Shell Rotella T6 15W-40?

[Katana29]

Anyone had any experience with this?

I recently switched to running the 5w-40 T6 compared to the Mobil 1 10w-40 high mileage.

I found that it burns off significantly faster than the M1 (about a quart every 2500 miles). Valve train is also slightly nosier at highway speeds (I have aftermarket cams and the lifters tick until I get to operating temp). Normally they'd be silent but with this oil they are slightly more noticeable.

I looked up the flashpoints.

M1 10w-40 High Mileage- 239 C
T6 5w-40- 233 C
T6 15w-40- 249 C

I'm thinking the higher flashpoint will help resist burn off and partially explains what I'm seeing but I could be wrong. The motor is built with forged rods and pistons so the clearances are wider with more blow-by. I'm trying to find the best balance between oil consumption and lubrication. Temps never get above 180 with the oil cooler and the car holds an extra 1.5 quarts over stock.

I would have thought the thinner oil would have lubricated the upper parts of the engine more effectively but the slight increase in noise is leading me to believe a thicker oil is actually better for my case.

Any thoughts on this appreciated

Thanks
-James

[wyso]

You have a diesel 370z?

[Elmo370z]

Originally Posted by wyso

you have a diesel 370z?

😂

[Elmo370z]

Rather pointless if it just a street car, still running OE rod bearing, thicker oil won’t help.

[Katana29]

Originally Posted by wyso

You have a diesel 370z?

Not a diesel but FI Long tube headers and no catalytic converters. Nothing to get poisoned.

[Katana29]

Originally Posted by Elmo370z

Rather pointless if it just a street car, still running OE rod bearing, thicker oil won’t help.

I mostly drive it on the street but the previous owner installed a built motor for track driving.

Is it the driving conditions or the engine clearances that matter most? The engine has forged rods and pistons I'm not sure about the bearings. But the clearances are definitely looser and I thought thicker oils would provide better protection.

[Spooler]

Any high quality 5w-30 will do for you. If you are burning oil, it is due to other reasons.

[SonicVQ]

With 5W30, the VQ37 has high oil pressure to begin with.
Using 15W40 would result is slightly higher oil pressure.

Are you trying to test your galley gaskets?

[2011 Nismo#91]

Yeah those aren't even close to the temps in the cylinders. It's not burn off it's blow by that is the cause of oil consumption in these engines.

"Air ventilationMain article: crankcase ventilation system
During normal operation, a small amount of unburned fuel and exhaust gases escape around the piston rings and enter the crankcase, referred to as "blow-by". If these gases had no controlled escape mechanism, the gasketed joints would leak (as they "found their own way out"); also, if the gases remained in the crankcase and condensed, the oil would become diluted and chemically degraded over time, decreasing its ability to lubricate. Condensed water would also cause parts of the engine to rust. To counter this, a crankcase ventilation system exists. In all modern vehicles, this consists of a channel to expel the gases out of the crankcase, through an oil-separating baffle, to the PCV valve, into the intake manifold. In a non-turbo engine, the intake manifold is at a lower pressure than the crankcase, providing the suction to keep the ventilation system going. A turbo engine usually has a check valve somewhere in the tubing to avoid pressurizing the crankcase when the turbo produces boost.

If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle. The gaps cause power loss, and ultimately mean that the engine needs to be rebuilt or replaced. Symptoms of excessive blow-by include oil being pushed up into the air filter, out the dipstick, or out the PCV valve. In rare cases of serious piston or ring damage, the oil filter housing's sheet metal can even burst at its seam."

This is why when excessive oil consumption was determined in engines the solution wasn't to get heavier oil but to replace the engine.

[Rusty]

Originally Posted by 2011 Nismo#91

Yeah those aren't even close to the temps in the cylinders. It's not burn off it's blow by that is the cause of oil consumption in these engines.

