hey guys . this is a weird one .
i have a 97 xj with 155,000 miles .
i hooked up my 4 wheeler trailer(1500lbs total) which i use rarely to go about 15 miles.. when i was waiting at the last light before i pulled into my destination , the check engine light came on , and my oil pressure went to like 2psi ! . and im driving like a grandma too.

it ides at 10-12, and is always one number above my RPM . for example ... if im going 60mph and its at 2k rpms , itll be at 30PSI . so thats on the low side, but normal . i know common knowledge says for every 1000 RPMs you need 10 PSI . so im good there.
anyways , shes old. i know . but never a problem . i put 10w40 in there this time since i read on the forum its better for an older engine than the 10w30 . i took a road trip for about 2.5 hours towing my trailer(not heavy) and the oil pressure was always fine.. not high , but good enough.
right when i get off the freeway on the off ramp , it plummets to 3psi .

heres my theory :
the oil heats up , it gets thin, and theres less pressure. problem solved. great.... i know its not the oil pump seeing how every time i start the car cold it goes right up to 40psi , then after 15 minutes of driving itll idle at 10-12 ... normal for an older one. and stays in the 10-30psi range just fine.
the engine PURS like a kitten too ... no knocking of front bearing or whatnot.

cars fine when not towing or going on long freeway trips .. but i could only imagine whats its gonna be like in July in the blistering heat!

can i switch to a 20 weight oil to help it out? i want to go on another trip with the trailer but dont wanna be stranded. thanks guys!

 

There is only one way I proceed with cases like yours.

CONFIRM.

Get a mechanical oil pressure gauge. They can be rented for a few bucks from many big box parts stores.

Temporarily install it where the oil pressure sending unit currently resides.

Good data = Good decisions.

The oil pressure spec for the 4.0 is as follows:

*Not less than 13 psi at HOT idle
*Between 37-75 over 1600 rpms

Let us know what you find out!

 

What he said. It almost sounds like a flaky sender.

 

it does, but the weird thing is it only has happened when i tow, and then one time recently when i was on the freeway for 15 minutes and got off, but that went away at the next stop light.

you might be right... it might be malfunctioning the sender when the temps go up . who knows..

 

Only one way to find out. Test with a mech. gauge.

 

if it is actual low pressure, don't go to a 20, maybe 20w50.

 

you say dont go to a 20 , but isnt a 20w50 a 20 weight? im confused. ill pull the sender , and thread a mech gauge in there , drive around , get it warm , then ill pull over and check it at hot idle.
go from there.

 

the 20 is the weight of the oil when it is cold, the 50 is the weight of the oil when it is hot. If you put in a straight 20 (I don't know if they even make it) it would be too thin.

 

oh , well i meant a 20w50 .. which is oddly what i run in my motorcycle and dirt bike

 

you better hope its a bad sending unit, and you weren't towing with almost no oil circulation lol

 

Only when towing...Do you have trailer lights?The only link I can see with that would be electrical. X2 on the mechanical gauge.This sound silly but try towing with out your lights plugged in, in an empty parking lot or someplace with no traffic.

 

well if that was the case , i think i would have blown a main bearing or a rod. plus, the pressure gauge wouldnt go up and down with the RPMs . its either weak or bad sending unit, or clogged oil pump filter, etc . even worse, oil pump, but again , doubtful due to the pressure being existent. well see

 

AUTOMATIC ,
i would think you might be right , but it did dip to 2-3psi when i was just driving on the freeway and got off , like described above. i think its a mechanical thing. and my wiring is great on my trailer and the 4 prong flat plug i just installed on the jeep .

 

is there a place to stick the mechanical gauge permanently? as into the oil line. i wanna hook mine up but i dont wanna leave the sending unit out of the equation.

 

Bad thing about a mechanical oil pressure guage is you have an oil line going through your fire wall and into the cabin. If that hose fails you have hot oil spraying inside the cabin. Not a good idea.