Low oil pressure 200 miles after rebuild - please help?

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Oct 21, 2003
Cincinnati, Ohio
Hello, this is my first post, but you guys have a GREAT site... Wonder if any of your could help me with a problem I have been having ? - Thanks in advance. I just got done with the rebuid on my 95 firebird 3.4 and after 200 miles it is doing the same **** thing it was doing, that caused me to rebuild the motor.... Today (and a few days ago) the "check gauges light" came on because the oil pressure was "in the red". Before the rebuild: 1. I replaced the oil pressure sensor 2. I teed off of the oil pressure sensor with mechanical gauge, the mechanical gauge read about 2-5 lbs higher (depending upon RPM), but for the most part they were the same. 3. This problem is made worse, when the car is stuck in traffic and the temp goes up to about 230 range, before the fans kick on at 235 (this is a STUPID design having a car go from 180 to 235 when stoped - the fans should kick on MUCH sooner). Currently when the car starts up the oil pressure reads about 60 lbs and 75 when cold out (it is about 55-60 deg F around here this time of year). After it warms up at idle it will be in the midle of the first tick mark and the read line (I am guessing around 10 Lbs). This only apears to be a problem at idle, if you to up to about 1,000 RPM the oil pressure is about 15-20 LBS I am using Valvaline 5W-30 and a AC Filter. Any suggestions? I did the rebuild myself, everything went smoothly. When I got the engine apart I noticed the cam barings were gold in color - like they were eating into the "core" of the barring or something... - I just assumed that was the problem. I did plastigauge the main caps before the rebuild (but not after - my mistake) it was about 0.030-0.035" - did not check the rod barrings (this is a mistake I will not make again - I should have gauged the entire engne after the build...) Also in the rebuild i replaced: 1. Cam 2. Lifters 3. Rings 4. All barrings 5. Freze out plugs 6. Timing chanin 7. Oil pump (stock flow) 8. Gaskets 9. Etc... Any suggestions?
Not to make you feel bad, but you made a few mistakes that most people make the first time they rebuild an engine! Good job for trying though! I would put my money on the fact that you really have no idea what your clearances are for your crank or your cam bearings! [Eek!] Now that you are where you are the only choice you have is to run a thicker oil!! Hasbeen
.030 to .035, that is a lot a of clearance. Did you have the crank turned? What undersize bearing did you use?? Did you measure the crank? The 3.4 have a softer crank then most, I had to replace 3.4 crank for the crank wearing and not the thurst bearing. If your crank is not true or smooth, it will wear bearings quickly. CRW
The mesurements were before the rebuild - they were at the upper end of the spec (according to the hanes manual), that is when I rebuilt the engine. It was not knocking and there were no noises from the engine - before the rebuild (with a stethoscope (sp??)) Also when I took the mesurements before the rebuild I did not torque the mains down per the spec (something like 30 lbs then 77deg, I skiped the 77 deg part, because I read the book wrong - did it right for the build up though). I did not take any mesurements after the build, but I did NO crank work - just a clean up with 600 grit. I used standard sized baring throughout, and the crank mesured with in tolarences. Again, thanks to all for the quick response ! 6T6Cuda
Of course, the oil you choose to run does thin like crazy under high temps. You might want to try Mobil 1 15W-50 in an attempt to retain pressure while hot. I have had very good luck with M1. Also, did you put in a high volume oil pump? In my past life when I worked on Chevy engines as a hobby, I always made sure to use a high volume oil pump. This was because the oil pressure would be low after backyard overhaul if I did not. Keep in mind that oil pumps do wear out too. Chris
No I did not go with the high pressure pump - Kind of wish I would have... But I did replace the pump with a Meldings (sp?) standard volume pump. The oil does fine at "normal" temps 180-195, but in the 230 range it apears to drop out... I do understand the difference between different oil brands, but you are recomending a thicker and different brand. I mean 15W-50 is MUCH thicker then the 5W-30 I have in there now. I would think if I put 15W-50 in there now it would give higher pressures no matter the brand (assuming they follow the requirements). 6T6Cuda
Originally posted by 6T6Cuda: The oil does fine at "normal" temps 180-195, but in the 230 range it apears to drop out... 6T6Cuda
If this is a problem, I don't know how to say it more simply...run a thicker oil!
Ok then, try a 10w-30 first, in no or not enough improvement, go with a 15w-40. It sounds like you just have excessive bearing clearance. It was probably checking good when you built it, but if the cam or crank is even minutly out of round or bent, it will eat into that new bearing and after a couple hunderd miles, be low in pressure due to larger clearances.
The first engine, a 283 CI Chevy I built, I used the Hot Rod Magazine article on how to rebuild and engine! I did everything right, Except I didn`t check the top compression ring for end gap! I checked all the others but didn`t check the top one as all the rest were ok! I purchased the rings from JC Whitney, (Go figure), Young and dumb and got what I paid for! I guess they just took a ring out of a standard sized package to make up the chrome ring pack! The rest were correct .60 over! Engine ran wonderfull as long as you didn`t put a load on it, Man it would blow the dipstick right out of the engine, oil everywhere! All the mechanics I talked to told me that the chrome ring wasn`t seated and give it some time! I put 5,000 Mi. on it the tore it down to re ring it! For some unknown reason I put the top ring in the cylinder to check the gap and it was 1/4"! We all live and learn!! Keep at it, I have to hand it to you for doing it yourself! I know that the front wheel drives of today are really no fun to work on! Hasbeen [Cheers!] [ November 07, 2003, 03:49 PM: Message edited by: Hasbeen ]
Has been, that reminds me of my buddies former vehicle, a 92 Mitsubishi Galant VR-4. They were a a 4 door Turbo Eclipse basically. It had around 150K on the clock with a turbo that was so worn out, you could see a 1/4 inch of daylight through the exhaust housing [Eek!] No boost whatsoever. So we slapped on a ported larger mitsubishi turbo and uped the boost and put a full exhaust on. We ran the CRAP out of that car for about 10,000 miles. By the time it was on it's death bed, it would shoot the dipstick literally 10 feet in the air with the hood off and a real good, hard launch. The instant that boost built, like before you even had the clutch out all the way, the dipstick would be airborn. We did this many times as it was just too **** funny. [crushedcar] Unfortunatly, it had so much blowby and was burning so much oil, it had to run on Valvoline 20w-50 racing oil, even in our cold winters, and that spelled the end of that motor. [Cool]
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