I was looking at the OEM oil cooler line on my S5 n/a trying to determine what to do. They are not leaking, but they are also twenty some years old. Mazdatrix and Race Beat all offer -10 AN braided SS lines and fittings, while CorkSport offer -10 AN braided SS lines with OEM type banjo fittings.

At first I thought I would just take the OEM hoses down to the local Parker-Hannifin store and have them replace the flex hose sections with one of their suitable products. But the one thing I do not like about 1-piece forged fittings as well as banjo fittings are their inherent flow restriction from turbulence that the sharp edged turns create - about 2 PSI drop for each fitting. Swept tubular fitting create no pressure drop. They are the preferred fitting to use as long as you have the space.

I took off the front cover OEM fitting and cooler line to measure the ID of the parts. I found that the ID of the OEM fitting is very close to the ID of -8 AN fittings and the ID of the OEM lines are even smaller than both the OEM fitting and the ID of -8 AN line. So my question then is why have all the aftermarket folks gone with -10 AN fittings and lines, when -8 AN is more than adequate when compared to the OEM lines? Other than purely the marketing reason of "bigger is better", I can not see why these lines need to be -10 AN size.

I was thinking of making my own oil cooler lines using a box of new -8 AN swept fittings and hose that I have out in the garage. I need to double check the clearance around the oil cooler fittings, but I also have 120 degree swept fittings that work in tight spots and have more clearance than the 90 degree swept fittings. I also have 45 degree fittings for the front cover to clear the PS and A/C mounting bracket. Summit Racing sells the required 16mm & 18mm metric to -8 AN fittings for $5 each as well as needed 16mm & 18mm aluminum crush washers.

 

Why replace something if its not broken?

 

Preventive maintenance.

 

I think you're putting too much thought into this. I suspect they've simply copied the original line ID as closely as possible with the SS braided versions.

 

The smaller ID may be okay at the connection points where it's too difficult to change size, especially without machining new connections. However, changing the line tubing itself for virtually nothing extra, it reduces the overall friction of the fluid system as a whole.

 

Well that is the problem and my point. The the ID of the factory fitting is about 0.385" and the ID of the original factory hard line is only 0.350" ID. The ID of the -8 AN fittings are about 0.375" and the ID of -8 AN hose is 0.500". That is more than adequate. The ID of -10 AN hose is 0.625", ID of the -10 AN fittings is 0.500" which is larger than the -8 AN fittings and they are way over sized compared to the factory fittings and lines.

With the factory hoses the flow limiting factory would be the 0.350" ID of the hard lines themselves. With with a -8 AN setup, the limiting flow restriction would be the 0.375" ID of the -8 AN fittings. I see no reason to setup the size of the lines and fittings further to -10 AN.

 

Yeah, I don't know. You'd have to ask the people who originally started designing the aftermarket oil cooler lines to know for sure.

 

I ran 1/2" pushlok on my car.

 

Thanks. I was also looking at the Parker-Hannifin PushLok High Temperature 836 hose in the 1/2" ID (-8 AN) size. The hose is rated for oil up to 302F degrees and 400 PSI.

http://www.parker.com/literature/Hos...20-%20Hose.pdf

Which makes it better than the GoodYear AutoGrip that is only rated to 200F degree for oil and 300 PSI.

Autogrip® | Goodyear® Engineered Products

 

So if you can't see yourself sleeping at night with -10an lines under the hood, manufacture your own -8an lines so that you can move on with life?

Also I would not refer to it as a "problem" since thousands of people, including myself, have run these lines for years without issue or adverse affect. The "problem" is clearly more in your head than in reality.

 

I don't think he's claiming it's keeping him up at night, but rather he's just wondering why that design decision was made. Welcome to an engineer's thought process.

 

Racer 1 - "Hey my oil cooler line is leaking and I have a race tomorrow."
Racer 2 - "I have some -10 line and fittings on the shelf."
Racer 1 - "Cool."

Engineering complete!

 

I already said, it lowers the overall friction of the oil system.

Pressure stays the same but friction is reduced; this reduces pumping losses and allows the oil pump to work a little easier.

The cost for -10 line over -8 is negligible, so the cost:benefit is there so companies go ahead and take advantage of it.

If you don't want -10, then make yourself some -8.

The stock exhaust is adequate, so why do companies make new ones? Because they're more efficient. The same applies here; while -8 is adequate, -10 is better.

It's not that hard of a concept.

 

I was responding to rotary resurrection. Your answer may very well be correct... I don't know enough fluid dynamics to know of that is the whole story.

 

He specifically called it a "problem" if I read the posts correctly.

 

I was focusing on tubing size, but then I noticed your numbers of the fittings themselves.

By your numbers above, the ID of a -8AN fitting is smaller than the factory (.375" vs .385"). You're measurement of .350"ID of the factory tubing isn't accounting for expansion under heat/pressure, so you can't use that number as the limiting factor.

Disregarding the size of the tubing in between, using -8AN fittings will decrease flow through these points. -8AN fittings would be a downgrade.

Problem solved.

