Oil Flow Direction for Gauge

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Sharecropper

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I'm planning on adding an oil temperature gauge to my custom gauge panel for my P400/700R4 build. All my gauges will be mechanical, so the gauge I purchased is the Autometer 5441 with a thermocouple line which runs from the thermo-bulb end to the gauge. The bulb has to actually be immersed in the oil to read properly. The bulb end of the thermocouple is a 1/2" NPT fitting, which is the same size as the oil inlet/outlet lines above the stock oil filter that run to the radiator cooler. It will be an easy task to simply plumb-in a 1/2" NPT Tee for the bulb fitting at this location. Problem is, I cannot figure out which line is the pressure line and which is the return line. I want to measure the oil temperature at the pressure line, not after the oil has been cooled at the radiator and returned to the engine. I have been through the TMs but cannot figure out which is which. Does anybody have a clue? No guesses please. I need to get this right the first time.

Thanks in advance for your help.

DSC_0270 - Copy.jpg
 

chevymike

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Looking at the pic, I would venture the rear lower port is pressure side. It appears to share the same plumbing up to the oil pressure sender port, if you look at how the block casting is. Seems like those two share that same internal routing. One in the side of the block is likely the return as it feeds into the block itself. That's just my observation.
 

ken

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Mike, according to diagram 2-35 in the GM 6.2 manual. The lower port is the pressure side to the cooler. And just a word of advice. Don’t restrict this flow in any way. You will starve the engine for COOLED oil. The diagram also shows there is a bypass valve on this line. In the Block. If the cooling loop is restricted it will send hot oil through the system and 1 give you a false reading and 2 send hot oil to the bearings.
 

Sharecropper

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Why not put it in the oil pan were it belongs?

That's where every heavy truck or Equipment engine I have seen is located.

Tom
Tom;
I agree that the best location for the sensor is in the pan, however the oil pan for this P400 engine is a unique, special one-of-a-kind heavy cast aluminum made especially for the P400 engine. I was trying to circumvent removing and drilling the pan because, heaven forbid, if something went wrong, there are no replacement pans available. I was simply exploring for alternate locations which would offer an oil flow across the sensor bulb, and the oil cooler lines seemed to provide an alternative location.

Ken:
Thanks for your comments. I fully recognize the need to NOT inhibit the flow of oil at this location. Both oil line ports are 1/2" NPT threaded, and my idea was to simply add a 1/2" NPT Tee off to one side at the block face for the 1/2" NPT sensor to thread into. This will allow the sensor (screwed into the "bottom" of the Tee) to barely protrude into the straight-through oil flow on the other end of the Tee. This design would not impede/restrict the oil flow in any way. If necessary I would alter the depth of the threads in the Tee to allow proper positioning of the bulb tip to just barely protrude into the oil flow. If this will work, I can leave my one-of-a-kind oil pan alone.

Anyway, I believe I will need to slightly reroute the oil cooler lines due to the headers. I plan to work through this issue in the coming days.

By the way, I had already abandoned my earlier plan of installing a pre-oiler pump on the new engine for the same reason of having to drill/install the oil pick-up at the pan.

Mike
 

richingalveston

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can you put it in the line that goes to your centerfuge. if it is close to where the block output is i think it would give you an accurate temp.
 

Sharecropper

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can you put it in the line that goes to your centerfuge. if it is close to where the block output is i think it would give you an accurate temp.
Rich -
Thanks for your suggestion however the line that supplies the centrifuge is a small -06AN hose and therefore is not large enough to install the 1/2" NPT sensor without an ugly arrangement of fittings. Also, the supply piping and valve for the centrifuge supply line would induce a radiant heat loss until the engine reached operating temperature, thereby causing an inacccurate gauge reading.

Unless I can find a reason not to, I intend to install the sensor in a Tee at the pressure port above the oil filter can. I will post photos in my rebuild thread over in the CUCV Hotrod forum.
 
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