Mitsubishi 3000GT & Dodge Stealth Forum banner

1 - 20 of 23 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
I recently bought what I've always wanted: a VR-4. 1993, 93k miles, all stock(I was told) except for wheels tires and exhaust and megan Coilovers. Has had 128 miles put on it in the last year until I bought it. Before that it sat in a climate controlled warehouse and wasn't driven much at all either. Everything seems to run smooth except for two things. Oil pressure/knock and small vibration between 35-40mph. The oil pressure tends to fade at idle after engine is warm. Not to bottom, not enough to turn the light on either. And an extra 300rpms from the pedal will bring it back to normal. When oil pres. is low there will be a low knock in the bottom end on the pass. side. I just changed the oil to Castorol 5w-30 full syn with Lucas oil stabilizer mixed in as well with a K&N filter. Operating oil pressure seems to be a tad higher and the knock is barely audible at idle. Pressure still fades at warm idle. I haven't strained the old oil for metal but I didn't notice any while draining or moving the container around. Ran a good magnet through it and didn't pick anything up either. Is there anything I should be worried about or should check? I used to have a 92 sl but didn't get to do much to it so this is kinda my first real foray into the 3s platform. I've read about clogged oil pickups, worn bearings etc, but like I said the knock is almost inaudible so I don't think major damage is happening. But I want to keep this beautiful machine in top shape so I would appreciate serious mechanical advice. I have video of the pressure from cold start to warm idle, and also from inside the wheel well before and after oil change. Can't post them here but will try to link them if needed. And no bickering please too much of that going around on posts.
 

·
Registered
Joined
·
13 Posts
I have a similar problem NA DOHC with 120k Castrol 5w-30 high mileage. Oil pressure was high when I bought the car, now 1500ish miles later it seems to be slowly dropping (I drive the car hard). IE it used to run at the top long hash line when warm and now is a few hashes lower when warm. Anyways.. Hopefully my plan of attack may be useful to you.

1. Send in an oil sample (Hard evidence)
2. Check pressure with a different pressure gage. something like this ( I hear the stock gauge is buggy ) Oil pressure may be fine, just bad gauge. (Sensor is somewhere under the car I believe)
3. Drop the oil pan and check the pickup.
4. Check the bearings
5. Replace the oil pump?

Hope this helps! Im pretty lazy & broke so 1 & 2 are a must for me. Might want to check your local auto store for a "free" pressure gauge rental. Im also switching to Valvoline vr1, hoping the higher zinc will help.
 

·
Registered
Joined
·
13 Posts
I am trying not too, but do on occasion. Lucky it isn't my daily driver. As long as you have some oil pressure and keep the RPM pretty low you should be okay. What kind of oil pressure are you getting when the car is cold & warmed up? The pressure should be pretty high at startup idle (somewhere around the middle) and pretty low once at operating temp at idle(pretty close to the bottom).
 

·
Registered
Joined
·
459 Posts
Advice above is good, but sending in a good oil sample may be difficult as this point if you just changed the oil and do not want to drive the car before figure out a potential issue. You need some mileage on the oil before an analysis like BlackStone labs will tell anything useful. Nonetheless would definitely do this if you do continue driving the car. Checking pressure with a mechanical gauge is also a good idea because the stock gauge is qualitative at best. If you are not getting the oil light, your warm idle pressure is at least >12psi.

How certain are you it is a knock and not from the top end, i.e. lifter tick?

Also where do you live? 5w-30 is quite thin for a VR-4. 20w50 is ideal, especially for hard driving and/or in a hot climate. I have run 20w50 for the last 110k miles on my VR4 and my 100k mile oil analysis at blackstone labs was perfect. I am located in CA so do not experience freezing temperatures. 20w50 is also popular among seasoned 3s members. I know valvoline VR-1 is a popular high performance oil of course for VR4s; others of course are fine as well.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #6
Bird: I have exactly what you describe for oil pressure.
Horne: I have the oil I changed out of the car two days ago in a clean container if I need a sample. Not sure how old it is though. I am in Tennessee so we get down to -10° max. Is VR-1 preferable to say AMSOil or pretty well the same? I always ran royal purple 5w20 in my evo x(stock) as it was recommended weight so I wasn't sure how different the 6g was.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #7
Say I am running too light an oil, could that cause the knock? And I'm 100% positive it's bottom end. Open the hood and there's nothing, listen at driver side and there's nothing. Only sound is if i listen at the passenger wheel well.
 

