Hello everyone,

Car has 88k on the odometer andhas the Mitsubishi built 6G73 2.5L SOHC engine.

Tale of woe: Water pump siezed...took out the timing belt & idlers. Interference engine, so it convenientlybent 8 of the 12 exhaust valves (thanks a million for that design flaw Mitsubishi). Word to the wise: Replace the timing belt on these things at 60k...along with the timing belt idlers anda brand new water pump. Lesson learned the hard way I suppose. Anyway, valve job andparts ran me in the neighborhood of $1500 (seems that every replacement part on this car is gold plated). Several weekends later andI finallyhave it back in operation...or at least I thought.

Engine starts and runs good...plenty of power and no odd noises other than the normal ticking of the fuel injectors. Seems that when the engine warms up, the oil light comes on at idle. Engine is idling around 650 RPM and running smooth. Checked the oil level...it's right on the money...I recently changed the oil (10W-30 Mobil 1 & a non-Fram oil filter). Thought the sending unit might be going bad so I replaced it. The oil pressure light issue persists.

Took out my trusty mechanical oil pressure gauge and adapted it to the engine. Fired herup to gather some real information. When cold, the engine holds 50 PSI at idle and gets close to 70 PSI at 2000 RPM. Looks great to me. As the engine warms up though, the oil pressure at idle gradually decreases. This makes sense -- oil thins as it gets hotter. After the engine is at full operating temp (radiator fan comes on), theoil pressure at idle looks dangerously low to me. My mechanical gauge isn't a full sweep unit, so the scale isn't as granular as it needs to be. It's hard to tell exactly what the pressure reading really is when it's this low...but it looks to be around 10 PSI at hot idle.

Question: What is the acceptable [hot] oil pressure range for this engine? My manuals don't list this spec.

Some thoughts regardingthe cause:

1) Perhaps this thing doesn't like synthetic oil. I might try going to 10W-30 dead dyno juice,straight 30 weight or perhaps even 15W-40 as a last resort.

2) Perhaps the replacement oil pressure sending unitis bad. I'll test that with air pressure and a regulator...more on that later.

3) Might be early signs of oil pump failure.

4) May be lower end wear, but, I doubt that since I noticeda cross-hatch hone pattern in the cylinders while the heads were off...no ridge either. Engine was very clean inside, no indications of sludge or blockage of any type.

5) I did have to replace some of the hydraulic lifters/tappets...old one's on one intake bank wouldn't pump up for some reason. Could it be that the rocker arms are bypassing too much oil for the engine to hold good oil pressure at idle?

Any wisdom to share?

Thanks a million,
-Me

 

Update: Picked up a full-sweep mechanical oil pressure gauge -- one with sufficient granularity at lower pressures. Oil pressure is great when engine is cold or slightly warm. When at full operating temp, the engineshowsright at 13 to 15 PSI at idle. OK, but that still seems a bit low to me.

Tested the replacement (aftermarket) oil pressure sending unit using an air compressor, the same mechanical oil pressure gauge,a pressure regulator and a mechanical ohm meter. Oil senderpresentsan open circut above5 PSI.

Put the sender back in the car and gave it a whirl. All is fine until the engine is at full operating temp...then the dog-goneoil pressure light comes on at idle.

I suspect that the replacement sending unit may be out of spec...meaning that it somehow presents a closed circuit at higher pressures when hot (bypassing internally perhaps?). Going to visit the local dealer parts counter and get the real mccoy for this car and see what comes of that.

-Me

 

I think 25 PSI is the lowest I would let a car go with oil pressure before seeing a mechanic.. of course thats still a bit above spec... but I believe 10 PSI qualifies as low oil pressure... Oil pump needs replacing maybe?

 

Pulled the oil pan and plastigauged the mains/rods. Clearance was excellent -- next to zero wear. Both mains and rodshad right at 0.0015 clearance which is well within spec. Bearings looked good too...no signs of excessive wear. Has to be the oil pump...time to dump my wallet again...

Chrysler wants FAR too much for a replacement oil pump. Found an aftermarket oil pump at 60% the price, installed and buttonedthings up. Oil pressure issue is history.

That said, a $80 water pump failure ended up costing me well over $1500 to repair (parts only at jobber cost -- only exception being the $700 valve job which included 8 exhaust valves). Labor was gratis since I did the work myself.

Time to stop the bleeding wallet syndrome. Car went up on a local for-sale boardfirst thing Sunday morning. Sold itto the 1st sucker carrying cash within 2 hours. Good riddance! That's the last Darned Old Dirty Gas Eatingvehicle that will ever have the privilege of being parked in my garage, that's for sure...lesson learned the hard way. Was good experience for my son though -- now he knows he's going to college since hedoesn't want to pursue auto mechanics!

-Me

 

Sorry to revive a very old thread but I just wanted to thank the OP for putting this up. I had the same thing happen after changing the timing belt. I suppose I should do the water pump before something bad happens. Anyway I have been trying to diagnose the oil pressure issue as well sine it seems it is causing misfire codes and the pressure at idle is low enough to cause the lifters to start collapsing. It sounds like a box of marbles when running.

I'm just curious if you looked at the pump to see where the pressure loss was coming from. Either the relief valve or the pump clearance?
If you are no longer on here I'll try to post what I find. I would love to get rid of this dodge but it's not mine to sell, just mine to pull hair while diagnosing this one problem.