flyrotary@lancaironline.net Mailing List Archive

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