Bethard728

I don't recall which O-ring I used. I might be able to go look into the left over gasket kit parts and see whats left. I did some research at the time to choose what I thought to be the correct one, but really dont remember where I landed. I believe my pump came with a blue and green but another gasket kit came with red and I think that is the one I ended up using because it seemed like the best fit on the pickup tube. Something that I have not mentioned since I started. There was absolutely zero sludge buildup anywhere in this engine. Even under the screen in the sending unit. I'd consider it one of the cleaner engines that I've had apart. I have several projects ahead of the truck right now as long as it keeps ticking. Next time it drops pressure and I have some time, I will do the added oil test and see what happens. If that doesnt change things, then I will swap in the HV pump. Thanks to everyone for the help.

I did replace the O-ring. Actually did it twice. Once when I did the valvetrain repair and again when I installed the new pump. I replaced the AFM manifold with a GM unit as well. I am fairly certain that these are good because the odds of the original doing the same as the replacement is rare. Especially the O-ring which I have now had 3 in there including the factory. (I know its not impossible, but unlikely) I can try the overfill. I know that's been mentioned, but since I only have issues approx 1500 miles after a filter change, I can't see how that O-ring would be the issue. I leave the oil in, change the filter, top it back off and its good again for awhile. If the O-ring was a fail point, I dont think changing the filter would temporarily fix it.

Thank you. Mine runs and sounds just fine, but loses oil pressure. I think it will be worth my time to swap in a HV pump and see what happens.

Is oil testing something that you believe should be done on a regular basis? If it could catch issues like this early, than I am on board with doing it. I am admitting that I have never thought of oil analysis as a benefit worth the cost, but the situation I am in is a different creature for me. The truck I am dealing with wasn't bought new by me, but I knew the original owner and it was always serviced on time and with good synthetic oil. Personally, I have never had this type of issue with a 5.3 before this one, but this is my first AFM engine. I always changed oil around 3-5K miles and never had an issue. I sold my old 2003 Yukon to a friend around 250K and it never had a problem. That particular vehicle ran whatever oil was cheap and always ran Fram cheap filters. (I am NOT saying that is the right move, but it was what I did when I was younger and poorer). From the day it was new, I used tech 2000 (I think that was what it was called) from Walmart. My buddy is still driving it today with over 300K. I suppose the reason I resisted oil analysis was because I was never in a situation where I thought it would benefit me...but that might not of been the correct outlook to have.

Thank you so much for the reply!! This is what I was hoping to find here; someone that has fixed the problem. After reading your reply, I'm hoping I can fix mine with the HV version of the oil pump. I used Felpro gaskets and everything else, except for the oil pump, were GM parts. I am very thankful that you mentioned the start up oil pressure activating the AFM lifters! I never thought of that happening if I were to plug the relief valve in the pan. Do you recall which pump you used? There seems to be some confusion on the difference between M365 and 10355. After talking with Summit and researching on the internet (which we know is 100% the true, every time) They are both standard volume, standard pressure unless you change the spring, which you could do in either. I did not think to ask about the HV versions of each but I would assume that the 10355HV would be considered the better unit. Thanks again for taking the time to reply! I'm excited to hear from someone that has actually fixed the problem!

