How hot is too hot? A good rule of thumb is that 250F+ is too hot. Also most of the oil cooler thermostats available open at 180F~190F, but it's best to keep your oil temperature above 200F, even a 220F opening temperature can work well.
Photography by Tom Suddard
In recent months, we’ve seemingly focused on everything but the drivetrain in our LS1-swapped Nissan 350Z time trials car. But just because we’ve been focused on suspension and aerodynamics doesn’t mean we’re finished with the engine: Let’s take a detour and talk about oil temperatures.
Oil Temperatures and You
Before we dive into the details, let’s talk about the basics: Oil gets less viscous as it warms up.
If you’d like a practical example of this phenomenon, think back to how you’d microwave some maple syrup to get it to flowing smoothly. Cars don’t run on sugar water, but the basic behavior of their lubricant is the same.
Unlike that syrup bottle, though, hot oil isn’t great for a race engine. In a perfect world, oil would have exactly the same viscosity the entire time, and that viscosity would perfectly match the tolerances engineered and subsequently machined into the engine.
[Ask an Oil Expert Part 2: Straight Talk on Oil for Track and Race Use]
Modern oils use science to target this goal, which is why your BMW M3 might call for 10W-60–those numbers mean oil that will be as viscous as a 10 weight at 0 degrees Fahrenheit, and as viscous as 60 weight at 212 degrees Fahrenheit–so, basically, the temperature at which water boils.
However, even fancy oil has it limits: Push oil temperatures too high–generally 300 degrees or more–and the oil itself starts to break down. An ideal temperature for a race car is usually 220-250 degrees Fahrenheit, which is warm enough to boil off contaminants, but cold enough to leave everything else untouched.
Measuring Oil Temperatures
What’s all this mean to us? Honestly, we have no clue: Our 350Z didn’t have any way to measure its oil temperature, which meant we were basically flying blind at Florida’s 85-degree test days.
We had a hunch, though, looking at our oil pressure trends over a 20-minute session. Pressure starts to drop after three our four laps. Our LS1 also doesn’t have any oil cooler, and that fact paired with this pressure data formed our hypothesis: Our 350Z was absolutely roasting its oil, and those high oil temperatures were lowering the viscosity.
There are a few ways to fix this: Add an oil cooler, change to different oil, mix cool-down laps in between flyers, etc. But the first thing we needed to do was test our hypothesis, which meant collecting data and running an experiment.
What’s the best way to collect oil temperature data? In our case, we already had the foundation laid: Our AEM CD-7L dash and CAN expansion module makes it easy to add and then record sensors and their data. But which sensors should we add?
[Replacing Our Steering Column and Dash With Something Racier | Project LS-Swapped 350Z]
Rather than scour junkyards or the dealer parts counter, we decided to jump into the world of aftermarket race car sensors. That led us to The Sensor Connection, a company that makes sensors for just about anything–including our 350Z.
We filled up our cart with nine different sensors, but we’ll get to those in a future update: The one we’re discussing today is a $26 quick-disconnect thermocouple. We screwed it into a spare ¼-inch NPT bung welded into our oil pan originally meant for a driver-side dipstick, which placed it directly into the hot oil.
Our AEM data system can’t read thermocouples directly, so we needed to add one more part: a thermocouple amplifier. Many companies offer these, including AEM, but we went with Sensor Connection’s own eight-channel TCA-MS-K-8-A4-IND, which can measure up to eight thermocouples simultaneously.
Prices and lead times vary, but you can plan on spending about $500 for this piece of the sensor puzzle for your race car–at least if you’re planning to add eight sensors like we are.
Sensor and amplifier installed, we wired up everything and calibrated the sensor: Just like that, our dash was displaying and logging oil temperature.
Testing our Hypothesis
It was time to find out what our oil temperature really looked like on track. We hitched up the trailer and took our 350Z to our official test track, the Florida International Rally & Motorsport Park, for one of their open track days.
Our plan was simple: Do a 20-minute session while logging oil temperatures, then see if or how they correlated to oil pressure and water temperature. With that data in hand, we’d figure out if we had a problem, then plan a fix.
Yeah, that grand plan didn’t exactly happen. Instead, we completed just two laps at 80% pace before our oil temperatures spiked to 260 degrees and showed no signs of stabilizing.
We’d barely tested the car, but we pulled into the paddock and called it a day before we hurt anything. We had a major oil temperature problem–time to go home and solve it.
How hot is too hot? A good rule of thumb is that 250F+ is too hot. Also most of the oil cooler thermostats available open at 180F~190F, but it's best to keep your oil temperature above 200F, even a 220F opening temperature can work well.
If 250F+ is too hot, than my old LSx swapped 951 failed that miserably. Even with an oil cooler I'd regularly peg my oil temp guage at 280F. All the CMC camaro drivers had the same oil temps, my friend in his C5 Z06 without an oil cooler would see 320F.
So I guess don't drive up at altitude in the summer time if you're going to stop at 250F....
Glad to hear the window is what I expected as well, the hottest I have seen is 248F so my system must be up to snuff, it usually hangs around 230-240 range while on stage but depends how hot the coolant gets up to.
docwyte said:If 250F+ is too hot, than my old LSx swapped 951 failed that miserably. Even with an oil cooler I'd regularly peg my oil temp guage at 280F. All the CMC camaro drivers had the same oil temps, my friend in his C5 Z06 without an oil cooler would see 320F.
So I guess don't drive up at altitude in the summer time if you're going to stop at 250F....
The LS corvette's have a high oil temp warning in the computer and it clicks on at 320. With an oil cooler on my completely stock LS3 my car typically reached 280 at the end of a 20 minute session. I ran 5w-50 oil last season which likely raises the temp but also keeps oil pressure in the middle of the gauge when the car is under load.
Depends on what oil you run. On my race cars I ran mostly dinosaur oil so if I saw more than 240 F or so I tended to get a bit antsy and wondered why. I finally fitted an oil cooler that had way more cooling than I would need (out of a Mazda rotary, which uses oil spray on the rotors as part of their engine cooling) and taped off some of it until I got the right level of cooling. I always ran an oil temp gauge in the race cars.
Modern cars that run synthetic aren't as big a concern.
GameboyRMH said:How hot is too hot? A good rule of thumb is that 250F+ is too hot. Also most of the oil cooler thermostats available open at 180F~190F, but it's best to keep your oil temperature above 200F, even a 220F opening temperature can work well.
I'm sure it was for emissions/efficiency, but the stock oil cooler thermostat on my 135i didn't open until just under 250.
I think most vehicles don't go into limp mode until oil is around 300 or more.
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