flyrotary@lancaironline.net Mailing List Archive

I'm using a Corvair, at the moment, and there is a big difference between a 60 year old engine and a 20 yr old, but....

Have you cleaned the core? I used paint remover. Filled it full and let it sit a day or two. Drained. Flushed with mineral spirits and filled it again. After couple of days, drained, fill half way with mineral spirits, shake around, and repeat it once more.

I don't know how the thing ever worked with the amount of ....????.....sand????.....I flushed out of it.

On Sunday, June 24, 2018 3:58 PM, "Todd Bartrim bartrim@gmail.com" <flyrotary@lancaironline.net> wrote:

I've spent a lot of time thinking about this as well.The way I see it as with everything else in life, there is no free lunch, rob Peter to pay Paul, etc.... So if we slow the flow through any cooler then the medium spends more time getting cooled and we get a bigger delta T, but the medium also spends more time in the heater (engine) getting heated and we get a bigger delta T there as well. So do these cancel each other out? Or are we better off with high flows that produce more even temps with lower delta T on both ends?

I have considered this a lot with regards to the EWP flows of coolant (but lets not go there right now), so with oil what are our biggest concerns? Do we need flow or pressure? I usually try to remind myself that the engineers at Mazda (or every manufacture) are usually pretty smart people, but then I remember that I'm not using there product for it's intended purpose.

So the cooler is restrictive to flow, but it cools well. But this gives me uncomfortable low oil pressures at idle.

Last night I did a little searching about aftermarket oil coolers and found this on the Mazdatrix site...

The factory oil coolers are the best we have ever found for cooling capacity. Virtually all of the aftermarket ones are not even remotely usable.

No mention at all about flow rates or pressure drop, but again they are talking to car guys. So at our higher duty cycle what is it that we are looking for? Do we need high pressure to have adequate cooling oil flowing though our rotors, or do we need high oil pressure in our rotor bearings to provide a thick oil film. The rotor bearing are large and I don't recall rotor bearing failure as being a problem.

With my newly calibrated sensors I'm realizing that all is not as good as I thought and oil pressure is a big concern. Bypassing the cooler proves that this is the restriction. I actually had pretty good pressure at start-up but after warm-up my pressure would suddenly drop. I was thinking that the oil thermostat looked pretty restrictive but when it was cold and in bypass mode my pressure was ok, but when it would close the bypass my pressure would drop. Examination of the thermostat plug through the port holes while heating housing with a torch, it appeared that as it closed the bypass it seemed to not fully open enough to cooler flow. This is why I removed it and plugged the bypass hole. Now I have the same low oil pressure as after warm-up, so it would appear that the thermostat was not as restrictive as the rest of the cooler. Air blows easily through it, but air flows pretty easily, so this doesn't prove anything other than it's not plugged completely.

I found some mention on a forum that suggests that the stock cooler has turbolator strip inside the cooling tubes and they could move and bunch up in the tubes, thereby restricting flow. This certainly sounds plausible and would explain why some have issues with stock coolers while other do not.

I really don't want to change to some other form/shape of cooler as that would involve fiberglass, painting, etc. of the cowl. I don't mind doing that work, but it is time consuming, and I don't have nearly enough of that resource at this time (I'm actually supposed to be fencing right now, but taking an extended beer break while I ponder this problem).

So I'm considering removing the cooler tonight and sawing off the end caps to examine the tubes. If I find that there are turbolator strips in the tubes, is it worth removing them. It would surely improve flow, but at the expense of cooling efficiency.

If I do this then before I weld them back up, I would like to weld up the bypass hole as well as weld a plate over the thermostat cap hole so I can eliminate that heavy brass plug. But that would mean that I can never reinstall that thermostat if required which would mean that if I find in cold weather if I found I needed it, I'd have to use an external thermostat at even more of a weight penalty. I realize this is an issue that most of you southern guys can't even imagine. But with synthetic multi-weight oils (I'm using synthetic 5W40), this might not be an issue at all.

Todd.... I wish I had as much oil pressure, as the pressure I've got to go build fences today.

Todd Bartrim

On Sun, Jun 24, 2018 at 11:08 AM, Charlie England ceengland7@gmail.com <flyrotary@lancaironline.net> wrote:

First, let me say that I'm far from being an authority on this subject.

The idea of coolant (oil, water, air, etc) moving too quickly through a heat exchanger comes up often. People who's opinion I trust (trained engineers) say that slowing flow does not improve efficiency. What I've been told is that yes, you may see higher delta T across the cooler with lower flow, but that's not a true and complete picture of what's happening. My understanding, based on what I've read & been told, is that the best heat exchange occurs with the max temperature difference between the media (oil>air, water>air, etc). If you slow the flow through the exchanger, then yes, you will see a bigger delta T across the exchanger, but that means that a lot of the oil (in this case) in the exchanger has already been cooled 'early' in the flow, so effectively, part of the exchanger is operating at a much lower temperature difference with the air, and therefore, its efficiency is reduced. So it follows that higher flow, keeping the entire exchanger hotter (lower delta T) actually improves efficiency. Yes, it's counter-intuitive (at least for me). But supposedly, the most BTUs get removed from the system when the entire exchanger is kept at close to the same temp across its face.

