Chevy Suburban 04 Low on Oil Again
| Username | Post: chevy suburban 5.7 oil pressure loss after warm up (Topic#313997) |
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| NVC Forum Newbie Posts: 4 Reg: 07-24-14 User Info Send Private Topic | 07-24-14 10:19 AM - Post#2471501 My 97 Suburban K1500 5.7 (325,000 mi) looses oil pressure after warm up. Have been using the recommended oil grade (5-30) since I bought the car at 75K. The oil pressure sending unit is fine. On cold start engine sounds great smooth no noise or smoke, pressure reads 40. After warm up (about 20 min at idle standing still) the oil pressure drops steadily but with a little gauge giggle. At the time the check gauges light comes on (at about 1-2 psi) and the engine becomes noisy but not lifter or tap noise. Kinda sounds like the engine is in labor. Before shutdown, increasing the RPMs increases the pressure, but the pressure immediately drops back down after letting up the gas. Since I don't feel like wreaking it, I shut it down when the check gauges light comes on. At first I thought the oil pump needed replacement> Since I do most repairs myself, I called the Chevy dealer regarding a new oil pump. I was told they rarely (almost never) need replacement. I trust this dealer since it has been under their advice that I have gotten the good mileage. They wanted me to bring it in, but 1) it is too far to drive and I don't want to pay for towing, 2) I would like to do the work myself. Lastly, I would not like to do an unnecessary pan pull if it is something else. Thanks in advance for your comments. |
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| 50hotrod Frequent Contributor Posts: 1081  Loc: Wisconsin Reg: 07-25-11 User Info Send Private Topic | 07-24-14 10:38 AM - Post#2471505 In response to NVC Engine is worn out plain and simple. Cheapest and quickest at this point is a replacement engine. 1950 CHEVY 2 DOOR 327 TRI POWER FENDERWELL HEADERS HEIDT FRONT SUSPENSION 700R4 TRANS 411 REAR |
 someotherguy Senior Moderator Posts: 29576  Loc: Texas Reg: 08-01-03 User Info Send Private Topic | 07-24-14 03:00 PM - Post#2471547 In response to NVC Welcome to Chevytalk, You *could* replace the oil pump - some find that with lots of miles, the spring inside does get weak and pressures drop. However as you've already read, most likely the engine is simply worn. To me, 325K out of a Vortec small block is pretty good, considering all of them suffered intake gasket failure around 100-150K and a large number got coolant in the oil, prematurely wiping out the bearings. If not for intake gasket failure I would say 300-350K would be an expected lifespan from the engine with normal use and care. (Yes, I know more than a few have gone much further.) Richard 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 |
 Vaughn Member #455 "15th Year" Gold Supporting Member Posts: 18770  Loc: Colorado Springs, CO Reg: 08-08-04 User Info Send Private Topic | 07-24-14 03:30 PM - Post#2471555 In response to someotherguy Switch to 20w-50 oil. Bearing wear causes an increase in the gap between the rods and mains on the motor, and the gap allows more oil to flow out from between the bearings and the rods/mains. Your bearings are worn, so you need to increase the viscosity of the oil in order to get some oil pressure back. Viscosity just means that the oil is thicker - so the thicker oil won't flow as easily out of the gap between the crank and the bearings. Yes, the ultimate way to fix the problem is to replace the motor - however, in the near term you need to switch oil viscosity. This is a common practice on motors that have high mileage. If you fail to switch to the higher viscosity oil, the damage to the bearings will increase the distance between the bearings and the crank, further shortening the life of your motor. During winter operation, you may have to switch to 10w-40 to get oil that will flow well enough at lower temperatures. |
| NVC Forum Newbie Posts: 4 Reg: 07-24-14 User Info Send Private Topic | 07-25-14 05:33 AM - Post#2471688 In response to Vaughn Thanks for your comments and advice. A new engine is not possible at this time ($$$). The intake gasket did fail some time ago but as far as I could tell the leak was to the outside because coolant was not seen in the crankcase. So the question is do I do the oil pump replacement or not? Also which grade oil do you recommend after the job? |
