Originally Posted by Savington
lol @ arguing with JKav
Here I go again.
Warning, this could fall into the TLDR category. So I put a TLDR synopsis at the end.
Originally Posted by JKav
I would have no problem mounting a cooler ports-down on something that I knew would only be started stone cold (basically if the starting vis was always consistently high). But I have been leery of Think/Mocal's recommendation to orient them in any position when there's an alternative orientation(s) where you are guaranteed to never have any air entrapment (or the cooler emptying to sump upon shutdown) under any conditions, with no doubts at all about whether the oil indeed chased out all the air. Especially nowadays where zero weight oils are the rage...
All other things being equal, I agree. But things aren't equal. Engineering is compromise. The compromise I made in post #81 yields the following objective, tangible benefits:
1. Easy mounting location -- the radiator already provides the mounting points. I make up for the decrease in oil cooler efficiency due to post-radiator air flow by using an oversized cooler, which, BTW, isn't much more expensive and fits better. In my flogging, it provides ample cooling at 40C shade temperatures, which was my goal.
2. The hoses are extremely short (less than 24 inches) and straight with mild, large-radius bends. It may be the lowest pressure-loss hose configuration possible for an air-oil cooler in a Miata.
3. The hoses are well protected by car structure and the undertray/ducting. They are never exposed to pebbles, rocks or other debris.
4. The hoses have good clearance to other structures and mechanisms in the car. Because the routing is so short and direct, flex and vibration doesn't overcome those clearances. Bottom line, no chance for sawzall action and no requirement for elaborate securing.
5. The short, direct hose routing and accessibility of the oil cooler makes maintenance/servicing a breeze.
6. Short hoses are lighter. Every little bit helps, right?
Objectively, based upon oil cooler manufacturer recommendations (backed up by testing I presume) and my own personal experience and IR probe measurements after 3 months of tracking . . . absolutely nothing.
Subjectively, I have to fight off all those little, nagging doubts in my mind. These doubts are summarized below:
1. Air entrapment. Sixshooter made the point well. We know that air entrapment can happen when low-viscosity (approaching "Newtonian") liquids are pushed through low-resistance closed passages with complex shapes that contain air. Many of us have experienced this first hand with air entrapment in cylinder cooling jackets or heads. I've also seen recommendations from manufacturers of transmission fluid coolers to avoid bottom entry/exit and Sixshooter has personally observed air entrapment in a transmission fluid cooler.
Apparently, though, this is rare or doesn't happen with high-quality engine oil coolers. The difference lies in:
-the oil's viscosity (compared to water/coolant/tranny fluid -- 0W"EPA" oils being a possible exception);
-the relatively high flow rate of an engine oil system as compared to transmission fluid; and
-the small passage size in the cooling matrix of high-quality oil coolers which means that almost all the pressure drop in the oil cooler will happen in the matrix rather than the plenum chambers leading into/out of the matrix.
Engine oil cooler manufacturers are so certain of this self-purging capability that they actually make affirmative statements that mounting orientation doesn't matter. Affirmative statements (as opposed to silence) means they are really darn sure. In addition to the quote I gave earlier from Mocal, here's another example from B&M: "[t]he cooler can be mounted with the fittings facing up, down or to either side as is convenient" (see http://www.bmracing.com/bmnew/pdf/9500358.pdf
My install, with an 11x11 cooler, is on the extreme side of things size-wise. Nonetheless, I've seen absolutely no evidence of air entrapment -- and I've been looking because I've been concerned about it. My conclusion is that there will be no air entrapment in an installation similar to mine that is using 10W30 through 5W40 engine oils, which is what I've used so far.
The only place I have ever seen assertions that mounting orientation of automotive engine oil coolers causes air entrapment is by individuals on internet forums. And I see it a lot. But I never see it accompanied by personal observations or cites to technical/manufacturer publications. Therefore, I think this falls within the realm of "internet lore/myth" and should be treated with skepticism. Anybody installing a quality oil cooler into an NA/NB Miata using oils similar to what I've used should confidently use the oil cooler orientation that works best for their particular installation location.
2. Dry starting. In the GRM forums, I saw a post by Keith Tanner describing drainback from the oil cooler causing false high dipstick readings. Because of that, I put a caution about it in Post #81. Some have inferred that this could lead to dry starting, which is logical.
For the past week and a half I've been looking for this phenomena on my Red car and haven't seen it, including one engine-off period that spanned 3 days. I'm using high-quality Wix filters. These filters have a good anti-drainback valve. My theory is that the oil filter valve, acting as a one-way check-valve, is providing drainback resistance for the oil cooler as well as the filter.
Related to not personally seeing drainback, I also haven't experienced anything but instant oil pressure indications on my starts. The only exception is after an oil change where I see about 2-3 seconds of idling before a pressure indication. This time period is similar to the pre-oil cooler behavior.
Originally Posted by JKav
FWIW I pinged Setrab for their input on oil cooler orientation. They didn't really resolve the question of air entrapment but rather brought up what can happen during low oil flow conditions.
Here's what they said:
"The problem is when there is not enough flow to completely fill the oil cooler before the oil begins to exit. As you would imagine, if a cooler is too large (considering the system flow) and is mounted in an orientation where the oil could begin to exit the oil cooler before completely filling the oil cooler you would not achieve optimal heat exchange because the oil is not being exposed to the entirety of the heat exchanger. Optimally, port location would be on top or if on sides entering from bottom exiting from top in all cases but in instances where you are certain you have enough flow to fill the cooler before exit the port orientation is of less concern."
The low-flow condition is interesting but not germane.
Where we need oil cooling is in the high-flow, high-RPM condition. I know that in my installation under normal oil pressure conditions the flow is high enough that the theorized under-utilization issue is not happening. I know this because I've hit the top and bottom of the cooler with an IR probe after coming off track and seen even temperatures.
Were I to encounter such a low-flow condition at high-RPM, it should be obvious on my oil pressure gauge. If this happened, I would either bring it in or immediately shut it down depending upon how low the oil pressure reading is.
I don't really care about oil cooling in the low-flow, low RPM condition. Oil temperature isn't an issue there.
The installation described in Post #81 has been working great so far. I have not detected any evidence of air entrapment or dry starting and I'm not aware of any other downsides. This is all based upon direct, personal experience and measurements. YMMV (but I doubt it will). I recommend you use the oil cooler orientation that gives the shortest, safest and most convenient hose routing for your particular install and don't worry about avoiding any particular orientation.