Thinner or thicker for short trips?

[hominid7]

Background:
I own a 2001 Mazda 626 with the Mazda KL 2.5 ltr V6 (non Ford engine). I live 1 mile from my office so I make several short trips each week. On the weekends I regularly drive a 90 mile round trip to Dallas and back at least once, sometimes twice, and take occasional road trips to OK, LA, and South Texas. My car owners manual calls for either 5w30 (all temps) or 10w30 (above 0*F). I live in North Texas, so we see temps here from 20*F to 100*F+. My driving style is very conservative around town, with occasional red-lines and spirited driving on the weekends on the highway.

Question:
What is the general thought about short trips? I'm wondering if a lighter oil (5w30) would be better for not only gas mileage at startup but also due to my multiple short trip driving. OR, would the heavier 10w30 be better due to gas dillution casued by lots of trips where the car doesnt get 100% warmed up?

I've owned the car since new and it now has 45K on the clock. I've used both 10w30 and 5w30 and have not noticed a big difference in the two. I change the oil at 3K intervals and have used mostly Havoline and Motorcraft with a few experimental runs on superflo, shell, valvoline, castrol, pennzoil, and QuakerState. The car burns no oil and the inside of the valve cover through the oil filler cap looks as clean as the day i bought it.

Your opinions are appreciated!

 

[UncleS2]

On the weekends, sounds like any decent oil will be fine- those road trips are *easy* on oil.

As far as fuel contamination/dilution, you're probably "cooking off" whatever may exist on those weekends trips. Combine that with 3K OCI's, & fuel dilution should be the least of your worries.(*unless* you can smell gas on the dipstick after a weekend road trip, & that would take some serious dilution)

For all those little short trips during the week, thinner should be better. When warmed up, there's little/no practical difference between 5w30 & 10w30, but for those "cold" starts & short trips I'd choose 5w30 over 10w30, and might even try 5w20 when the weather got cooler. Though for the next 3-4 months in NT, I suspect there'll be little difference between cold-flow performance of a 5w30 & 10w30. JMO

 

[GoldenRod]

In addition to what Stuart said, keep in mind that 5W-30 is only thinner at 40C. At full operating temp 100C, it's actually supposed to be a little thicker than 10W-30, but not much.

GR

 

[Titan]

the thinnest oil that is appropriate for your application is always the one to go with. Keep in mind that "appropriate" considers manufacturer's recommendation, your use conditions (short or long trips), low temperatures, load, and consumption issues.

BTW, I've never heard that 10-30 is supposed to be thinner than 5-30 at operating temps. Although Castrol syntec GC 0-30 is thicker than most x-30 weights, I'm thinking the variability between manufacturers makes a blanket statement like that inaccurate when comparing 5-30's and 10-30's across the board.

 

[GoldenRod]

Titan,

Just look at the PDS's on the 5W-30's. They are always thicker@ 100C than 10W-30's. That is because they are loaded up with viscosity index improvers or VII's as some guys like to write it.

For Example: Castrol GTX

5W-30 is 10.8 cSt@100C

10W-30 is 10.6 cSt@100C

[ May 01, 2006, 08:21 AM: Message edited by: GoldenRod ]

 

[hominid7]

Thanks a bunch for the responses...

Considering i tend to change my oil often (3K or less) I guess it's all over-kill. However as my car reaches the 50K mark, and i want to keep it another 50K miles and beyond i just wanna make sure my thinking of the correct vis oil is at least in agreement with the masses here

I've used Havoline and Motorcraft as my 2 "main" oils and both have a vis at 40*C a tad higher than many oils (62) and both have decent base numbers (7.6 and 7.8 respectively) so i think i should be in good shape with 5w30.

Thanks!

 

[bighead]

quote:

---

Originally posted by GoldenRod:
Titan,

Just look at the PDS's on the 5W-30's. They are always thicker@ 100C than 10W-30's. That is because they are loaded up with viscosity index improvers or VII's as some guys like to write it.

For Example: Castrol GTX

5W-30 is 10.8 cSt@100C

10W-30 is 10.6 cSt@100C

---

Not ALL oils fit this same profile, and not only that, many feel that 10w30's shear less because of fewer VII's. So after awhile the 5w30 might end up being thinner anyway, not to mention the fact that a .2 cSt@100c I would think is hardly even worth mentioning.

 

[GoldenRod]

bighead,

If you look back up at my 1st post you will notice that I said: ".... but not much." The thread starter (hominid7) asked if thinner or thicker oil is better for short trips; I would like to know the answer to this question as well.

 

[hominid7]

My main concern would be as to the shear-rate of a 5w30 and the rate at which it is thinned due to fuel and condensation contamination when compaired to a 10w30, both driven for multiple short-trips.

I think the consensus is in my particular situation, my weekend highway trips likely help in un-doing the damage and contamination that builds up during the week.

It would be interesting to see how a vehicle that is used exclusively for short trips, lots of starts and stops (something like a postal delivery vehicle) holds up on 5w30 vs a 10w30 or 15w40.

 

[Matt89]

Just a simple sailor's opinion here...

If fuel dilution is thinning your oil a bit (due to never warming up), it won't be a problem, because the oil will still be thicker when cold than when it's at operating temps. In other words, fuel dilution is not going to make the oil 'too thin' for you at startup.

Then, when you do get it up to operating temps, teh fuel should burn off - minimzing the impact of thinning.

Case in point is the trend of recommending 0W-20 oils for hybrids.