Took my truck in the dealership to have the warping dash looked at. He knew I wanted the 30000 mile service but said wait till ford decides what to do with the dash and do it all at once. Then he asked me how many miles I currently have on this oil change. I told him about 8500 miles and he gave me a deer in the headlights look. "You can't go that long, that's so bad for your engine". I said I go by the oil life monitor (mostly). Then he said something like " but it's south Texas, it's too hot out to go that long. He stopped freaking out when I told him I did the last change and used full synthetic but it did get me wondering.

Does outside temperature even matter when an engine reaches operating temperature? Does engine operating temperature fluctuate a little based on whether the outside temp is hot or cold or does the engines cooling system maintain the same temp regardless?

 

I should add, I'm aware the coolant temp gauge gives me a reading and it pretty much doesn't move when it reaches operating temperature, so I'm assuming the engine operating temp also stays constant.

 

The service guy is trying to sell service.

 

I figured that at first but he doesn't work in the quick lube bays. He's on the repair side.

 

Nope. But almost all automakes buffer the coolant temp gauge so owners don't freak out. If temp was constant, the fans would be on all the time. Normal operating temperature is about 185ºF to 230 or so. Any higher than that, and the gauge starts moving. Having said that, you can program it on the F-150 to be accurate (with a digital display), and that's what I did. Surprisingly, even with max cool, my truck doesn't get below 200 (it's around 203). That also enables trans actual temperature, by the way. Hope this helps.

 

By "program" do you mean with forscan? Which digital display? I have an xlt with the 4" (I think) gauge cluster.

 

Service writers job is to scare customers into paying for extra service.

 

People used to know this but in the last 40 years it's been forgotten. YES, outside temperature matters.

Your engine is not like the cooling system in your home where the thermostat keeps the house at a constant temperature by quickly kicking on/off. The temperatures inside your engine block varies all over the place. The thermostat in your cooling system is designed to get your engine up to temp quickly by blocking flow then it opens up and stays open (remember the whole engine compartment is heat soaked after so long). Your oil will lag your coolant temperature by 30mins or so but will eventually exceed it. Only in the arctic do they block off the radiation with a cover so when the thermostat opens it doesn't try to close again with the flow of water that's too cold.

So....what is your actual oil temp? what is your peak coolant temp?.....that will go up and down by engine load and outside temperature. Multi weight oils in the 1970's were designed so cover both summer and winter (which is probably why people forgot outside temp matters).

Finally, here is a way to think about the difference between a xW-20 and a xW-30...about 10-15 degrees F.

 

I drive around southern Arizona, New Mexico, and Texas with ambient temperature reading over 105 to 120 degrees, and engine temps hitting 230 degrees. I change my oil every fall regardless of mileage. Our fleet manager of over 800 vehicles, conducted a test of oil at various mileages and decided on oil changes to be done at 5000 miles.

So for me it's 5000 to 6000 miles max if no towing, sooner if pulling a trailer during the high heat.

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Only the 8" screen cluster (Lariat+ models) can be programmed to display the actual digital temperatures of the engine & transmission temps above those gauges. You can upgrade to the 8" screen on an XL/XLT if you so choose.