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picking the right oil - is it so hard??

S

Sandydog

NAXJA Forum User
Location
Albany, NY
So recently replaced the cylinder head on a 2000 Jeep with 145K miles that I purchased.

Got low oil pressure.. confirmed with mechanical gauge. 40psi at cold start, 10 psi at warm idle, 20PSI at 1600 rpm. (I already swapped the oil sensor - no change)

I went from 10W30 to 15W40 with no noticeable increase in PSI but do feel the engine is a bit noisy now. (used Rotella 15W40 with a Napa gold filter).

I was at a shop today and a guy suggested I go with a synthetic 20W40 - I'm in the Northeast, but he said synthetic starts as water and thickens as it warms up, standard oil goes the other way starts thick and thins with heat. Is this accurate? As you can tell I am clueless - and here I thought oil is just oil.

Sandy
 
It's not an oil problem. Low oil pressure is a symptom. Verified with a mechanical gauge means something. Could be something simple like a bad oil filter, oil pump bypass is stuck, or or could be that 145K everything is worn.

-Ron

Edit: Replaced Cylinder head? How long did you let it go with a milkshake in the lower end?
 
Sandydog said:
I was at a shop today and a guy suggested I go with a synthetic 20W40 - I'm in the Northeast, but he said synthetic starts as water and thickens as it warms up, standard oil goes the other way starts thick and thins with heat. Is this accurate?
Click to expand...
No, that is incorrect. Synthetic and non synthetic will be thicker when colder.

As said previously, it could be and issue with the oil pump or filter. What you most likely have is bad bearings in the bottom end (crank main, rod and cam bearings). Coolant + oil = acid that attacks bearings.
 
Talyn said:
No, that is incorrect. Synthetic and non synthetic will be thicker when colder.

As said previously, it could be and issue with the oil pump or filter. What you most likely have is bad bearings in the bottom end (crank main, rod and cam bearings). Coolant + oil = acid that attacks bearings.
Click to expand...

x2. Run far far away from that shop.
 
Sigh!

So today my son took the Jeep for a short ride and returned telling me the oil pressure went to 0 psi and the check gauge light came on.

Am I totally screwed at this point? Although the low pressure was low it was at 10psi at worst. Would it just go to zero in a matter of a day? I had 15w40 with a Napa gold filter. I had the oil sensor changed a week ago. Could an oil pump fail like that? Help.
 
No pressure doesn't mean the pump isn't working. The bearings are apparently offering no resistance, as the oil is probably just gushing out of the mains. This also means that not enough oil is making it up to the head, hastening its wear also. Like has been stated earlier, pull the pan and verify what has been suspected. Hopefully you bought it right, as it would be worth it to fix. A re-man short block would seem to be in order, and with the recent head, you'll have a good start.
 
heyhar said:
No pressure doesn't mean the pump isn't working. The bearings are apparently offering no resistance, as the oil is probably just gushing out of the mains. This also means that not enough oil is making it up to the head, hastening its wear also. Like has been stated earlier, pull the pan and verify what has been suspected. Hopefully you bought it right, as it would be worth it to fix. A re-man short block would seem to be in order, and with the recent head, you'll have a good start.
Click to expand...

this.

very rarely do oil pumps fail. They're just two gears that mash together.

sounds like the bottom end is wiped out.

and I've been running 15-40 rotella for years in my 4.0 now and never has it sounded badly, even when the temp gauge says 280.....
 
Before you drop the pan, hook the mechanical gauge up again. My replacement sender caused me more problems than the original sender it replaced. The new sender didn't mate to the stock harness well, and would occasionally work loose and trip the check gauges light. The (now clean) original sender is back in the Jeep and working normally.
 
heyhar said:
No pressure doesn't mean the pump isn't working. The bearings are apparently offering no resistance, as the oil is probably just gushing out of the mains. This also means that not enough oil is making it up to the head, hastening its wear also. <- very likely A re-man short block would seem to be in order, and with the recent head, you'll have a good start.<- don't run it any more than you have to if you plan to reuse the valvetrain
Click to expand...
 
well I took the jeep for a 30 min ride and I did not see the pressure drop to 0. Still running at 10 psi warm idle and 20 psi at 1500 rpm. Could it be a temporary blockage or sensor issue? I will put a mechanical gauge on it this weekend. I have 15w40 rotella running.... Some one recommended adding a quart of Lucas , others STP oil treatment. Is one better then the other?
 
None of those additives will help. You could have a problem with the sensor, gauge or wiring. Using a mechanical gauge will tell you. I'm betting on bearing problems from the coolant leak.

However, driving it with possibly low oil pressure isn't helping anything. Park it until you can correctly diagnose to prevent further damage.
 
Sandydog said:
he said synthetic starts as water and thickens as it warms up, standard oil goes the other way starts thick and thins with heat. Is this accurate?
Click to expand...
They all do that. It's from the polymers in the additives. They change shape based on the temperature (clump up or stretch out) which causes the oil to flow slower or faster based on temperature.

The oil weight refers to the time it takes for a fixed amount of oil to flow at a specific temperature. Higher number is longer time==slower rate. 10w30 is 10 weight at cold temperature, 30 weight at high temperature.
 
No, what you said was they all do that, but you didn't say which part you were quoting. Learn to quote.

A 10w30 is not thinner/less viscous when cold than hot. Better way to say it is that a 10w30 will act like a 10 weight oil would act at that temp and a 40 weight when hot. It will still be more viscous when cold.
 
Sandydog said:
well I took the jeep for a 30 min ride and I did not see the pressure drop to 0. Still running at 10 psi warm idle and 20 psi at 1500 rpm. Could it be a temporary blockage or sensor issue? I will put a mechanical gauge on it this weekend. I have 15w40 rotella running.... Some one recommended adding a quart of Lucas , others STP oil treatment. Is one better then the other?
Click to expand...

Adding 1 quart of Lucas (drain a quart of oil first), will raise the viscosity, and give you about 10-15 psi more pressure cold, and about 2-3 psi more pressure hot. So will using a 20W50 oil instead of the 15W40 you are using.
 
I used to play the 50W game with my '72 Pinto. It cut the blue haze a bit, but the car would not go above 55 MPH. Although, that was the speed limit back then, so it was a sort of safety device. And, it got a whopping 10 MPG while full of the molasses. It's amazing that back in the day, a lot of cars were tapped out by the time they hit 80k miles. While the four XJs here on the ranch are approaching 200k, and they all run as good as they did when new! (Don't mind the oil spots under them, though!)
 
heyhar said:
I used to play the 50W game with my '72 Pinto. It cut the blue haze a bit, but the car would not go above 55 MPH. Although, that was the speed limit back then, so it was a sort of safety device. And, it got a whopping 10 MPG while full of the molasses. It's amazing that back in the day, a lot of cars were tapped out by the time they hit 80k miles. While the four XJs here on the ranch are approaching 200k, and they all run as good as they did when new! (Don't mind the oil spots under them, though!)
Click to expand...

The multi weight oils are not like the old straight 50W oils. My 73 pinto would not run on 50wt at all. The 20W50 we have these days, acts more like a straight 40 weight at full temperature IMHO, and after a few highway miles the polymers seems to give out after a 10-20 minute highway run, and so the 20W50 only yields a few more psi at hot idle than the 15W40. Once they oil cools off, the polymers seem to revert back to the higher viscosity.

the difference between 180 F and 220 F coolant temp on my 87 means the difference between 30 psi and 20 psi hot idle!!!! I use the 20W50 here on two jeeps and a 2001 Saturn, all with 120,000 to 287,000 miles. They all pass emissions tests here.
 
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