Oil Temperature

[Joel T.]

How important is oil temperate to Corvette engine operation and when is an engine really considered "warmed up"? I know that in air cooled engines (i.e. a Harley V-Twin or a vintage Porsche) watching oil temp is critical... From what I have seen in late model Vette engines, the water jacket will get up to operating temperature well before oil... Are there any rules of thumb regarding what oil temp needs to be before the engine is driven hard... and what is a safe operating range?

Thanks!

Joel

[Joe C.]

Re: Oil Temperature

How important is oil temperate to Corvette engine operation and when is an engine really considered "warmed up"? I know that in air cooled engines (i.e. a Harley V-Twin or a vintage Porsche) watching oil temp is critical... From what I have seen in late model Vette engines, the water jacket will get up to operating temperature well before oil... Are there any rules of thumb regarding what oil temp needs to be before the engine is driven hard... and what is a safe operating range?


Thanks!

Joel

Joel,

If you're talking about your "modern" Corvette which is using full synthetic oil, then you have much less to consider from a cold start point of view. Ultra low viscosity combined with much better affinity film retention than mineral based oils makes cold start lubrication issues a thing of the past.

As far as oil temps are concerned, I can tell you that for mineral based oil, (about) 215 is considered ideal since any entrained moisture will boil off, yet this temp will still enable sufficient cooling of the piston undersides (the hottest area of the rotating assembly) without coking. Absolute safe limit of mineral based oil is (about) 250 degrees. Normal range is within 200-230. FULL synthetic oils will resist breakdown and coking on pistons/rings beyond 400 degrees Fahrenheit.

Under normal driving conditions, oil temps climb and stabilize after about 20 minutes during steady state highway cruising. I have measured stabilized cruise oil temps of 10W-30 mineral based oil versus 15W-50 Mobil 1 full synthetic on consecutive summer days with very similar ambient temps, and on the same stretch of highway at the same 70 MPH steady state cruise conditions. The Mobil 1 oil temp stabilized at a full 8 degrees lower than the 10W-30. Also, for your information, I have found that ambient temperature variation (between about 95 degrees and 70 degrees) has little effect on cruise stabilized oil temperature. Vehicle speed has a greater effect.

[Joel T.]

Re: Oil Temperature

Joe;

Thanks! Great information! To your point, I only have the "modern" Corvette to monitor... What I typically see, based upon a lot of local driving is that the oil temp almost never gets up to 200.., truth be known, it is more often than not in the 160 to 180 range....

My main concern is how high does the oil temp need to get before the engine is considered safe to "push" (i.e. high revs and hard pulling).. One car I had a number of years ago, also a synthetic oil motor, talked about needing to reach 140 degrees before you ran it above 4000 RPM.... I was wondering if there was a similar school of thought for the Vette engines.

As an aside, a few years back I managed to find that temperature limit on a HD Twin Cam with mineral oil.... cost me a motor tear down and a new set of rings!

Thanks again,

Joel

[Jim T.]

Re: Oil Temperature

Joe;

Thanks! Great information! To your point, I only have the "modern" Corvette to monitor... What I typically see, based upon a lot of local driving is that the oil temp almost never gets up to 200.., truth be known, it is more often than not in the 160 to 180 range....

My main concern is how high does the oil temp need to get before the engine is considered safe to "push" (i.e. high revs and hard pulling).. One car I had a number of years ago, also a synthetic oil motor, talked about needing to reach 140 degrees before you ran it above 4000 RPM.... I was wondering if there was a similar school of thought for the Vette engines.

As an aside, a few years back I managed to find that temperature limit on a HD Twin Cam with mineral oil.... cost me a motor tear down and a new set of rings!

Thanks again,

Joel

Been there and have done that Joel. Years ago I rode my 69Triumph 650 motorcycle 20 miles one way to work. One very early morning about 29 degrees and to much speed the oil tank never had a chance to have hot oil. One piston pin did not get enough lubrication. To much throttle cost me a top end job. Lesson learned. I use the oil temperature indicator on my 85 and 96 and wait untill I see 190 oil temperature before unnecessary RPM's.

[Michael W.]

Re: Oil Temperature

Jim,

Having considerable experience with 60-70s British motorcycles, I'm pretty sure your engine would have gone bang anyway, irrespective of oil temp.

Durability was not a big selling feature in those days.

[Duke W.]

Re: Oil Temperature

Joe;

Thanks! Great information! To your point, I only have the "modern" Corvette to monitor... What I typically see, based upon a lot of local driving is that the oil temp almost never gets up to 200.., truth be known, it is more often than not in the 160 to 180 range....

My main concern is how high does the oil temp need to get before the engine is considered safe to "push" (i.e. high revs and hard pulling).. One car I had a number of years ago, also a synthetic oil motor, talked about needing to reach 140 degrees before you ran it above 4000 RPM.... I was wondering if there was a similar school of thought for the Vette engines.

As an aside, a few years back I managed to find that temperature limit on a HD Twin Cam with mineral oil.... cost me a motor tear down and a new set of rings!

