Hot ambient temps and engine oil question.

[Astro14]

Originally Posted By: mechtech2
Originally Posted By: volk06
Why do people think or consider 100F ambient temp is hard on oil? Flows easier in the engine than colder temps. If engines run at 180-210F how can 100F ambient temprature be hard on the oil and be considered severe service?


Easy-peezy:
Because that 100 deg F starting temp means it is just that much warmer at running temps [warmer than 25 deg F ambient temps,let's say]
[Not an insurmountable situation, but a legit reason to note ambient temps as a very real factor ]


That's not been my experience, though. I've lived where it's cold (Vermont, Colorado) and where it's hot (Texas, Mississippi) and the engine operating temp doesn't vary much once the thermostat is open - even running the AC, in stop and go traffic, in a black Trans-Am, on a 100 degree day, the coolant temp stayed right at normal. The only time I got that car to run hot was when I was pushing it really hard on a drive in Big Bend Park, moderate speed, full throttle, 95+ day, it warmed a bit.

Before you say that the gauge was an idiot light, I noticed it run a hair cooler on the gauge once I installed a Hypertech chip and a 180 degree thermostat, so I think it was a real gauge.

So, even though it's hot outside, my cars have always run at the thermostat temp in weather from extreme cold to pretty hot (100) unless I was really pushing them. Normal driving, including idling in traffic with AC on, didn't raise the temp.

Further, on the cars on which I had an oil temp gauge, hot weather did not appreciably change the oil temp. On a -25 degree day in Vermont, the oil temp would run 85C in my Volvo 240 turbo. On a 90+ degree day in NYC traffic, AC on, the same car would run 90-95C oil temp. Only time I got the oil warmer was by running it hard (lots of full-throttle boost), and even then, I never saw over 110C.

So, my experience is that coolant temp and oil temp are not that affected by outside air temp. It's less affected than people think.

Steve has expressed it as a matter of heat transfer, and he's right. If the car in question has a good cooling system, it will transfer enough heat at 100F to run the same temp. The only time I've seen an oil temp or coolant temp rise was when I was putting a LOT of heat into the cooling system in the form of full throttle driving. Regular highway driving, or idling in traffic does not generate the heat load that full throttle does.

A car with a properly functioning cooling system will run at the thermostat temp over a wide range of ambient temps. The oil temp will follow the coolant temp closely.

 

[bluesubie]

Originally Posted By: volk06
Why do people think or consider 100F ambient temp is hard on oil? Flows easier in the engine than colder temps. If engines run at 180-210F how can 100F ambient temprature be hard on the oil and be considered severe service?

Because my owner's manual requires it. It's actually the only time that the word "required" is even used. 5w30 is "preferred" for fuel economy.

-Dennis

 

[Jim Allen]

I see, and have seen, more of a spread of oil temps due to ambient temps on my equipment. The '05 F150HD (7 qt cap + bypass filter) has about a 20-30F spread between winter and summer oil temps. In winter, on the coldest days, 0-20F, 170-180 is the stabilized oil temp but it takes a good 20 miles of steady driving to get there. Coolant temp is about 180-185 at that point. On hotter 90-100F days (normally rare here but not this year), oil temp runs ins the 190-200 range and takes about 10-12 miles of steady driving to get there. Coolant temp runs 195-205 in that situation. OIl temps were 4-5 degrees cooler when I was running a 5W20 synthetic vs the 10W30 HDEO mineral I am running now. These temps are from aftermarket gauges and taken in the truck's unloaded state. With a heavy load, all temps are a bit higher, but the highest oil temp I have seen so far is 210. I know... why am I running 10W30. Long story.

I've had oil temp gauges on a couple of other rigs but I don't have as detailed records. My old Land Rover 2.25L held 7 qts. IIRC and ran at about 180F coolant temp. With 20W50 oil out in the deserts of SoCal and Nevada, 100F or higher, I never saw more than 190F sump temp. I had that LR in Vermont for a year and over the winter, but but I didn't have the oil temp gauge in it then. I do know that when winter struck, and -25 or so was reached, the 20W50 didn't cut it.

I've had temporary mechanical oil temp gauges (same gauge actually) on two engines, my old diesel Blazer and the '86 F250 6.9L diesel I still have. The diesel Blazer ran very cool oil temps.. never more than about 185-190 even in the hottest temps. It had a big, radiator mounted oil-to-water cooler and I ran mostly 15W40 in that truck. The 6.9L diesel is about the same and it also has a good sized oil-to-water cooler. Probably for 60 percent of it's life, the 6.9L has had 10W30 in it, with the remainder 15W40. 10W30 in it now. What I like about both those diesels is that the oil warms up very fast due to the oil-to-water coolers. By the time coolant temp is up to max, oil temp is not far behind.

 

[dave1251]

Originally Posted By: Garak
Yep, degrees Celsius are larger than degrees Fahrenheit, so you're experience is similar to what I'd see in mine, though I routinely saw much colder than 25 F. Heck, at 25 F, the Audi called for 15w40. As far as cold starts go, my Audi then (and my G now) was stored in a heated garage all winter, so a -40 C start with the sump actually at that temperature was extremely rare.


I should of clarified that my experiences are nearly identical.

 

[mechtech2]

The shorter the trip, the more difference in oil temps summer/winter .
Long drives start to even things up.

 

[Garak]

It's also relevant to note that from the varied experiences different posters have with respect to their variations on sump temperatures, not all vehicles are the same. The old Audi had a small sump size with a turbo and an effective, thermostatically controlled oil cooler. So, it wouldn't be too difficult to regulate oil temperatures within a few degrees at operating temperatures.

Those vehicles with larger sumps and less tightly controlled oil cooling systems would experience a wider swing. And as mechtech2 points out, trip length makes all the difference. No matter how small your sump is, a one block trip in the dead of winter isn't going to cook the oil.