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wlf89

82 720 very low oil pressure

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rebuilt my z22 engine in my 82 pickup 7k miles ago, i have noticed oil pressure has been alittle lower than normal and has gradually got worse. i figured it was just the elec. sending unit that was going bad, so today i put mechanical gauge on it and its got very little pressure at idle and around 10psi at 2000rpm.

 

i have changed oil and filter, checked to make sure the pickup screen in pan wasnt clogged and checked the bypass valve in pump to make sure it wasnt hung open, all was good.  all i know to try now is a new pump, anyone have any ideas what it could be?  it normally had 45-60 while on the road driving and around 20 idle.

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Possibly pan dented causing no clearance to pickup?

Had a timing cover gasket misinstalled allowing air to enter on suction side between oil pickup and oil pump. There was no oil leakage to the outside of the engine.

Also,try a known good oil pump.

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I would look for a new engine rebuilder for your next engine.

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Bearing clearances a little on the large side of spec.?

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The relief spring broken? It's quite stiff. Try the relief spring and piston from another pump. Any L or Z series oil pump will work for a test. If you can't find a pump, at least remove and take apart and look at the rotor. If 10 PSI at idle the pump will be trashed completely. If replacing it, get the pump from a D21 Hardbody with KA24E or DE engine, it's a high volume unit and will boost low engine speed pressure although top pressure will be the same.

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after 7k i hope the bearings aint that wore out, ive never seen a engine with wore out bearing not atleast have decent oil pressure on cold start, pan isnt dented, nothing looked wrong with the relief valve, ive got one of the high volume oil pumps ordered,hope that fixes it if not, aint sure what to try next.

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try 20 50 Castrol

try a NAPA oil filter

then fuck it get a high vol pump as Mike says.

 

I have alwasy ran stock and used on my firstmotor I built

 

If ever do it again I do Hivolume

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I have had problems with the Napa filters leaking on my Z24s. I use WIX.

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 Napa filters are WIX.  Just painted a different color and a NAPA logo.  Same filter inside.

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The clearance in the main bearings help control the oil pressure. Anything over .003" clearance will show signs of low oil pressure, but it won't degrade over time, unless there's a major problem with the assembly. Another area that helps control oil pressure is the center main thrust bearing. Again, too much thrust can lower the oil pressure. A lot of thrust bearings need fitting by the engine assembler, so if your engine builder didn't know what he was doing, he could have screwed this up.

 

Believe it or not, a misadjusted clutch master or slave can damage the thrust bearing by holding constant pressure on the back of the crank, which wipes away the oil causing it to wear. You can check the thrust by pushing/pulling on the crank pulley, but if your clutch slave is applying constant pressure (which it should not), then you will have to remove the clutch slave to check the thrust. Worst case, your thrust bearing and your crank can wear out.

 

Do you know if your clutch was adjusted properly? With play at both the pedal and the slave?

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pedal and slave have free play and there is not movement in the crankshaft pulley. high volume oil pump will be here tues so wed morning ill get it on and see if thats the problem.

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got the oil pump on this morning, getting about 18psi at idle and about 30 going down the road at 55mph can get it up to 35 if in 4th gear and around 3300rpm. this is still low isnt it? it used to be between 45-60 going down the road, but that was with old gauge and sender that i never was sure if was working right, but i guess it was because it showed about the same as the mechanical i have in now before i changed the pump.

 

anything else yall know to check other than bearing clearances? the was on the tight end of specs when i put it together i just cant see them being wore out after 7k miles. i used a dnj kit maybe they aint no good?

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My tired old truck L20B using a 720 gauge and sender hot idled at 17 PSI. With just a high volume pump added it jumped to 29.

 

 

My 710 with the same gauge and pump hot idles around 29PSI also. It cold idles at 65. I have a new digital gauge and will report on those readings. 

 

So yes I would say the gauge is wrong or you have an internal leak. I'm going to go with a faulty oil pressure gauge because it's the easiest cheapest fix.

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the gauge is new and has been checked on my tractor to verify that it reads the same as the gauge installed on the tractor and it does

 

where would a internal leak most likely be and how would i find it?

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That's a very good question. If leaking it must be internal. If not the bearings maybe an oil jet fell out. The L series had one just above the crank sprocket to oil the chain.

 

JXjXFLb.jpg

 

Also there is the timing gasket that seals the oil from the pickup tube and the oil under pressure to the filter. The hole above and to the left of the 13 is the pressure gallery to the oil filter,  and the one higher and above the 13 is the pressure line gallery from the filter that feeds all the mains. A leak could just return the oil to the pan. 

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guess i will be pulling front cover and checking that out. is the oil jet your talking about the dowel looking thing in middle of chain just above crank? looks like a tiny hole in it for oil to squirt out.

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got the oil pump on this morning, getting about 18psi at idle and about 30 going down the road at 55mph can get it up to 35 if in 4th gear and around 3300rpm. this is still low isnt it? it used to be between 45-60 going down the road, but that was with old gauge and sender that i never was sure if was working right, but i guess it was because it showed about the same as the mechanical i have in now before i changed the pump.

 

anything else yall know to check other than bearing clearances? the was on the tight end of specs when i put it together i just cant see them being wore out after 7k miles. i used a dnj kit maybe they aint no good?

 

I get a solid 50psi at speed with a KA pump. Probably about 25 at idle.

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There's a gasket on the pick up tube where it mounts on the block, if those bolts were not tightened properly the tube will start separating from the block causing air to get sucked in thus losing oil pressure.

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I've seen some of the pick up tube flanges warped also.

I put those to a belt sander, and grind them flat again.

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finally getting around to working on the 720, so far i have determined the bearings are still well within spec and no damage, and the oil pickup was nice and tight still and gasket wasnt broke or nothing. guess its on to the timing cover now and see if see anything wrong there.

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neither do i but i am running out of ideas here, told it could be the timing cover gasket to, but i cant see it just blowing out after 7k miles, but got to look for something

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ok got the cover off and didnt see nothing wrong gasket wise no broke spots or signs of leakeage. but the timing chain tensioner bolts had backed loose, one was pretty much all the way out and the other was loose. it looks like it bolts over a oil hole so im hoping with it loose and not sealing the oil was leaking around it and loosing pressure and this is my problem. would everybody agree?

 

and mine doesnt seem to have the oil jet above the crank sprocket, there is a little brass looking pin there but it doesnt stick out past the block any. is that right or is something about that wrong? in the pic earlier in the post that showed the jet was said to be a L series engine and mine is a Z so maybe a design difference?

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L series had them and Z series may have dropped them... I've heard this. I have a Z20 and it has one but it's basically an L20B block anyway.

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I am voting for the loose tensioner body, good catch.

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