Thanks again,

Joel

As a general rule of thumb, the oil should be at about 120F before you venture beyond the mid-rev range, and 160 F before you demand maximum revs. Since your modern Corvette calls for 5W-30 its absolute viscosity is lower at 160 than a 15W-40 in a vintage Corvette at the same temperature.

Engines without oil coolers can see highest oil temperatures in hot weather stop and go driving, and extended high RPM, like race track hot lapping, can send oil temperatures into the danger zone within five minutes.

Some modern Corvettes have oil coolers, but I'm not sure if they all do.

Using a synthetic that rarely gets over 200F is why the oil monitor can allow over 10K miles before you get to the point where it recommends changing the oil.

If you are using the recomended Mobil 1 5W-30 in a modern Corvette and your typical operating temperature range is 160-180F you have nothing to worry about and should be getting at least 10K miles before the oil monitor recommends a change.

Duke

[Clem Z.]

Re: Oil Temperature

As a general rule of thumb, the oil should be at about 120F before you venture beyond the mid-rev range, and 160 F before you demand maximum revs. Since your modern Corvette calls for 5W-30 its absolute viscosity is lower at 160 than a 15W-40 in a vintage Corvette at the same temperature.

Engines without oil coolers can see highest oil temperatures in hot weather stop and go driving, and extended high RPM, like race track hot lapping, can send oil temperatures into the danger zone within five minutes.

Some modern Corvettes have oil coolers, but I'm not sure if they all do.

Using a synthetic that rarely gets over 200F is why the oil monitor can allow over 10K miles before you get to the point where it recommends changing the oil.

If you are using the recomended Mobil 1 5W-30 in a modern Corvette and your typical operating temperature range is 160-180F you have nothing to worry about and should be getting at least 10K miles before the oil monitor recommends a change.

Duke

my 08 corvette run a oil temp in 200 degree range most of the time. the ZO-6 corvettes with the oil cooler and the dry sump run under 180 most of the time

[Chuck S.]

Re: Oil Temperature

...To your point, I only have the "modern" Corvette to monitor... What I typically see, based upon a lot of local driving is that the oil temp almost never gets up to 200.., truth be known, it is more often than not in the 160 to 180 range...

I wondered how your "modern" Corvette could have such cool oil temps, and then I saw your "modern" Corvette was a 2010 GS. It's been a few years since I followed C6 specs closely, but I suspect your GS has a separate external oil cooler across the bottom of the radiator like the early Z06s.

As I recall, the oil temp is not thermostatically controlled by that cooler, leading to constant cooling and abnormally cool oil temps, especially in cold weather. It was a characteristic I was not particularly impressed with on Z06. On recip industrial engines, you like to keep the oil temp and coolant temp pretty close to avoid reliability problems. But...I'm sure the General's engineers knew what they were doing.

The C6 Z51s, at least the early ones, had an oil cooler but it was integral with the radiator like the automatic transmission cooler. This provided oil temps at least as hot as the coolant. As I recall, actual hard racing conditions could lead to dangerously high oil temps on the Z51s.

[Duke W.]

Re: Oil Temperature

It's important to understand the oil flow circuit and where the temperature is measured.

If it's measured after the cooler this will be the coolest temperature in the circuit, and the oil dropping down from the engine may be 10-30 degrees hotter, depending on how hard the engine is being run.

Wet sump systems usually measure the pan temperature, which is somewhat of an average as oil dropping down from the engine is hotter.

The new Grand Sports with manual transmission have the LS7 dry sump with a cooler, but I'm not sure where the cooler is in the circuit or where the oil temperature is measured.

Oil cooler systems that use coolant out the the block can actually be beneficial in heating up the oil to operating temperature more quickly, but high coolant outlet temperatures may have little cooling effect on the oil.

Conventional oils are okay to about 230, but continuous temperatures above this leads to more rapid oxidation.

Synthetics are okay to maybe 250-260F. I think GM says that modern Corvettes running synthetic oil can tolerate 300F, but IMO that is way too high, even for short periods.

Beyond oxidizing the oil, seal materials need to be considered. Conventional nitrate seal materials begin to degrade rapidly above 200F and the relationship is exponential. Modern materials like Viton that are typically used in modern engines are much more resistant to oxidation in the mid 200 degree range.

Before I started running my Cosworth Vega on race tracks in the early eigthies, I installed a decent size Serck type air to oil cooler under the radiator with a thermostatic adapter sandwiched between the oil filter boss and oil filter and made some changes to the OE spoiler behind the Chevrolet accessory air dam to ensure that the cooler sees maximum dynamic pressure.

I knew that without the cooler the engine would get fried in no time, and even with the cooler I saw 250F in 100 degree weather. I always changed the oil after every event.

One track day, which was typically about 120 miles of hot lapping noticeably darkened the oil.

Duke

[Jack H.]

Re: Oil Temperature

You got away easy! My '72 Triumph 650 decided to 'grenade' itself on a dirt track road running to the Mexican Yucatan. It took all the king's horses and all the king's men to get out of that situation!

[Chuck S.]

