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Oil Pressure - thoughts or advice??

C

ChrisR

NAXJA Forum User
Location
NY
So... I bought a 2000 Jeep Cherokee 4.0 and the next day I found it had a crack cylinder head.

I had the cylinder head replaced and I am worry about the oil pressure reading

Cold start it's 40+ psi
Warm idle after 30 minutes just at 10 psi
Cruising at 45-60 at 1500-2000 rpms around 20psi.
PSI does increase with acceleration but nevers seems to go above 30-35 psi.

I had the mechanic check it with a mechanical gauge today and he read 14psi at warm idle and 35-40psi at cold start. He is telling me it's lower then he would like but to add 40 weight oil and keep an eye on it.

Thougths on my readings? Acceptable? dangerously low??

Keep or sell it? I bought it for $3600 and already spent $2000 it 3 weeks on this Jeep.

If Keep? Add 40 weight? Drop oil pan at some time to replace oil pump?
 
What type/Weight oil/Filter are you using? The type of oil/filter you use can make a huge difference in your oil pressure.

Not lower than 13PSI at hot idle is the Jeep Spec.
 
Those numbers are not great, but acceptable. Run it till it blows. If you can get it to start in the winter with thicker oil, that may help with the pressure.
 
Garr - Currently 10W30 with a Purolator Standard filter. Being in NY and temps can get into the teens sometimes, I',m thinking of going with 10W40, filter wise any suggestions?
 
I use 20W50, API SL spec, on all of mine. But it never gets below 20 -30 F here.

What oil brand, and API spec are you using, dyno or synthetic oil? How many miles?

I would step up to 10W40 or 20W50.

I swapped out the oil pump on one of mine with a high capacity oil pump at 224,000 miles, on my 87, and went to 20W50 ( over 4 years ago, about 55,000 miles ago). I went from 9 psi (dash gauge) to 18-25 psi (dash gauge) at hot idle, but that varies between winter and summer, and A/C on or off as my hot idle oil temp varies about 20 F, from 180 F to about 200 F.
 
jeep has 136k. I only had it 3 weeks so .... I may go with a 10w40 grade and a Napa filter as recommended by muddymike. As for oil, should I good with synthetic or just a standard brand like rotella, mobil1 or valvoline? Is one any better to keep my oil pressure running higher?
 
Try and find out what the prior owner was using first, synthetic, or not.

If it was not synthetic, try and find an API SL spec, the old oil spec (I find mine at NAPA sometimes, and at Autozone, in a store brand bottle).

If it has API SM or SN approval of any kind (even it also list API SL) run as fast as far as you can!!! They do not have enough ZDDP in the newer oils for our flat tappet engines.

I would not use synthetic, unless the prior owner used synthetic regularly in it.
 
Oil is oil, buy whatever is on sale. Current ZDDP levels are high enough for modern Jeep 4.0L engines.
 
ChrisR said:
Garr - Currently 10W30 with a Purolator Standard filter. Being in NY and temps can get into the teens sometimes, I',m thinking of going with 10W40, filter wise any suggestions?
Click to expand...

I am in NY also (Nassau County LI). I would switch to a premium filter & synthetic oil . I like Mobil 1, Wix or NAPA gold filters & whatever Synthetic oil walmart has on sale (Mobil one, Pennzoil platinum, Castrol syntec). My truck seems to like 10W40 M1 or Synthetic Shell Rotella 5W40 diesel oil year round, I use the oversize m1-301 filter (I scored a bunch of them from a going out of business sale), They hold 1/2 quart extra oil.

Funny thing my 2001 odo also just turned 136K miles !
 
Last edited:
I second Rotella 5w40 synthetic. It's thin enough (being a synthetic) for the cold NY starts, but thickens / thins up to a 40 wt oil.

My XJ doesn't have oil pressure issues - overheated with a 5w-30 I have 20psi hot idle but I have read that 4.0s get GREAT wear numbers on a 40wt oil.
 
Since you already have a low oil pressure problem, I would steer clear of Synthetics.

Might also want to check for gasoline odor in the oil from leaking injectors.
 
Miller88 said:
It's flow, not pressure that lubricates.
Click to expand...


So are you suggesting that pressure is irrelevant? I always thought it was the oil that lubricated, not flow, LOL?
 
ok so today I changed the oil. I used a Napa gold filter and 6qts of 15w40 Rotella, I noticed no increase in oil pressure and I believe the engine now sounds louder more clanking sound. I was really hoping the 15w40 weight would boost the psi a bit. Still seeing 10psi at warm Idle and 20psi running at 1500-2000 rpm

I had a mechanical gauge on it and readings were about the same as what I see on the dash. Now what?
 
What is the oil pressure cold?

Did you use synthetic or Dyno oil?

Is the idle speed too low??????

Sounds like it is time to drop the oil pan, and install a high flow oil pump, and check and service as needed the crankshaft bearings. Also, there may be junk in the oil pan clogging the oil pump inlet screen. Might as well change the front and rear seals at the same time.
Mine reached about 8 psi hot idle when I did that to mine, 7 years ago.
 
ChrisR said:
ok so today I changed the oil. I used a Napa gold filter and 6qts of 15w40 Rotella, I noticed no increase in oil pressure and I believe the engine now sounds louder more clanking sound. I was really hoping the 15w40 weight would boost the psi a bit. Still seeing 10psi at warm Idle and 20psi running at 1500-2000 rpm

I had a mechanical gauge on it and readings were about the same as what I see on the dash. Now what?
Click to expand...

How did the oil you removed look?
Did you check under the oil filler cap for milky residue?
 
I recently had the cylinder head replaced and oil now seems clear. I recently purchased the jeep and with the head replacement and other stuff I already spent 2k on a jeep I spent 3600 on. I'm ready to throw the towel in. I will likely take a hit in selling it and may leave it to the next owner to try the oil pump.
 
ChrisR said:
I recently had the cylinder head replaced and oil now seems clear. I recently purchased the jeep and with the head replacement and other stuff I already spent 2k on a jeep I spent 3600 on. I'm ready to throw the towel in. I will likely take a hit in selling it and may leave it to the next owner to try the oil pump.
Click to expand...

I would just drive it & forget it, many 4.0 have run for an addidtional 100k miles @ 10Psi hot idle.
The old oil pressure rule of thumb is 10Psi for every 1k rpm, so you are OK.
As for Much of the noise you are hearing, The 4.0 is a loud clanking old truck engine, Mine sounded like crap when it was brand new!

Next oil change (after the winter is over & it is warmer outside) try Mobil 1 15W50 & a M1 filter, I would bet your pressure will come up 3-4PSI.
 
Last edited:
Just throwing this out there. When I got mine it had almost no oil pressure. The window sticker said it had 5w30 in it. My book said it requires 10w30. Changing the oil fixed my issue. Now it is 15-20 at idle but take this for what its worth. My hi has a 302 in it. I lost all oil pressure on the trail but I was too far from the trailer so I didn't have a choice so I kept driving it all weekend and since it didn't smoke or make noise for the next six months wheeling whenever I could and not being easy on it. I changed it only because. I got a nice roller mustang engine for next to nothing otherwise it would still be in there.
 
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