·
Registered
Joined
·
459 Posts
Bird: I have exactly what you describe for oil pressure.
Horne: I have the oil I changed out of the car two days ago in a clean container if I need a sample. Not sure how old it is though. I am in Tennessee so we get down to -10° max. Is VR-1 preferable to say AMSOil or pretty well the same? I always ran royal purple 5w20 in my evo x(stock) as it was recommended weight so I wasn't sure how different the 6g was.
You should consider sending to blackstone labs for analysis then, even if you don't know the mileage or age. I have no personal experience with amsoil so cant comment, just know what i have read in other threads. Your favorite 20w50 should do fine. I believe owners manual for vr4 ranged from 10w30 up to 20w50, so 20w50 is not necessarily outside OEM spec.

Say I am running too light an oil, could that cause the knock? And I'm 100% positive it's bottom end. Open the hood and there's nothing, listen at driver side and there's nothing. Only sound is if i listen at the passenger wheel well.
I'm not sure if it would cause a audible knock unless there was an underlying issue, but again i am not really sure what you are describing as knock. Sending the sample for analysis and trying 20w50 are probably your easiest and cheapest options to start.
 

·
Registered
Joined
·
5,557 Posts
The stock warning light is 8 psi.
Once these cars get close to 100K, anything is possible from a bearing wear standpoint. I tore my stock engine down at 104K and all bearings were pretty deep into copper layer (100% stock car).
Lightest oil I'd run on a TIGHT stock engine is 10W30. More likely 10W40. My last two builds were "loose" by design so I run 20W50 Redline. Hot oil pressure (not warm) has always been a solid 15-16 psi. No noises, oil always clean (at least visually. Some say that's too low, others don't say that (me included based on my experience). There are too many variables for a blanket statement.
The stock gauge is pretty worthless, for real. I wouldn't make make any conclusions from it alone. I'd get (2) real gauges and compare those.
Good luck!
 

·
Registered
Joined
·
5,557 Posts
To be clear - I wouldnt run 20W50 in the winter :)
But I don't drive mine in the winter.

Edit: I just figured out how to edit.
 

·
Registered
Joined
·
5,557 Posts
Anyone know the "Healthy engine" oil pressures? I looked in the service manual but did not find a definitive answer.
I think most will say 20 psi....but it's all clearance related. (Oil pump clearances, bearing clearances, etc). Those are all different based on engine age/mileage, build clearances. I think the manual just states a "minimum" of 11 psi (at hot idle).
 

·
Registered
Joined
·
7 Posts
Discussion Starter #13
Link to video of the noise I'm concerned with. Let me know if it works or not. Note, I tried to get the mic as close to source as possible.
 

·
Registered
Joined
·
459 Posts
Link to video of the noise I'm concerned with. Let me know if it works or not. Note, I tried to get the mic as close to source as possible.
The video works. Is that knock RPM dependent? It doesnt sound like its exactly following engine RPM at idle... could just be the way the video is though. I used to have a similar sounding rattling noise from my transmission, but it would go away when the clutch was pushed in. I assume yours does not do that if you are convinced it is from the engine? It would have helped if you revved it a little also so we can hear how it varies with engine rpm. Maybe by setting the phone/camera on the tire with mic facing in if you dont have a 2nd person to hold it.

Anyone know the "Healthy engine" oil pressures? I looked in the service manual but did not find a definitive answer.
Someone once made a chart of user-reported oil pressures but there were only 4 (engine) data points and as mentioned above it is highly varible with engine age, build specs, engine oil used, etc. So its not worth much. I downloaded it many years ago and will post here:

285083
 

·
Registered
Joined
·
76 Posts
It does sound like clutch or flywheel chatter which can be caused by aftermarket clutches/flywheels. Set up your phone, make sure it is making the noise, then get in and push the clutch in while it is recording and see if it goes away.
 

·
Registered
Joined
·
13 Posts
Thanks so much jrhorne. I will see how my data matches up.

DCham Im not sure what that noise is. My only contribution is that the transmission is next to the wheel and I hear the transmission is a serious weak point of our vehicles. Other than that I would try the old screwdriver-to-ear trick to try to track down the rattle. Your engine sounds nice and healthy to me, it's holding a tight steady idle. I wouldn't be at all surprised if it was just a loose bolt on the body or some loose piece of metal that someone once dropped.

I have an old 65' TBird and I thought the engine was on the out but it turned out to be a bolt rattling around I had left in the engine bay that got stuck inbetween some panels🤣.
 

·
Registered
Joined
·
5,557 Posts
Yeah, that sounds clutch or trans related. My car makes a similar noise, always has. I thought 5 speeds were more prone to it, but maybe not. As stated above, mine goes away when clutch is pressed in.
 

·
Registered
Joined
·
5,557 Posts
To me it sounds like trans, but it's hard to tell without some throttle manipulation to see how the sound changes...
 
1 - 20 of 23 Posts
Top