| someotherguy Senior Moderator Posts: 29576 Loc: Texas Reg: 08-01-03 User Info Send Private Topic | 07-25-14 07:22 AM - Post#2471706 In response to NVC You could do the oil pump as in inexpensive gamble (that is, if you're doing the work yourself.) It won't solve excessive bearing clearances due to wear, but IF the pump is weak at all, the new one might bring your pressure up to a more acceptable level. It is a gamble in that it may help nothing at all. If it brings pressure up to normal using 5W30, by all means continue using 5W30. If it doesn't, then chalk it up as a good try, and bump up the viscosity to something thicker as suggested, in an attempt to bridge the gap. It's a band-aid at best but may get you through for a while. Start saving for a replacement. Richard 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 |
| Vaughn Member #455 "15th Year" Gold Supporting Member Posts: 18770 Loc: Colorado Springs, CO Reg: 08-08-04 User Info Send Private Topic | 07-25-14 03:52 PM - Post#2471822 In response to someotherguy If you are going to go to the trouble of replacing the oil pump, I would convert to a high volume Melling oil pump. Melling is the industry standard, don't use anything else. I have done this on a few motors with badly worn bearings, it helped some, but not a lot. If you are going into the motor that much to swap oil pumps, I would pull the main caps one at a time to check on the condition of the mains, then do it again on the rods. Only do one at a time, and re-torque them back into place. If you find that most of the crank rod and main journals are OK (not all of them will be), you can put new upper and lower bearing shells on the UNDAMAGED rod and main journals - to try to get the oil pressure back up near where it belongs. IF any of the bearings are into the copper, don't try to replace them. This will be simple enough to do on the rods, but you will probably be able to only remove/replace the bottoms of the mains (unless you went to the trouble of removing the timing cover and unbolting and moving back the transmission - in that case you could completely remove the crank and have it turned, and put new bearing shells on all of it). This is a seriously bad way to bring oil pressure back up, but it would probably work until your compression (bad rings) is too low or you break a piston ring. It would generally be better to get a long block from a junkyard and replace yours, it will be a lot easier than the above method. You can generally find a truck in the junkyard that had a new(er) motor put into it, then 10-50K miles later the truck was t-boned or something similar. It may take a while to find one, but they are out there. You usually can get one for less than half of a rebuild, if you keep at it. This is the dirt cheap method to getting an older truck back on the road. It also helps if you have friends at the junkyard. |
| Stinky Senior Member Posts: 1825 Loc: Whitewater, CO Reg: 05-25-01 User Info Send Private Topic | 07-25-14 08:16 PM - Post#2471858 In response to Vaughn Vaughn, why not change the bearings if they are in the copper? |
| someotherguy Senior Moderator Posts: 29576 Loc: Texas Reg: 08-01-03 User Info Send Private Topic | 07-26-14 08:09 AM - Post#2471917 In response to Stinky Bearing journals already likely scored at that point. Richard 06 Silverado ISS / 06 Silverado SS / 06 300C SRT8 |
| Vaughn Member #455 "15th Year" Gold Supporting Member Posts: 18770 Loc: Colorado Springs, CO Reg: 08-08-04 User Info Send Private Topic | 07-26-14 01:39 PM - Post#2471994 In response to someotherguy If the journals are into the copper, they are badly scored, and only having the crank turned will fix it. If you replace those bearings that are into the copper, they will just wear rapidly - causing the oil system and the motor to be flooded with bearing material. IF you leave the bearings that are into the copper alone, the motor won't be flooded with bearing material, and then there is less chance of a critical oil journal being plugged up. |
| Stinky Senior Member Posts: 1825 Loc: Whitewater, CO Reg: 05-25-01 User Info Send Private Topic | 07-26-14 09:19 PM - Post#2472096 In response to Vaughn Vaughn, thanks for the info, it makes sense. |
| NVC Forum Newbie Posts: 4 Reg: 07-24-14 User Info Send Private Topic | 07-27-14 10:37 PM - Post#2472364 In response to Vaughn To ALL: Thank you for all your comments and suggestions. This weekend I was able to get every thing apart in a few hours. The under belly of the engine looked great - clean and no sludge except some brown at the very bottom of the pan (maybe a 1/16" deep) and absolutely no carbon anywhere. This indicated to me that my rings are good. The lower tip of the oil pump screen was gunked with some brown sludge. This sludge may be a residual from the intake gasket failure. I did find a few (3) small very thin flakes (slivers) about 1/16th x 1/8" of metal in the pan which may be bearing material. There is some play in the connecting rods where they are attached to the crank