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Low Oil Pressure When Engine Is Hot


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#1 miniminiman

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Posted 21 July 2017 - 06:59 PM

Hello,

 

My A/T mini is suffering a serious problem after engine/gearbox-rebuilding by an unskilled mechanic.

 

The symptom is that the automatic transmission is working well in idle time, but when the engine is hot, I can hear terrible gear grinding sound.

( I guess it is the non-matching of the gears)

 

I googled the problem can happen when the oil pressure is low, so that I've checked the oil pressure with pressure guage.

 

When cold, it's okay, but hot, It dropped (I think due to viscosity on temperature) and the gear is non-matching still for the warmed engine

 

What can be the problem? 

 

- oil pump?

- oil pressure switch?

- oil relief valve?

- and another?

 

My guess is as follows:

- oil pump would be okay, because the pressure is normal in idle.

- oil pressure switch: I'm not sure that it controls the oil pressure electrically. I think the switch is just showing warning light. Am I right?

- oil relief valve: the spring tension is weak when oil temperature rises.

 

But that's my guess just without certainty.

 

 

Please help me!

 

Thank you in advance

 

 

 

SJ 


Edited by miniminiman, 21 July 2017 - 07:04 PM.


#2 Northernpower

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Posted 21 July 2017 - 07:06 PM

I'd go for the easy one first, check there is no swarf in the oil pressure relief valve.

#3 ukcooper

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Posted 21 July 2017 - 07:09 PM

oil and new fillter as the oil might be breaking down



#4 nicklouse

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Posted 21 July 2017 - 07:19 PM

i would also be asking the mechanic what was done if the plunger is not sticking.

 

as pressure is the result of two things the pump and the restriction to flow by the bearings. either failing and things go down hill very fast.



#5 Northernpower

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Posted 21 July 2017 - 08:10 PM

Which oil has it got in?

#6 miniminiman

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Posted 21 July 2017 - 08:48 PM

Which oil has it got in?

 

I have gotten in Repsol 15W50.



#7 miniminiman

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Posted 21 July 2017 - 08:50 PM

i would also be asking the mechanic what was done if the plunger is not sticking.

 

as pressure is the result of two things the pump and the restriction to flow by the bearings. either failing and things go down hill very fast.

 

If the low oil pressure in hot engine is caused by the two (pump, and bearing), the oil pressure switch is not affecting on the problem. Am I right?



#8 Northernpower

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Posted 21 July 2017 - 09:01 PM

The pressure light switch is just a measure, not a control.

#9 KernowCooper

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Posted 21 July 2017 - 11:17 PM

So what reading on oil pressure have you got ? Hot






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