Excessive oil pressure in newly built 3.2

[Bassboyron]

Hi, I'm wondering if anyone else has run into an off the chart oil pressure reading, like me, when starting my freshly rebuilt 3.2 in my 914-6 conversion. I did send out the oil pump to be rebuilt. I have an auxillery oil cooler in the front that bulged and leaked shortly after start-up. I set up a pressure gauge in the fittings after removing the front cooler and it quickly pegged when the engine was started. I blew out all of the oil lines that I could to see if they were blocked, but none were that I could tell. The engine ran great for the short time I ran it. It's not easy to remove this engine and trans assembly in this car.
Any suggestions would be welcomed before I remove and disassemble the engine.
Thanks
Ron

[AlistairWallace]

When you say high, how high?

[targa72e]

How is your oil system plumbed? Coolers are generally on the scavenge side of the pump, there should be almost no pressure on the scavenge side. If lines are clear from engine, to cooler and back to tank I would check the return fitting at tank is not restricted.

john

[stownsen914]

There can be LOTS of pressure on the scavenge side, especially on a cold startup when an engine is full of oil. First thing the scavenge pump does is empty the crankcase, which may have a lot of oil in it if it's been sitting a while. And remember, no blow off or safety valves on the scavenge side of a 911 oil system to keep pressure in check.

A couple q's:
Do you have an external thermostat regulating flow to your front cooler? Is it working?
What was the ambient temp when you started the engine?
For comparison, what pressure did you see on the pressure side of the oil system (the gauge in your dash)?

It's possible the cooler might not like cold, thick oil under high pressure, and leak.

Was any work done to the oil circuit while the engine was out? Lines, tank/filter console disassembled, etc? I did hear once about a filter console being reassembled incorrectly once, blocking the scavenge circuit's path back to the tank, and resulting in massive oil pressure backing up into the oil lines and cooler (and ruining the cooler).

[Bassboyron]

The pressure gauge that I installed between the inlet/outlet hoses at the oil cooler pegged at 155 psi. Oil pressure should be around 58 psi. I have a Mocal thermostat running on the scavenge side of the engine with a Setrab oil cooler. I have a 914-6 so the thermostat and cooler run up the right side of the car and the return line runs under the engine to the oil tank/oil filter on the left side of the car. The the mocal thermostat, lets the oil run through to the cooler and is supposed to ‘by pass’ until the oil warms up. But the oil pressure at the cooler pegs in less than a minute. I was thinking of by passing the thermostat and the cooler lines by connecting the oil lines that run to the thermostat with the oil pressure gauge and see if it is still excessive.

[Bassboyron]

I do not have a oil pressure gauge in the instrument panel, it’s a light and a temp gauge.
The temperature in my garage is probably around 65-70 degrees

[Bassboyron]

Yes it did ruin my oil cooler. No extra work done with regards to the tank/oil filter.

[VFR750]

Is the tank and breathers open to atmospheric?

[Bassboyron]

I see two breather hoses coming from the oil tank. One goes to under the throttle body. The other is questionable as to where it goes. I thought it goes to a fitting that is near the rear of the engine near the thermostat. Could that cause a problem?

[VFR750]

The symptoms seem to be you are dead-heading the system. The scavage side should not be pressurized enough to bulge an oil cooler.

[Bassboyron]

Dead heading?

[winders]

Originally Posted by Bassboyron

Dead heading?

VFR750 is not referring to the Grateful Dead….

Dead head is a no flow condition.

[boyt911sc]

Originally Posted by VFR750

The symptoms seem to be you are dead-heading the system. The scavage side should not be pressurized enough to bulge an oil cooler.

Ron,

You need to locate or identify the location where the flow restriction occurs. My first suspect is the auxiliary thermostat. You will need a mechanical pressure gauge at the engine side and one at the oil line side. Do not run the motor and use the starter to generate oil pressure internally. Keep us posted.

Tony

[VFR750]

Does the thermostat have a bypass like the factory one? Or is it a open/close.

If the oil line is blocked, the scavenge pump will continue to pump both oil and air. And it could be the air being compressed over time that gives you the trend of increasing oil pressure as the engine runs.

[dannobee]

Bypass the cooler and thermostat using an appropriate sized AN union and see if the pressure drops to normal (closer to zero). If so, one of those is restricted, aka "dead headed."

[Bassboyron]

Thank You for all of the helpful suggestions guys! I’ll follow out the lines and find the restriction
And maybe Jerry Garcia

[stownsen914]

The Mocal thermostats work a little differently than the factory ones. The “cold” position just opens a shunt to allow the oil to take a path of lesser resistance back to the tank. It never positively shuts off the flow path to the cooler, even if the thermostat fails.

It might be worth double checking the flow path of your scavenge circuit to make sure you didn’t inadvertently create a dead end. “Dead head”

Checking your scavenge pressure again while cranking only as suggested should reveal this if it’s the case.

[Walt Fricke]

I had a Mocal fail on me, but it was because the oil pressure forced the sealing ring on the part (a cone?) which determines which way the flow (or most of it) goes off its seat. Just meant no real warm-up function, with no damage to anything.

My beef with Mocal is that (25 years ago, anyway) they had decided not to cast flow arrows or other identification into their castings. So you had to depend on where bolt heads were. Maybe they have corrected this by now? I gave up on it - it looked like pressure would force the O ring off its tapered part, rather than farther onto the thicker direction. The O ring wasn't going anywhere, as there was a rod running through things so that when loose it was still captured by the rod. But lots of guys have been fine with the use of the Mocal, so maybe I had it hooked up wrong, despite best efforts, writing down where the bolt heads were supposed to be, etc.

But bypassing the thermostat and just cranking sounds like a sensible troubleshooting approach. Among other things, if the scavenge line doesn't return oil to the tank, you will fairly quickly run out of oil along with more almost burst aluminum coolers.

The picture, I assume, shows how you installed the Mocal? A picture of where you installed the pressure gauge would be helpful - I'm a bit unsure what "between the inlet and outlet" means in this context.

Here is another suggestion on troubleshooting pressure: As close to the outlet from the engine's scavenge outlet as you have an AN fitting, get a steel plug fitting, probably female, which you can screw into the outgoing Aeroquip line. Drill and tap that fitting so you can screw a male air hose connector into it. Now you can attach pressurized air from your compressor to do your checking. If you put a pressure regulator, like the ones used for spray painting, into this line, you can even control the inlet pressure. You could make another one for where you have the return line attached to the tank (maybe the engine side outlet of the Mocal) and drill/tap it to take a pressure gauge. Now you have taken the engine out of the equation.

[Tea Tray]

The problem will be between the oil cooler back through the thermostat then to the filter/ tank. The restriction asked the pump to build pressure which it did. The oil cooler was the lowest pressure fail point.
Hook an air hose to the oil cooler return line as mentioned above and check component by component.
Please tell us what you find.

[bosejuke]

Originally Posted by AlistairWallace

When you say high, how high?

the needle was pegged and went around to the 0 psi stop that would be at least past the 155 psi +