 

Good point about pumping losses through smaller diameter hoses. But there will also be a pumping loss when it has to reduce down from -10 to match the oil cooler and engine fittings. Which are closer to -8.

IMO, the oil pump (at least the turbo version) is adequately sized. So pumping loses aren't much of an issue. The -8 is better suited than -10 because of the limitations of stock fittings on the engine. Just by replacing the sharply bent hardlines with flexible hose, you'll improve the 'flow' of the system. Decades of dedicated race cars using stock oil coolers/lines is enough to tell me there is no real-world benefit. And the price on the -8 stuff is right.

 

I know this is just preventative maintenance but...

Oil cooler lines actually failing is like a leprechaun sharing his gold.

In my almost 5 years here, I have heard of only a few threads about failed oil cooler lines. It's usually the wax pellet that dies first.

 

Check my post right above yours. The -8 fitting are even smaller than the stock fittings.

The friction created by reducing the -10 back down to stock would not offset the gain of going to -10 for the tubing.

The real-world benefit is in the company's pocket. The oil pumps are fine and don't need the larger diameter hose. As I said above, it's cost:benefit. It certainly doesn't hurt to put larger lines and it costs the company virtually nothing extra.

If people are willing to buy it, sell it.

-8AN fittings are smaller than stock. -10AN fittings are larger than stock. Regardless of what hose you use, the -8AN fittings will hinder your oil flow capability compared to stock fittings. -10AN hose may pose zero performance benefit over stock, but they don't restrict flow like -8AN fittings would.

Mine did. Replaced with junkyard OEM lines, now those leak. I got what I paid for, but I assumed that risk so I'm not complaining, just saying.

I'm still shopping for the lines I want to replace these with.

 

I am sorry that happened, because it is rare. I damn sure wouldn't want to be in the same situation myself.

 

Thanks, it is what it is. I need to have a custom brake line made for my bike, so I may just ask what they (whatever shop "they" may be) can do for me for those as well.

 

I wouldn't call it rare. The original lines are partially rubber hose, and rubber does not last forever when subjected to 20+ years of heat. The OEM lines on my car leaked, then the rebuilt lines I had leaked. I'm on set # 3 now (corksport braided).

 

Could you tell me what fluid velocity, density, temperature, pipe roughness, you used to calculate your Reynolds number for the flow?

If you haven't calculated it, then it's your opinion. And we have different opinions.

I think we agree there is no real-world benefit in a car of -10 vs -8 vs stock. Companies sell what they want and people buy them.
But wouldn't it make sense to produce the equivalent product with -8 lines and offer it at a lower price?
They would maintain their same profit margin and sell more parts. = more profit.
They're not going to go out of their way to make less money. They're just too lazy to change.


I disagree that the -8 (.375 ID) to stock fitting (.385) causes a significant restriction.
Even though the -8 is smaller, the ratio of areas is .97.
The corresponding pressure drop coefficient (KL) is close to 0, but we'll call it 0.01
The -10 line to stock fitting ratio is .75 which equates to approximately 0.1

Your "problem" with the -8 lines is actually 10x worse with -10 lines!

Your pressure drop through larger tubing has merit, but without numbers and a lot of assumptions, neither of us can definitively say which is a bigger factor.

So in conclusion, OP, I can tell you what equations you need to use, but you'd need to do a lot of experimentation to find out which is really better. Or maybe someone can just try both.

 

We do have different opinions, except mine is based on my daily experience of designing commercial fluid systems using ammonia, steam, water (and like fluids) and ... wait for it ... oil. I haven't done the math for this specific case because I've done enough math to know the generalization off the top of my head.

Why change what's making money? Stock lines are small, the companies offer larger sizes, people buy them, why add another product to their shelves/inventory for the stockers to screw up orders with when their existing stock of inventory is working fine?

I'm sure if there were a huge run of people demanding -8AN lines, they might make them, but apparently there isn't or they don't care to (as outlined above).


You're not considering both ends of the line. Going from the engine to the oil cooler, using a -8AN hose w/fittings, you're restricting the passage down (smaller than stock) then opening it back up to a larger than stock hose; then you're restricting it down (smaller than stock) and back up again to stock at the other end. That's two spots in one line where the oil passage is smaller than stock; there's two lines.

With the -10AN fittings and hose, you don't have the restriction down to smaller-than-stock; it only enlarges then restricts back down at the end only to the stock size and no less.

The ratio number is irrelevant in regard to flow as the system can only flow as much as its most restrictive point will allow. Your area ratios only apply to friction in the system in regard to the pumps output capabilities, which we've already agreed is not an issue.

Which what is a bigger factor? The "less pressure drop through larger tubing" does have merit because it's true, I just don't care to spend my time calc'ing it out to satisfy someone's curiosity when I have other people paying me (nicely) to do theirs. Sorry.

If there's an oil passage in the pump system smaller than these that we're talking about (besides the jets), then this entire thread is just a moot point as that passage is the limiting factor and the hoses matter nothing at all as long as they're larger.

 

How many oil line replacements do you think they sell in a year?
Would the sales volume justify the inventory increase?