dromomaniac

Hi all, wondering if anyone has some definitive advice on motor oil. My truck, a 94 with the 3.0, has gone from the Pacific Northwest to the Sonoran desert. I'm currently running 10w-40 high mileage Castrol GTX in it, but with temps sometimes up around 100-115, I've been considering 20w-50. Some people have told me it's too thick, while others have sworn by it. How about hearing from any yotatech folk living in the desert?

1990yota-pickup

i think you will be just fine with the 10-40.. thats just me...

i lived out in high desert of california for 5 years and i always used 10/40 and i never had a issue.. when i live in the desert.. i just wouldnt keep the 20/50 during the winter if thats what you want to end up with..

MudHippy

Hmmm, your location still says Pacific Northwest. But don't we all wish to be back here once we leave?

It's a little old...still applies though. IMO.

xxxtreme22r

^^^ was just gonna mention that. fyi after my 5,000 mile break in on the rebuilt motor on the truck and also on my BMW I use the 15W-40 conventional diesel oil. Valvoline or Rotella is all I will use.

Yopar

iTrader: (2)

You're gonna get a lot of opinions on this, but I like the Rotella 15/40. You could add a shot of STP to that. I would also consider running the 20/50 at those temps, I'm in Florida and it gets dern hot and I've run 20/50 with success.

pruney81

In those temps I would probably use 20W50 or the Rotella 15W40 is a good option. I'd be using either one of those except where I live it only gets up to about 70 and gets into the 30's at night so I've been using rotella 5W40 synthetic instead

MudHippy

Yah, diesel oil good, any brand or weight, synth or no, just fine by me. Heavy Duty stuff...STP too...engine like that.

SoCal

I frequent the desert and I run 10w40 synthetic, I see no reason for a 20w anything being that a thicker oil for startup is not necessary once the motor oil is up to temp 40 weight is 40 weight.

I also run a 160 Degree thermostat and she stays cool when it's 120 out.

pruney81

true.

sb5walker

The right-hand number of an oils rating is the viscosity (thickness, or resistance to flow) of the oil at 212 deg F (100 C). Assuming your cooling system is functioning correctly, the motor should not be too much hotter in the desert than in the Pacific Northwest. Assuming the motor isn't overheating, somethingW40 would be my rec. But if the motor does get hotter than normal, then a 20W50 is worth considering. When I lived in Albuquerque, I ran Castrol Syntec 20W50 in my veezy during the summer and when I changed head gaskets at 218k miles, I found the cross hatching in the cyl walls was still in good shape, nice and even. At 285k the motor is still going strong.

If the motor is at normal op temp, tho, 20W50 is probably too thick. Thick oil does not flow into and through bearings nearly as well, which can lead to oil starvation, overheating and bearing damage.

The left number of an oil rating is the "weight" equivalent at 0 deg F (-18 C). Since any oil is WAY thicker below freezing than at op temp, there's always a risk that you could get bearing damage if you don't use a low enough "W" weight for the coldest temps experienced. To be on the safe side, I wouldn't use a 20W below freezing, nor a 15W below about 20 F, nor a 10W below 5-10 F. Most 5W rated oils will flow down to -15 F, but to be on the safe side I'd use a 0W if temps get below -10 F. When an oil is new, there is no problem using a low W weight, even in the desert in summer. At 212 deg F, a 0W-40 for example will be in the same weight range as a 15W-40, and it will be thicker at 70 deg F than it is at 212 degrees.

The only problem with using oils with low W ratings happens with conventional mineral (petroleum) oils because of viscosity breakdown (shear). In order to make a mineral oil multi-weight, polymer molecules called viscosity index improvers (VIIs) are added. These thicken the oil as it gets hot. A 10W30 is a 10 weight oil with VIIs added, and a 5W30 is a 5 weight oil with more VIIs added.

Over time, heat and mechanical stress cause the VIIs to break down, and the oil loses viscosity as it begins to revert to it's true weight, the lower number.

SO... long winded way of saying that if you use an oil with a W weight below 10, it's a good idea to use synthetic. Synthetic oils have a naturally high viscosity index (they don't thin too much when hot nor thicken too much when cold.) They don't need much or any VIIs, so they don't experience near as much viscosity breakdown as mineral oils do.

If you do use a mineral oil, you're better off using a 15W40 in the summer than a 10W40 because the 15W40 has less VIIs and will not suffer as much viscosity breakdown. Rotella T3 is a great conventional oil. If using a synthetic, you could use almost anything that has the right-hand weight that you want. Rotella T6 5W-40 is an excellent syn that will be the same viscosity as the 15W40 when at operating temp. Pennzoil Platinum and Valvoline Synpower are excellent too. All three are "Group III" synthetics that are derived from petroleum base stocks but which offer much of the benefits of the "true synthetic" Group IV (PAO) and Group V (ester). Amsoil is an excellent Group IV and will take more heat abuse than almost any other oil.

pruney81

That's why I finally settled on the Rotella T6. Plus, it's only about $18 for a gallon jug at Wally World. Not to mention the ZDDP which is good for our flat tappet engines.

sb5walker

I've read a lot of great reports about that oil. I was going to switch to it myself, but my veezy started losing some oil from the front and rear main seals, so I switched to Valvoline MaxLife 10W40 instead. The stuff does work - my oil leaks stopped after about three weeks, and the guys over on bobistheoilguy have great things to say about the oil. I might switch to the T6 for the winter, since I just replaced the front main seal which was the main culprit.

pruney81

I've been running it for about 4500 miles, on my second oil change and no leaks. My engine definitely starts up much easier than before when I was using castrol and even the valvoline maxlife

1990yota-pickup

i dont even remember when i changed my oil last..

xxxtreme22r

that deserves a

1990yota-pickup

double face palm or not.. i dont even drive it enough to change the oil ever 3,000 miles i would just be wasting money... when i had my 82 toyota the owner manual said to change the oil every 10,000 miles

xxxtreme22r

you know oil brakes down after 3-6 months even without being used right?

1990yota-pickup

i know.. but i just dont my exact dat to change it.. i'll probelly be doing everything next weekend..

sb5walker

It would have to be pretty lousy oil to break down in 3 months! Any quality mineral oil should last 6 months, assuming the vehicle is rarely driven. Two things to look for are a flash point above 400 degrees F and a relatively high base number (TBN) which is the additive that neutralizes acidity. A tbn over 9 is good. Diesel oils and synthetics tend to have higher base numbers.

Group III synthetics may last a little better than conventional, but probably not much more since they're made from petroleum.

Group IV PAOs like Amsoil are the best bet for longevity - they would probably last a year without experiencing much breakdown.

Group V Esters like Red Line tend to absorb moisture, so I wouldn't run them over 6 months either.