"Air ventilationMain article: crankcase ventilation system
During normal operation, a small amount of unburned fuel and exhaust gases escape around the piston rings and enter the crankcase, referred to as "blow-by". If these gases had no controlled escape mechanism, the gasketed joints would leak (as they "found their own way out"); also, if the gases remained in the crankcase and condensed, the oil would become diluted and chemically degraded over time, decreasing its ability to lubricate. Condensed water would also cause parts of the engine to rust. To counter this, a crankcase ventilation system exists. In all modern vehicles, this consists of a channel to expel the gases out of the crankcase, through an oil-separating baffle, to the PCV valve, into the intake manifold. In a non-turbo engine, the intake manifold is at a lower pressure than the crankcase, providing the suction to keep the ventilation system going. A turbo engine usually has a check valve somewhere in the tubing to avoid pressurizing the crankcase when the turbo produces boost.

If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle. The gaps cause power loss, and ultimately mean that the engine needs to be rebuilt or replaced. Symptoms of excessive blow-by include oil being pushed up into the air filter, out the dipstick, or out the PCV valve. In rare cases of serious piston or ring damage, the oil filter housing's sheet metal can even burst at its seam."

This is why when excessive oil consumption was determined in engines the solution wasn't to get heavier oil but to replace the engine.

That's Think about how much pressure is needed to split a oil filter open. The stock oil pump on the Z puts out over 115 psi already on a cold start.

[2011 Nismo#91]

Originally Posted by Rusty

That's Think about how much pressure is needed to split a oil filter open. The stock oil pump on the Z puts out over 115 psi already on a cold start.

It was probably a Fram filter.

[Katana29]

So just making sure here.......

This engine was built by Rebello Racing and has around 20K miles on it. It has been very well maintained and it was recommended that either 0w-40 or 10w-40 oil be used, as it has forged internals that are looser than stock. I actually bought the car off a member (look up ban25's track journal for the specific car).

I have run both these oils and the consumption rate is night and day, with the 10w-40 burning off at less than half the rate and oil analysis samples coming back cleaner.

Like I said, the engine runs cooler and the valvetrain is definitely quieter with the 10w-40.

So I here what you guys are saying but the engine seems to prefer the thicker oil and that's why I'm confused.

The 15w-40 T6 has very similar properties to the 10w-40 but has a significantly higher flash point so I thought logically it should burn off slower. I know I've got blow-by and that's fine, it's supposed to have a bit of that. But the fact that the oil analysis, consumption, and temps seem to say the same thing..... I would think there would be other factors at play.

[Katana29]

Anyone with a built motor have suggestions?

[SonicVQ]

Is your concern valve train noise or oil consumption?

If it is oil consumption, as you have stated "The motor is built with forged rods and pistons so the clearances are wider with more blow-by. "

With "more blow-by' you are loosing oil through the PCV system and it is what it is.

If it is noise, it may be normal for your built engine.

[Katana29]

Originally Posted by SonicVQ

Is your concern valve train noise or oil consumption?

If it is oil consumption, as you have stated "The motor is built with forged rods and pistons so the clearances are wider with more blow-by. "

With "more blow-by' you are loosing oil through the PCV system and it is what it is.

If it is noise, it may be normal for your built engine.

Both, but mainly consumption. I drive long distances pretty frequently and I'd rather not carry oil around with me if I can help it.

And yeah I would have thought it is what it is with blow by, but the burn off rate was doubled with the 0w-40 compared to the 10w-40 and there's no way the properties of the oil aren't factors with such a significant change.

I only discussed the valve train noise because the thicker oil also seemed to run quieter than the thinner oil (lubricating things better).

Looking at the data sheets for these oils, I think the primary determining factors are film strength (kinematic viscosity) and flash point. The T6 has very similar properties to the 10w40 (which the engine seems to like) but a much higher flash point.

So I would have thought if anything it would burn off less. It's funny when I was researching it, the 15w40 T6 containers actually say 'lower oil consumption' right on the front as what that oil was specifically designed for.

But hey, I'm just trying to learn new stuff and maybe find a better oil for the engine.