There's obviously a point of diminishing returns, where you're actually adding heat by overpressurizing the flow path trying to speed up flow, but I doubt we're there yet. :-)

Perhaps a real engineer could step in and clarify.

On 6/23/2018 9:35 PM, Andrew Martin andrew@martinag.com.au wrote:

Lynn, my setup is pretty much stock where most oil should pass through cooler direct to rear iron ocv, only oil that enters oil gallery is filtered, pressure, temp & redrive oil taken from a block after filter,

But the cooler issue is a bit more incidious in that without a pressure gauge at pump outlet there is no indication of the restriction. I have no problem with having “some” restriction in the cooler but as it builds markedly with increased flow at rpm, Oil delta t drops as oil flow is too fast through the core to cool the oil, and when front cover relief opens at high rpm due to the restriction, only part of pump output is getting cooled and temps rise more.

Setrab, Fluidyne etc do claim low pressure drop but I have struggled to find at what flow rates, Adding smaller coolers in parallel is an option but the data is still needed to choose the correct sizes that allows all oil to pass through a cooler without pressure drop and have just enough surface area to transfer heat to air.

My test showed 140psi pump output 80psi at back iron, I still dont know what my front cover relief is set at, as 140 was max pressure of gauge I had. But front cover relief valve should never operate in normal operation as it is a safety valve for the pump,front cover & cooler only.

Only engine that is diferent is 2009+ renesis as that has only one valve in the system & diferent oil flow design to the rest of the mazda rotaries.

Andrew

On Sun, 24 Jun 2018 at 7:51 am, Accountlehanover lehanover@aol.com <flyrotary@lancaironline.net> wrote:

A restrictive cooler would (might) show a higher oil pressure than the control valve will allow if measured before the cooler. Because the stock relief valve is at the end of the system. So the stock valve might allow for 80 PSI, but never open if the full 80 PSI never gets to it so as to activate. Racers measure oil pressure where the oil enters the engine. Usually in an aluminum block that replaces the stock oil filter stand.

What do the bearings see, is the information you want. We raced for years with 80 PSI entering the engine.

And that was turning the engine to 9,000 RPM on each shift. Oil coolers are constructed of many sharp edged tubes . Pushing oil or any liquid or gas into the end of a sharp edged tube is nearly impossible. So many more tubes than you would calculate necessary are used in order to overcome the sharp tube flow problem. So, if the stock relief were set at 79 PSI (stock on early engines) you would want to see 79 PSI on you oil pressure Gage as taken out of that aluminum block. Mistral calculated the cooler size required on the test Piper. The plane would overheat the oil while still within sight of the airport.

The were also using aircraft oil in the engine. 20-50 if I remember correctly. So, flow got worse as the oil heated up.

The racer had an external oil pump with one pressure section (adjustable up to any pressure you might want) and two scavenge sections. The scavenge sections returned oil and air to a storage tank through a set of bug screen filters and two Setrab 44 row coolers in series. The pressure section pulled from the tank and pressurized oil went through two K&N oil filters in parallel and then through a single 44 row Setrab cooler. So, we ran 100 PSI at the engine. Shifting at 9,700 RPM. 250 HP. Oil is Red Line 20-50 racing synthetic. A common choice for rotary racing. Not a single oil related failure in 30 years. Oil coolers (and filters) in parallel reduce flow resistance. Coolers and filters in series increase flow resistance. Racing oils collect heat and give it up more quickly than do conventional oils.So any cooler performs a bit better with a synthetic.

Lynn E. Hanover

lehanover@aol.com

Any question, any time.

In a message dated 6/23/2018 4:59:30 AM Eastern Standard Time, flyrotary@lancaironline.net writes:

Just got around to plumbing in mechanical gauge before cooler to see whats really happening with my oil flows, wish I’d done it years ago! Learnt so much in a couple of minutes on things that I have wasted so much time second guessing. my second attempt oil cooler did work better than the original mazda cooler, but was atrocious overall, Pressure drop was about 60psi at 1400 prop rpm. No wonder I cant cool the oil, bugger all is going through it, just enough to give me about 80psi oil pressure.

Ended up bypassing cooler all together to confirm it is the cooler that is problem not lines or anything else, well what a diference pressures constant at 78psi at all rpm’s

Trouble is no cooler manufacturer here seems to have charts of flow & pressure drop on their coolers, very frustrating especially as prices seem to range between $100-900 for similar sizes, so makes it very hard to select correct one.

Andrew
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Regards Andrew Martin Martin Ag

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Regards Andrew Martin Martin Ag

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