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1995-2002 Range Rover P38A
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Discussion Starter #1
My 2001 4.6 P38 has low oil pressure and a knock at hot idle; I'm trying to determine what to do next. I just put it back together after replacing the timing chain, oil pump, and rod bearings. The rods didn't look bad at all and the oil pump wasn't cracked like some people have experienced. I replaced the o-ring on the pressure relief valve while I had the front cover off as well. I've looked up at the cam and all the bearings are where they should be, none have "walked out". Here are the oil pressure numbers:Cold (idling @750) = 23psigCold (@2000) = 43psigHot (idling) =3psigHot (@2000)= 22psigI'm running Mobil1 5W40Should I go ahead and pull the motor, or do you think I should try replacing the main bearings with the motor in and see if that fixes my oil pressure problem?
 

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Hi. I know that the earlier Gems engines like a thick oil (I ran 20-50 full mineral). Maybe other members can possibly confirm if this is correct for your engine also. If so then change to a non synthetic and check your reading again - you will probably gain 15-20 psi oil pressure. Just a thought from my own experience.
 

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1995-2002 Range Rover P38A
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My 2001 4.6 P38 has low oil pressure and a knock at hot idle; I'm trying to determine what to do next. I just put it back together after replacing the timing chain, oil pump, and rod bearings. The rods didn't look bad at all and the oil pump wasn't cracked like some people have experienced. I replaced the o-ring on the pressure relief valve while I had the front cover off as well. I've looked up at the cam and all the bearings are where they should be, none have "walked out". Here are the oil pressure numbers:Cold (idling @750) = 23psigCold (@2000) = 43psigHot (idling) =3psigHot (@2000)= 22psigI'm running Mobil1 5W40Should I go ahead and pull the motor, or do you think I should try replacing the main bearings with the motor in and see if that fixes my oil pressure problem?
Where did you connect the mechanical oil pressure gauge to get those readings?
 

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1995-2002 Range Rover P38A
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Discussion Starter #5
I took the alternator off, pulled the pressure sensor out, and screwed it into the pressure sensor hole.
 

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I was recommended by the engine builder to run 10W-60 in mine after the engine had been rebuilt but if you've put a new oil pump in I would have thought 10W-40 or 15W-40 would be fine. It certainly sounds like you are losing pressure somewhere.
 

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1995-2002 Range Rover P38A
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I’d run 20/50 full mineral, when these engines where designed and built, synthetic of any kind wasn’t around.
 

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1970-1995 Range Rover Classic
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Yes 20W50 Respsol mineral is what we use 5Wxx is definitely for Tierra de Fuego or Alaska :). The later ones get 20W50 semi
I imagine Alabama being the south of the US you'd be at 30ºC + at the moment that that is the same as here.
besides.. i calculate you oil pressure is between 1.6 when hot and 2.7 when cold.

"2,06 a 2,7 bares a 2400 rpm con el motor caliente" says my manual
since you are fine when cold it is definitely the oil
 

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1995-2002 Range Rover P38A
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I took the alternator off, pulled the pressure sensor out, and screwed it into the pressure sensor hole.
OK, thanks for the reply. That pressure sensor is hard to get at so I was wondering if you had found another place to connect to.
 

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1995-2002 Range Rover P38A
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Try running the engine with the rocker covers removed to see what kind of flow you are getting at the top end. Excessive play in the rocker shaft can affect pressure. If you’re getting a knock though then my money is on the mains.
 

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1995-2002 Range Rover P38A
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Discussion Starter #14
Try running the engine with the rocker covers removed to see what kind of flow you are getting at the top end. Excessive play in the rocker shaft can affect pressure. If you’re getting a knock though then my money is on the mains.

The knock is cyclical though.. I almost feel like I have two things going on. Maybe low oil pressure from opened up clearances (mains, cam, rocker shaft) and a wrist pin know / piston slap. I was so positive the knock was from the rods, because it is way more noticeable on the bottom end.
 

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Worn mains tend to rumble rather than knock and my engine builder said that wear in the little ends is very common but nothing to worry about and they will carry on like it for years. As the little ends aren't pressure fed, but splash fed, they would knock but wouldn't cause low oil pressure. Piston slap again wouldn't cause low oil pressure but tend to be more noticeable when cold before the pistons expand with heat, not the other way round. Did it have low oil pressure before you did the work on the engine? I'd be inclined to check the work you've done to make sure you haven't done anything silly.
 

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Thanks, I'm going to take the front cover back off and take another look at the oil pump and relief valve. I'm not exactly sure how to verify the piston makes its way all the way back down, but I'll verify it is installed correctly.
 

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