Rebuilt motor (LS1, of course), new bearings, clearances checked out good, had 70 lbs. oil pressure cold, and 40-50 hot. Have Melling Hi volume pump. This pump had about 30,000 miles on it from previous build. Always worked fine. NO PROBLEMS!! After I put about 600 miles on this rebuild, using same oil pump, we took about a 35 mile ride in it, and at about the 33 mile mark, we shut off car to go into a bank. Came out 5 minutes or so later, fired car up, and got about another mile and the oil pressure dropped so fast that I suspected an electrical problem. Also, the motor NEVER made a sound, no knocks, clicking sounds, NOTHING. I got a mechanical pressure gauge and checked the pressure with this gauge, bypassing the cars electrics/gauge, etc. When cold, at idle, I only got about 20lbs.! Revved it up (CAREFULLY) and keeping close watch on gauge, it hit about 40lbs. at maybe 2,500-3000 RPM. Shut it down and re-started within 1 minute and got ZERO at idle and maybe 20lbs. at 2000 RPM. It hasn't run since, as I haven't had time to look into it. What do you think? I first thought the O-ring, but now am thinking that the relief valve is stuck. Must admit that I DID NOT dis-assemble pump and clean it out for new rebuild. The reason being that the motor had no shrapnel in it from first build, I was using a magnetic drain plug, and the pump looked real clean and was kept in a plastic bag between builds. Please advise, but I think I am looking at dropping the front end (AGAIN!) and pulling pump to free up the relief valve. Thanks, guys.

 

Unless you changed the oil requirement of the engine by adding piston oil squirters, turbo or supercharger that uses engine oil there is no reason to install a higher volume oil pump. The excess oil gets dumped through the relief valve which can cause extreme heating of oil and the oil pump, cause aeration of the oil and in extreme cases the main or rod bearing to be hydraulically floated off their seats with spinning of the bearing shells, and major engine failure. You may have lucked out and have only a stuck relief valve. If it were mine I'd be replacing the oil pump, and if non of the earlier mentioned items requiring more oil flow were present, it would be a stock volume oil pump.

Hope you get it fix..

 

You may want to do a mechanical oil pressure test therefore verifying the electrical indications. Minimum for the engine is 6 psi but it sure sounds like something isn't right.

 

Sorry, guess you misunderstood my post. I didn't want reasons-pro or con- of using these pumps. I was looking for help with the problem I NOW have. I emphasize NOW because I ran this pump, with GREAT results, I might add, for over 30,000 miles, and for whatever reason, it DID NOT "hydraulically float the bearings off their seats", etc. By the way, in air cooled motorcycle engines that see over 10,000 RPM on a daily basis and which run for years between rebuilds without problems, I have run pumps with 100 lbs.-or MORE- of oil pressure, and NEVER hydraulically floated the bearings off their respective journals!! But, thanks for trying.

 

Wow-guess you missed the part where I stated-I thought pretty clearly-"I got a mechanical gauge and checked the oil pressure, thereby by-passing the cars electrics"..... But thanks for reading part of my post!!

 

ttt......-Can ANYONE give me some accurate ideas on this?

 

Hit LS1tech they might be able to give you some better answers

 

You were right! Sorry about that.

 

I think you already know what your next step is. You have to rule out th pump as this point. At least the pump is cheap. Sorry but you are pulling the damn rack out.

 

Hey, sorry misunderstood you post too. It seems you have a great understanding of lubrications systems and probable didn't really need to post your question anyway. By the way, your comparison to a 10K motorcycle engine lubrication system to your LS1 is quite unique. I'm sure in your case there's no need to factor in the major differences in journal sizes and surface area between the motorcycle engine and a LS1. Hey, if you find that your relief valve is stuck open, just do away with the spring and fill the area with washers so you get max pressure all the time. If 100 psi is good for your motorcycle then is must be good for an LS1 too! Thanks for letting all of us know that took the time reply to your insightful post we didn't give you the answer you were looking for. I know in my case we won't bother again.

