SW86 Posted June 2, 2011 Share Posted June 2, 2011 alright so as of late my oil pressure has been reading about 30. when its cold after i start it up its about 45-50. then when i start to drive and fully warmed up, it drops. it never goes below 25 but it hangs around the 30-35 mark. surely that can't be right. I'm running 15w40 and its a 4.0. could it be the gauge? oil pump? thanks Link to comment Share on other sites More sharing options...
jimoshel Posted June 2, 2011 Share Posted June 2, 2011 Sounds OK to me. All symptoms you describe are normal for a high mileage engine. On a newer. lower mileage engine there won't be as much of a pressure drop. 30psi is adequate for an engine not being abused. Link to comment Share on other sites More sharing options...
SW86 Posted June 2, 2011 Author Share Posted June 2, 2011 thanks. well its only 114k on it. not really high miles in my book. and even when at 55-60mph its still the same. is that normal for it? Link to comment Share on other sites More sharing options...
jeep_freek88 Posted June 2, 2011 Share Posted June 2, 2011 Do you need an oil change? ...... I know I'm going to get shunned for this, oh well try changing your oil and replacing one quart of oil with lucas heavy duty oil stablizer..... That will get your pressure up for sure :thumbsup: I use 10w-30 fyi Link to comment Share on other sites More sharing options...
jimoshel Posted June 2, 2011 Share Posted June 2, 2011 114K is just broke in good. On your next oil change might switch to 10-30W and see what it does. 40 won't hurt anything but it is a bit thick. Also maybe change to synthetic. Synthetic won't change the OP drop but it does help the engine, in my opinion. After trying synthetic in my '88 MJ I've been switching all my vehicles over. Link to comment Share on other sites More sharing options...
SW86 Posted June 2, 2011 Author Share Posted June 2, 2011 nope don't need an oil change. i switched to 15w40 rotella after reading how good it was for the engine and would knock out the valve clicking. which it did knock out the clicking and the engine seems to run good. i knew id loose some pressure when switching over but i didnt expect to loose that much. plus down here in the heat/humidity i figured the thicker would be better for the summer but i used to run 10w30. as for synthetic i run it in all my other cars but just not the MJ. i don't know. thats just how it always seems to work out. :dunno: Link to comment Share on other sites More sharing options...
Eagle Posted June 3, 2011 Share Posted June 3, 2011 The highway pressure is a bit low, but if the idle pressure doesn't go below 25 psi you're good. The factory spec is 13 psi minimum at idle, and 37 to 75 psi above 1600 RPM. And that's for a NEW engine. Link to comment Share on other sites More sharing options...
1987Comanche Posted June 4, 2011 Share Posted June 4, 2011 The oil pressure on my '90 is about 8psi hot idle and 20-25psi at 2K RPM highway. I verifed the sender with a mechanical gauge and it's within 1-2 psi. I'd love higher oil pressure but she runs ok on 10W-40. Using 10PSI per 1K RPM rule of thumb I don't go past about 73mph (2300RPM on the tach). Been like that since the day I bought her... Link to comment Share on other sites More sharing options...
Akula69 Posted June 4, 2011 Share Posted June 4, 2011 Son gets 20 PSI at warm idle and flucutates between 50-60 PSI at 2500 RPM in his MJ with 264000 orig. miles When its cold it sits at 70-75 PSI and if he gets impatient and tries to drive it off before warming up it reads 80-85 PSI. Link to comment Share on other sites More sharing options...
Eagle Posted June 4, 2011 Share Posted June 4, 2011 The oil pressure on my '90 is about 8psi hot idle and 20-25psi at 2K RPM highway. I verifed the sender with a mechanical gauge and it's within 1-2 psi. I'd love higher oil pressure but she runs ok on 10W-40. Using 10PSI per 1K RPM rule of thumb I don't go past about 73mph (2300RPM on the tach). Been like that since the day I bought her... Switch to 15W50 full synthetic. Link to comment Share on other sites More sharing options...
SW86 Posted June 4, 2011 Author Share Posted June 4, 2011 The highway pressure is a bit low, but if the idle pressure doesn't go below 25 psi you're good. The factory spec is 13 psi minimum at idle, and 37 to 75 psi above 1600 RPM. And that's for a NEW engine. see and i thought it was a bit low for highway speeds. it never goes below 25 at idle but at times it sits right at it. I'm thinking about just upgrading my oil pump to one of those higher flow ones. that factory one was rough looking when i had to take it out to drop the pan and as i stated it just started to do this so it might just be clogged. :dunno: Link to comment Share on other sites More sharing options...
1987Comanche Posted June 5, 2011 Share Posted June 5, 2011 Switch to 15W50 full synthetic Do they have this weight in non-synthetic? I have the early 4.0 head gasket oil leak and go through a fair amount of oil. Link to comment Share on other sites More sharing options...
jimoshel Posted June 5, 2011 Share Posted June 5, 2011 Yes at Wally World or any auto parts. If for some reason you can't find any, let me know. I've got a couple cases of it. Link to comment Share on other sites More sharing options...
kro10000 Posted June 5, 2011 Share Posted June 5, 2011 Got valvoline vr1 20-50 in her now, keeps the pressure from 20-50 psi... Usually it sits at 40ish, but for whatever reason it drops to 20 if driven on the highway for a while. This happens maybe after 1/2 hour, wondering if the oil pump is going out... Link to comment Share on other sites More sharing options...
SW86 Posted June 11, 2011 Author Share Posted June 11, 2011 well i switched out the oil pump for a Melling one and it raised the pressure a little bit. maybe about ten. it still sits below fourty even when driving highway speeds. i guess this is just the way my engine is..?... :dunno: at least it doesnt get as low as it did. Link to comment Share on other sites More sharing options...
SW86 Posted June 11, 2011 Author Share Posted June 11, 2011 problem solved. changed the oil, after throwing on the new pump. put on a WIX filter to replace the STP. as soon as i fired it up oil pressure went back to almost prefect specs by those stated above. it actually goes up and down again when i press on the gas and idle is a solid 30psi. so all that time my dumbass left that part out and it was the problem! :grrrr: :dunce: CHANGE YOUR FILTERS PEOPLE!!!! :rotf: Link to comment Share on other sites More sharing options...
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