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Old 08-14-2011, 11:16 PM   #1
buckinbronco94
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low oil pressure at idle please help

hey there, i would really appreciate any help i can get on this topic. i recently bought a 1985 ford bronco full size xlt with the 5.8l 351 windsor v8. truck is all original. has roughly about 170k. i bought the truck 100% stock down to it still having the original spark plug wires from ford. only thing taken out was the reservoir tank (no truck does not overheat ever) and the emisssions pump. other than that all original like i said. now, i changed out all 3 belts cause they were loose and would squeal after 55mph and at start up. i also decided to change the oil pressure sensor. gauge would always mark normal usually never under the n and never over the o/r. i changed the oil. old oil was super thick almost like mud, guess pevious owner never changed it often, lol, i put 6 quarts of castrol gtw 10w40 with a motorcraft oil filter. ever since it starts up and drives with oil pressure half way on normal no lower than on the r/o. so it deffenitely drives with higher oil pressure than before with oil change and new sensor. but why does it at a complete stop when truck isnt moving drop all the way down to the L before the word normal like if it has no oil pressure. when you stop at a gas station etc.. and start up it will stay on L and gauge will not move up until truck is moving. it doesnt knock or ping or rattle when at idle and oil pressure is on L what can this be? thanks it never dropped under the word normal especially all the way pegged down on the L until after the oil change and until i changed the oil pressure gauge sensor
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Old 08-14-2011, 11:51 PM   #2
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thinner oil not pumping as well as the old(thicker) oil at idle.?.?
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Old 08-15-2011, 12:00 AM   #3
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it used to knock like hell with the old (thicker oil due to it not being changed over time, it literally looked like mud) at a cold morning start up. pressure used to never drop to L like showing there was no oil pressure at all. it would never go under the letter n on the normal it would always stay between the two white lines. now with the new oil and oil pressure sensor changed it just pegs on L out of the normal 2 white lines box until the truck is moving then it will shoot back up to the letters o/r in the word normal. but yet now with the new oil it doesn't knock at start up.
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Old 08-15-2011, 01:42 AM   #4
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put in a mechanical gauge and post up the numbers. the stock gauge doesnt tell you much
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Old 08-15-2011, 01:43 AM   #5
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put in a mechanical gauge and post up the numbers. the stock gauge doesnt tell you much

^^ that

except i recommend a decent aftermarket electronic gauge with numbers.. i've had those damn teflon lines break and the oil run on me 3 times so far on different vehicles. one ended badly with spun bearings.
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Old 08-15-2011, 03:22 AM   #6
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^^ that

except i recommend a decent aftermarket electronic gauge with numbers.. i've had those damn teflon lines break and the oil run on me 3 times so far on different vehicles. one ended badly with spun bearings.

Not to mention oil all over the interior.
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Old 08-15-2011, 09:44 AM   #7
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Wrong oil

Switch to 15w40 diesel oil. Problem solved.
Worn windsors behave like that.
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Quote:
Originally Posted by buckinbronco94 View Post
hey there, i would really appreciate any help i can get on this topic. i recently bought a 1985 ford bronco full size xlt with the 5.8l 351 windsor v8. truck is all original. has roughly about 170k. i bought the truck 100% stock down to it still having the original spark plug wires from ford. only thing taken out was the reservoir tank (no truck does not overheat ever) and the emisssions pump. other than that all original like i said. now, i changed out all 3 belts cause they were loose and would squeal after 55mph and at start up. i also decided to change the oil pressure sensor. gauge would always mark normal usually never under the n and never over the o/r. i changed the oil. old oil was super thick almost like mud, guess pevious owner never changed it often, lol, i put 6 quarts of castrol gtw 10w40 with a motorcraft oil filter. ever since it starts up and drives with oil pressure half way on normal no lower than on the r/o. so it deffenitely drives with higher oil pressure than before with oil change and new sensor. but why does it at a complete stop when truck isnt moving drop all the way down to the L before the word normal like if it has no oil pressure. when you stop at a gas station etc.. and start up it will stay on L and gauge will not move up until truck is moving. it doesnt knock or ping or rattle when at idle and oil pressure is on L what can this be? thanks it never dropped under the word normal especially all the way pegged down on the L until after the oil change and until i changed the oil pressure gauge sensor
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Old 08-15-2011, 02:05 PM   #8
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PaulW it has 6 quarts of 10w40 now and a motorcraft oil filter, when it drops to low oil pressure at idle on the gauge will that screw up my motor cause when it's moving it has oil pressure marking at almost half way. should i stop driving it like that or should it be fine.. thanks bro
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Old 08-15-2011, 02:07 PM   #9
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Camo Horse is it difficult to change the oil pump pick up tube? would you know of anyone who would be able to help me out with this project? if it's not that then i'd go to the more serious extreme and change the oil pump now how hard would that be to do? thanks again bro
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Old 08-15-2011, 03:25 PM   #10
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before droping the pan, drain the current oil and put a 75(carb)/25(oil) mix of carb/parts cleaner/oil in the oil pan over night, run it for a sec or 2, turn off engine, let it sit overnight and drain and add new oil

cant find it, but someone did that on explorer forums on a 4.0 with no oil pressure and it brought back oil press,
you could do 100% parts/carb cleaner but i wouldn't run it, just let the pickup soak overnight(the longer the better).


