Need Help! Low Oil Pressure

Hi

I need some help. My mechanical skills are lacking.

I have a F-134 engine and it runs fine. Doesn't smoke and seems to have enough power for a four cylinder. My concern it with the low oil pressure. I have a new oil pressure gauge w/ the cooper line leading to the sending unit at the block.

When I start it up and rev it up, it has about 25 to 30lbs of pressure. It seems to drop down to around 15 to 20lbs after the oil is warmed up. My mechanic friend said that is pretty low. He asked how many miles are on the engine? Answer: I dont know, speedo was broke when I got my Jeep.

Is 15 to 20lbs too low to put a little strain on the engine? Can you guys tell what oil pressure your Jeeps are running?

If I switch to 40 wt oil, will that help boost the oil pressure? I'm currently running 30 wt oil.

Will a new oil pump cure my problem?

Anybody have any luck with oil additives to help boost oil pressure?

Sorry for the long post. I just dont want to "throw a rod" of something.

Thanks in Advance,
Skully

 

Good rule of thumb is 10 pounds of pressure for every 1000 rpms. So 30psi @ 3000 rpm and so on.. If you think the engine has a million miles on it, I wouldn't be hesitant of switching to 40 weight at all. A new engine has tight tolerances that thick oil can't get into...Once everything wears a little, the thicker oil gets in there just fine. To quote my race engine builder, "In 25 years, I've only seen 1 oil pump go bad...Hell, all it is is 2 little gears spinning around in oil." I doubt your pump is bad... My Dauntless was down to about 18psi at cruise before I swapped it for the smallblock and it never came apart... If I were you, I'd just change the oil to 40weight and keep on driving her

 

Mine runs at 40 psi idiling when cold and when it is warm it is 15 psi but when i rev it it goes up to 60 when cold or when warm 40 psi

 

My experience is basically the same as the other responses. I think your Oil Pressure reading is probably ok, especially since the engine does seem to have some wear on it.

From my experience when an oil pump goes bad is just goes completely bad and takes your engine along with it - no special detective work required when a rod is sticking through the block.

Most engines I have seen (and I have seen a lot) have almost the exact same behavior as your engine - that includes "built" High Perf engines with high volume racing oil pumps.

The older an engine gets and the more worn the bearings get, the lower the oil pressure gets. Just beacuse the pressure is low that does not mean that there is not a volume of oil flowing. As the oil flow passages become less constricted (i.e., wear of bearings) the pressure may drop (beacuse the constriction is less) but the FLOW of oil will continue. At least that is what I have learned.

 

Just be aware that a heavier oil may cause hard cranking/starting in the cold weather.

Pete

 

Concerning Heavy Weight Oil, here's my 2 cents.

If you expect cold weather (below freezing) I'd suggest not using heavy oil weight at all. I have seen oil pumps break their shaft trying to pump cold oil. The heavyer the oil the worse the problem is.

I experienced the temptation to use 50W oil when an engine of mine developed low oil pressure. Yes, the pressure went up with 50W, but no more oil was flowing to lubrice the parts than it was before and maybe there was actually less oil flowing, especially on cold mornings. So I felt better having the pressure gauge read what it used to read, but was the engine any better? I have learned the answer is no.

 

Sounds normal, skully!
Russell: good info. I've got low O.P. on my '64, and currently I have the highest wt. available in it. Winter'll bring zero degree weather, so I'll consider changing oil type/wt. beforehand. Thanks!
-alan

 

Does anyone know if low oil pressure can be caused by an oil filter being clogged?

 

Genrally, I'd say the oil filter does not affect oil pressure. For most modern screw-on filters there is a shunt that will bypass the oil arond the filter when it gets clogged. That might actually increase the pressure while reducing the volume of oil making the circuit through the engine :? For the early CJ removable cartridge filter like I have on a F134....I don't know how that works for sure.

I could be off base here but that's what I think.

 

My jeep had not been running for a number of years when I got it & have I just gotten through rebuilding it. When my engine gets up to operating temperature my idiot light comes on at idle. Bump up the idle a couple hundred rpms & the light goes off. I have been aiming to add a O.P. gauge to monitor actual pressure but I have not gotten to it yet.

Also my temp needle never moves. I installed a new sending unit. I do not know if it just runs that cool of if there is a failure in the circuit somewhere. I got a 160 degree tstat in it and it is cool at operating temperature in comparison to my late model truck.

Cheers

:hurrican:

 

FWIW from the FSM: F4-134 safe mininum oil pressure at idle: 6 psi, at which point the oil light should go out.
Safe mininum pressure at 2000 rpm: 20 psi

 

Thanks to all that responded!
I feel a lot better about my "low oil pressure".
Glenn- I did have the "nylon tube" before and switched to the cooper tube. That might be the reason ref. the inside diameter.
Russell- thanks for all the info on oil pumps, oil wt, etc. Thats the kind of info that really helps this rookie mechanic.
Southtowns27- thanks for the "10lbs per 1000rpm" rule. That one I will remember.

I did switch to the 40 wt and it seems that I gained a little more oil pressure.

Thanks,
Skully

 

i don't believe that the oil filter will affect it, as the F head does not have a full flow oil filter. only a small percentage of the oil is filtered.

 

The fsm calls for 30w (or 20w for cold weather) and see if that helps. older engines (such as :v6: and :hurrican have alot lower oil pressure than modern engines.

I have more oil pressure with striaght 30 weight then I ever did with 15w40, it also cranks over faster.

 

Yes,this has been discussed at length in almost every forum dedicated to the f4/l4 134. These are low pressure engines to start with, as the Service Manual states 6 PSI minimum and 20 PSI at 2000 RPM. The Manuel also states shims can be installed under the relief pressure spring. This will not increase the pressure at idle but will increase at higher RPM. My L4 134 after a recent rebuild has 30 PSI at idle and drops off to about 20 PSI at idle after reaching operating temp.