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Oil pressure question

Oil pressure question

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D4guy
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During the initial starting of my newly rebuilt D4 engine (7U31604sp) the oil pressure was very slow coming up but after a few minutes the pressure would build up to peg the needle at the top. It seems that the time to build up pressure has been getting longer and longer each time I start the engine.

Now while cranking the beast, the oil pressure goes up about 1/3 of the way. It does not change much when the compression lever is set to compression. When the throttle is advanced the engine starts normally but the oil pressure falls to zero or near zero in just a few seconds. I have been more and more anxious about leaving it run to see if the pressure would finally come back up as it had before.

The pressure gauge is new, but suspicious about it, I substituted another with the same results. Not the gauge.

I bled the oil cooler thinking that somehow the oil circulation was air-bound but that made no change. I did get only a dribble of oil out of the vent while the engine was running. The engine sounds normal and warms up to the low edge of the operating temp.

Does anyone out there have any suggestions about what may be happening or what to do about it?

Thanks a lot.

Merv
1955 D4 Traxcavator, 1926 Model T Roadster, 1930 Model A Tudor, 1940 Diamond T 201, 1954 JD 40 dozer
www.mervbergman.net
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Tue, Oct 9, 2012 8:54 AM
Old Magnet
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Mount your gage directly to the oil manifold and see if that makes any difference. May be a clogged or crimped oil line.

Not getting much flow from the oil cooler vent line when running would indicate there is an engine oil pressure problem or something isn't right with the oil cooler bypass valve operation in the oil filter base. Do you have all the correct parts for the full flow oil filter installation?
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Tue, Oct 9, 2012 9:44 AM
D4guy
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Reply to Old Magnet:
Mount your gage directly to the oil manifold and see if that makes any difference. May be a clogged or crimped oil line.

Not getting much flow from the oil cooler vent line when running would indicate there is an engine oil pressure problem or something isn't right with the oil cooler bypass valve operation in the oil filter base. Do you have all the correct parts for the full flow oil filter installation?
Hi Old Magnet,

Thanks for your response to my post about my low/no oil pressure. I think that I have the answer---at least all the cues fall into place.

The oil pressure gauge on my D4 is piped right off the rear end of the oil manifold and the tube is clear. A substitute gauge indicated the same readings. Also I am confident that the full flow filter is assembled correctly.

My oil pressure problem got worse and worse over time. Clue one: The weather in west central Wisconsin got colder and colder. The oil thickened.

The oil pressure comes up normally while cranking the engine but goes down when the engine starts. Early on, when the weather was warmer the pressure would eventually come back up. When the engine was warm the pressure was good.

In a Cat manual I found information about the pressure regulator in the oil pump. A piston with a tapered end is arranged to be able to constrict the oil flow through a passage to the input to the pump. A spring normally forces the piston out of the oil flow. The other end of the piston is fed oil from a bypass at one of the main bearings. This oil pressure drives the piston against the spring. The higher the pressure, the more the piston constricts the input to the pump.

This fits with my observation that the oil pressure comes up while cranking (low pressure) but falls off when the engine starts (higher pressure) from the main bearing bypass.

My guess is that the piston is hanging up somehow or the spring is weak or broken and fails to clear the piston from the input path.

It sounds like a major effort to service the pressure regulator is in order.
1955 D4 Traxcavator, 1926 Model T Roadster, 1930 Model A Tudor, 1940 Diamond T 201, 1954 JD 40 dozer
www.mervbergman.net
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Wed, Oct 10, 2012 7:28 AM
ag-mike
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Reply to D4guy:
Hi Old Magnet,

Thanks for your response to my post about my low/no oil pressure. I think that I have the answer---at least all the cues fall into place.

The oil pressure gauge on my D4 is piped right off the rear end of the oil manifold and the tube is clear. A substitute gauge indicated the same readings. Also I am confident that the full flow filter is assembled correctly.

My oil pressure problem got worse and worse over time. Clue one: The weather in west central Wisconsin got colder and colder. The oil thickened.

The oil pressure comes up normally while cranking the engine but goes down when the engine starts. Early on, when the weather was warmer the pressure would eventually come back up. When the engine was warm the pressure was good.

In a Cat manual I found information about the pressure regulator in the oil pump. A piston with a tapered end is arranged to be able to constrict the oil flow through a passage to the input to the pump. A spring normally forces the piston out of the oil flow. The other end of the piston is fed oil from a bypass at one of the main bearings. This oil pressure drives the piston against the spring. The higher the pressure, the more the piston constricts the input to the pump.

This fits with my observation that the oil pressure comes up while cranking (low pressure) but falls off when the engine starts (higher pressure) from the main bearing bypass.

My guess is that the piston is hanging up somehow or the spring is weak or broken and fails to clear the piston from the input path.

It sounds like a major effort to service the pressure regulator is in order.
one won't believe the sludge build up in the oil pan, my screen was practically covered with it and oil had tobe restricted.
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Wed, Oct 10, 2012 7:38 AM
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