98 2.4L Oil Pressure Problem

[amcswebs]

Hi all.. I have a stumper for you all. Hope you can help as at this point I could have put a used engine into this car for less.. LOL.

Anyhow.. Here is the story.

We bought this wonderful 5-speed standard 2.4l car a few months back. It RUNS wonderful and looks great. Never seen a newer looking used car.

Thing is I noticed that the engine seemed a bit noisy.

1. Our favorite Mechanic said he was sure it was the Timing Chain so we gave it to him to pull apart and fix. He determined that it was NOT the timing chain creating the noise.

2. Okay.. It was time for me to do some reading so I spent days reading about other peoples 'noisy' engines and because this is an overhead cam engine and it appeared all the noise was up in that area (to me) I once again pulled apart the timing (myself this time) and continued on to pull the cams so I could inspect them. Sure enough there was some minor scoring so I changed them and put it all back together again.

Guess what.. still noisy.

Well.. whats next. I wondered what the oil pressure was like. Seemed hard for me to believe it could be bad as the light wasn't on and it ran VERY well.. but to be sure I pulled off the pressure sender and installed a mechanical tester to test it.. LOW PRESSURE. Almost none to be more exact.

3. Back to the mechanics.. this time to have the oil pressure double checked (just in case my guage was bad) and if so to replace the oil pump. Well, the oil pump was replace and the opinion of this mechanic (and a couple of others) was that the main bearings were fine and not the cause of the low oil pressure.

What is left? Why would the mechanics agree that it appears the lower end is getting pressure and the upper end isn't? Where could it be losing the pressure? It leaks NO oil.. The whole system is VERY clean so a blockage seems very unlikely (have already tried flushing it).

Any suggestions? The last mechanic had one, but I would rather hear from the experts on here before I tell you what it was..

Thank you in advance for ANY and ALL suggestions and comments.

[carlover626]

I have the same engine/trans and I will tell you that I think the engine is a bit noisy. What kind of oil are you using? I have 10/30 in it right now, and it seemed a bit more muffled after that. I hear synthetic helps as well. Although it is getting cold here again, I am changing back to 5/30 next time.
I had a horrible ticking noise at idle the first two days I had the car and it turned out to be my harmonic balacer for the timing chain failed. All of the cogs/gears and the chain was replaced in it and it does seem noisy to this day. How noisy is yours?
How many miles does it have? I would have thought that the Oil pressure warning light would be pretty reliable? But I have never taken apart an engine???

[Coondog]

How low is your pressure? Does it rise when you rev?

[rixGAphx]

1. If you got 'zero' psi on the 'mechanical tester' (not sure what that is), then you prolly weren't using it right.

2. What is the oil pressure, in psi, as measured at the stock oil pressure sensing port:
At idle?
At about 3000 rpm?

3. I don't follow the logic in your description that the 'Oil pressure is fine at the main bearings but not at the upper end'.
I know that the top of an engine can be 'starved' for oil, but the pressure can't really be measured and compared to the pressure in the block: You just look at the broken/destroyed stuff and say, "boy, those bearings were starved for oil". :roll2:
Frankly, you would have had a LOT more damage than "some minor scoring" (which I asseme was on the bearings, not the cam lobes).

4. I assume that when you replaced the cams, you also replaced the bearing shells and pre-lubed them. Right?

5. I further assume that when the machanic investigated the timing chain as the noice source, he did NOT replace the chain, gears, or chain tensioner assembly, right?

6. OHV hydraulic-tappet engines, like the V-6, do not need pressurized oil to the heads (oil is via the pushrods), but your 4-cyl OHC has passages within the block and head for oil to be pushed upward to lube the cam bearings.
If somebody did a head job, then the gasket might have been misplaced or junk could have fallen into the passage, thereby preventing good oil flow. There are special brushes, like long thin baby-bottle brushes, for 'chasing' the oil passages on engines.

7. If the oil pressure reads low (less than 15 psi idle), what leads a mechanic, or anybody, to believe that the 'lower end' rod and "main bearings were fine"?
Unless the bearings were physically inspected with plastigage and visual observation, the only thing to base "fine" on is the facts that 1) they aren't making much noise and 2) they haven't blown-up (yet).
What I'm saying is, you may have crappy oil pressure everywhere, and the main and rod bearings just haven't succomed yet.
* * * *

Finally, what is your definition of, "the engine seemed a bit noisy"?
You may be chasing your tail relative to the 'normal' clatter of a DOHC 16-valve, or the noise might be from the exhaust, clutch, etc.
Or, the previous owner may have run low on oil, and the entire valvetrain may have excessive clearances at valves, lobes, etc.

Standing by,
-Rick

[amcswebs]

>If you got 'zero' psi on the 'mechanical tester' (not sure what that is), then you prolly weren't using it right.

Lack of pressure on the top end was confirmed by mechanic.

>You just look at the broken/destroyed stuff and say, "boy, those bearings were starved for oil

I have to take the word of the last mechanic on this one.. he said he 'believed' there was nothing wrong at the bottom end.

>Frankly, you would have had a LOT more damage than "some minor scoring" (which I asseme was on the bearings, not the cam lobes

Correct.. the cam lobes looked just fine.. the bearings (which are machined in as part of the camshaft (and housing) were somewhat scored.

>I assume that when you replaced the cams, you also replaced the bearing shells and pre-lubed them. Right

it is not possible to replace the bearing shells on this engine.. you must replace the casing.. as for pre-lube.. yes. They were pre-lubed.

>I further assume that when the machanic investigated the timing chain as the noice source, he did NOT replace the chain, gears, or chain tensioner assembly, right?

Correct... When the second Mechanic contacted the first he said he DID replace the tensioner.. Between both of these I had it all apart as well (necessary to get to the cams)... I did not replace anything in the timing chain area other than gaskets.

>If somebody did a head job, then the gasket might have been misplaced or junk could have fallen into the passage

I have no knowlege of anyone doing heads on this car... it does not appear to be the case, but who knows. It would be pretty hard to put the gasket on wrong when it needs to fit over 'dowels' but I presume it IS possible.. As for something falling into the passages.. yup.. could be, no way to know without tearing down the engine. These suckers do not allow for easy access on anything. Removing the heads pretty much requires you take apart most of the engine.. LOL

>you may have crappy oil pressure everywhere

Very possible this is the case... As for the guage reading.. you take it at the top end (off the intake side of the cam housing) and it is pretty much non-existant... Rev the engine to your hearts content and it won't change...

>You may be chasing your tail relative to the 'normal' clatter of a DOHC 16-valve

I would actually agree with this if not for the oil pressure.. these engines ARE somewhat noisier than many and it runs smooth as silk.. I would just love to be able to pump oil over the cams some other way just to see what the difference in sound is when i know they are not being starved for oil.

Next week I am going to check for the unlikely.. twist off the oil cap a hair, disconnect the electric from the plugs and crank it to see if oil is even getting to the pump... If not i will try priming it. perhaps it is just a case of no prime (I doubt it).. If that doesn't work it seems i have three choices.. pull the engine completely appart and see about re-building... throw in a different engine.. sell the car cheap and let someone else fix it.

Suck.. this is a very clean, fun car to drive (even if I have only had it for 7000 miles)..