 

My magic wand it out for repair, and the batteries in my crystal ball are dead.......good luck..

 

Pulling the pump out sounds like the only reasonable thing you can do for now. I would guess that is the source of the issue since you heard no sounds at the time it went to zero... hopefully excluding a spun bearing.

 

Since the oil pressure dropped so abruptly, I'm guessing that the pressure relief valve in the oil pump is not closing fully.

 

Thank you for your post/reply. I am grateful for any help from anyone who is genuinely interested in helping out. You and dgrant3830 and, I guess rob, have tried, and the relief spring is where I was/am heading. Just wanted some knowledgable 2nd and 3rd opinions. Sorry it took so long to get back to you guys. Didn't mean to sound arrogant to some of the "would be helpers", but the old saying, "nothing succeeds like success" is still applcable, I believe. And when I try to make my posts as thorough as possible to help people help me (albeit, they DO get long!), it is hard to read responses that suggest things you have ALREADY tried! And, as I said about "success", if the pump design itself, what with higher pressure/volume, was the issue, it NEVER would have made it 30,000+ miles the first time around. That, and I see a LOT of these Melling/QTP pumps out there, street and strip alike, and I haven't heard ANY complaints about bearings being overwhelmed with oil. That said, and since I DON'T know it all (Contrary to popular opinion!), Why do these pumps have the bad rap they have as far as the relief springs sticking? Is it because the traditional SBC had a gear type pump and the relief spring was somewhat stiffer? Or is it because these LS1 type (Trochoidal?-Hypoid?) pumps have a low pressure spring rate, or could it be that the tolerances are very close, or maybe the liberal use of aluminum, and with its use comes the increased chances of galling/increased expansion/contraction rates? Maybe ALL of the above? I really don't know. I DO know that this issue was NEVER seen in ANY of the SBC engines that I have wrenched on in the past. Like Rob was saying, it looks like I am going to have to drop the rack, at the VERY LEAST! And if anyone knows any good shortcuts/ways around dropping the whole cradle out, PLEASE ADVISE!! Thanks again

 

You can take the rack out without dropping the cradle.

 

Sorry you took offense at my reply to your post/response. This forum has great potential to help people that share a common interest/love. However, like ALL things internet, it can also quickly become something FAR DIFFERENT from its intended purpose; i.e.-people sharing a common interest (Corvettes), that are GENUINELY INTERESTED in sharing info/HELPING one another out of a jam/ saving some time/money, etc.. When it degenerates into some of the comments that you have posted, such as the "washers" comment you made, or "letting us ALL(2 people?) know....", it does make one wonder why you would even go there. I am sorry, again, that you have responded in the fashion/manner that you have. I will be the first to admit that, while knowledgable, I certainly do NOT know it all! And frankly, the last line of my reply back to you, with the possible exception of the word knowledgable, CERTAINLY applies to you, as well!!

 

Thank you!! How and do you have pics, or a link, or a good description? I am an older dude(55) and I can't stay bent in there as long as I used to!!! I also have a 2 piece timing cover and wonder if it is possible to somehow access the relief spring from above, if done patiently/carefully. Seeing as how I have a NIB C5 Z06 oil pump on the bench, and have seen the relief valve and how it is accessed, it sure looks like a tough one, if not impossible!Thank you, again, for your response.

 

There is a pretty good write up on LS1Howto for C5 Heads/cam. Just don't follow the procedure for installing the pulley with the stock bolt - use a proper tool. You won't be able to access the relief spring without pulling the timing cover - even a 2 piece. Relief spring port is on bottom of pump. On my car the rack came out the drivers side very easy....although some just slide it out of the way on passenger side.

 

Thanks, man. I DOappreciate it. I didn't think I could possibly get it out the bottom either, even with a 2 piece timing cover, but I was sure as hell hopin' for somebody to post up saying they HAD done it!!!

 

Sounds like a possible spun main bearing. Have you removed the oil filter and cut it open yet?