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View Full Version : Chevy .65L Duramax Diesel Problem


SLC, LLC
08-31-2008, 10:10 PM
Looking for anyone with knowledge on the Chevy 6.5L Duramax Diesel. I have a 2004 2500hd that I bought used last December. It only had like 50,000 miles on it when I bought it. When I hit 55,000 miles - I changed the oil. After I did this, I noticed that my oil pressure gauge started to act like a tachometer. When my RPM's went down, so did the oil pressure gauge. When the RPM's went up, so did the oil pressure gauge.
I spoke with my mechanic, who is not a specialist in diesels. The problem is that there are no diesel mechanics in this area that I am aware of other than the dealer. We both agree that this is not correct, but cannot figure out why this is happening.
We have done the following things in troubleshooting:

1. Changed oil filter again.
2. Replaced the sending unit
3. Changed the oil to Delvic 15-40 (as we were told by the dealer that this is the specific brand used in chevy)

IA_James
08-31-2008, 10:27 PM
That's what should happen. The problem is you have an actual oil pressure gauge, as opposed to the "idiot light with a stick" like many new vehicles. Spin the engine faster, the oil pump goes faster. There is only a limited amount of space in the galleys and passages, so oil pressure increases. As long as you're carrying about 10 psi per thousand RPM, you're good to go.

Milwaukee
08-31-2008, 10:28 PM
What oil filter you use? Fram?

I have see that due gunk in passage get slow then sudden clog then oil pressure go raise little then try push finally it out. It happened on Ford 300 and Chevy 350 that never run hot enough most short drive for several years.

Do you see oil get dirty short time like sludge?

SLC, LLC
08-31-2008, 10:36 PM
That's what should happen. The problem is you have an actual oil pressure gauge, as opposed to the "idiot light with a stick" like many new vehicles. Spin the engine faster, the oil pump goes faster. There is only a limited amount of space in the galleys and passages, so oil pressure increases. As long as you're carrying about 10 psi per thousand RPM, you're good to go.


There is a pretty good fluctuation in the oil pressure gauge. I am not questioing you, just trying to explain what is going on. I am trying to avoid the damn dealer because I know that will cost a fortune. The thing that concerns me is that it did not do this before I changed the oil.

What oil filter you use? Fram?

I have see that due gunk in passage get slow then sudden clog then oil pressure go raise little then try push finally it out. It happened on Ford 300 and Chevy 350 that never run hot enough most short drive for several years.

Do you see oil get dirty short time like sludge?

I use Wix filters. No, the oil does not seem to be producing sludge. I change every 5000 miles. Was using Rotella oil before the mechanic switched brands.

Milwaukee
08-31-2008, 10:52 PM
You mean when you stop at light engine idle at 650 rpm so oil pressure go down like middle when you touch pedal to go did oil pressure go high?

My 79 F150 alway do that if I stop it 15 psi at 600 rpm but go to 45 mph at 1,850 rpm oil pressure is 35 to 40 psi. it been do that when I switch to 15w40 diesel oil since 5w30 oil make worst it get 0 to 5 psi during hot run. Keep mind it have 327,100 miles now it still use everyday but not now we are still work on fuel system.

IA_James
08-31-2008, 11:04 PM
That's odd that it wasn't doing it before. Honestly though, if it was my truck, as long as I had over 10 psi per thousand RPM, I wouldn't sweat it. What are the hi/lo readings on your gauge? What does it seem to operate at most of the time?

FIRESCOOBY
08-31-2008, 11:37 PM
Looking for anyone with knowledge on the Chevy 6.5L Duramax Diesel. I have a 2004 2500hd that I bought used last December. It only had like 50,000 miles on it when I bought it. When I hit 55,000 miles - I changed the oil. After I did this, I noticed that my oil pressure gauge started to act like a tachometer. When my RPM's went down, so did the oil pressure gauge. When the RPM's went up, so did the oil pressure gauge.
I spoke with my mechanic, who is not a specialist in diesels. The problem is that there are no diesel mechanics in this area that I am aware of other than the dealer. We both agree that this is not correct, but cannot figure out why this is happening.
We have done the following things in troubleshooting:

1. Changed oil filter again.
2. Replaced the sending unit
3. Changed the oil to Delvic 15-40 (as we were told by the dealer that this is the specific brand used in chevy)

First, the motor you have is a 6.6 Duramax, the 6.5 was the former GM Diesel.

Secondly, my Duramax (as well as every other vehicle) does that. The oil pressure will be fairly high first thing in the morning. After that the oil pressure will fluctuate with RPM's (engine load).

02DURAMAX
09-01-2008, 12:01 AM
First, the motor you have is a 6.6 Duramax, the 6.5 was the former GM Diesel.

Secondly, my Duramax (as well as every other vehicle) does that. The oil pressure will be fairly high first thing in the morning. After that the oil pressure will fluctuate with RPM's (engine load).

Exactly...You need to pay more attention on your trucks!

TXNSLighting
09-01-2008, 12:32 AM
your 6.6! Duramax is normal. Nothing wrong with it there.

SLC, LLC
09-01-2008, 11:09 PM
Exactly...You need to pay more attention on your trucks!

Sorry, our 2000 Chevy Diesel is a 6.5L, got them mixed up. The 2004 is a 6.6L.

SLC, LLC
09-01-2008, 11:11 PM
The gauge reads 0 - 120 for the oil pressure. It will fluctuate between 30 and 60 on the gauge as the RPM's go up and down.

So you think this is normal? Anyone have ideas as to why it was not doing that before?

I was wondering if the pump was going bad, and then all of a sudden one day the pump would stop pumping.

IA_James
09-01-2008, 11:13 PM
Sounds like a sketchy sender or wiring harness....30 to 60 lbs is good stuff.

SLC, LLC
09-01-2008, 11:19 PM
We did switch out the sending unit, and the same thing happened.

mybowtie
09-02-2008, 11:01 PM
My 07's oil pressure is high when its cold, but after warming up it varries like others have said...:usflag:

SLC, LLC
09-02-2008, 11:02 PM
Thank you all for your input. I guess I will not worry too much about it at this time.

kratzsc
09-04-2008, 07:40 PM
For all questions regarding GM diesels try this web site "diesel place". The web site is dedicated to conversations about GM diesels (6.2,6.5 &6.6's).

GravelyNut
09-05-2008, 03:51 AM
The gauge reads 0 - 120 for the oil pressure. It will fluctuate between 30 and 60 on the gauge as the RPM's go up and down.

So you think this is normal? Anyone have ideas as to why it was not doing that before?

I was wondering if the pump was going bad, and then all of a sudden one day the pump would stop pumping.

May have been clogged and was only allowing the sender to go up and not drop back in reading quickly. If you see it flucuating at a steady speed, that is when you need to worry. Pressure readings vary on all engines when the RPM changes and vary between hot and cold too. Some engines *cough* Cummins 8.3 *cough* will pulsate a gauge so bad you have to put a snubber inline with the gauge/sender to get a true reading.

jaybird24
09-05-2008, 04:58 PM
30-60psi sounds just about right for that truck. As to why it did not do it before- who knows, it seems to be fixed so don't worry about it. Mine reads 70psi first thing in the morning then goes 30-65 and has for 6 years. The new LMM 's have a low pressure high volume pump which reads different, so don't ask anybody with a new duramax. I only know this because the low reading in our new one seemed real low so I took it in and found out.