Cruising Oil Pressure

Is this bad for a warmed up, cruising (1550 RPM) 1989 4.0L cherokee?

The needle was where the red one is now. Also I don't understand the numbers? (I'm in Canada btw)

For the record, I'm using Shell 10w30 dinosaur oil, with an AutoExtra oil filter.

The Canadian one is marked in Bars I think. One bar is one atmosphere, one atmosphere is 14.7 PSI.

Not sure about the two needles issue? 13 PSI is factory minimum at hot idle of 750 RPM. You should have more like 30 psi or higher at 1500 rpm so that looks low. IF its got a lot of miles I would move up to a lot thicker oil in the summer like 20W50. Then 10W40 or 0w40 in the winter.

Also a plugged, plugging oil filter, or bad oil pressure sensor can give you a low reading.

Also be sure and read the latest oil thread here on the zinc additive issue (problem) with all the current oils.

mattbred said:

Is this bad for a warmed up, cruising (1550 RPM) 1989 4.0L cherokee?

The needle was where the red one is now. Also I don't understand the numbers? (I'm in Canada btw)

For the record, I'm using Shell 10w30 dinosaur oil, with an AutoExtra oil filter.

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I painted the red needle on it to show where the white needle was at while cruising.

So it would be just under 14.7 PSI at cruising? eek.. I don't like that. hm. The engine was rebuilt 50,000 kms ago, so it's definitely not worn.

Ecomike said:

The Canadian one is marked in Bars I think. One bar is one atmosphere, one atmosphere is 14.7 PSI.

Not sure about the two needles issue? 13 PSI is factory minimum at hot idle of 750 RPM. You should have more like 30 psi or higher at 1500 rpm so that looks low. IF its got a lot of miles I would move up to a lot thicker oil in the summer like 20W50. Then 10W40 or 0w40 in the winter.

Also a plugged, plugging oil filter, or bad oil pressure sensor can give you a low reading.

Also be sure and read the latest oil thread here on the zinc additive issue (problem) with all the current oils.

Click to expand...

What are some good additives to bandaid my situation until I do the oil again?

If you'r looking for a good additive/"bandaid" probably the best out there would be Lucas oil additive. Deff. the best out there, its about 8 bucks (u.s.) a quart but that stuff is wonderful. Makes for good preventitive maintance too. But yeah you shouldn't be running less than 30 p.s.i. at cruising speeds, I think 10-15 is like the min. at idle. (dont qoute me here) ill leave the conversion table up to you for the psi to bar's conversion seeing as I suck at that stuff.

Hope this helps.

Alex
henderson nv.

mattbred said:

What are some good additives to bandaid my situation until I do the oil again?

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Read the thread on here now about oil. It was posted by Ecomike and is now up to 4 pages. It will give you some choices and some oils to avoid. All in all a good read.

Yeah I saw that. I guess Shell isn't a good oil. Oil pressure seems down when it's warmed up. I'll try adding some lucas to it.

Btw it looks like I'm getting between 15 and 20 PSI at cruise. - IF the gauge is correct.

mikeforte said:

Read the thread on here now about oil. It was posted by Ecomike and is now up to 4 pages. It will give you some choices and some oils to avoid. All in all a good read.

Click to expand...

I had a similar problem with my 2000 I6, pressure gauge shows 0 in idle but would climb up to about a quarter of the way up on the gauge (position of needle should be the same, bars and PSI print on gauge is the only difference) when engine is revved above 2000 rpm in either idle or taking off in drive reaching above 2000 rpm, but would return to zero when engine returned to idle as if it just turned off, though it didn't obviously. After much poking around electricals, cleaning sensors, and reading the forums here, I bought a new oil pressure switch (pressure sensor really, but its called a switch) at Autozone for $46.99US (part # PS401 for 2000 I6 engine) and it is working fine now. If you choose this route, I hope it works for you too. Good luck!

P.S. here's a link for autozone's part for my 2000 http://www.autozone.com/R,APP260266/vehicleId,2578202/initialAction,partProductDetail/store,2838/partType,00134/shopping/partProductDetail.htm
and here is for 1989 http://www.autozone.com/N,15300134//shopping/partTypeResultSet.htm

I did the math, and you're running about 22 psi; that's a little low (depending on actual RPM of engine) but can be helped. If I were in your shoes, I'd switch to a good quality oil (Valvoline MaxLife for me) and replace one pint/quart/litre with equivalent amount of Lucas oil additive. I'd also look around at various parts shops and ask for a Wix brand oil filter. I did this, and saw a 5 psi jump right across the board.

It's hard finding a Wix filter here in Canada, but should be possible. Also, snag a new oil pressure sending unit; it's worth it to have a good one in there as they're notorious for going south on you.

Good luck, and I hope this helps!

PS: Whereaboots in Canada are you? Are you Matt from the office? Do you know him? He's from Canada too...

