View Full Version : Low oil pressure
Hi all,
My 6.2 na has developed a low oil pressure problem. The engine is a Diesel Depot build with just over 60,000 miles on it and has the later high volume oil pump on it.
In the last few days the idle oil pressure (hot) has gone low enough to bring on the light (about 6 PSI). It doesn't always happen (somtimes it stays up at 12-14 psi which was around normal for it). Driving along the road has also been a bit erratic. Somtimes it may be 35 psi and can then drop to 15-20 psi.
Previously when starting in the morning it would hit 75psi and gradually over the next few mile come back to its normal 35ish psi. Now it doesn't go to 75 and comes back to lower pressures within a minute to two.
I know the electic gauge I have has been acting up in the last few weeks (stops working the odd time but if I tap the face it reads again) so I stuck a mechanical test gauge on it last night and it reads very close to the electrical one.
I'm also running a bypass oil filter and disconnected it last night to eliminate it but no difference. Also changed the oil and no difference (Oil I am using is Castrol Tection 15W40, CF classification)
Anybody got any ideas. Probably looking at dropping the pan but said I'd ask first before I do
Thanks,
Ken
DmaxMaverick
10-16-2009, 11:43
Your high volume pump probably blew the regulator. They aren't designed to be used on a 6.2 (or low volume 6.5). Many have said there is no problem using a high volume pump on a low volume engine, but I disagree. I've seen this before on a couple 6.2's, and many other engines. The pressure lubrication system on these, and most every V-x engine is much more simple than most try to make it. Once the minimum flow is achieved, more is not necessarily better. The only reason a high volume pump creates more pressure, is the oil outlet path (including the regulator/relief valve, bearing clearances, etc.) is overwhelmed. This translates to higher perceived pressure, with little to no increase in actual volume. It also requires a significant amount of additional parasitic power to operate the high volume pump.
It's also possible you've spun a cam bearing. Many times, there'll be no noise or other indication of it early on. An oil analysis would be very helpful to see just what's floating around in your oil. Higher than normal copper would be a solid indicator of a bearing failure.
Thanks for the reply. I have a Haynes manual for it but it doesn't mention where the relief valve is. Is it on the pump itself or maybe somewhere around the oil filter/cooler lines. How much stripping need to be done to check for a spun bearing. Does the cam need to come out to check?
The relief is in the oil pump cover. It has a spring and a little valve in there.
When the pressure goes above the preset limits the valve moves and uncovers a port and allows the excess oil pressure/volume to blow off and drain back to the pan.
I used the squirt block pump on the DaHooooley with a non squirt engine block. The pressure cold pops to about 75 PSI and then falls to about 40 at idle when hot and 60 running at speed
The squirt blocks absolutely need the HO oil pump to keep up with the "Internal Bleeding" of the squirt nozzles.
I have seen a buttload of 6.5's built with the HO pumps and haver yet to see any issues.
I would not recommend winding the suckers to the moon when cold though.
Use 15-40 oil only.
60 PSI hot running will not hurt a thing.
Now as far as why your pressure has fallen off ?????
If a manual gauge is showing low too, then there is an internal leak somewhere.
The bypass filter may be the issue.
Possibly something stuck the relief valve open. This will cause low pressure.
Gonna have to poke around and possibly rip it apart.
Missy
Use 15-40 oil only.
Missy
Why do you advocate the use of 15-40 only? Would 5-40 hurt anything?
In very cold weather 5-40 would be fine.
The gold standard and most widely recommended oil for these engines is a good diesel rated 15-40 oil
I have run 15-40 to ambient temps as low as 5F (personal experience) and as high as 110F
Your call though, but unless your dealing with some severe cold the 15-40 is probably the best all around choice.
Hope this helps
Robyn
Humding
Yank the oil pump drive out (or vac pump, depending on whats there) and have a look at the pump drive internal hex and the drive gear to be sure all is well.
These things dont take a lot of effort to run the pump so likely this is not an issue.
I have primed these things using a 3/8 drive speed handle on the priming tool and it does not take much to turn the pump.
Just best to not leave any stones unturned though.
Missy
Hi Guys,
Thanks for all your input. I have a couple of scrap blocks here so I went fiddling and found the valve in the oil pump and the 2 inside the oil filter housing. Anyhow decided to pull the pan and check the oil pump one. Never got as far as it, as looking at the empty sump I could see filings a few inches back from the front. From a previous bad experience I started to look at the main bearing webs and sure enough the tell-tale signs were there. Like my previous one the three centre webs have cracks despite having a stud-girdle kit installed. To be honest I don't know where to go now.
For those of you who don't know I am on the wrong side of the Atlantic (Ireland) and the engine is a conversion fitted in a Land Rover. The first engine I had in it did all the usual problems that these have and finished it off with the cracked webs at 61,000 miles
Engine no 2 (this one) was build by the Diesel Depot with stud girdle kit, balanced, ported, timing gears, ceramic coated pistons, 4911 pump and turbo injectors etc. It has been a dream up to now and to be fair was a far superior rebuild to the first one. However this one has only done 3000 miles more than the first one.