Sounds like you are doing us all a favor by only logging in once or twice a year. I assume that is because it takes you that long to save up enough rude comments. It sounds like you are one hell of a keyboard mechanic and should be really proud of yourself. I don't recall ever saying that I expected the engine to be like original condition. I measured the lifter bores and inspected the cam so I am fairly confident that is not my problem. The components I replaced, other than the oil pump, were all parts I would of replaced anyway when servicing the lifters and AFM system....so I don't see the reason for "Wow. Consider how many components have already been changed out". Your next statement is what clued me in to the fact that you are a wicked keyboard mechanic...."Then, consider what it takes to properly evaluate the dumbel." What is there to consider??? Dropping the transmission and T-case to replace it and change the rear main seal at 180 some thousand miles?? We are talking a couple hour job here that requires no skill. It was a quick little project that I did with my son one afternoon. I will admit that I failed to conduct a proper scientific protocol....but to be fair, I didn't realize that I needed data backed by science. It is a general statement saying it happens around 1500 miles after a filter change. It might happen at 1012 miles or it might make it 1853 miles....I don't think that the exact mileage really makes a difference. As far as oil analysis goes, I will fully admit that I havn't been thrilled about doing it. I couldn't see how it was an oil issue since leaving the oil in and changing the filter restored my pressure for about the same amount of miles. (I apologize that I didn't keep a scientific log) I was thinking that the suggested analysis was to identify dilution by fuel, which I was confident enough that was not the problem. Recently a suggestion was made to get an oil analysis to look for other things that could point to other issues. This makes sense to me and will get an oil analysis the next time I lose oil pressure. I have a mechanic friend that warned me about asking for help on a forum. He commented that "a bunch of non-mechanics playing like they know ****** from Shinola" will be all that you get. I was pleasantly surprised that was not the case with this forum. Up until GhostWriter crawled out from under his keyboard to add a bunch of useless comments to the post, I was impressed with the knowledge and willingness to help. GhostWriter, you are the exact type that gives these forums a bad name. Good luck with all that you do and any of your scientific endeavors, but feel free to leave your rude comments to yourself if you can not contribute anything worth while.

This is exactly the way mine started. It would lose pressure, but shutting it down and restarting would cause it to go back up for awhile. My first thought was oil not getting back to the pan in time, but why would that change with a filter. To answer your question about blowing into the pressure relief. If memory serves me correctly, the pressure relief is immediately behind the oil filter housing and, in theory, you could blow into the port. However, I'm not sure you could get enough pressure to blow off the pressure relief because it will also backfeed through the pump and into the pan. I can't think of anything that would stop the backflow of air that direction. I completely agree that it has to be the filter or relief valve since you have pressure before the filter, but not after. In my case, I have been through over a dozen filters, so its not really possible that all of my filters have malfunctioned...so the relief valve makes sense. Whatever actual issue is causing the pressure loss, surely it could be mitigated by removing and plugging the relief valve. And what issue could be caused by plugging it? I wonder if it would have enough pressure to blow out the filter? That would be interested to see if I can plug it and find out what would happen.

This helps, thanks. I assumed, incorrectly, that the 10355 was referred to as 355. I do know for sure that my 10355 pump came with the standard pressure spring but included a high pressure also, which I installed. So, in my case, the 10355 was a standard pressure, standard volume until I changed the spring. It's very possible that in some cases it comes factory loaded with the high pressure spring though. The question I would like answered is what is equivalent to the factory installed pump? The 10355 was identical in size, thickness, and appearance when compared to the OEM pump that came out of my truck. (other than maybe some part numbers) The reason I ask is that someone in an earlier post said something similar to "that little ironblock pump is not doing you any favors" and stated that I had the wrong pump in my truck. I am assuming that "standard pressure" on all of the pumps mentioned above have the 33% increased volume when compared to the older ironblock pumps. The bottom line for me is that I should of done more research and went with one of the HV pumps. The good news is that the oil pumps are a breeze to change....the bad news is that there is cost associated with buying another pump and getting the truck aligned again. (I have not found a way to get the steering rack back in the same place in the past)

I just wanted to follow up since I have seen no responses about my last post regarding the 355 vs 365 pump. After talking again to Summit, I have found that the M355 is indeed the correct pump that has the upgraded pressure meant for the demands of the AFM and/or VVT aluminum block engines. It does everything the M365 does and also comes with the high pressure spring. This IS the better replacement pump. The other option is to get the M355HV which has an additional (approximately) 20% over the M355 (which already has 33% over the original ironblock pumps.) If I had known this last year, I would have went with the HV version.....but the whole hindsight story.

