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Which oil to use on hot days?

Ive been reading that the nissan sentra used 5w-30 and 10w-30, where i live is always hot, 90°-100° every single day, which one should i use?

The owner’s manual should tell you if one or the other is best for that ambient temperature range. If not, visit a dealership parts& service department and they’ll tell you. Especially if you engine uses variable valve timing technology it is very important you use the exact oil the manufacturer recommends.

If you’ve been reading it in your owner’s manual, use the 10W30.
Otherwise, use what your owner’s manual recommends.


It doesn’t make any difference how hot the day is, when it is warmed up, the engine is running at about 180F in the coolant and up about 250-300F for the oil. Both are grade 30 at the engine operating temperature. The first number (before the W) is significant for cold weather. See your owners manual for the correct grade according to the lowest temperatures in your area.


I have not had a car with a 180 degree thermostat in many, many years.

0W20 has proven to work quite satisfactory in the desert but just use the weight listed on the oil cap or in the owners manual.

We had a week of over 110F temperatures this month and all the vehicles endured the heat, there is no need to deviate from the recommended oil.

Holy smokes I HOPE the oil temp is not that high! Anything over 240 F starts breaking down conventional oils and the seals that contain the oil. Even synthetic gets iffy at 300 F and the seals wear very fast.

More typical oil temp in any street car is slightly higher than the water temp, so 200 - 215 F.


Still Keith makes a good point. Your car doesn’t care what the outside temp is. It maintains its own temp much higher than the outside temp. Just like your house if you have air cond and a furnace. It doesn’t care if its -10 or +100 out, it still maintains the same inside temp.

There are several obvious points that have not been made.

  1. A car with a less than perfect cooling system might get hotter than the thermostat setting under those conditions.
  2. More importantly, yes, use the oil viscosity in the owners manual, but using synthetic will help it hold up to high temperatures better.

Use a good quality synthetic that fits the specifications in your Owner’s Manual. Full synthetic oil flows better at low temperatures and protects better at high temperatures with less sludge formation.

Are you changing oil yourself? Wal-Mart has several good oils in 5 quart jugs in the $20 -$25 range. Castrol Edge Full Syn, Valvoline Syn Power, Mobil-1 Extended Performance, to name a few.

Oil was originally straight weight, 20w, 30w, 40,w, etcetera. One had to switch back and forth depending on the seasons. Modern multi-weight is supposed to make the switching unnecessary.

However, some of my GM cars specify conventional 5w-30 to a certain low temperature and then 0w-30 is recommended (silly and complicated) OR they recommend 5w-30 SYNTHETIC for both situations. To me it’s a “no-brainer.” I use full synthetic, same weight (viscosity), same oil, year-around.

Use a good grade full-synthetic of the manufacturer specified viscosity. End of story, problem solved, case closed!

I’m pretty sure they didn’t specify both for 90-100 degrees. If both are specified then the 5w-30 is for cooler temperatures and the 10w-30 is for higher temperatures, like you have.

If that’s all true (check the Owner’s Manual) then you want 10w-30 and I’d go with the synthetic version.

I’ve never encountered a different oil specified for cars with a “less than perfect cooling system” and “less than perfect” would be hard to qualify and would be subject to great debate and opinion.

I’ve owned cars with a “less than perfect cooling system” and I’ve always repaired them almost immediately, otherwise they would destroy themselves, regardless of my choice of oil.

Cars require cooling systems capable of maintaining engine temperatures in the “normal” range (not in the hot zone). Period.

Please, melott and everybody else, correct me if I’m wrong.

I have owned cars which had underperforming cooling systems, which would run somewhat hot when stressed.

Don’t know the year of your car but mine is 2006, 1.8S and it takes 5W-30, according to the manual. 10W-30 or 10W-40 if you are considering the hotter weather.

Most car manufacturers have maintenance schedules for “normal” driving conditions and “severe” driving conditions. Under “stressed” operating circumstances I’d follow the “severe” operation maintenance schedule.

Rather than specify a different oil viscosity or a different oil, most schedules I’ve seen would just list more frequent oil changes and more frequent maintenance, in general.

Lots of people drive cars within “severe” parameters. They just don’t know it or bother to consult the Owner’s Manual.