The easiest way out now I think would be a short block and use all my own heads etc. However I don't fancy having to do it again in another 60,000. So I am thinking it is time now to say goodbye to GM diesel V8's for good. The beautiful exhaust note (especially with exhaust disconnected) will be sadly missed but so it will have to be.
Thanks again Guys,
Ken
Sorry to hear of the bad news.
Missy
Don't give up so fast! My '95 was still going strong after 148 K miles pulling a trailer that weighed as much as your Land Rover!
Just wondering do more webs crack with manual transmissions that automatics. Just a thought.
john8662
10-19-2009, 14:50
I'd bet there are much more web cracks on standard shifts, although I don't have any evidence to support that theory.
J
Its someting I would be thinking as well. Every time you press the clutch you are putting an end load on the shaft that an Automatic doesn't. Not much but probably matters over time (especially on our crap roads). I suppose next question is that are there engines out there which have the mains splayed but still cracked?
I would like to stay with a 6.2 but a 6BTA conversion is nibbling at my ankles.
john8662
10-19-2009, 17:56
Splayed 6.5's haven't been out long enough to tell.
I have two blocks that are splayed, and it's a process that really strenghtens up the bottom end. It's a very detailed process to do it, and not just any speed shop can do the process correctly. You'll have to find a shop that knows every step of the process well in regard to more than just small block chevy's before attempting to let them do the job.
If you're considering splaying a 6.2, it cannot be done. It will take a 6.5 block in order to splay. The reason is the type of rear main seal used on the 6.2. The rear main bearing cap on a 6.2 cannot facilitate a finish align hone, because the idiots at GM made the seal bore size smaller than the housing bore size for the main bearings. 6.5's have a single piece rear main seal housing that doesn't interfere in any way.
If you were in the states, I could help you out with a splayed 6.5.
There are several sinister things working here.
The big one is the crap quality of the castings.
Now this said, the Red blocks that were used in 82 were touted as being great castings.
I have a red one that I did Lock and Stitch inserts on the middle three mains. Yup they were cracked. Not bad but cracked.
Some crack right in the bolt hole and others crack at the register fit.
Cracks at the register are a death nel for the block. Cracks in the hole as long as they are not beyond the holes depth are easily fixed.
I have seen 6.5 blocks with cracks at the register fit that have spread open .030 to 040". Now this is real plain to me. These were green castings that have cured under use and then cracked and opened up.
Poor quality casting me thinks.
The action of the clutch throwout bearing does not place enough stress on the crank to cause breakage of the webs.
If this were the case then the thrust mains would be totally burned up.
Auto tranny equipped rigs crack the main webs and in numbers too.
The one possibility is that a stick shift engine that is lugged could see torsional vibrations that an auto does not and that could result in a broken crank.
I had a 6.5 that I bought that had snapped a crank and the block was perfect.
Placed a mainline standard bar in the bores with the caps toqued and the thing was fine.
So go figure.
The reasons that these things crack are the result of several engineering flaws.
Alloy, the design of the bottom end, stress during operation and likely some thermal issues too.
Had the 6.5 been designed with a deep skirted block and cross bolted mains they would probably live forever.
The blocks do a lot of moving around while they are under load and lord knows what exactly is happening.
A better alloy in the block helped a bunch when GEP/AMG took over.
The solid main girdle/caps all in one has made these engines real tough.
I recently built a 6.5 for my Dually 1 ton and used a 929 block and inserted all 6 outer holes on the three middle webs.
I seriously doubt that this puppy will ever have another issue.
The engine that came out had low miles and the #4 main saddle had cracked through the oil squirt hole lengthwise with the bore and then up into cyl's 6 and 8
Hit water and it was downhill from there.
Best
Missy
A friend of mine called tonight and I was showing him the engine. On closer inspection we found at least one crack that had travelled up not far off the camshaft so it looks like it is well & truly dead. I have been doing a good bit of "surfing" and researching during the week and it is getting more likely the next engine will be a Cummins. I could do without these catastrophic failures I had on the last 2 engines. The 6BT was used in DAF (Paccar) trucks over here so parts will be easier and quicker to get at. Sad day and will miss the V8.
Thanks for your help over the years,
Ken
83Blzr62
11-05-2009, 09:25
I dont know what the overall cost would be to go to a cummins, but you may consider the AMG P400. It should be close to a simple engine swap. Converting to a cummins might require more conversion parts and things that will add up. Just a thought because the AMG P400 is not going to crack like the old blocks. However, it may be difficult to get in Ireland.
Powered by vBulletin® Version 4.2.5 Copyright © 2025 vBulletin Solutions Inc. All rights reserved.