Who do you recommend? I have never sent off an oil sample before. Also, is there a standard test? or what should I ask them to look for? Thanks,

I started a post, but apparently it didn't save, so I'll try it again. First of all, thank you Swathdiver for the article!! That's a lot of great info! I see the size difference in the Gerotor but I am wondering if that is comparing to the OEM ironblock version? Below is copied from Mellings website and it appears as if the 355 already has the larger gerotor in it since it states 33% increase in volume over the standard pump. I can't find where Melling offers a M365 pump on their site, but they do offer a M355HV which says "Exclusive high volume (+20%) rotor design". I wish I would of knew that existed before I changed mine out. I did find the M365 on Jegs, but it stays its a standard volume, standard pressure pump. Looks like it is used to combat cavitation at high RPMs. This is all damn cunfusing! From Melling site: 10355, Standard Volume, High Pressure Gen IV Oil Pump Melling improved the standard volume GM Gen IV oil pump. To support AFM and VVT components the output of this pump is 33% more than the Gen III standard volume oil pump (Melling #10295). Design changes to the housing, cover, and components together combine to improve the performance, durability, and capability of the oil pump. It can be used in any GM Gen IV application that uses Melling’s stock replacement M355 or M365 oil pumps. From JEGS site: GM LS Engine Oil Pumps The Melling M365 pump is a standard pressure, standard volume pump that is considered a suitable replacement for the factory oil pump (GM part # 12612289) and offers improved resistance against cavitation at higher RPMs. The cast aluminum housing is CNC-machined and hardcoat anodized. The cast iron cover is CNC-machined and phosphate coated. The relief valve features a screw-in valve plug. The factory LS oil pump suffers from cavitation above 6,200 RPM, which results in a drop in oil flow of nearly 1 GPM by 7,000 RPM. This cavitation can also aerate the oil, which causes drops in oil pressure and can result in oil starvation. This is why we do not recommend shifting any higher than 6,200 RPM with a stock engine. Engines that run at RPM's above 6,200 should use an upgraded Melling pump to prevent these issues. Features: 33 PSI Pressure Relief Valve Spring 1.28 Displ (cuin/rev) The cast aluminum housing is CNC machined and hardcoat anodized The cast iron cover is CNC machined and phosphate coated. The cover also features countersunk screws for more timing cover clearance. The relief valve features a screw in valve plug with the optional lower stock pressure spring supplied Compatible with factory GM oil pickup tubes

I just went back and found my notes from when I was talking with Melling and Summit. I could be wrong because they were just hand notes taken while on the phone with Summit, but it looks like I misspoke on my early posts. I think the 10355 is 33% higher volume and standard pressure, unless you change out the spring. If what I wrote down is correct, then I should have both higher volume and higher pressure because I changed out the spring to the highest one in the set.

I have not tested the oil as I feel like it couldn't be the oil since leaving the oil in and changing only the filter "fixes" the pressure for awhile. I get around 1000-1500 miles on each filter regardless if the oil is new or old. The pressure is essentially zero when it happens. The needle drops all the way down and I get a low oil pressure message.

So your thought is that my factory pump wore out the first time? And then I replaced it with the wrong pump? If so, that would be the best explanation I have heard...as everything else I have done didn't help. I did speak with a Summit salesperson about the pump, (Although they might not know much about it) and he took my VIN number and recommended the M355 oil pump with a high pressure spring. I also did some research and found this on the Melling sight. This is a quote from Melling. "Thanks for the question, 10355 is the performance version of the M365, it will have a hard coat anodized body, and a high pressure spring installed, either pump will work for your engine it is just a matter of preference." Swathdiver, please do not take this as me arguing, because I really want you to be right. I would love to just swap out my new pump with the M365. Have you had experience with the 365 solving issues? And I wonder why both Melling and Summit are giving out bad recommendations? This would for sure make sense though....why so many people can not solve this issue if they are putting the wrong pump in.

Yes, that is my though too. That is what's so baffling to me. I think I have replaced nearly everything relating to oil pressure outside of the non-AFM lifters and bearings. All lifters and bores were in spec, so it seems the only thing left is bearings. I am absolutely lost.