shaft, but I had to apply a great deal of wiggle pressure to notice it. I partially disassembled the oil pump and it looked good. I will measure the clearances on Mon. (7/28). If changing the lower half of the connecting rod bearings is unlikely to improve pressure, I'd rather not mess with them. However, if removing them will allow me access to oil ways that I may check for clogging or other reasons, I would like to know. I liked the idea of measuring the bearing gap, but what do I do with info if I can only reach the bottom half? Will not changing the bottom half of the bearing cause the connecting rod to rotate around a point off center? The pan is still off. If anyone has any suggestions prior to installing the new pump and reassembly, I would be interested in hearing them. After assembly I'll let you know the results. Thanks in advance, NVC (Nick) PS. I am still utterly amazed at how clean everything was - nothing like the black and varnish encrusted motors they used to throw at us in high school auto shop. |
| Vaughn Member #455 "15th Year" Gold Supporting Member Posts: 18770 Loc: Colorado Springs, CO Reg: 08-08-04 User Info Send Private Topic | 07-28-14 04:32 PM - Post#2472570 In response to NVC No, changing the bearing halves will not cause them to rotate off center. Bearing halves, when joined, create their own center around which the crank will rotate. As long as the clearance around the bearing isn't enough to allow the crank to move inside the bearing, then the crank will not rotate off center. Almost all of oil pressure problems are bearing related. If you have the engine far enough apart to get at them, I would change them (it isn't expensive, and it isn't hard to do). An analogy would be like putting a band aid on a cut (oil pump) while a few stitches (bearing shells) would do much more. I guess I should amend my previous comment to say that if the crank journals are mostly undamaged, replacing the bearings can affect a large portion of the oil pressure problems you are having, but if they are damaged then you might as well leave them alone. The lower shells of the MAIN bearings is where most of the bearing wear comes into play. The lower shells take all the force from the piston being forced down by the explosion in the combustion chamber, and they can often be pounded thinner over the lifetime of the engine. You can change both the upper a lower shells of a ROD bearing. Feeling how loose a rod bearing is side to side is NO indicator of how much bearing clearance there is between the rod and the rod bearing. It needs to be measured. (There is a measurement that is side to side though, you measure it with a feeler gauge, it has to be within a certain tolerance.) For this you would use an inside and outside micrometer, or more realistically some plastigauge (it is a lot easier to get a measurement using plastigauge). You can get it from your parts store. Plastigauge is "squeezed" in between the rod/main journal surface when the cap is torqued down. The more it is squeezed, the wider it gets. You use a gauge printed on the sleeve of the plastigauge to determined how much clearance there is between the journal and the bearing. Your bearing clearance needs to be on the order of .002 to .003. If it is more than .003, it is too much. I would probably lean towards .002 for a motor with oil pressure problems. You can change the upper shells of a MAIN bearing, if you have enough play in them to get them out. Sometime you can remove the rearmost main bearing cap, and then pry downwards on the crank to get at most of the main bearing upper shells. You won't be able to get to the front one unless you pull the timing chain cover, but you should be able to get to the 3 rear ones and possibly the 4th (there are a total of 5). Your oil pump may look good and measure within specs, but it is still not providing enough volume for your bearings at hot idle. If you went to the trouble of dropping your oil pan, the very minimum that you should do is to replace the oil pump with a high volume pump. It isn't a high pressure pump (although they have high volume/high pressure pumps), it pumps a lot more volume to keep up with the bleed rate of oil out of the bearings. If you take a look at your current oil pump gears, just imagine a pump with taller gears in it - it will pump out more volume to keep up with oil pressure loss. This is exactly what a high volume pump does, and it does have taller gears. This is a high volume pump, for less than $50. http://www.jegs.com/i/Melling/689/M55HV/1 0002/-1 This is a high volume and high pressure pump for less than $70: http://www.jegs.com/i/Melling/689/M99HVS/ 10002/-1 |
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