind the extra heat since the windows are down and there's plenty of wind.

Follow-up thread here.
 
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Have you tried using some Redline water wetter? This will help bring down cylinder head temp, raise boiling temp higher. If those things come down a few degrees in temp, oil temp will also. Maybe get a little larger oil cooler, or maybe put a electric fan on it.
 

Emperors6

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I do have the coolant concentration to be just 20% coolant, 80% water, and Red Line Water Wetter. I am looking at a larger oil cooler to replace the existing one that should fit within the same profile.
 
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