It looks to me like you are almost at 2 bar. 2 bar is 29.4 psi, which you are a little under. I've always heard that you want 10 psi for every 1000 rpm. Anything under that is not supposed to be good. I'd try to WIX filter if you can get one. If you have a Napa Autoparts, buy a Napa Gold filter from them as they are made by WIX. What is your oil pressure at idle? Also, you might try putting a mechanical oil pressure gauge on it as the electrical gauge system can give you some bad readings sometimes.

Couldn't see the mileage. Those are bars....imagine the 3 being 40lbs and where the red line is is 20lbs. I think low is 13lbs min. I had an 88 that went down to about 8lbs and still ran o.k. does it go lower at idle?

I am confused by the second needle. What is that all about?

I can't read the number under the white needle, is it 1 or 0?

If it is zero, then I have to ask if that gauge is linear, in other words is the first line 1 or 2 bars?

Go buy or borrow a mechanical presure gauge and hook it up where the sender sensor is on the bottom of the oil filter / side of the oil filter adapter. Same presure gauge can be used for checking engine vacuum and fuel pressure. Costs about $35.

Oil filters can get dirty and drop the oil pressure the engine and gauge sees. Don't buy or use Fram filters, stick with K & N, Mobil 1, Wix, Napa Gold and you cant go wrong. Most others are private labeled and are or could be Fram filters in disguise.

Shell Rotella T is ( or was until recently a great oil). I will leave the rest of the new oil selection issue / problem for the other thread here, but once you figure out what the real oil pressure is on your engine, if it is less than say 22 PSI at 600 rpm idle, or less than 30 psi (2 bar) at 2000 rpm, I would first go to higher viscosity oil, before using Lucas as an oil pressure boost additive. Try a 15W40 like Shell Rotella T, or a 20W50 if your oil pressure is down to say 10 psi at idle already with the current oil, a properly working gauge and new oil filter. Find out what the real pressure is with a new oil filter and a mechanical gauge before you do anything. And figure out where 20 PSI and 30 psi is on that dash gauge???

Some good information here. Man I love Naxja.

Ecomike, I took the picture and edited it to add a fake needle where the white one WAS while cruising at 1550 RPM. If the middle is 3 bar, and far left is 0 bar, then I should be running at around 15-20 PSI. Which is what the gauge says. When it is cold, the needle is at or above the 3 mark, which is good. I'm thinking it could be a sending unit, and I want to replace one. They're a bit pricy at napa though (30-40 bux).

Thanks for all the tips. I think I will get the pressure checked and confirmed and go from there!

I have a 89 and I had the same issue when I bought it. It has 189k miles and the idle reading was 5 PSI and 25 at speed. I changed the pressure sending unit and it went up from 5 to 19 warmed up and from 25 to just above 50 at speed. If you have not changed the sending unit start there. You can get a bad unit that will fail in just a short time. Don't ask how I know.

Good luck

Got it, finally figured out what you had done there. That middle spot just above the red needle mark looks to be 1.5 bar (apx) or about 22 psi. Try changing the oil filter first, much less expensive, and see if the hot and cold idle pressure increases. Dirt in them causes a pressure drop. If the dirt is casuing an overall 5 psi pressure drop that would be part of it. Could have gotten a slug of sludge breaken loose that is clogging the oil filter.

What does it read hot and cold at idle?

mattbred said:

Some good information here. Man I love Naxja.

Ecomike, I took the picture and edited it to add a fake needle where the white one WAS while cruising at 1550 RPM. If the middle is 3 bar, and far left is 0 bar, then I should be running at around 15-20 PSI. Which is what the gauge says. When it is cold, the needle is at or above the 3 mark, which is good. I'm thinking it could be a sending unit, and I want to replace one. They're a bit pricy at napa though (30-40 bux).

Thanks for all the tips. I think I will get the pressure checked and confirmed and go from there!

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When cold, idle is around the half way mark I believe (3).

I'll try changing the oil filter. Is it possible to change it without draining the oil first?

mattbred said:

When cold, idle is around the half way mark I believe (3).

I'll try changing the oil filter. Is it possible to change it without draining the oil first?

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Yes, depending on the oil filter size, you will loose only 1/2 to 1 quart of oil when changing the filter. That is oil that is in the filter, if the antidrainback valve in the filter is working properly. IF it is not you will loose much less oil as it drained back into the oil sump already.

The anti drain back valve is desgined to keep the oil filter full of oil so that the engine gets oil at start up, not a few seconds later.

Don't forget to top off the oil level. You might test the oil pressure before adding the 1/2 to 1 quart back in. Then if the pressure is really low you have room for adding some oil thickener to raise the oil pressure with out draining more oil, until your next oil change (if you decide to wait to change the oil). A one quart low oil fill should not affect the oil pressure!