I've made more progress toward good cooling but have a long way to
>> go. At an OAT of 92 F I was able to climb to 5500 feet and cruse at
>> 23 inches MP. Water was 195 F and Oil went up to 209 - 210 F.
>> Oil pressure was 60 psi.  I noticed my oil pressure went down to
>> about 58 psi as the oil pressure approached 210.  This was after
>> about 20 minutes of flight.  Is this an indication of oil foaming? 
>> Also, is this too low oil pressure at 5500 rpm?

The lowest setting for a pressure relief valve is 71.1 pounds up to the twin turbo engines with a 115 pound relief..

 

So the oil pressure you should see on start up when the oil is cold, is about 71 pounds. The pump is too small to maintain this pressure at idle, but by the time you have 2,000 RPM you should have your 71 pounds.

 

The engine is not being stressed at 5,500 RPM, so the oil pressure is still OK, but I would want to know why my oil pressure is below the relief setting at cruise.

 

Note that in climb that a great deal of the oil in piled up in the front case, where the oil pump chain and sprockets add more air. The same thing happens quickly in a race car when from high speed you brake hard for a few seconds. You can put nearly all of the oil in that case. Then when you power up to leave the corner, the pressure sags until the pick up is again submerged.

 

The stock pick up and bug screen is a flow disaster. The sharp edge of the pick up tube creates a lot of drag and that low pressure helps oil bubbles expand, and makes oil foaming that much worse.

 

You can run without the screen. I braze a big thick washer around the end of the pickup.

I then die grind a big radius into the end of the tube, making it look like a trumpet bell.

 

Lap the engine end of the pickup dead flat and install dry with no gasket. Drill and safety the mounting bolts.

 

Mistral had that problem, and suffered oil cooling problems because of it. The foamed oil becomes an insulator as the entrained air volume increases. It neither picks up heat from the rotors nor dumps it in the cooler.  Their biggest improvement came when they removed the bug screen. They produced a pump cover that has a much improved pick up with no screen at all. They added a screen to the center of their oil control plate sandwiched between  the engine and the pan. A similar plate is used in racing to prevent that oil going up into the front case.

 

Low pressure can be caused by crimped or partially failed "O" ring in the front cover. I would replace this problem junction with a copper "O" ring that is thicker in diameter so as to create more pressure at the junction. It cannot crimp. And it cannot fail.

 

The bearings have been damaged by an over rev and the clearance has opened up. Probably not your problem if you have owned the engine since new or overhaul.

 

Just for the fun of it, open the oil filter can. Lay out the paper media, and look for sparklies.

Silver, and even copper. A very small fleck here and there is just normal stuff. Lines in the crotch of the folds is very bad news. If the engine is running fine, with an obvious bearing failure going on, that is good news. It may be that just a clean up and a bearing change is all that is needed.  

 

Using a multi grade oil. The long polymer chains make foaming worse. A straight weight racing synthetic will have much higher film strength, more anti foaming agents, and better heat transfer. I use Redline Racing straight 40 wt. Good to 9,600 RPM. Real good at 5,500 RPM. It remains oil even when way over heated.

 

As an oil pump, the Mazda pump is just a bit odd and the shaded rotors (to reduce noise)add to foaming. Mistral's pickup and housing feeds oil from both ends of the pump like the FD (twin turbo engines). Very good idea.

 

Even new stock pumps may have more end clearance than is optimal. The book says up to .007", but that is a bunch of clearance. Lower idle pressure, and more RPM before the rear relief opens to control pressure.  And more foaming.

 

When I used the internal pumps, I shortened the pump bodies to get .002". The pump primes quickly after a long sit. You get 45-50 PSI of idle oil pressure. Oil pressure goes to 70 PSI when you touch the throttle. Before you reinstall a pump, pack it with Vasolene. No gaskets, and no sealant of any kind.

 

There is a front relief valve also, to protect the oil cooler. Very old ones set at 100 pounds, and later to 110 pounds. Now the FD's are set at 140 pounds. Place 1/8" of washers under that spring, to be sure it is not limiting oil pressure.  

 

There you go. More than you wanted to know about oil pressure.

 

 

Lynn E. Hanover