also keep in mind ive heard on the 5.0s if the oil pressure is low at idle it could be the main bearings going out.
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Old 08-15-2011, 04:06 PM   #11
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im confused. how can it possibly be the oil tube filter or even the oil pump if rite before i changed the oil it was always perfect. now with the new oil in it runs with a higher oil pressure but at idle drops to the minimun if any pegged all the way down to the L as low as that needle on the dash can go. it has to be that the oil is too thin. im going to try and find something i can add to the oil to clean and make thicker for now until it's next oil change. im assuming it should be fine as long as the motor has oil in it at all times it shouldnt lock up if oil gauge reads L rite? thanks.
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Old 08-15-2011, 05:16 PM   #12
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The oil you drained out was likely thick to avoid the low pressure at hot idle you have run into. When an engine has worn bearings, thin oil will run out of the bearings as fast as the pump can supply it at low RPMs. At higher RPMs the pump is better able to keep up. It is normal for the idle oil pressure with hot oil, to be a good bit lower than the cruising oil pressure, but you would like for it to stay in the "normal" range.

Before I replaced my 302, I had to run 20W50 and two bottles of STP to get the oil thick enough to stay in the normal range at hot idle. I did this a couple years summer and winter. I eventually put in a re-manufactured long block that is so much tighter than the original engine was when it was new. After 80,000 miles on it, there is still almost no drop in oil pressure when idling.

I doubt that the new sender had anything to do with the low idle pressure, however you could try reinstalling the old one to see. Different senders can give slightly different readings.
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Old 08-15-2011, 05:57 PM   #13
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the recent oil change consisted of 6 quarts of castrol gtx 10w40 and a motorcraft oil filter. oil was thick like mud because previous owner wasn't on top of it i guess. i just added half a bottle of lucas heavy duty oil stabilizer to see how it does.. if no change then next oil change it will take 6 quarts of 20w50 and if that doesnt help as much i will put in a half bottle of that lucas heavy duty oil stabilizer. but lets see how it does now with the 6 quarts of 10w40 and that half bottle of lucas.. i'll let ya know. that lucas stuff seems to be good stuff and very thick
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Old 08-15-2011, 06:57 PM   #14
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Im going to say worn bearings.
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Old 08-15-2011, 08:29 PM   #15
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I would bet that when you get the oil thick enough to get passable oil pressure at hot idle, it will look like what the OP had in it, as far as its thickness is concerned.
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Old 08-15-2011, 08:34 PM   #16
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Camo Horse the recent oil change consisted of 6 quarts of castrol gtx 10w40 and a motorcraft oil filter. oil was thick like mud because previous owner wasn't on top of it i guess. i just added half a bottle of lucas heavy duty oil stabilizer to see how it does.. if no change then next oil change it will take 6 quarts of 20w50 and if that doesnt help as much i will put in a half bottle of that lucas heavy duty oil stabilizer. but lets see how it does now with the 6 quarts of 10w40 and that half bottle of lucas.. i'll let ya know. that lucas stuff seems to be good stuff and very thick, what do you think? do you know of anyone who would be able to help me change out the screen and/or pump?
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Old 08-15-2011, 08:35 PM   #17
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nelbur so your saying just to get the oil as thick as i can and i should be fine?
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Old 08-15-2011, 10:19 PM   #18
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just sent you a pm camo horse
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Old 08-15-2011, 10:20 PM   #19
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The 40 is for high temps. the 10 or 15 is for low temps. Dump the 10w40 and put in 15w40 and report back. If the PO was so negligent the and the load of good oil should help to flush out the junk.
Thes motors seem to survive low press at idle, at least mine did until I went to 15W40. My press is higher at idle and at 2000 rev.
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Quote:
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PaulW it has 6 quarts of 10w40 now and a motorcraft oil filter, when it drops to low oil pressure at idle on the gauge will that screw up my motor cause when it's moving it has oil pressure marking at almost half way. should i stop driving it like that or should it be fine.. thanks bro
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Old 08-15-2011, 10:35 PM   #20
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so paul your recommending i just thicken my oil and not change the oil pump or screen being that the problem is that the oil is just to thin?
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