Re: Oil Temperature

...The new Grand Sports with manual transmission have the LS7 dry sump with a cooler, but I'm not sure where the cooler is in the circuit or where the oil temperature is measured...

My 2006 service manual seems to show the LS7 oil cooling lines (healthy ones I might add) coming off a bolted adapter just above the oil filter. The engine oil temp sensor is located in the bottom of the oil tank.

Yes, I'm thinking you are correct...it's reporting the "cooled oil" temp.

[Chuck S.]

Re: Oil Temperature

...Synthetics are okay to maybe 250-260F. I think GM says that modern Corvettes running synthetic oil can tolerate 300F, but IMO that is way too high, even for short periods.

Beyond oxidizing the oil, seal materials need to be considered. Conventional nitrate seal materials begin to degrade rapidly above 200F and the relationship is exponential. Modern materials like Viton that are typically used in modern engines are much more resistant to oxidation in the mid 200 degree range.

Before I started running my Cosworth Vega on race tracks in the early eigthies, I installed a decent size Serck type air to oil cooler under the radiator with a thermostatic adapter sandwiched between the oil filter boss and oil filter and made some changes to the OE spoiler behind the Chevrolet accessory air dam to ensure that the cooler sees maximum dynamic pressure.

I knew that without the cooler the engine would get fried in no time, and even with the cooler I saw 250F in 100 degree weather. I always changed the oil after every event.

One track day, which was typically about 120 miles of hot lapping noticeably darkened the oil...

OK, Duke...I gots to know...Do you spring for synthetic oil for the Vega, or make the poor thing run on cheap Walmart mineral oil?

[Duke W.]

Re: Oil Temperature

Back when I ran the CV in track events from the early eighties to the late nineties, I used the most current spec S-category 20W-50 oil, all of which were dual rated and included the most current C-category certification. In fact I ran the same oil in all my vehicles including my Honda CB1100F.

I ran four to five track events per year - usually two in the Spring and Two in the Fall. I usually changed the oil after every event, so it never accumulated much mileage between changes, but I'd say a track event was equivalent to several thousand miles of normal driving for both the oil and brake pad wear.

This was all before the P limitations came to be in the 2000s beginning with SL, and the P concentration in the dual-certified oils I used back then was typically about 1200 PPM.

I've never used a so-called "synthetic" oil in any vehicle I own.

Nowadays I run 15W-40 CJ-4 in everything.

Speaking of Walmart, after they began carrying the national brands new CJ-4s about three years ago, their SuperTech house brand was still CI-4, so that's what I bought.

About a year ago their house brand became CJ-4, and in the last few months I don't see their house brand on the shelves of my local Walmart anymore - just the national brand CJ-4s.

Duke

[Joe C.]

Re: Oil Temperature

Since we've strayed a bit off topic into the realm of oil brands and weights, I'll tell you that I use Shell Rotella 10W-30 in my bone stock '85 with Z51 (which includes a thermostatically controlled oil cooler and independently controlled dual cooling fans). The digital readouts are great for monitoring things like oil and coolant temps. The oil temp is typically 10 or more degrees hotter than the coolant, and the radiator fan(s) never come "on" unless I'm in stop-and-go traffic with the A/C "off". I do most of my driving when ambient temps are in the 70 - 100 degree range. When the air conditioner switch is in the "off" position, the cooling fans cycle on and off: they come "on" when the coolant temp reaches 227 degrees, remain on for about 30 seconds as the coolant temp drops to about 190, when they shut "off". When the air conditioning is "on", the fans are on constantly, and coolant/oil temps never rise above (about) 200 degrees.

The L76 is another matter since the water jacket has been 3/4 filled with rigid material. I installed the oil temp sender in the 1/4" NPT tap in the main gallery exiting the oil filter. I have not installed an oil cooler on this engine, and extended cruising at 70-75 MPH sees oil temps stabilize at 280 degrees after about 25 minutes. Local town/country driving sees oil temps at between 230-240 degrees, Fahrenheit. Short blasts down the track don't last longer than 13 seconds, so temp rise here is not an issue. I run Mobil 1 FULL synthetic race 15W-50 in this engine for 2 reasons. First, is because of the elevated oil temps, and secondly, because this blend of oil has higher zddp levels, at 1400ppm, than any API CJ-4 service class oil. The higher phosphorous level is necessary for the slightly more aggressive than stock, solid flat tappet cam that is installed. Coolant temps are easily controlled at 165 degrees under all conditions because the radiator has shed the extra load involved in cooling the engine oil.

[Jim T.]

Re: Oil Temperature

Jim,

Having considerable experience with 60-70s British motorcycles, I'm pretty sure your engine would have gone bang anyway, irrespective of oil temp.

Durability was not a big selling feature in those days.

Michael I am still riding my 69 Triumph 650, starts on first kick. From what I remember, that was the last top end job I have done. That was over 25 years ago. It did sit in the garage for 9 years (1999-2008) until I repaired/replaced a broken gear tooth in the transmission. I wish I knew how miles I have ridden it. Two speedometers and the last one quit many years ago.