Tolerances on new Engines

[Scout1]

I've read some of the forum posts and it's pretty clear that nobody here recommends putting a 5W-40 wt oil in an engine designed for 5w-20 wt. I have a 2004 Accord 2.4 liter 4 cyl and am wondering about using Rotella-T-Synthetic which I have for some of my other vehicles and I understand is a pretty good general purpose oil.

When I e-mailed the Shell "expert" he pretty much said it wouldn't be a good idea - oil pressure may be too high and pointed out the newer engines had much tighter tolerances so they need a thinner oil.

Now I can buy the fact that a thinner oil will work in tighter clearances, but does that mean that a 40wt oil would not be able to get between the bearing surfaces? Are the hydraulic lifters designed so that a 40 wt oil will make them malfunction? What would really happen if I put a 5W-40 wt oil in the Honda... besides a bit less fuel economy?

 

[MrCritical]

I can't say about Honda, but GM will void your warranty for using any viscosity combination of 40wt in a gasoline engine.

 

[Scout1]

Yeah, I've heard that too. I just cleared my 3 year warranty so I'm not too concerned about that, although I suppose if there was a recall or something I might be out of luck. But to be honest with you, I've not had many warranty claims in recent years. These newer vehicles seem to be pretty well designed and manufactured.

 

[Brogy]

Honestly for the $20 it would cost to use the correct grade oil, might as well buy the correct stuff. You have a very nice car, treat it well.

 

[Scout1]

To date I've run it on Castrol GTX since new. 5w-20 for the first couple of years but now 5w30 GTX since it claimed to meet the Honda requirements and I began to hear the rumors about the 20 wt oils shortening engine life.

I'd really like to know more about the Castrol. Is it decent stuff?

 

[Coug]

According to the relative viscosity chart in the PCMO forum GTX 5w20 is darned close to a lighter 5w30 in HTHS and *presumably* in viscosity. GTX is a "heavier" 5w20.

-Coug

 

[unDummy]

Actually, its the CLEARANCES that you should be worrying about. Tolerance is how close to spec you are.

All the mineral oils, that meet the newest performance specs, are all decent stuff.

20wt oils have NOT been proven to shorten engines life when used by the common daily driven consumer vehicles.

 

[Camu Mahubah]

I think what you said, "I will get a bit less fuel economy,"
Anyways the Australian Prius uses 20w50!

 

[Scout1]

Really!?! Why would they do that? Since the whole idea of that Hybrid is to get the max fuel economy, why would they want such a heavy oil? I think they run 0w-20 in the Prius state-side. What's different about the Australian version?

 

[Scout1]

Point well taken. I should have said "clearances". So does a 40 weight oil have difficulty flowing through bearing clearances as tight as on my 2004 Honda? Does such a phenomena exist where the film will break down cause the oil can't squish down thin enough? I find it hard to believe...

 

[TallPaul]

Quote:

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Anyways the Australian Prius uses 20w50!

---

If the manual says use 20 weight, then it looks like there is a "20" in the 20w50 designation. I would guess it's a good 20 weight oil, with a heavy duty margin of safety on the thick side. Yep, my kind of a 20 weight.

 

[FowVay]

Looking through the service manuals for two cars I get the following bearing clearances:

2004 Accord 2.4 liter:
Main bearing .0007 - .0016, max serviceable is .0020
rod bearing .0008 - .0020, max serviceable is .0024

1985 Accord 1.8 liter:
Main bearing .0010 - .0022,
rod bearing .0008 - .0015,

There certainly isn't enough variance in these specifications to claim that any oil other than xW-20 is too thick. In fact the rod bearing clearance is tighter on the 1985 model engine.

The oil recommendation in 1985 was 10W-40.

 

[Scout1]

Great data FowVay, thanks! I hadn't thought to look up bearing clearances. I happen to have owned one of the 1984 1.8 L Accords and I ran everything on 10w-40 back then. My old accord got 28 mpg while my new Accord gets 31 mpg. I always thought it was due to having a carburator versus fuel injection on the new model, but maybe the oil had something to do with it!

So it's probably not that the clearances are too tight on the bearings... wonder if it's an issue of the hydraulic lifer design or the oil pump design. If I understand it correctly, if the oil pressure gets too high with heavier weight oil, the bypass valve opens in the oil filter and you get unfiltered oil circulated through the engine... do I have that right?

Also, if a 40 weight oil creates higher oil pressure, don't I have a higher risk of blowing a gasket or seal somewhere?

Does anyone know how much higher the oil pressure might be on the Honda with a 40wt oil?

 

[Brogy]

Your car will have a long healrhy life on 5w20, stick with it. There was a post about someone hitting 200,000 miles on a crown vic using 5w20, and the engine still had a lot of life left in it. If anything you'll put the 10w40 in, and drain it out because it'll make your engine feel so sluggish.

 

[Scout1]

You may be right! AEHaas sent me a link to his writings on viscosity and flow theory of lubrication that has me re-thinking my opinion about wanting to use a heavier weight oil in the first place. What he says makes a lot of sense, particularly since the way I drive certainly doesn't raise the temps of the oil in my Honda so the heavier weight oil will likely stay too thick to do a good job of flowing through my engine.

Hummm... gotta think more about this. So many opinions about oil! Maybe I need to go back to school and study fluid dynamics

 

[biomed_eng_2000]

I would stop listening to rumors and start listening to used oil analysis. Your car is unique from the unreferenced rumor mills.

 

[Gary Allan]

You won't have any worries from lack of lubrication. Your insult will be in turning/churning heavy oil. That's it. Your 5w-40 SURELY is the same as some poor Canadian's 5w-20 at -40. Hondas work there ...they work in Texas ..blabla.

Clearances shmearances.

 

[JohnBrowning]

I would not hesisitate to run a 5W40 in a vechile recomending 5W20 if that is what I wanted to run. I run what I want within reason. Obviously if you live inthe artic circle and winter is comeing then 5W40 would be stupid but other then that extreme I think that any oil viscosity can be used in any application under the right conditions. My Mom's Camry recomends 0W20 and 5W20 but has never seen it since the OEM fill. Even the Toyota dealership does not carry 5W20 or 0W20. To date it has been run on Mobil 1 5W30 and 10W30. It runs like a top.

Their have also been members that have run 5W20,5W30,10W30 and 5W40 in applications calling for 5W20 and did not find any change in wear rate's. The most comprehensive was in a Ford Modular V8 in a truck used for towing.

Tolerance have nothing to do with oil viscosity recomendations but clearances do. The clearance on most part's in an engine have not changed much over the last 15 years. The tolerances have improved and tolerance stacking has been greatly diminished. The oil pump is about the only part that is routinely re-clearanced by some OEM's when switching to XW20 recomendation.