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High Oil Pressure w/ Melling

EZridaz

NAXJA Forum User
Location
Charleston, WV
I have a 1998 XJ with 112,500 miles,4.0. About a week ago I had to replace the rear main seal as it was leaking a drop here and there. I really could have waited but I am anal retentive about things like that and take care of them asap. So while I have the pan off I decide to do the oil pump with a Melling high volume pump with pick-up tube since it was cheaper than an OEM without the tube. Nothing was wrong with the old pump as it held good pressure.Cold idle was around 35-40 psi and 2200 rpm was around 40-45 psi and hot idle around 20-25 psi. So I changed the rear main and torqued the cap from 40-60-80 ft. lbs.. I "massaged" the pan as I did have a clearance issue with it hitting and had to carefully bend the tube up from the bottom a little bit as it was hitting as well. Next I add the oil back in which is Valvoline Max Life Full Synthetic 10w-30 and a WIX 51515 filter as I always use. So now I have a cold idle oil pressure of 55 psi.,a hot idle oil pressure of 40 and at 2200 rpm/ 60-65 mph and an oil pressure of 65-70 psi.. That was the part that was worried about is the 65-70 psi while I'm running on the interstate. I am afraid that the pressure will make the cam walk or wear my distributor gear. I do hear a tink tink tink in there that wasn't there before but I believe I didn't bang the pan out enough and am getting a vibration from the pump against it. The pan went on fine which lead me to believe I had clearance but I guess it was just enough to clear it. So I went and bought a mechanical gauge and it confirmed my dash readings, so I ruled out the oil pressure sender and dash gauge going bad. So today I take the high volume one out and put in a "regular" Melling oil pump and the readings is even higher! WTF!!! It is about 55-60psi at cold or hot idle at 600rpm and when I get to say 1500-1800 rpm it pegs over to 80psi on the dash gauge and mechanical gauge. Sorry to be so long winded but I'm trying to get all the details out of the way. Any help would be greatly appreciated!!!
 
I put a Melling in my 90 RENIX when it was rebuilt. it does run some high oil pressure. Between 50-70.

Note my engine is completly new, the only thing reused was the head itself, the block itself, the valves and the crank which was turned and polished.
 
Just because you have a mechanical gauge doesn't mean it's accurate. I took my compression tester into work and calibrated it with some pressure calibrating equipment. My tester was showing 5 psi high. I see many gauges that are inaccurate when hooked to calibrated test equipment.
 
mccastlej said:
Just because you have a mechanical gauge doesn't mean it's accurate. I took my compression tester into work and calibrated it with some pressure calibrating equipment. My tester was showing 5 psi high. I see many gauges that are inaccurate when hooked to calibrated test equipment.

It's not a matter of if the gauge is "exact" as much as it's much higher than normal. I would have better odds of hitting the lottery than both gauges bein off by 30psi immediately after changing RMS with no other problems.

I would double check bearing clearances and verify that the oil has room to get past the bearing (not too tight)

--Shorty
 
UPDATE: Well I just put the old pump back in with 112,000 miles on it and the pressure is fine now. I don't know why the Melling pumps jumped up so high on me. The high volume one I understand why but not the regular Melling. I believe I might have been able to get away with the HV one but I'm not pushing it. I'm just glad my old one was still fine instead of worn out. I think it had something to do with the pressure relief valves on the pumps. Oh well I'm back on the road so that is all that matters. Thanks for feedback!!!
 
My oil pressure gauge (stock one) goes from about 60 to 90 most of the time. When I first got it about 8 months ago it worried me, but now I just figure it's a bad gauge or sending unit. Do y'all think that's what it is since I've ran for 8 months without any problems. Or, perhaps the high pressure is a cause for my oil leaks?
 
AlabamaDan said:
My oil pressure gauge (stock one) goes from about 60 to 90 most of the time. When I first got it about 8 months ago it worried me, but now I just figure it's a bad gauge or sending unit. Do y'all think that's what it is since I've ran for 8 months without any problems. Or, perhaps the high pressure is a cause for my oil leaks?

Well I would definately start fixing your leaks and clean the motor real good to see where some might be coming from. I would also get a manual oil pressure gauge that you hook into the oil pressure sensor outlet and see if the readings are the same as your dash. I figure it might just be the oil pressure sensor but I would get a gauge to verify.
 
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